a study on fine grinding process in jet mill - ePrints@USM
a study on fine grinding process in jet mill - ePrints@USM
a study on fine grinding process in jet mill - ePrints@USM
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
A STUDY ON ULTRA FINE GRINDING OF SILICA AND TALC<br />
IN OPPOSED FLUIDIZED BED JET MILL<br />
by<br />
SAMAYAMUTTHIRIAN @ THILAGAN PALANIANDY<br />
Thesis submitted <strong>in</strong> fulfillment of the<br />
Requirements for the degree<br />
Of Doctor of Philosophy<br />
JANUARY 2008
ACKNOWLEDGEMENTS<br />
I wish to express my s<strong>in</strong>cere gratitude towards Prof. Dr. Khairun Azizi Mohd Azizli for<br />
her supervisi<strong>on</strong>, undy<strong>in</strong>g encouragement, helpful suggesti<strong>on</strong>s and c<strong>on</strong>sistent<br />
assistance throughout this research work.<br />
The greatest debt of gratitude is also owed to Dr. Hashim Huss<strong>in</strong> and Dr. Syed Fuad<br />
Saiyid Hashim for their <strong>in</strong>terest and support <strong>in</strong> this research work. Special thanks to<br />
Prof. Za<strong>in</strong>al Arif<strong>in</strong> Ahmad, Ir. Dr. Mior Termizi Mohd Yusof and Assoc. Prof. Dr. Azizan<br />
Aziz for their c<strong>on</strong>t<strong>in</strong>uous encouragement and support dur<strong>in</strong>g this research work.<br />
I’m thankful to Universiti Sa<strong>in</strong>s Malaysia, School of Materials and M<strong>in</strong>eral Resources<br />
Eng<strong>in</strong>eer<strong>in</strong>g, USM, and Institute of Postgraduate Studies, USM for giv<strong>in</strong>g the<br />
opportunity to c<strong>on</strong>duct and complete this <str<strong>on</strong>g>study</str<strong>on</strong>g>.<br />
I’m thankful to every<strong>on</strong>e <strong>in</strong> School of Materials and M<strong>in</strong>eral Resources Eng<strong>in</strong>eer<strong>in</strong>g<br />
who had helped me <strong>in</strong> the completi<strong>on</strong> of this thesis.<br />
I would like to thank my parents Mr. M. Palaniandy and late Madam A. Kamachyamah,<br />
brother, Soorianamtham and sisters, P. Yogamalar and P. Puganeshwary for their<br />
c<strong>on</strong>t<strong>in</strong>uous support and encouragement until today.<br />
Lastly, a special thanks to my wife, Dr. Srimala and beloved daughter, Shemmalarvily<br />
for their support and love.<br />
ii
CONTENTS<br />
Page Number<br />
ACKNOWLEDGEMENT ii<br />
CONTENTS iii<br />
LIST OF TABLES viii<br />
LIST OF FIGURES x<br />
LIST OF ABBREVIATIONS xvii<br />
LIST OF SYMBOLS xviii<br />
LIST OF PUBLICATIONS xxii<br />
ABSTRACT xxiii<br />
ABSTRAK xxiv<br />
Chapter 1 INTRODUCTION<br />
1.0 Introducti<strong>on</strong> 1<br />
1.1 Mechanochemical Effect Induced By F<strong>in</strong>e Gr<strong>in</strong>d<strong>in</strong>g<br />
Process<br />
1.1.1 Mechanochemical Effect Induced In Jet Mill 5<br />
1.2 Problem Statement 6<br />
1.3 Objective 8<br />
1.4 Scope Of Work 8<br />
Chapter 2 LITERATURE REVIEW<br />
2.1 Introducti<strong>on</strong> 10<br />
2.2 Energy <strong>in</strong>tensive <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s 13<br />
2.3 Jet <strong>mill</strong> 15<br />
2.4<br />
Parameters affect<strong>in</strong>g <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> <strong>in</strong> <strong>jet</strong> <strong>mill</strong> 19<br />
iii<br />
3
2.4.1 Particle Breakage Mechanism <strong>in</strong> Jet <strong>mill</strong> 20<br />
2.4.2 Jet <strong>mill</strong> design parameters<br />
2.4.2.1 Effect of angle of nozzles<br />
2.4.2.2 Effect of nozzles distance<br />
2.4.2.3 Nozzles and types of nozzles<br />
2.4.3 Jet <strong>mill</strong> operat<strong>in</strong>g parameters<br />
2.4.3.1 Effect of feed rate<br />
2.4.3.2 Effect of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure<br />
2.4.3.3 Effect of classifier rotati<strong>on</strong>al speed<br />
2.4.3.4 Effect of types of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> fluids<br />
2.4.4 Feed Characteristics<br />
2.5 Mechanochemical effect <strong>in</strong>duced by <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> 39<br />
2.6<br />
2.5.1 Theoretical c<strong>on</strong>siderati<strong>on</strong><br />
2.5.1.1 Shr<strong>in</strong>k<strong>in</strong>g and polymorphic transformati<strong>on</strong><br />
2.5.1.1.1 Shr<strong>in</strong>k<strong>in</strong>g<br />
2.5.1.1.2 Polymorphic transformati<strong>on</strong><br />
2.5.1.1.3 Distorti<strong>on</strong> of crystal lattice<br />
2.5.1.1.4 Amorphizati<strong>on</strong><br />
2.5.2 Interacti<strong>on</strong> of particle dur<strong>in</strong>g <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong><br />
Characterizati<strong>on</strong> of structural changes dur<strong>in</strong>g <strong>f<strong>in</strong>e</strong><br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong><br />
2.6.1 X-ray Diffracti<strong>on</strong> method<br />
2.6.2 Infrared Spectroscopy Method<br />
iv<br />
24<br />
24<br />
25<br />
27<br />
28<br />
28<br />
31<br />
32<br />
36<br />
38<br />
41<br />
43<br />
44<br />
44<br />
46<br />
46<br />
49<br />
55<br />
56<br />
58
Chapter 3 METHODOLOGY<br />
3.1 Introducti<strong>on</strong> 63<br />
3.1.1 Sampl<strong>in</strong>g of raw materials 63<br />
3.2 F<strong>in</strong>e Gr<strong>in</strong>d<strong>in</strong>g Test work 65<br />
3.2.1 Sampl<strong>in</strong>g of Ground Product 67<br />
3.2.2 Sampl<strong>in</strong>g of holdup of silica and talc <strong>in</strong> the<br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber<br />
3.2.3 Height measurement of holdup <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
chamber<br />
3.2.4 Measurement of classifier current and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
chamber pressure<br />
3.3 Characterizati<strong>on</strong> of Raw Materials And Ground Product 72<br />
3.3.1 Particle Size Analysis<br />
3.3.1.1 Particle size and its distributi<strong>on</strong><br />
3.3.2 Phase Analysis and Quantitative Analysis Of<br />
Physicochemical Effect<br />
3.3.2.1 Profile fitt<strong>in</strong>g procedure<br />
3.3.2.2 Microstructure characterizati<strong>on</strong><br />
3.3.2.3 Qualitative Analysis of Physicochemical<br />
Effect<br />
3.3.3 Chemical Compositi<strong>on</strong> 78<br />
3.3.4 Morphology Analysis 78<br />
3.4 Specific K<strong>in</strong>etic Energy 80<br />
Chapter 4 Results And Discussi<strong>on</strong><br />
4.1 Raw materials characterizati<strong>on</strong> 82<br />
4.1.1 Particle size analysis 82<br />
v<br />
67<br />
69<br />
70<br />
72<br />
74<br />
75<br />
75<br />
76<br />
77
4.1.2 Morphological Study<br />
4.1.3 Phase analysis<br />
4.1.4 Chemical compositi<strong>on</strong><br />
4.1.5 B<strong>on</strong>d<strong>in</strong>g movement<br />
4.2 Effect of the operati<strong>on</strong>al parameters of <strong>jet</strong> <strong>mill</strong> <strong>on</strong> the<br />
product <strong>f<strong>in</strong>e</strong>ness<br />
4.2.1 Effect of Operati<strong>on</strong>al Parameters <strong>on</strong> the Particle<br />
Size, d(4.3) and particle Size Distributi<strong>on</strong> (Span<br />
Value)<br />
4.3 Effect Of Inside Mill C<strong>on</strong>diti<strong>on</strong> 102<br />
4.3.1 Effect Of The Gr<strong>in</strong>d<strong>in</strong>g Chamber Pressure 102<br />
4.3.2 Effect of <strong>jet</strong> <strong>mill</strong> operati<strong>on</strong>al parameter <strong>on</strong> the<br />
holdup<br />
4.3.2.1 Holdup Height<br />
4.3.2.2Holdup mass<br />
4.4 Determ<strong>in</strong>ati<strong>on</strong> of silica and talc breakage mechanism 116<br />
4.4.1 Silica<br />
4.4.2 Talc<br />
4.5 Mechanochemical effect of silica and talc 138<br />
4.5.1 Phase transiti<strong>on</strong> of silica and talc<br />
4.5.2 B<strong>on</strong>d<strong>in</strong>g movement of silica and talc<br />
4.6 Specific Energy C<strong>on</strong>sumpti<strong>on</strong><br />
Chapter 5 C<strong>on</strong>clusi<strong>on</strong> And Suggesti<strong>on</strong><br />
5.1 C<strong>on</strong>clusi<strong>on</strong> 174<br />
5.2 Future Work 176<br />
vi<br />
82<br />
84<br />
85<br />
85<br />
87<br />
87<br />
111<br />
111<br />
113<br />
116<br />
128<br />
139<br />
155<br />
165
REFERENCES 178<br />
APPENDIX 1 : Volume moment diameter of ground silica and talc<br />
APPENDIX 2: Holdup height and mass of ground silica and talc<br />
APPENDIX 3:Classifier current and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber pressure of<br />
ground silica and talc<br />
vii<br />
187<br />
190<br />
193
Table 1.1<br />
LIST OF TABLES<br />
Characterizati<strong>on</strong> of silica and talc as m<strong>in</strong>eral fillers <strong>in</strong><br />
various <strong>in</strong>dustries<br />
Page number<br />
2<br />
Table 1.2 Power bulk densities <strong>in</strong> various <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s 2<br />
Table 2.1 Key physical properties of selected m<strong>in</strong>eral fillers<br />
13<br />
Table 2.2 Typical <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> data for <strong>jet</strong> <strong>mill</strong><br />
Table 2.3<br />
Applicati<strong>on</strong> of <strong>jet</strong> <strong>mill</strong> <strong>in</strong> various sectors<br />
Table 2.4 Geometrical parameter and operati<strong>on</strong>al c<strong>on</strong>diti<strong>on</strong> of a <strong>jet</strong><br />
<strong>mill</strong><br />
Table 2.5 The effect of angle of nozzles <strong>on</strong> the product <strong>f<strong>in</strong>e</strong>ness<br />
Table 2.6 Particle size distributi<strong>on</strong> of ground clay and kaol<strong>in</strong><br />
Table 2.7 Particle size distributi<strong>on</strong> of barite at various feed size<br />
Table 2.8 Properties of silica and talc<br />
Table 2.9 Effect of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> time <strong>on</strong> crystall<strong>in</strong>ity (%) for basal<br />
planes<br />
Table 3.1 Dimensi<strong>on</strong>s of the <strong>jet</strong> <strong>mill</strong><br />
Table 3.2 Range of operati<strong>on</strong>al parameters<br />
Table 4.1 Chemical compositi<strong>on</strong> of silica and talc<br />
Table 4.2 The average airflow rate at each level of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
pressure<br />
Table 4.3 Operati<strong>on</strong>al parameters range for structural changes<br />
analysis <strong>in</strong> <strong>jet</strong> <strong>mill</strong><br />
viii<br />
18<br />
19<br />
20<br />
25<br />
38<br />
38<br />
39<br />
47<br />
66<br />
67<br />
85<br />
94<br />
139
Table 4.4<br />
Table 4.5<br />
Table 4.6<br />
Table 4.7<br />
Table 4.8<br />
Table 4.9<br />
Table 4.10<br />
Table 4.11<br />
Difference <strong>in</strong> peak positi<strong>on</strong> (<strong>in</strong> degree) of silica at various<br />
feed rate, classifier rotati<strong>on</strong>al speed and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
pressure<br />
Degree of crystall<strong>in</strong>ity (<strong>in</strong> %) of silica at various feed rate,<br />
classifier rotati<strong>on</strong>al speed and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure<br />
Crystallite size (<strong>in</strong> nm) of silica at various feed rate,<br />
classifier rotati<strong>on</strong>al speed and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure<br />
Lattice stra<strong>in</strong> of silica at various feed rate, classifier<br />
rotati<strong>on</strong>al speed and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure<br />
Difference <strong>in</strong> peak positi<strong>on</strong> (<strong>in</strong> degree) of talc at various<br />
feed rate, classifier rotati<strong>on</strong>al speed and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
pressure<br />
Degree of crystall<strong>in</strong>ity (<strong>in</strong> %) of talc at various feed rate,<br />
classifier rotati<strong>on</strong>al speed and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure<br />
Crystallite size (<strong>in</strong> nm) of talc at various feed rate,<br />
classifier rotati<strong>on</strong>al speed and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure<br />
Lattice stra<strong>in</strong> of talc at various feed rate, classifier<br />
rotati<strong>on</strong>al speed and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure<br />
ix<br />
144<br />
144<br />
145<br />
145<br />
152<br />
152<br />
153<br />
153
LIST OF FIGURES<br />
Figure 1.1 Loss of regularity <strong>in</strong> the crystall<strong>in</strong>e network<br />
Figure 2.1 Schematic diagram of opposed fluidized bed <strong>jet</strong> <strong>mill</strong><br />
Figure 2.2 Gr<strong>in</strong>d<strong>in</strong>g and classify<strong>in</strong>g chamber of opposed fluidized<br />
<strong>jet</strong> <strong>mill</strong><br />
Figure 2.3 Schematic representati<strong>on</strong> of breakage mechanism of<br />
hydrargillite particles <strong>in</strong> <strong>jet</strong> <strong>mill</strong><br />
Figure 2.4 Fragmentati<strong>on</strong> scheme for gibbsite ground <strong>in</strong> <strong>jet</strong> <strong>mill</strong><br />
Figure 2.5 Variati<strong>on</strong> of the circularity average values and the<br />
standard deviati<strong>on</strong><br />
Figure 2.6 Effect of separati<strong>on</strong> distance <strong>on</strong> the rate of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> for<br />
target plate <strong>jet</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
Figure 2.7 Effect of separati<strong>on</strong> distance <strong>on</strong> the rate of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> for<br />
two oppos<strong>in</strong>g nozzles <strong>jet</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
Figure 2.8 Types of nozzles: (a) abrupt nozzles (b) Laval shaped<br />
nozzles<br />
Figure 2.9 Median size of talc producti<strong>on</strong> as a functi<strong>on</strong> of feed rate<br />
for 7000 rpm (■), 9000 rpm (●), 11000 rpm (▲) and<br />
13000 rpm (▼)<br />
Figure 2.10 Influence of feed rate <strong>on</strong> product <strong>f<strong>in</strong>e</strong>ness <strong>in</strong> <strong>jet</strong> <strong>mill</strong><br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
Figure 2.11 Difference specific surface area created as the functi<strong>on</strong><br />
of the factor P/N 2 for the fluidized bed <strong>jet</strong> <strong>mill</strong><br />
Page number<br />
4<br />
Figure 2.12 Pr<strong>in</strong>ciple of an impeller air classifier 34<br />
Figure 2.13 Mass held <strong>in</strong> the <strong>mill</strong> at different classifier speed: 7000<br />
rpm stable (■), 7000 rpm unsteady (□), 9000 rpm stable<br />
35<br />
x<br />
16<br />
17<br />
21<br />
22<br />
24<br />
26<br />
27<br />
28<br />
30<br />
30<br />
32
(●), 9000 rpm unsteady (○), 11000 rpm stable (▲),<br />
11000 rpm unsteady (Δ), 13000 rpm stable (▼) and<br />
13000 rpm unsteady (∇)<br />
Figure 2.14 d50 of talc producti<strong>on</strong> as a functi<strong>on</strong> of feed rate for 7000<br />
rpm (■), 9000 rpm (●), 11000 rpm (▲) and 13000 rpm<br />
(▼)<br />
Figure 2.15 d50 of talc producti<strong>on</strong> as a functi<strong>on</strong> of mass of talc held<br />
up <strong>in</strong> the <strong>mill</strong> chamber for 7000 rpm (■), 9000 rpm (●),<br />
11000 rpm (▲) and 13000 rpm (▼)<br />
Figure 2.16 Specific energy c<strong>on</strong>sumpti<strong>on</strong> vs. average particle size<br />
for various motive gases<br />
Figure 2.17 Specific energy c<strong>on</strong>sumpti<strong>on</strong> vs. Specific surface area<br />
Figure 2.18 Solid behavior under stress<br />
Figure 2.19 Translati<strong>on</strong> the glide plane<br />
Figure 2.20 Edge dislocati<strong>on</strong> through a crystal dur<strong>in</strong>g plastic stra<strong>in</strong><br />
Figure 2.21 XRD patterns of anatase as a functi<strong>on</strong> of time<br />
Figure 2.22 X-ray diffracti<strong>on</strong> of arag<strong>on</strong>ite sample<br />
Figure 2.23 X-ray diffracti<strong>on</strong> patterns of orig<strong>in</strong>al and ground talc <strong>in</strong><br />
planetary <strong>mill</strong> at various <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> period<br />
Figure 2.24 Amorphizati<strong>on</strong> and relative <strong>in</strong>tensity at various specific<br />
energy <strong>in</strong>put<br />
Figure 2.25 Lattice stra<strong>in</strong> at various specific energy <strong>in</strong>put<br />
Figure 2.26 Crystallite size at various specific energy <strong>in</strong>put<br />
xi<br />
35<br />
36<br />
37<br />
37<br />
42<br />
43<br />
43<br />
45<br />
46<br />
47<br />
48<br />
49<br />
49
Figure 2.27 Particle size distributi<strong>on</strong> of kaol<strong>in</strong>ite ground <strong>in</strong> Herzog<br />
oscillat<strong>in</strong>g <strong>mill</strong> at different <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> period, 60 s, 120 s<br />
and 600 s<br />
Figure 2.28 Micrographs of kaol<strong>in</strong>ite ground <strong>in</strong> Herzog oscillat<strong>in</strong>g <strong>mill</strong><br />
(a) feed (b) ground at 120 s and (c) ground at 600 s.<br />
Figure 2.29<br />
Schematic representati<strong>on</strong> of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong><br />
Figure 2.30 Change <strong>in</strong> specific surface area of quartz (A), cement<br />
cl<strong>in</strong>ker (B) and limest<strong>on</strong>e (C) with <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> time<br />
Figure 2.31 Particle size distributi<strong>on</strong> of Product C ground <strong>in</strong> <strong>jet</strong> <strong>mill</strong> at<br />
(a) low energy trials (b) high energy trials<br />
Figure 2.32 Span of the size distributi<strong>on</strong> from five different types of<br />
<strong>mill</strong>s<br />
Figure 2.33 Change <strong>in</strong> X-ray diffracti<strong>on</strong> pattern of calcite caused by<br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
Figure 2.34<br />
B s<strong>in</strong>θ<br />
versus<br />
λ<br />
B cosθ<br />
plot<br />
λ<br />
Figure 2.35 IR spectra of hydroxyl stretch<strong>in</strong>g regi<strong>on</strong> for samples<br />
ground for (A) 0 m<strong>in</strong>, (b) 60 m<strong>in</strong>, (c) 180 m<strong>in</strong>, (D) 300<br />
m<strong>in</strong>, (E) 400 m<strong>in</strong> and (F) 600 m<strong>in</strong><br />
Figure 2.36 FTIR spectra of diphasic mullite gel: (A) – Unground (B)<br />
– ground<br />
Figure 2.37 FTIR spectra of gypsum mixed with 35% of talc,<br />
unground and ground for 240 m<strong>in</strong><br />
Figure 3.1<br />
Detail flow sheet of test work 64<br />
Figure 3.2 Riffle splliter 65<br />
Figure 3.3 Alp<strong>in</strong>e 100 AFG fluidized bed <strong>jet</strong> <strong>mill</strong><br />
65<br />
xii<br />
50<br />
50<br />
52<br />
52<br />
54<br />
55<br />
56<br />
57<br />
60<br />
61<br />
62
Figure 3.4 Schematic diagram of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> and classify<strong>in</strong>g chamber<br />
of <strong>jet</strong> <strong>mill</strong><br />
Figure 3.5<br />
(a) Nozzles <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber (b) Holdup <strong>in</strong> the<br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber<br />
Figure 3.6 Top of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong>-classify<strong>in</strong>g chamber and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
chamber pressure sensor<br />
Figure 3.7 Flowchart for raw materials characterizati<strong>on</strong> studies<br />
Figure 3.8 Particle size distributi<strong>on</strong> of (a) ground silica and (b)<br />
ground talc<br />
Figure 4.1 Particle size distributi<strong>on</strong> of silica and talc<br />
Figure 4.2 Photomicrograph of (a) silica (b) talc magnified 500X<br />
Figure 4.3 Photomicrograph of (a) silica (b) talc magnified 5000X<br />
Figure 4.4 X-ray Diffractogram of silica<br />
Figure 4.5 X-ray Diffractogram of talc<br />
Figure 4.6 Infrared spectroscopy of silica<br />
Figure 4.7 Infrared spectroscopy of talc<br />
Figure 4.8<br />
Particle size distributi<strong>on</strong> of feed and ground (a) silica<br />
and (b) talc<br />
Figure 4.9 d(4.3) of silica at various feed rate and classifier<br />
Figure 4.10<br />
rotati<strong>on</strong>al speed (a) 2 bars (b) 3 bars (c) 4 bars (d) 5<br />
bars (e) 6 bars<br />
d(4.3) of talc at various feed rate and classifier rotati<strong>on</strong>al<br />
speed (a) 2 bars (b) 3 bars (c) 4 bars (d) 5 bars (e) 6<br />
xiii<br />
68<br />
69<br />
70<br />
73<br />
74<br />
83<br />
83<br />
83<br />
84<br />
84<br />
86<br />
86<br />
88<br />
91<br />
93
Figure 4.11<br />
bars<br />
d(4.3) of silica at various level of P/N 2<br />
Figure 4.12 d(4.3) of talc at various level of P/N 2<br />
Figure 4.13 Span value of silica at various feed rate and classifier<br />
rotati<strong>on</strong>al speed (a) 2 bars (b) 3 bars (c) 4 bars (d) 5<br />
bars (e) 6 bars<br />
Figure 4.14 Span value of talc at various feed rate and classifier<br />
rotati<strong>on</strong>al speed (a) 2 bars (b) 3 bars (c) 4 bars (d) 5<br />
bars (e) 6 bars<br />
Figure 4.15<br />
Span value of silica at various level of P/N 2<br />
Figure 4.16 Span value of talc at various level of P/N 2<br />
Figure 4.17 Gr<strong>in</strong>d<strong>in</strong>g chamber pressure of silica at various feed rate<br />
and classifier rotati<strong>on</strong>al speed (a) 2 bars (b) 3 bars (c) 4<br />
bars (d) 5 bars (e) 6 bars<br />
Figure 4.18 Gr<strong>in</strong>d<strong>in</strong>g chamber pressure of talc at various feed rate<br />
and classifier rotati<strong>on</strong>al speed (a) 2 bars (b) 3 bars (c) 4<br />
bars (d) 5 bars (e) 6 bars<br />
Figure 4.19<br />
Figure 4.20<br />
95<br />
95<br />
98<br />
100<br />
101<br />
101<br />
104<br />
106<br />
d(4.3) of silica at various <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber pressure 109<br />
d(4.3) of talc at various <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber pressure<br />
Figure 4.21 Span value of silica at various <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber<br />
pressure<br />
Figure 4.22<br />
109<br />
110<br />
Span value of talc at various <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber pressure 110<br />
Figure 4.23 d(4.3) various level of holdup height of silica and talc 112<br />
xiv
Figure 4.24<br />
Figure 4.25<br />
Figure 4.26<br />
Figure 4.27<br />
Figure 4.28<br />
Figure 4.29<br />
Figure 4.30<br />
Figure 4.31<br />
Figure 4.32<br />
Figure 4.33<br />
Figure 4.34<br />
Figure 4.35<br />
Figure 4.36<br />
Figure 4.37<br />
Span values at various level of holdup height of silica<br />
and talc<br />
112<br />
(a) d(4.3) and (b) span of silica at various level of holdup 114<br />
(a) d(4.3) and (b) span of talc at various level of holdup<br />
Particle size analysis profile of feed and ground silica at<br />
various operati<strong>on</strong>al parameters<br />
Photomicrograph<br />
parameter<br />
of silica at various operati<strong>on</strong>al<br />
Circularity of ground silica at various feed rate and<br />
classifier frequency (a) 2 bars (b) 4 bars (c) 6 bars<br />
Suggested breakage mechanism of silica ground <strong>in</strong> <strong>jet</strong><br />
<strong>mill</strong><br />
Particle size analysis profile of feed and ground talc at<br />
various operati<strong>on</strong>al parameters<br />
Photomicrograph of talc at (various operati<strong>on</strong>al<br />
parameters<br />
Circularity of ground talc at various feed rate and<br />
classifier frequency (a) 2 bars (b) 4 bars (c) 6 bars<br />
Suggested breakage mechanism of talc ground <strong>in</strong> <strong>jet</strong><br />
<strong>mill</strong><br />
X-ray diffracti<strong>on</strong> profile of silica at various <strong>jet</strong> <strong>mill</strong><br />
parameters<br />
115<br />
119<br />
123<br />
126<br />
124<br />
131<br />
135<br />
137<br />
138<br />
142<br />
X-ray diffracti<strong>on</strong> profile of talc at various <strong>jet</strong> <strong>mill</strong><br />
parameters<br />
150<br />
Infrared spectroscopy profile of feed and ground silica 158<br />
xv
Figure 4.38<br />
Figure 4.39<br />
Figure 4.40<br />
Figure 4.41<br />
at various operati<strong>on</strong>al parameters<br />
Abs475/Abs1100 ratio of ground silica at various classifier<br />
rotati<strong>on</strong>al speed at (a) 2 bars, (b) 4 bars and (c) 6 bars<br />
Infrared spectroscopy profile of feed and ground talc at<br />
various operati<strong>on</strong>al parameters<br />
Abs465/Abs1017 ratio of ground talc at various classifier<br />
rotati<strong>on</strong>al speed at (a) 2 bars, (b) 4 bars and (c) 6 bars<br />
160<br />
164<br />
166<br />
d(4.3) of silica at various specific k<strong>in</strong>etic energy 168<br />
Figure 4.42 d(4.3) of talc at various specific energy c<strong>on</strong>sumpti<strong>on</strong> 168<br />
Figure 4.43 Span values of silica at various specific k<strong>in</strong>etic energy 169<br />
Figure 4.44 Span values of talc at various specific k<strong>in</strong>etic energy<br />
Figure 4.45 Degree of crystall<strong>in</strong>ity of silica and talc at various level of<br />
specific k<strong>in</strong>etic energy<br />
Figure 4.46 Diagram show<strong>in</strong>g the characteristics of ground silica at<br />
various operati<strong>on</strong>al parameters<br />
Figure 4.47 Diagram show<strong>in</strong>g the characteristics of ground silica at<br />
various operati<strong>on</strong>al parameters<br />
xvi<br />
169<br />
170<br />
172<br />
173
Rj rupture of jo<strong>in</strong>ts<br />
CI cleavage<br />
Ch chipp<strong>in</strong>g<br />
Gr ultimate <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
LIST OF ABBREVIATION<br />
ICDD Internati<strong>on</strong>al Center for Diffracti<strong>on</strong> Data<br />
FR Feed rate<br />
CRS Classifier rotati<strong>on</strong>al speed<br />
GP Gr<strong>in</strong>d<strong>in</strong>g pressure<br />
GCP Gr<strong>in</strong>d<strong>in</strong>g chamber pressure<br />
xvii
P Gr<strong>in</strong>d<strong>in</strong>g pressure<br />
LIST OF SYMBOLS<br />
N Classifier rotati<strong>on</strong>al speed<br />
ρ density<br />
B half width<br />
θ the Bragg angle of (h k l) reflecti<strong>on</strong><br />
ε lattice stra<strong>in</strong><br />
D crystallite size<br />
C crystall<strong>in</strong>ity <strong>in</strong>dex<br />
BBo<br />
background of the feed<br />
B background of the ground samples<br />
Io<br />
<strong>in</strong>tegral <strong>in</strong>tensities of diffracti<strong>on</strong> l<strong>in</strong>es for feed<br />
I <strong>in</strong>tegral <strong>in</strong>tensities of diffracti<strong>on</strong> l<strong>in</strong>es for ground samples<br />
Am amorphous fracti<strong>on</strong><br />
Ao<br />
areas under the prom<strong>in</strong>ent plane for feed<br />
A areas under the prom<strong>in</strong>ent plane for ground sample<br />
Hh<br />
Hc<br />
height of holdup<br />
the distance between surface of holdup and classifier<br />
x distance between top of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong>-classify<strong>in</strong>g chamber and surface<br />
x<br />
of holdup<br />
average value<br />
n number of samples<br />
xi<br />
data collected<br />
d(4.3) Volume moment diameter<br />
d50<br />
xk<br />
dk<br />
Mean particle size<br />
number percentage of detected diameter<br />
detected diameter<br />
xviii
ψ span values<br />
di<br />
Kα<br />
βf<br />
βh<br />
βg<br />
Dv<br />
i% smaller than<br />
K c<strong>on</strong>stant<br />
spectral l<strong>in</strong>e for an element<br />
<strong>in</strong>tegral breadths of the <strong>in</strong>strumental<br />
<strong>in</strong>tegral breadths observed<br />
<strong>in</strong>tegral breadths of measured profile<br />
volume weighted mean of the crystallite size<br />
θ Bragg angle of (h k l) reflecti<strong>on</strong><br />
λ wavelength of X-rays used<br />
ε lattice stra<strong>in</strong><br />
r rotor radius<br />
vϕ<br />
vr<br />
xc<br />
ρs<br />
circumferential velocity<br />
radial velocity<br />
cut size<br />
density of solids<br />
η dynamics viscosity<br />
R maximum reducti<strong>on</strong> ratio<br />
( 4.<br />
3)<br />
max<br />
f<br />
d . 3<br />
4 volume moment diameter of feed<br />
p<br />
d . 3<br />
4 volume moment diameter of ground product<br />
Absn<br />
Ek<strong>in</strong>etic<br />
mg<br />
Absorpti<strong>on</strong> at wavelength n<br />
k<strong>in</strong>etic energy<br />
mass of gas<br />
v gas velocity<br />
ϕ gas c<strong>on</strong>stant<br />
P gas pressure<br />
xix
ρg<br />
Gas density<br />
SEC specific energy c<strong>on</strong>sumpti<strong>on</strong><br />
F feed rate<br />
C Circularity<br />
Deq<br />
A Area<br />
P Perimeter<br />
Equivelent diameter<br />
xx
LIST OF PUBLICATION<br />
Samayamutthirian Palaniandy, Khairun Azizi Mohd Azizli, Hashim Huss<strong>in</strong> and Syed<br />
Fuad Saiyid Hashim. (2007) Mechanochemistry of silica <strong>on</strong> Jet Mill. Journal of<br />
Materials Process<strong>in</strong>g Technology. Accepted for publicati<strong>on</strong>.<br />
Samayamutthirian Palaniandy, Khairun Azizi Mohd Azizli, Hashim Huss<strong>in</strong> and Syed<br />
Fuad Saiyid Hashim. (2007). Effect of operati<strong>on</strong>al parameters <strong>on</strong> the breakage<br />
mechanism of silica <strong>in</strong> a <strong>jet</strong> <strong>mill</strong>. M<strong>in</strong>erals Eng<strong>in</strong>eer<strong>in</strong>g. Accepted for publicati<strong>on</strong><br />
Samayamutthirian Palaniandy, Khairun Azizi Mohd Azizli, Mariatti Jaafar, Farrah<br />
Noor Ahmad, Hashim Huss<strong>in</strong> and Syed Fuad Saiyid Hashim. (2007) Effect of<br />
structural changes of silica filler <strong>on</strong> the coefficient of thermal expansi<strong>on</strong> (CTE) of<br />
underfill encapsulant. Powder Technology, In Press, Accepted Manuscript.<br />
F.N. Ahmad, Mustapha Mariatti, Samayamutthirian Palaniandy and Khairun Azizi<br />
Mohd Azizli. (2007). Effect of particle shape of silica m<strong>in</strong>eral <strong>on</strong> the properties of<br />
epoxy composites. Composites Science and Technology, In Press, Corrected Proof.<br />
Samayamutthirian Palaniandy, Syed Fuad Saiyid Hashim, Hashim Huss<strong>in</strong> and<br />
Khairun Azizi Mohd Azizli. (2004). Structural Defects dur<strong>in</strong>g F<strong>in</strong>e <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> Process.<br />
Journal of Solid State Science and Technology Letters .11, 2 (Supplementary).<br />
Samayamutthirian Palaniandy, Khairun Azizi Mohd Azizli Syed Fuad Saiyid Hashim,<br />
and Hashim Huss<strong>in</strong>. Microstructure characterizati<strong>on</strong> of mechanically activated<br />
nanocrystallite quartz us<strong>in</strong>g XRD l<strong>in</strong>e broaden<strong>in</strong>g. (2006) Proceed<strong>in</strong>g of Internati<strong>on</strong>al<br />
xxi
C<strong>on</strong>ference <strong>on</strong> X-Ray and Related Techniques <strong>in</strong> Research and Industry. Penang,<br />
Malaysia. Putrajaya, Malaysia.<br />
Samayamutthirian Palaniandy, Syed Fuad Saiyid Hashim, Hashim Huss<strong>in</strong> and<br />
Khairun Azizi Mohd Azizli. (2004). Effect of hardness <strong>on</strong> the particle morphology<br />
dur<strong>in</strong>g <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> <strong>in</strong> <strong>jet</strong> <strong>mill</strong>. 13 th Scientific C<strong>on</strong>ference Electr<strong>on</strong><br />
Microscopy Society Of Malaysia. Putrajaya, Malaysia.<br />
Samayamutthirian Palaniandy, Khairun Azizi Mohd Azizli Syed Fuad Saiyid Hashim,<br />
and Hashim Huss<strong>in</strong>. Effect of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure and classifier frequency <strong>on</strong> the<br />
particle shape of silica ground <strong>in</strong> Opposed fluidized be <strong>jet</strong> <strong>mill</strong>. (2006) 15 th Scientific<br />
C<strong>on</strong>ference Electr<strong>on</strong> Microscopy Society Of Malaysia. Penang, Malaysia.<br />
Samayamutthirian Palaniandy, Khairun Azizi Mohd Azizli Syed Fuad Saiyid Hashim,<br />
and Hashim Huss<strong>in</strong>. Effect of Jet Mill’s Operati<strong>on</strong>al Parameters <strong>on</strong> the product<br />
quality dur<strong>in</strong>g Silica Gr<strong>in</strong>d<strong>in</strong>g. (2007). Proceed<strong>in</strong>g of PSU-UNS Internati<strong>on</strong>al<br />
C<strong>on</strong>ference <strong>on</strong> Eng<strong>in</strong>eer<strong>in</strong>g and Envir<strong>on</strong>ment, Phuket, Thailand.<br />
Samayamutthirian Palaniandy, Khairun Azizi Mohd Azizli Syed Fuad Saiyid Hashim,<br />
and Hashim Huss<strong>in</strong>. Microstructure Characterizati<strong>on</strong> of Mechanically Activated Talc<br />
<strong>in</strong> Jet Mill us<strong>in</strong>g L<strong>in</strong>e Broaden<strong>in</strong>g Technique. (2007) Proceed<strong>in</strong>g of Internati<strong>on</strong>al<br />
C<strong>on</strong>ference <strong>on</strong> Advancement of Materials and Nanotechnology. Langkawi, Malaysia.<br />
xxii
A Study <strong>on</strong> Ultra F<strong>in</strong>e Gr<strong>in</strong>d<strong>in</strong>g of Silica and Talc<br />
In Opposed Fluidized Bed Jet Mill<br />
ABSTRACT<br />
F<strong>in</strong>e <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> is normally carried out <strong>in</strong> energy <strong>in</strong>tensive <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s such as <strong>jet</strong> <strong>mill</strong>.<br />
Besides size reducti<strong>on</strong>, <strong>jet</strong> <strong>mill</strong> also <strong>in</strong>duced mechanochemical effect <strong>on</strong> the ground<br />
product. F<strong>in</strong>e <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> testwork of silica and talc was carried out <strong>in</strong> <strong>jet</strong> <strong>mill</strong> by vary<strong>in</strong>g<br />
the feed rate, classifier rotati<strong>on</strong>al speed and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure at five levels. In this <strong>jet</strong><br />
<strong>mill</strong>, <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> and classificati<strong>on</strong> took place simultaneously. The <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber<br />
pressure, holdup height and mass, classifier current and specific energy c<strong>on</strong>sumpti<strong>on</strong><br />
were determ<strong>in</strong>ed. The ground products were characterized <strong>in</strong> terms of particle size<br />
distributi<strong>on</strong> and mechanochemical effect via X-ray diffracti<strong>on</strong> and Infrared<br />
Spectroscopy (IR). The ground product exhibit poly-modal distributi<strong>on</strong> so its particle<br />
size was characterized by volume moment diameter. Coarser particle size distributi<strong>on</strong><br />
was obta<strong>in</strong>ed at higher classifier rotati<strong>on</strong>al speed due to the fluctuati<strong>on</strong> of <strong>in</strong>side <strong>mill</strong><br />
c<strong>on</strong>diti<strong>on</strong> and particles characteristics which deviated from Stokes law. The optimum<br />
feed rate, classifier rotati<strong>on</strong>al speed and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure for silica and talc were 4<br />
kg/h, 13000 rpm, 5 bars and 8 kg/h, 7000 rpm, 3 bars respectively. The optimum<br />
holdup mass ranged from 200g to 400g. The optimum holdup height and distance<br />
between the holdup surface and classifier were 10 cm and 12.5 cm respectively. Under<br />
pressure c<strong>on</strong>diti<strong>on</strong> <strong>in</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong>-classify<strong>in</strong>g chamber produced <strong>f<strong>in</strong>e</strong>r particles. At lower<br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure, abrasi<strong>on</strong> breakage mechanism is dom<strong>in</strong>ant for silica whilst<br />
delam<strong>in</strong>ati<strong>on</strong> of nano-layer was dom<strong>in</strong>ant for talc. At high <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure, silica and<br />
talc exhibited destructive breakage mechanism. Ground silica and talc exhibited<br />
reducti<strong>on</strong> <strong>in</strong> circularity values. Ground silica and talc exhibited mechanochemical effect<br />
where the degree of crystall<strong>in</strong>ity ranged from 71.1% to 90.9% and 43.3% to 85.3%<br />
respectively. The crystall<strong>in</strong>e size and lattice stra<strong>in</strong> of silica ranged from 22.71 nm to<br />
35.54 nm and 0.024 to 0.037 respectively. The crystall<strong>in</strong>e size and lattice stra<strong>in</strong> of talc<br />
ranged from 147.69 nm to 353.72 nm and 0.08 to 0.2 respectively. Reducti<strong>on</strong> of<br />
hydroxyl band and broaden<strong>in</strong>g of Si-O stretch<strong>in</strong>g band for silica and Si-O-Mg and<br />
hydroxyl band for talc were observed via IR. Optimum specific energy c<strong>on</strong>sumpti<strong>on</strong><br />
was 100kWh/t<strong>on</strong> and 1000 kWh/t<strong>on</strong> for silica and talc respectively.<br />
xxiii
Kajian Tentang Pengisaran Ultra Halus Silika Dan Talkum Di Dalam Pengisar Jet<br />
Lapisan Bendalir Bertentangan<br />
ABSTRAK<br />
Proses pengisaran halus biasanya dilakukan di dalam pengisar <strong>in</strong>tensif tenaga seperti<br />
pengisar <strong>jet</strong>. Sela<strong>in</strong> daripada pengurangan saiz, pengisar <strong>jet</strong> juga meghasilkan kesan<br />
mekanokimia terhadap partikel yang dikisar. Kajian pengisaran halus silika dan talkum telah<br />
dilakukan di dalam pengisar <strong>jet</strong> dengan mengubah kadar suapan, halaju putaran pengkelas<br />
dan tekanan pengisar pada lima per<strong>in</strong>gkat. Proses pengisaran dan pengkelasan berlaku<br />
serentak di dalam pengisar <strong>jet</strong> <strong>in</strong>i. Tekanan dandang pengisar, jisim dan ket<strong>in</strong>ggian lapisan<br />
bendalir, arus pengkelas dan penggunaan tenaga spesifik telah ditentukan. Produk terkisar<br />
dicirikan berdasarkan taburan saiz partikel dan kesan mekanokimia menggunakan Belauan<br />
S<strong>in</strong>ar-X dan Spektrskopi Inframerah. Produk terkisar menunjukkan taburan saiz partikel polimodel<br />
maka saiz partikel dicirikan dengan diameter momen isipadu. Saiz partikel yang<br />
kasar diperolehi pada halaju putaran pengkelas yang t<strong>in</strong>ggi disebabkan perubahan keadaan<br />
di dalam pengisar dan ciri partikel bercanggah dengan Hukum Stoke. Kadar suapan, halaju<br />
putaran pengisar dan tekanan pengisaran yang optimum untuk silika dan talkum mas<strong>in</strong>gmas<strong>in</strong>g<br />
adalah 4 kg/h, 13000 rpm, 5 bar dan 8 kg/h, 7000 rpm, 3 bar. Jisim lapisan<br />
terbendalir optimum adalah diantara 200g h<strong>in</strong>gga 400g. Ket<strong>in</strong>ggian optimum lapisan<br />
terbendalir dan jarak optimum antara lapisan terbendalir dan pengkelas adalah mas<strong>in</strong>gmas<strong>in</strong>g<br />
10 cm dan 12.5 cm. Keadaan tekanan bawahan menghasilkan produk yang lebih<br />
halus. Pada tekanan pengisaran rendah, mekanisme pemecahan lelasan adalah dom<strong>in</strong>an<br />
untuk silika manakala dilam<strong>in</strong>asi lapisan-nano pula dom<strong>in</strong>an untuk talkum. Pada tekanan<br />
pengisaran yang t<strong>in</strong>ggi, silika dan talkum mengalami mekanisme pemecahan memb<strong>in</strong>asa.<br />
Silika dan talkum terkisar menunjukkan pengurangan nilai <strong>in</strong>deks kebulatan. Silika dan<br />
talkum terkisar mengalami kesan mekanokimia di mana darjah pengkristalan adalah mas<strong>in</strong>gmas<strong>in</strong>g<br />
diantara 71.1% seh<strong>in</strong>gga 90.9% dan 43.3% h<strong>in</strong>gga 85.3%. Saiz kristal dan terikan<br />
kekisi silika mas<strong>in</strong>g-mas<strong>in</strong>g di dalam julat diantara 22.71 nm h<strong>in</strong>gga 35.54 nm dan 0.024<br />
h<strong>in</strong>gga 0.037. Manakala, saiz kristal dan terikan kekisi talkum mas<strong>in</strong>g-mas<strong>in</strong>g dalam julat<br />
diantara 147.69 nm h<strong>in</strong>gga 353.72 nm dan 0.08 h<strong>in</strong>gga 0.2. Pengurangan jalur hidroksil dan<br />
pengembangan jalur regangan Si-O untuk silika dan jalur Si-O-Mg dan hidroksil untuk talkum<br />
diperhatikan melalui FTIR. Penggunaan tenaga spesifik optimum mas<strong>in</strong>g-mas<strong>in</strong>g untuk silika<br />
dan talkum adalah 100 kWjam/tan dan 1000 kWjam/tan.<br />
xxiv
1.0 Introducti<strong>on</strong><br />
CHAPTER 1<br />
The scope of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> can be divided <strong>in</strong>to three categories which are coarse <strong>gr<strong>in</strong>d<strong>in</strong>g</strong>,<br />
<strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> and mechanical activati<strong>on</strong> and is dist<strong>in</strong>ct by the amount of energy<br />
delivered by the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s to the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> tools and the materials to be ground<br />
(Boldyrev et. al., 1996; Tkacova, 1989). The objective of coarse <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> is for size<br />
reducti<strong>on</strong> while mechanical activati<strong>on</strong> is for structural changes of the ground particles<br />
to <strong>in</strong>crease the reactivity of the particles. F<strong>in</strong>e <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> is an <strong>in</strong>termediate case between<br />
coarse <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> and mechanical activati<strong>on</strong> and is ga<strong>in</strong><strong>in</strong>g its importance as the demand<br />
for <strong>f<strong>in</strong>e</strong> particles from various <strong>in</strong>dustries such as paper, pa<strong>in</strong>t, plastic, pharmaceuticals,<br />
ceramics, cosmetics, foods and <strong>f<strong>in</strong>e</strong> chemicals is <strong>in</strong>creas<strong>in</strong>g drastically (Belaroui et. al.,<br />
1999; Belaroui et. al., 2002; Mol<strong>in</strong>a-Boisseau et. al., 2002; He et. al., 2004; Frances et.<br />
al., 1996). These <strong>in</strong>dustries demand very str<strong>in</strong>gent <strong>f<strong>in</strong>e</strong> particle specificati<strong>on</strong>s <strong>in</strong> terms<br />
of particle size and its distributi<strong>on</strong> (Belaroui et. al., 2002). Besides these two criteria,<br />
lately the degree of crystall<strong>in</strong>ity of <strong>f<strong>in</strong>e</strong> m<strong>in</strong>eral particles below 10 µm is becom<strong>in</strong>g more<br />
important as <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> produces particles with nanocrystallite structure<br />
which exhibits abnormal behavior such as enhance hydrometallurgy <strong>process</strong>, low<br />
anneal<strong>in</strong>g temperature, reactivity improvement of cementitious materials, formati<strong>on</strong> of<br />
metastable phases and particles with high surface energy (Tkacova, 1989). Table 1.1<br />
shows the characteristics and applicati<strong>on</strong> of silica and talc as m<strong>in</strong>eral fillers by various<br />
<strong>in</strong>dustries.<br />
F<strong>in</strong>e <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> is normally carried out <strong>in</strong> high <strong>in</strong>tensity <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s such as planetary<br />
<strong>mill</strong>, attriti<strong>on</strong> <strong>mill</strong>, oscillat<strong>in</strong>g <strong>mill</strong> and <strong>jet</strong> <strong>mill</strong>. These <strong>mill</strong>s deliver huge amount of energy<br />
for particle breakage to produce particles below 10µm. However, mechanochemical<br />
effect is <strong>in</strong>duced by <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> when the power bulk density is more than 0.1<br />
kWm -3 (Tkacova, 1989). The severe and high <strong>in</strong>tensity energy delivered by the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
1
<strong>mill</strong> <strong>on</strong>to the particles leads to structural changes near surface regi<strong>on</strong> where the solids<br />
come <strong>in</strong>to c<strong>on</strong>tact under mechanical forces besides size reducti<strong>on</strong>. The structural<br />
changes <strong>in</strong>duces changes <strong>in</strong> crystall<strong>in</strong>ity, crystallite size and lattice stra<strong>in</strong>. These<br />
changes are generally termed as mechanochemical effect (Venkataraman and<br />
Narayanan, 1998). Vibrati<strong>on</strong> <strong>mill</strong>, stirred <strong>mill</strong>, <strong>jet</strong> <strong>mill</strong> and planetary <strong>mill</strong> experienced<br />
mechanochemical effect dur<strong>in</strong>g the <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong>, which agrees with Table 1.2.<br />
Table 1.1: Characterizati<strong>on</strong> of silica and talc as m<strong>in</strong>eral fillers <strong>in</strong> various<br />
<strong>in</strong>dustries (J<strong>on</strong>es, 2002; O’Driscoll, 1992; Loughbrough, 1993)<br />
Industries M<strong>in</strong>erals d50, μm Functi<strong>on</strong> Phase<br />
Plastic<br />
Silica 2.5-13 Filler/extender/<br />
re<strong>in</strong>forcement<br />
Talc 1-20 Filler<br />
Crystall<strong>in</strong>e/<br />
amorphous<br />
Adhesives Silica 0.05-2 Filler amorphous<br />
/Sealant Talc 10 Filler/Extender NA<br />
Pa<strong>in</strong>t<br />
Silica 2.5-10 Filler Crystall<strong>in</strong>e<br />
Talc 1.7-9 Filler/Extender Crystall<strong>in</strong>e<br />
Paper Talc 5 Filler Crystall<strong>in</strong>e<br />
Cosmetics Talc 5 Filler/Lubricant NA<br />
Pharmaceutical Talc 1 Filler/dust<strong>in</strong>g Crystall<strong>in</strong>e/<br />
amorphous<br />
NA – Not available<br />
Table 1.2: Power bulk densities <strong>in</strong> various <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s (Tkacova, 1989)<br />
Gr<strong>in</strong>d<strong>in</strong>g <strong>mill</strong>s Power bulk densities (kWm -3 )<br />
Ball <strong>mill</strong> 0.01 - 0.03<br />
Peripheral <strong>mill</strong> 0.03 – 0.10<br />
Vibrati<strong>on</strong> <strong>mill</strong> 0.03 – 0.90<br />
Jet <strong>mill</strong> 0.07 – 2.00<br />
Stirred <strong>mill</strong> 0.10 – 1.00<br />
Planetary <strong>mill</strong> 0.50 – 5.00<br />
2
Although <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> will <strong>in</strong>duce mechanochemical effect that enhances certa<strong>in</strong><br />
properties of the downstream <strong>in</strong>dustries, but certa<strong>in</strong> applicati<strong>on</strong> needs crystall<strong>in</strong>e<br />
particles (Samtani et. al., 2001). The mechanochemical effect can’t be avoided dur<strong>in</strong>g<br />
<strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> as it happens c<strong>on</strong>currently with the size reducti<strong>on</strong> <strong>process</strong> (Beg<strong>in</strong>-<br />
Col<strong>in</strong> et. al., 2000). The challenge is to c<strong>on</strong>trol the energy <strong>in</strong>tensity <strong>in</strong>duced <strong>on</strong> the<br />
particles so that the ground product can ma<strong>in</strong>ta<strong>in</strong> its crystall<strong>in</strong>ity if needed. The c<strong>on</strong>trol<br />
of partially amorphous and crystall<strong>in</strong>e particles at certa<strong>in</strong> percentages to <strong>in</strong>crease the<br />
particle reactivity without jeopardiz<strong>in</strong>g the quality will be the future for the producti<strong>on</strong> of<br />
<strong>f<strong>in</strong>e</strong> particles.<br />
1.1 Mechanochemical Effect Induced By F<strong>in</strong>e Gr<strong>in</strong>d<strong>in</strong>g Process<br />
Dur<strong>in</strong>g mechanical stress<strong>in</strong>g <strong>in</strong> <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong>, part of the energy is stored <strong>in</strong> the<br />
materials (Iguchi and Senna, 1985). In the case of n<strong>on</strong>metallic m<strong>in</strong>erals which have low<br />
thermal c<strong>on</strong>ductivity, the energy delivered by the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s is not stored <strong>in</strong> the<br />
particles as thermal energy but applied to bend<strong>in</strong>g or break<strong>in</strong>g of crystal. In <strong>f<strong>in</strong>e</strong><br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong>, apart from produc<strong>in</strong>g important changes <strong>in</strong> the properties of the solid,<br />
leads to structural alterati<strong>on</strong> by loss of regularity <strong>in</strong> the crystall<strong>in</strong>e network<br />
(amorphizati<strong>on</strong>) as well as formati<strong>on</strong> of active surfaces and leads to <strong>in</strong>crease reactivity<br />
as shown <strong>in</strong> Figure 1.1 (Aglietti et. al., 1986a; Al-Wakeel, 2005; Tkacova, 1989).<br />
Accord<strong>in</strong>g to Juhasz and Opoczky (1990), 3.7% of the total energy supplied to a<br />
vibrati<strong>on</strong> <strong>mill</strong> dur<strong>in</strong>g quartz <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> was used for phase transformati<strong>on</strong> while the major<br />
porti<strong>on</strong>s were lost as heat and mechanical losses.<br />
3
Slip plane<br />
Edge dislocati<strong>on</strong><br />
Shear stress<br />
Figure 1.1: Loss of regularity <strong>in</strong> the crystall<strong>in</strong>e network (Tkacova, 1989)<br />
Mechanochemical effect <strong>in</strong> <strong>f<strong>in</strong>e</strong> particles has created <strong>in</strong>terest am<strong>on</strong>g researchers due<br />
to the abnormal behavior of the ground <strong>f<strong>in</strong>e</strong> particles which has crystallite size <strong>in</strong><br />
nanometer range (Bid et. al., 2001). These particles exhibit abnormalities such as<br />
<strong>in</strong>crease <strong>in</strong> reactivity, reducti<strong>on</strong> <strong>in</strong> <strong>in</strong>itial thermal decompositi<strong>on</strong> temperature, phase<br />
transformati<strong>on</strong>, decrease <strong>in</strong> s<strong>in</strong>ter<strong>in</strong>g temperatures and enhancement of leach<strong>in</strong>g<br />
<strong>process</strong> due to amorphizati<strong>on</strong> and smaller crystallite size. (G<strong>on</strong>zalez et.al., 2000;<br />
Zhang et. al., 1996; Temuuj<strong>in</strong> et. al., 1999; Beg<strong>in</strong>-Col<strong>in</strong> et. al., 1999; Sanchez et. al.,<br />
2004; Mi et. al., 1999; Welham, 1998; Kal<strong>in</strong>k<strong>in</strong> et. al., 2003; Ryou, 2004; Hu et. al.,<br />
2003; Benezet and Benhassa<strong>in</strong>e, 1999).<br />
Another issue that relates to mechanochemical effect dur<strong>in</strong>g <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> is<br />
the exist<strong>in</strong>g of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> limit. Boldyrev et. al. (1996) menti<strong>on</strong>ed that there was a certa<strong>in</strong><br />
size called tough-brittle transiti<strong>on</strong> size where particle above this size particle would<br />
experienced brittle breakage whilst particles smaller than this size would experienced<br />
plastic deformati<strong>on</strong>. The stress required to break a small particle may be rather high,<br />
especially if the material is hard. The mechanical impacts <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong> were<br />
obvious to be limited by <strong>in</strong>tensity which was determ<strong>in</strong>ed by <strong>mill</strong> design and the<br />
operat<strong>in</strong>g c<strong>on</strong>diti<strong>on</strong> (Boldyrev et. al., 1996). Mechanochemical effect took place if the<br />
particle size was smaller than the tough-brittle transiti<strong>on</strong> size, and sec<strong>on</strong>dly, the stress<br />
4
<strong>on</strong> the particle should be higher than yield stress, which depended <strong>on</strong> the particle size<br />
(Boldyrev et. al., 1996).<br />
Ground product produced through <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> exhibited high surface energy.<br />
The <strong>in</strong>creased <strong>in</strong> the surface energy <strong>on</strong> the ground particles led to a major problem<br />
which was <strong>in</strong>teracti<strong>on</strong> between <strong>f<strong>in</strong>e</strong> particles which resulted <strong>in</strong> the formati<strong>on</strong> of larger<br />
particles especially when the particle size was less than 10 µm. Juhasz and Opoczky<br />
(1990) had suggested that there were three stages of <strong>in</strong>teracti<strong>on</strong> between the particles<br />
which were adherence, aggregati<strong>on</strong> and agglomerati<strong>on</strong>. At adherence stage, particles<br />
would coat the apparatus and the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> bodies. At aggregati<strong>on</strong> stage, the particles<br />
were associated by weak van der Waals type of adhesi<strong>on</strong> and it was reversible<br />
<strong>in</strong>teracti<strong>on</strong>. Agglomerati<strong>on</strong> was de<strong>f<strong>in</strong>e</strong>d as a very compact, irreversible <strong>in</strong>teracti<strong>on</strong> of<br />
particles <strong>in</strong> which chemical b<strong>on</strong>d<strong>in</strong>g may also play a role which may occur dur<strong>in</strong>g <strong>f<strong>in</strong>e</strong><br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong>. Agglomerati<strong>on</strong> is detrimental to both the activity and the quality of the<br />
product. Currently, <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> aids are used to avoid the agglomerati<strong>on</strong> dur<strong>in</strong>g <strong>f<strong>in</strong>e</strong><br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> (Godet-Morand et. al., 2002; Rajendran and Paramasivam, 1999;<br />
Frances et. al., 1996).<br />
1.1.1 Mechanochemical Effect Induced In Jet Mill<br />
Jet <strong>mill</strong> is classified as a high <strong>in</strong>tensity <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong> which is normally used to produce<br />
particles below 10 µm (Alfano et. al., 1996; Esk<strong>in</strong> and Voropayev, 2001; Tasir<strong>in</strong> and<br />
Geldart, 1999; Benz et. al., 1996). It is widely used <strong>in</strong> m<strong>in</strong>eral, pharmaceutical and <strong>f<strong>in</strong>e</strong><br />
chemicals <strong>in</strong>dustries compared to other types of size reducti<strong>on</strong> mach<strong>in</strong>es due to its<br />
narrow size distributi<strong>on</strong> as obta<strong>in</strong>ed by Choi et. al. (2004), the absence of<br />
c<strong>on</strong>tam<strong>in</strong>ati<strong>on</strong> due to autogeneous <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> mechanism, low wear rate, small footpr<strong>in</strong>t,<br />
low noise and the ability of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> heat sensitive materials (Berthiaux and Dodds,<br />
1999; Midoux et. al., 1999; Kolacz, 2004; Muller et. al., 1996).<br />
5
Mechanochemical effect normally takes place when batch <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> is carried out for<br />
l<strong>on</strong>ger <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> period <strong>in</strong> high <strong>in</strong>tensity <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s (Kanno, 1985; G<strong>on</strong>zalez et. al.,<br />
2000). Jet <strong>mill</strong> is a c<strong>on</strong>t<strong>in</strong>uous type <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong> with <strong>in</strong>ternal classificati<strong>on</strong> which means<br />
size reducti<strong>on</strong> and classificati<strong>on</strong> will take place simultaneously. In <strong>jet</strong> <strong>mill</strong> the retenti<strong>on</strong><br />
time of particles <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber is very short because the particles will be<br />
classified out as so<strong>on</strong> as it reaches the desired size.<br />
Not much attenti<strong>on</strong> is given <strong>on</strong> the mechanochemical effect <strong>in</strong> c<strong>on</strong>t<strong>in</strong>uous <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
<strong>process</strong> especially when the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> and classificati<strong>on</strong> <strong>process</strong> occur simultaneously<br />
<strong>in</strong> short <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> period. Although <strong>in</strong> <strong>jet</strong> <strong>mill</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> and classificati<strong>on</strong> <strong>process</strong><br />
occurs simultaneously and the retenti<strong>on</strong> time of the particles is believed to be very<br />
short, but the energy <strong>in</strong>tensity delivered to the particle is huge which may result <strong>in</strong><br />
mechanochemical effect <strong>in</strong> short <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> period. Chung et. al. (2003) and Choi et. al.<br />
(2004) reported that significant structural changes did not take place when<br />
ursodeoxycholic acid was ground <strong>in</strong> <strong>jet</strong> <strong>mill</strong> where the reducti<strong>on</strong> of crystall<strong>in</strong>ity was <strong>on</strong>ly<br />
2%. C<strong>on</strong>tradict<strong>in</strong>g to Chung et. al. (2003) and Choi et. al. (2004), Juhacz and Opoczky<br />
(1990) reported that cement cl<strong>in</strong>ker, dolomite, limest<strong>on</strong>e and silica ground <strong>in</strong> <strong>jet</strong> <strong>mill</strong><br />
showed the highest reactivity due to the feed which suffered deep-seated changes <strong>in</strong><br />
its crystal structure <strong>in</strong>duced by high velocity impact.<br />
1.2 Problem Statement<br />
Besides size reducti<strong>on</strong>, <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> <strong>in</strong>duces mechanochemical effect that<br />
changes physicochemical characteristics of particles <strong>in</strong> energy <strong>in</strong>tensive <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s<br />
(Venkataraman and Narayanan, 1998). The amount of energy delivered to the particles<br />
and breakage mechanism c<strong>on</strong>trols the <strong>in</strong>tensity of mechanochemical effect of particles<br />
ground <strong>in</strong> <strong>jet</strong> <strong>mill</strong>. These two factors are c<strong>on</strong>trolled by the operat<strong>in</strong>g parameters and<br />
<strong>in</strong>side <strong>mill</strong> c<strong>on</strong>diti<strong>on</strong>s of the <strong>jet</strong> <strong>mill</strong>. The <strong>in</strong>side <strong>mill</strong> c<strong>on</strong>diti<strong>on</strong>s such as <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber<br />
pressure and amount of holdup <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber which will <strong>in</strong>fluence the<br />
6
eakage mechanism are c<strong>on</strong>trolled by the operat<strong>in</strong>g parameters such as feed rate,<br />
classifier frequency and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure.<br />
Jet <strong>mill</strong> is operated through autogeneous <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> where the particle breakage<br />
is due to high velocity <strong>in</strong>ter-particles impact collisi<strong>on</strong>. The autogeneous <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
promotes particle breakage al<strong>on</strong>g the weak planes thus produc<strong>in</strong>g str<strong>on</strong>ger <strong>f<strong>in</strong>e</strong><br />
particles with smooth surfaces. The attriti<strong>on</strong> <strong>process</strong> between the particles <strong>in</strong> the<br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber removes the sharp edges especially for brittle particles produc<strong>in</strong>g<br />
more spherical particles.<br />
The breakage mechanism is an important factor <strong>in</strong> determ<strong>in</strong><strong>in</strong>g the <strong>in</strong>tensity of<br />
mechanochemical effect <strong>in</strong> ground particles. The shear and impact breakage<br />
mechanism is believed to c<strong>on</strong>tribute to the mechanochemical effect <strong>in</strong> the ground<br />
product <strong>in</strong> <strong>jet</strong> <strong>mill</strong>. The breakage mechanism <strong>in</strong> the <strong>jet</strong> <strong>mill</strong> is very much dependent <strong>on</strong><br />
the operati<strong>on</strong>al c<strong>on</strong>diti<strong>on</strong> of the <strong>jet</strong> <strong>mill</strong> which c<strong>on</strong>trols the impact or shear breakage<br />
<strong>in</strong>tensity and also the retenti<strong>on</strong> time of the particles <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber. Gr<strong>in</strong>d<strong>in</strong>g<br />
chamber pressure plays an important role <strong>in</strong> determ<strong>in</strong><strong>in</strong>g the retenti<strong>on</strong> time of the<br />
particles <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber. The amount of holdup <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber is<br />
essential to obta<strong>in</strong> successive particle breakage which later leads to mechanochemical<br />
effect. The types of breakage mechanism which is either abrasi<strong>on</strong> or destructive will be<br />
determ<strong>in</strong>ed by the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure where by at high <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure impact<br />
breakage is more dom<strong>in</strong>ant whilst at low <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure shear breakage is<br />
prom<strong>in</strong>ent (Berthiaux and Dodds, 1999). The degree of crystall<strong>in</strong>ity, crystallite size and<br />
lattice stra<strong>in</strong> of the ground particles are directly related to the <strong>in</strong>tensity of<br />
mechanochemical effect, which is actually c<strong>on</strong>trolled by the operat<strong>in</strong>g c<strong>on</strong>diti<strong>on</strong> of <strong>jet</strong><br />
<strong>mill</strong>. Thus, the <str<strong>on</strong>g>study</str<strong>on</strong>g> <strong>on</strong> the c<strong>on</strong>trol of the operat<strong>in</strong>g parameters and <strong>in</strong>side <strong>mill</strong><br />
c<strong>on</strong>diti<strong>on</strong>s is very essential to optimize the size reducti<strong>on</strong> <strong>process</strong> and<br />
mechanochemical effect of the ground particles.<br />
7
Silica and talc have great <strong>in</strong>dustrial applicati<strong>on</strong> <strong>in</strong> the form of <strong>f<strong>in</strong>e</strong> particles especially<br />
when the particle size is below 10µm. Silica is widely used as filler <strong>in</strong> plastic, adhesive,<br />
pa<strong>in</strong>t whilst talc applicati<strong>on</strong>s as filler is <strong>in</strong> plastic, pa<strong>in</strong>t, paper, cosmetics and<br />
pharmaceutical. These <strong>in</strong>dustries have set a str<strong>in</strong>gent specificati<strong>on</strong> for the filler which<br />
<strong>in</strong>cludes particle size and its distributi<strong>on</strong>, particle shape and degree of crystall<strong>in</strong>ity<br />
(Sanchez et. al., 2004).<br />
1.3 Objective<br />
The ma<strong>in</strong> objective of this research work is to <str<strong>on</strong>g>study</str<strong>on</strong>g> the size reducti<strong>on</strong> <strong>process</strong> and<br />
mechanochemical effect <strong>in</strong>duced <strong>in</strong> <strong>jet</strong> <strong>mill</strong> dur<strong>in</strong>g <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> of silica and<br />
talc and the <strong>in</strong>fluence of operat<strong>in</strong>g parameters and breakage mechanism. The<br />
measurable objectives of this <str<strong>on</strong>g>study</str<strong>on</strong>g> are:<br />
1. To determ<strong>in</strong>e the effect of operat<strong>in</strong>g c<strong>on</strong>diti<strong>on</strong>s such as feed rate, <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure<br />
and classifier rotati<strong>on</strong>al speed <strong>on</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber pressure and amount of<br />
holdup <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber.<br />
2. To determ<strong>in</strong>e the breakage mechanism <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber accord<strong>in</strong>g to the<br />
operat<strong>in</strong>g c<strong>on</strong>diti<strong>on</strong>s of the <strong>jet</strong> <strong>mill</strong>.<br />
3. To <str<strong>on</strong>g>study</str<strong>on</strong>g> <strong>on</strong> mechanochemical effect of silica and talc at various operat<strong>in</strong>g<br />
c<strong>on</strong>diti<strong>on</strong>s which <strong>in</strong>cludes determ<strong>in</strong>ati<strong>on</strong> of degree of amorphism, crystallite size<br />
and lattice sta<strong>in</strong> of the ground product.<br />
4. To <str<strong>on</strong>g>study</str<strong>on</strong>g> the specific energy c<strong>on</strong>sumpti<strong>on</strong> of <strong>jet</strong> <strong>mill</strong>.<br />
1.4 Scope Of Work<br />
The scope of this work <strong>in</strong>cludes <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> of silica and talc <strong>in</strong> <strong>jet</strong> <strong>mill</strong> by<br />
vary<strong>in</strong>g the operati<strong>on</strong>al parameters such as feed rate, classifier rotati<strong>on</strong>al speed and<br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure. The specific k<strong>in</strong>etic at each operat<strong>in</strong>g parameters will be<br />
determ<strong>in</strong>ed. The <strong>in</strong>side <strong>mill</strong> c<strong>on</strong>diti<strong>on</strong> such as amount of holdup and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber<br />
pressure will be studied. The breakage mechanism of the particles at different<br />
8
operat<strong>in</strong>g parameters will be studied as well. The <strong>in</strong>fluence of breakage mechanism<br />
and specific k<strong>in</strong>etic energy <strong>on</strong> the mechanochemical effect of products will be<br />
determ<strong>in</strong>ed. The outcomes of this research work will provide a fundamental<br />
understand<strong>in</strong>g <strong>on</strong> the effect of breakage mechanism <strong>on</strong> mechanochemical effect of<br />
ground product and therefore optimiz<strong>in</strong>g the size reducti<strong>on</strong> <strong>process</strong> <strong>in</strong> the <strong>jet</strong> <strong>mill</strong>.<br />
9
2.1 Introducti<strong>on</strong><br />
CHAPTER 2<br />
LITERATURE REVIEW<br />
F<strong>in</strong>e m<strong>in</strong>eral particles rang<strong>in</strong>g from 1μm to 10μm play an important role as fillers <strong>in</strong><br />
various <strong>in</strong>dustries such as plastics, pa<strong>in</strong>t, paper, sealant and adhesives, cosmetics,<br />
detergent, ceramics, agriculture and pharmaceutical (Benz et al., 1996). Normally <strong>f<strong>in</strong>e</strong><br />
m<strong>in</strong>eral particles is produced through <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> <strong>in</strong> various energy <strong>in</strong>tensive<br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s such as oscillat<strong>in</strong>g <strong>mill</strong>, planetary <strong>mill</strong>, vibrati<strong>on</strong> <strong>mill</strong>, stirred <strong>mill</strong> and <strong>jet</strong><br />
<strong>mill</strong>.<br />
F<strong>in</strong>e <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> is de<strong>f<strong>in</strong>e</strong>d as producti<strong>on</strong> of <strong>f<strong>in</strong>e</strong> particles <strong>in</strong> the size range of<br />
several micrometers (Benz et al. 1996). Tkacova (1989) menti<strong>on</strong>ed that energy<br />
<strong>in</strong>tensive <strong>mill</strong>s are often used for ultra <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> and mechanical activati<strong>on</strong> purposes<br />
due to the huge amount of energy delivered to the particles that were be<strong>in</strong>g ground.<br />
Although the ma<strong>in</strong> objective of <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> is size reducti<strong>on</strong> <strong>in</strong> several<br />
micrometer range, there are other phenomen<strong>on</strong> that take place dur<strong>in</strong>g this <strong>process</strong> due<br />
to the amount of energy delivered. Severe and <strong>in</strong>tense mechanical acti<strong>on</strong>s <strong>on</strong> solid<br />
surfaces are known to lead to physical and chemical changes <strong>in</strong> the near-surface<br />
regi<strong>on</strong> where the solid come <strong>in</strong>to c<strong>on</strong>tact under mechanical forces. These mechanically<br />
<strong>in</strong>itiated chemical and physicochemical effects <strong>in</strong> solids are generally termed as<br />
mechanochemical effects (Venkataraman and Narayanan, 1998).<br />
As <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> is an <strong>in</strong>termediate <strong>process</strong> between size reducti<strong>on</strong> and<br />
mechanical activati<strong>on</strong> hence the amount of energy delivered to the particles dur<strong>in</strong>g <strong>f<strong>in</strong>e</strong><br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> will dictate the <strong>in</strong>tensity of mechanochemical effect <strong>on</strong> the ground<br />
10
particles and it takes place simultaneously dur<strong>in</strong>g the <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> (Boldyrev<br />
et. al., 1996).<br />
Known for its high energy c<strong>on</strong>sumpti<strong>on</strong> and <strong>in</strong>efficiency, <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> of materials has<br />
been l<strong>on</strong>g looked at as an area with huge scope of development. It c<strong>on</strong>sumes a major<br />
porti<strong>on</strong> of the power drawn from a typical m<strong>in</strong>eral <strong>process</strong><strong>in</strong>g plant and c<strong>on</strong>sumes<br />
approximately 3% of the electricity generated <strong>in</strong> the <strong>in</strong>dustrialized country of the world<br />
(Ipek et al., 2005). F<strong>in</strong>e <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> is normally performed to produce particles below<br />
10μm as its demand is becom<strong>in</strong>g very important <strong>in</strong> various fields. These reas<strong>on</strong>s have<br />
motivated researchers around the world to achieve optimum energy utilizati<strong>on</strong> with<br />
substantial ec<strong>on</strong>omic benefits. Currently, these <strong>f<strong>in</strong>e</strong> particles are very expensive and<br />
the producti<strong>on</strong> rates are relatively small. It is not easy to meet the str<strong>in</strong>gent demand <strong>on</strong><br />
its <strong>f<strong>in</strong>e</strong>ness, purity, shape and crystall<strong>in</strong>ity due to the follow<strong>in</strong>g reas<strong>on</strong>s:<br />
• The particle strength <strong>in</strong>creases str<strong>on</strong>gly with decreas<strong>in</strong>g particle size, so the<br />
particle breakage <strong>in</strong>tensity has to be high.<br />
• Particles of brittle materials deform plastically below the tough brittle transiti<strong>on</strong><br />
size which depends <strong>on</strong> the types of materials. The breakage of this particle<br />
becomes difficult (Boldyrev et al., 1996).<br />
• The adhesi<strong>on</strong> force <strong>in</strong> the <strong>f<strong>in</strong>e</strong> particles causes agglomerati<strong>on</strong>.<br />
Am<strong>on</strong>g the <strong>in</strong>dustrial m<strong>in</strong>erals, <strong>f<strong>in</strong>e</strong> particles of silica and talc are vastly used as m<strong>in</strong>eral<br />
fillers <strong>in</strong> various <strong>in</strong>dustries. Silica and talc have comm<strong>on</strong> use as m<strong>in</strong>eral fillers <strong>in</strong> pa<strong>in</strong>t,<br />
plastics, ceramics and agriculture <strong>in</strong>dustries. Silica is largely c<strong>on</strong>sume <strong>in</strong> sealant and<br />
adhesives, glass, build<strong>in</strong>g applicati<strong>on</strong>, chemicals and metallurgical <strong>in</strong>dustries, whilst<br />
talc is used <strong>in</strong> paper, cosmetics, detergent and pharmaceutical.<br />
11
Micr<strong>on</strong>ized silica used as extender and filler <strong>in</strong> the pa<strong>in</strong>t <strong>in</strong>dustry will <strong>in</strong>crease the<br />
resistance to chemical attack due to its acid resistance, whilst its hardness improve<br />
scrub ability and burnish resistance. Its narrow size distributi<strong>on</strong> and bright colour<br />
m<strong>in</strong>imize the res<strong>in</strong> demands and improve colour acceptance. Silica is chosen as<br />
m<strong>in</strong>eral filler due to its heat resistance, low thermal expansi<strong>on</strong>, chemical resistance and<br />
high dielectric strength. Its <strong>in</strong>ertness and durability enhances the physical strength of<br />
large epoxy cast<strong>in</strong>g for example laboratory bench top (Moore, 2002).<br />
Talc is used as filler, to c<strong>on</strong>trol pitch and stickies and <strong>in</strong> coat<strong>in</strong>g formulati<strong>on</strong> <strong>in</strong> paper<br />
<strong>in</strong>dustry. The advantages of talc as filler are improve smoothness, porosity, opacity,<br />
abrasi<strong>on</strong> and yellow <strong>in</strong>dex. Talc is am<strong>on</strong>g the most comm<strong>on</strong> extender used <strong>in</strong> pa<strong>in</strong>ts<br />
due to its platy shape can reduce permeability. The functi<strong>on</strong> of talc <strong>in</strong> pa<strong>in</strong>t is as<br />
re<strong>in</strong>forcement, reduce sagg<strong>in</strong>g and allow it to flatten out result<strong>in</strong>g smooth film. This<br />
property has enhanced the c<strong>on</strong>sumpti<strong>on</strong> of talc <strong>in</strong> domestic, <strong>in</strong>dustrial and protective<br />
coat<strong>in</strong>g. Ultra <strong>f<strong>in</strong>e</strong> talc is used <strong>in</strong> plastic to improve its mechanical and surface<br />
properties such as stretch resistance. Talc is loaded <strong>in</strong> plastic rang<strong>in</strong>g from 20% to<br />
40% to enhance stiffness, tensile strength and creep resistance. The optimum particle<br />
size for this applicati<strong>on</strong> is 8µm. Another talc applicati<strong>on</strong> of talc <strong>in</strong> the plastic <strong>in</strong>dustry is<br />
as antiblock<strong>in</strong>g agent for films (Russell, 1989).<br />
Most of these applicati<strong>on</strong>s need <strong>f<strong>in</strong>e</strong> particles below 10µm with narrow size distributi<strong>on</strong>.<br />
The str<strong>in</strong>gent demand from the <strong>in</strong>dustries accord<strong>in</strong>g to the specific applicati<strong>on</strong> has<br />
made the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>in</strong>dustry to move ahead to produce custom made m<strong>in</strong>eral fillers that<br />
specially can suit for the specific <strong>in</strong>dustrial product applicati<strong>on</strong>. Table 2.1 shows the<br />
<strong>in</strong>dustrial demand for various m<strong>in</strong>eral fillers used <strong>in</strong> product manufactur<strong>in</strong>g (Russell,<br />
1989).<br />
12
Table 2.1: Key physical properties of selected m<strong>in</strong>eral fillers (Russell, 1989)<br />
M<strong>in</strong>eral d50( μm) Surface area,<br />
(m 2 /g)<br />
Specific<br />
gravity (g/m 3 )<br />
Aspect<br />
ratio<br />
Mohs’<br />
hardness<br />
Ground silica 2-6 1-2 2.65 Low 7.5<br />
Talc 1-1.5 6-10 2.8 Moderate 1.5<br />
2.2 Energy Intensive Gr<strong>in</strong>d<strong>in</strong>g Mills<br />
High <strong>in</strong>tensity <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s such as planetary <strong>mill</strong>, stirred <strong>mill</strong>, <strong>jet</strong> <strong>mill</strong>, vibrati<strong>on</strong> <strong>mill</strong> and<br />
peripheral <strong>mill</strong> could exhibit mechanochemical effect due to the high power bulk density<br />
compared to ball <strong>mill</strong> (Tkacova, 1989). These <strong>mill</strong>s are normally used for <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
or mechanical activati<strong>on</strong> <strong>process</strong>. These <strong>mill</strong>s are chosen for <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> as<br />
they have huge amount of energy that can be use for <strong>f<strong>in</strong>e</strong> particle breakage and the<br />
excessive energy will be used for crystal structural changes besides transformati<strong>on</strong> to<br />
heat energy.<br />
Gr<strong>in</strong>d<strong>in</strong>g <strong>mill</strong>s can be divided <strong>in</strong>to three ma<strong>in</strong> groups accord<strong>in</strong>g to the method of energy<br />
transfer from <strong>mill</strong> to ground material. K<strong>in</strong>etic energy from the <strong>mill</strong> can be transmitted as<br />
follows (Juhasz and Opoczky, 1990):<br />
• to <strong>mill</strong> body, from where it is transferred to the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> media and charge to be<br />
ground by fricti<strong>on</strong>, centrifugal and gravitati<strong>on</strong>al force such as ball <strong>mill</strong>.<br />
• directly to crush<strong>in</strong>g elements such as peripheral <strong>mill</strong> and roller <strong>mill</strong>s.<br />
• directly to material be<strong>in</strong>g ground by means of a flow<strong>in</strong>g stream of the carrier gas<br />
which creates vigorous collisi<strong>on</strong> between particles and their imp<strong>in</strong>gement <strong>on</strong> a<br />
rigid obstacle such as <strong>jet</strong> <strong>mill</strong>.<br />
Various types of energy <strong>in</strong>tensive <strong>mill</strong> <strong>in</strong> which, the energy density is several times<br />
greater than ball <strong>mill</strong>, is often used for <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong>. These types of <strong>mill</strong> can be grouped<br />
13
<strong>in</strong>to two categories, n<strong>on</strong>-rotary ball or beads <strong>mill</strong> and impact <strong>mill</strong>. The n<strong>on</strong>-rotary <strong>mill</strong>s<br />
are planetary, vibrati<strong>on</strong> and stirred <strong>mill</strong>. Jet <strong>mill</strong> is an impact type <strong>mill</strong>.<br />
The <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>in</strong>tensity <strong>in</strong> these <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s is based <strong>on</strong> accelerati<strong>on</strong> and<br />
predom<strong>in</strong>ant mode of stress (Tkacova, 1989). The accelerati<strong>on</strong> of the vibrati<strong>on</strong> <strong>mill</strong> is<br />
specified by its frequency and amplitude. The <strong>in</strong>dustrial vibrati<strong>on</strong> <strong>mill</strong> which operates at<br />
frequencies of 16-19 revoluti<strong>on</strong> s -1 and amplitudes below 6 mm accelerates ten times<br />
greater than gravitati<strong>on</strong>al accelerati<strong>on</strong>. Besides accelerati<strong>on</strong>, density and shape of<br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> media, c<strong>on</strong>t<strong>in</strong>uous operati<strong>on</strong>s and the fill<strong>in</strong>g rate also affect the <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
<strong>process</strong> (Juhasz and Opoczky, 1990). Gr<strong>in</strong>d<strong>in</strong>g and activati<strong>on</strong> effect <strong>in</strong>crease with the<br />
<strong>in</strong>crease of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> media density <strong>in</strong> vibrati<strong>on</strong> <strong>mill</strong>. The materials <strong>in</strong> the vibrati<strong>on</strong> <strong>mill</strong>s<br />
are predom<strong>in</strong>antly stress by compressive and impact mode pulses imparted by the<br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> media. Attriti<strong>on</strong> particle breakage mode is effective between the media with<br />
different speeds and between the media and drum shell.<br />
Planetary <strong>mill</strong> is relatively new but a promis<strong>in</strong>g equipment due to its high energy bulk<br />
density. The enhancement of accelerati<strong>on</strong> <strong>in</strong> relati<strong>on</strong> to c<strong>on</strong>venti<strong>on</strong>al ball <strong>mill</strong> is<br />
achieved by the comb<strong>in</strong>ed acti<strong>on</strong> of two centrifugal fields. Laboratory and pilot plant<br />
planetary <strong>mill</strong> atta<strong>in</strong> accelerati<strong>on</strong> which may exceed gravitati<strong>on</strong>al accelerati<strong>on</strong> by a<br />
factor of 100 (Juhacz and Opoczky, 1990). The ultra <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> and mechanical<br />
activati<strong>on</strong> <strong>in</strong> this <strong>mill</strong> is very efficient. The breakage mechanism <strong>in</strong> planetary <strong>mill</strong><br />
depends <strong>on</strong> the moti<strong>on</strong> of the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> media. The modes of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> media movement<br />
<strong>in</strong> planetary <strong>mill</strong> are cascad<strong>in</strong>g, cataract<strong>in</strong>g and hurricane (Juhacz and Opoczky, 1990).<br />
Special types of n<strong>on</strong>-rotary bead <strong>mill</strong> <strong>in</strong>clude the stirred <strong>mill</strong>s. In stirred <strong>mill</strong>, the material<br />
is comm<strong>in</strong>uted by means of free flow<strong>in</strong>g beads which are set <strong>in</strong> moti<strong>on</strong> by a stirrer. The<br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> effect depends <strong>on</strong> the stirrer speed, chamber geometry, rheological properties<br />
of slurry, bead size and types and amount of charge. Stirred <strong>mill</strong> can be used for<br />
14
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> soft materials such as soft pigments and also very hard ceramics as the<br />
operat<strong>in</strong>g c<strong>on</strong>diti<strong>on</strong> and design can be varied accord<strong>in</strong>g to material properties. The<br />
breakage mechanism <strong>in</strong> stirred <strong>mill</strong> is through shear supplemented with compressi<strong>on</strong>.<br />
Two types of impact type <strong>mill</strong>s used <strong>in</strong> <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> are high peripheral speed <strong>mill</strong> and<br />
<strong>jet</strong> <strong>mill</strong>. In high peripheral speed <strong>mill</strong>, two wheels rotate with different speeds, usually <strong>in</strong><br />
the opposite directi<strong>on</strong> thus doubl<strong>in</strong>g the shock velocity. P<strong>in</strong> breakers are situated <strong>on</strong> the<br />
rotor al<strong>on</strong>g the c<strong>on</strong>centric rows of circle. Materials are centrally fed and when it moves<br />
from the center to the periphery of rotor, <strong>in</strong>dividual particles collide with p<strong>in</strong> breakers<br />
and each other. The mode of stress is determ<strong>in</strong>ed by relative circumferential velocity of<br />
rotor. The relative circumferential velocity may be as high as 200ms -1 to 300 ms -1<br />
(Juhacz and Opoczky, 1990).<br />
2.3 Jet <strong>mill</strong><br />
Jet <strong>mill</strong> has ga<strong>in</strong> its importance <strong>in</strong> produc<strong>in</strong>g high purity <strong>f<strong>in</strong>e</strong> particles rang<strong>in</strong>g from 1μm<br />
to 10μm s<strong>in</strong>ce it was first <strong>in</strong>vented <strong>in</strong> 1960 (Midoux et al, 1999). There are two comm<strong>on</strong><br />
types of <strong>jet</strong> <strong>mill</strong> which are the spiral <strong>jet</strong> <strong>mill</strong> and the fluidized bed <strong>jet</strong> <strong>mill</strong>. The<br />
advantages of <strong>jet</strong> <strong>mill</strong> <strong>in</strong> produc<strong>in</strong>g <strong>f<strong>in</strong>e</strong> particles are high <strong>f<strong>in</strong>e</strong>ness comb<strong>in</strong>es with<br />
narrow size distributi<strong>on</strong>, high degree of dispersi<strong>on</strong>, low <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber temperature,<br />
no agitated built <strong>in</strong> elements, high turbulence <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber, which means<br />
high heat transmissi<strong>on</strong> and high mass transfer with no product c<strong>on</strong>tam<strong>in</strong>ati<strong>on</strong> through<br />
wear (Muller et al, 1996).<br />
Although <strong>jet</strong> <strong>mill</strong> has several advantages but it is still an energy <strong>in</strong>tensive <strong>process</strong> as<br />
<strong>on</strong>ly 2% - 5% of the energy supplied is used to create new surfaces (Mebtoul et al.,<br />
1996; Alfano et al., 1996; Lecoq et al., 2003). Gommeren et al. (2000) had carried out<br />
the modell<strong>in</strong>g of the <strong>jet</strong> <strong>mill</strong> plant to reduce the energy by 50%. The development of<br />
more energy efficient <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> <strong>in</strong> <strong>jet</strong> <strong>mill</strong> implies a better fundamental<br />
15
understand<strong>in</strong>g of the various mechanisms <strong>in</strong>volved <strong>in</strong> the fragmentati<strong>on</strong> of the particles<br />
such as <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber pressure, amount of holdup <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber, particle<br />
shape, air flow <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> and classificati<strong>on</strong> chamber besides the operati<strong>on</strong>al<br />
parameters and design parameters such as, classifier speed, nozzle distance, feed<br />
rate and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure (Kolacz, 2004).<br />
Figure 2.1 shows the schematic diagram of opposed fluidized bed <strong>jet</strong> <strong>mill</strong>. The<br />
fluidized-bed <strong>jet</strong> <strong>mill</strong> c<strong>on</strong>sists of a vertical <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber with oppos<strong>in</strong>g gas <strong>jet</strong>s near<br />
its lower end. Particles c<strong>on</strong>ta<strong>in</strong>ed <strong>in</strong> the hopper is c<strong>on</strong>t<strong>in</strong>uously fed by screw feeder <strong>in</strong>to<br />
the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber where they are ground at the meet<strong>in</strong>g po<strong>in</strong>t of the three<br />
c<strong>on</strong>current air <strong>jet</strong>s formed by ceramic nozzles supplied with compressed air. The<br />
breakage mechanism <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber is primarily due to impact and abrasi<strong>on</strong><br />
with other particles and very much dependent <strong>on</strong> the operat<strong>in</strong>g c<strong>on</strong>diti<strong>on</strong> of the <strong>jet</strong> <strong>mill</strong>.<br />
After <strong>gr<strong>in</strong>d<strong>in</strong>g</strong>, the particles are carried out by air flow up to the wheel classifier, which<br />
removes the <strong>f<strong>in</strong>e</strong> particles and return the coarser <strong>on</strong>es to the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> z<strong>on</strong>e result<strong>in</strong>g <strong>in</strong><br />
relatively tight particle-size distributi<strong>on</strong>s (Godet-Morand, 2002). Figure 2.2 shows the<br />
flow of the particles <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong>-classify<strong>in</strong>g chamber. The <strong>f<strong>in</strong>e</strong> particles are collected<br />
<strong>in</strong> a c<strong>on</strong>ta<strong>in</strong>er below an air cycl<strong>on</strong>e (Berthiaux and Dodds, 1999).<br />
Hopper<br />
Screw feeder<br />
Gr<strong>in</strong>d<strong>in</strong>g<br />
air<br />
Ground<br />
product<br />
Figure 2.1: Schematic diagram of opposed fluidized bed <strong>jet</strong> <strong>mill</strong> (Berthiaux and<br />
Dodds,1999)<br />
Classifier<br />
Cycl<strong>on</strong>e<br />
16<br />
Filter bag house<br />
Air outlet<br />
Blower
Nozzle<br />
Nozzle<br />
Classifier<br />
Nozzle<br />
Movement of particles<br />
<strong>in</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber<br />
Figure 2.2: Gr<strong>in</strong>d<strong>in</strong>g and classify<strong>in</strong>g chamber of opposed fluidized <strong>jet</strong> <strong>mill</strong><br />
(Berthiaux and Dodds,1999)<br />
The feed for <strong>jet</strong> <strong>mill</strong> will be pre-<strong>mill</strong>ed and it will produce a mean particle size of less<br />
than 10μm depend<strong>in</strong>g <strong>on</strong> the design and operati<strong>on</strong>al parameters of the <strong>jet</strong> <strong>mill</strong>. The<br />
<strong>gr<strong>in</strong>d<strong>in</strong>g</strong> fluid <strong>in</strong> the <strong>jet</strong> <strong>mill</strong> is usually air up to a pressure of 2 bars or steam up to 6<br />
bars (Zhao and Schurr, 2002). If volatile material is be<strong>in</strong>g <strong>mill</strong>ed, the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> fluid can<br />
be <strong>in</strong>ert compressed gas such as nitrogen or carb<strong>on</strong> dioxide. Most <strong>in</strong>dustrial m<strong>in</strong>erals<br />
are <strong>in</strong>sensitive to temperature and thus the optimum size reducti<strong>on</strong> can be achieved<br />
us<strong>in</strong>g high temperatures and high pressure super heated steam. This is typically <strong>in</strong> the<br />
range of 3 bars – 6 bars and 315 o C – 370 o C. However, with some m<strong>in</strong>erals such as<br />
ir<strong>on</strong> oxide based m<strong>in</strong>erals pigments, the high temperature will affect the colour t<strong>in</strong>t of<br />
the pigment. Typical <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> data of the <strong>jet</strong> <strong>mill</strong> <strong>on</strong> some m<strong>in</strong>erals are shown <strong>in</strong> Table<br />
2.2.<br />
17
Table 2.2: Typical <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> data for <strong>jet</strong> <strong>mill</strong> (Russell, 1989)<br />
M<strong>in</strong>erals Mill diameter<br />
(cm)<br />
Gr<strong>in</strong>d<strong>in</strong>g fluid Feed rate<br />
(kg/h)<br />
d50 (μm)<br />
Al2O3 20.3 Air 6.8 3<br />
TiO2 76.2 Steam 1020
Table 2.3: Applicati<strong>on</strong> of <strong>jet</strong> <strong>mill</strong> <strong>in</strong> various sectors (Russell, 1989)<br />
Sector Ground Product<br />
Agrochemicals Carbendezim, deltamethr<strong>in</strong>e, fungicide, germicide, herbicide,<br />
sulphur.<br />
Chemicals Adipic acids, barium titanate, calcium chloride, catalyst, chrome<br />
oxide.<br />
Ceramic Alum<strong>in</strong>ium hydrates, ferrites, glass, silic<strong>on</strong> carbide, zirc<strong>on</strong>ium oxide<br />
Metals Copper, molybdenum disulphide, noble metals.<br />
M<strong>in</strong>erals Bauxite, calcite, graphite, gypsum, mica, talc, tantalum ore.<br />
Pa<strong>in</strong>ts Carb<strong>on</strong> black, fluorescent pigment, pr<strong>in</strong>t<strong>in</strong>g <strong>in</strong>k.<br />
Pharmaceutical Albendazole, antibiotics, aspir<strong>in</strong>. Bulk drug, cosmetics, omeprezole,<br />
oxfendazole.<br />
Plastics ABS res<strong>in</strong>s, PVC stabilizers, phenolics, PTFE.<br />
Others Asbestos, chocolate, food colours, fuller earth, precipitated silica,<br />
wolframite ore.<br />
2.4 Parameters affect<strong>in</strong>g <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> <strong>in</strong> <strong>jet</strong> <strong>mill</strong><br />
The design and operati<strong>on</strong>al parameters of <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> <strong>in</strong> <strong>jet</strong> <strong>mill</strong> affects the<br />
ground product <strong>in</strong> terms of its product <strong>f<strong>in</strong>e</strong>ness, particle size distributi<strong>on</strong> and the<br />
<strong>in</strong>tensity of mechanochemical effect. The product <strong>f<strong>in</strong>e</strong>ness and its particle size<br />
distributi<strong>on</strong> are affected by feed rate, <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> air flow rate, height of classificati<strong>on</strong> tube,<br />
angle of nozzles, types of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> fluids, amount of holdup, <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure and<br />
classifier frequency (Tuunila and Nystrom, 1998; Kolacz, 2004; Zhao and Schurr, 2002;<br />
Choi et al., 2004; Gommeren et al., 2000; Nakach et al., 2004; Godet-Morand et al.,<br />
2002). Juhacz and Opoczky (1990) reported the <strong>in</strong>creased <strong>in</strong> the reactivity of the<br />
product ground <strong>in</strong> <strong>jet</strong> <strong>mill</strong> due to mechanochemical effect but the operat<strong>in</strong>g c<strong>on</strong>diti<strong>on</strong><br />
was not menti<strong>on</strong>ed. Boldyrev et al. (1996) menti<strong>on</strong>ed that mechanochemical effect was<br />
directly related to the operat<strong>in</strong>g c<strong>on</strong>diti<strong>on</strong> of the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong> as the rate of stress and<br />
number of impulses <strong>on</strong> the particles would be determ<strong>in</strong>ed by the operat<strong>in</strong>g parameters<br />
of the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s.<br />
19
The parameters which affect the product <strong>f<strong>in</strong>e</strong>ness <strong>in</strong> a <strong>jet</strong> <strong>mill</strong> can be classified as the<br />
geometrical parameters which is c<strong>on</strong>cerned with the design of the <strong>mill</strong> and operati<strong>on</strong>al<br />
c<strong>on</strong>diti<strong>on</strong>. Table 2.4 shows the parameters that <strong>in</strong>fluence gr<strong>in</strong>dability <strong>in</strong> a <strong>jet</strong> <strong>mill</strong><br />
(Midoux et al., 1999).<br />
Table 2.4: Geometrical parameter and operati<strong>on</strong>al c<strong>on</strong>diti<strong>on</strong> of a <strong>jet</strong> <strong>mill</strong> (Midoux<br />
et al., 1999; Benz et al., 1996; Nykamp et al., 2002; Nakach et. al., 2004)<br />
Geometrical parameter Operati<strong>on</strong>al c<strong>on</strong>diti<strong>on</strong><br />
Diameter of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber Solid feed rate<br />
Shape of nozzles Gr<strong>in</strong>d<strong>in</strong>g pressure<br />
Number of nozzles Classifier speed<br />
Angle of nozzles Types of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> fluids<br />
Distance between the nozzles Gr<strong>in</strong>d<strong>in</strong>g aids<br />
2.4.1 Particle Breakage Mechanism <strong>in</strong> Jet <strong>mill</strong><br />
Type of materials to be gr<strong>in</strong>d<br />
The breakage mechanism of particles <strong>in</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s is very much dependent <strong>on</strong> its<br />
design and operat<strong>in</strong>g parameters. In <strong>jet</strong> <strong>mill</strong>, the ma<strong>in</strong> breakage mechanism is<br />
destructive breakage due to impact and abrasi<strong>on</strong> due to attriti<strong>on</strong> between particles<br />
(Berthiaux and Dodds, 1999; Frances et. al., 2001). Figures 2.3 and 2.4 show the<br />
breakage mechanism of hydragillite and gibbsite respectively which exhibit the same<br />
particle breakage mechanism. This phenomen<strong>on</strong> <strong>in</strong>dicates that the breakage<br />
mechanism of particles is <strong>in</strong>fluenced by the types of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> mechanism. High <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
pressure (therefore, a higher <strong>jet</strong> velocity and greater <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> energy) leads to<br />
destructive breakage, therefore the product will be less block-shape and platelets but<br />
exhibit<strong>in</strong>g sharp edges. If lower <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> pressure is used, abrasi<strong>on</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
mechanism will be more dom<strong>in</strong>ant result<strong>in</strong>g <strong>in</strong> chipp<strong>in</strong>g of the particle edges.<br />
20
(Berthiaux and Dodds, 1999; Tasir<strong>in</strong> and Geldart, 1999; Mebtoul et al., 1996).<br />
Abrasi<strong>on</strong> breakage mechanism will produce more rounded particles with less sharp<br />
edges.<br />
Tasir<strong>in</strong> and Geldart (1999) found that coarse particles broke due to destructive<br />
breakage rather than abrasi<strong>on</strong> and the probability of coarser particles chosen for<br />
breakage was higher than smaller particles. In general, smaller particles were more<br />
difficult to break than larger <strong>on</strong>es because smaller particles c<strong>on</strong>ta<strong>in</strong>ed fewer faults,<br />
flaws or disc<strong>on</strong>t<strong>in</strong>uities.<br />
Abrasi<strong>on</strong> breakage mechanism <strong>in</strong> <strong>jet</strong> <strong>mill</strong> is dependent <strong>on</strong> the c<strong>on</strong>centrati<strong>on</strong> or amount<br />
of particles <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber. The <strong>in</strong>crease <strong>in</strong> the amount of <strong>f<strong>in</strong>e</strong>s and creati<strong>on</strong> of<br />
new surface area when the amount of holdup <strong>in</strong>creases, is the characteristics of<br />
abrasi<strong>on</strong> breakage mechanism tak<strong>in</strong>g place <strong>in</strong> <strong>jet</strong> <strong>mill</strong> (Mebtoul et al., 1996). Abrasi<strong>on</strong><br />
breakage mechanism is characterized by formati<strong>on</strong> of <strong>f<strong>in</strong>e</strong>s without noticeable change<br />
<strong>in</strong> mean diameter of particles.<br />
Primary<br />
cleavage<br />
Sec<strong>on</strong>dary<br />
cleavage<br />
Destructive<br />
breakage<br />
Destructive<br />
breakage<br />
Figure 2.3: Schematic representati<strong>on</strong> of breakage mechanism of hydrargillite<br />
particles <strong>in</strong> <strong>jet</strong> <strong>mill</strong> (Berthiaux and Dodds, 1999)<br />
21
Rj<br />
Rj Ch<br />
Cl<br />
Ch<br />
Gr Gr<br />
Figure 2.4: Fragmentati<strong>on</strong> scheme for gibbsite ground <strong>in</strong> <strong>jet</strong> <strong>mill</strong>. Rj – rupture of<br />
jo<strong>in</strong>ts, Ch – chipp<strong>in</strong>g, CI – cleavage, Gr – ultimate <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> (Frances et al., 2001).<br />
Quantitative morphology analysis allows <strong>on</strong>e to better evaluate the fragmentati<strong>on</strong><br />
<strong>process</strong>es (Lecoq et al., 1999). There are several methods of particle quantificati<strong>on</strong>.<br />
P<strong>on</strong>s et al. (1999) classified three different levels of shape descriptors which are<br />
macroscopic descriptor, mesoscopic descriptors and pseudo-3D shape. The<br />
macroscopic descriptors are calculated from size measurements made <strong>on</strong> the particle<br />
silhouette.<br />
The basic macro-shape descriptors are equivalent circular diameter, el<strong>on</strong>gati<strong>on</strong> and<br />
circularity. Equivalent circular diameter is the diameter of a disc hav<strong>in</strong>g the same area<br />
as the projected silhouette. The calculati<strong>on</strong> for equivalent circular diameter is shown <strong>in</strong><br />
Equati<strong>on</strong> 2.1.<br />
D eq<br />
C1<br />
A<br />
= 2<br />
Equati<strong>on</strong> 2.1<br />
π<br />
22
The circularity (C) is a measure of both rugosity of the silhouette c<strong>on</strong>tour and its<br />
el<strong>on</strong>gati<strong>on</strong> as shown <strong>in</strong> Equati<strong>on</strong> 2.2. Circularity is equal to 1 for a disk and <strong>in</strong>creases<br />
when the silhouette departs from this reference shape, either because it gets el<strong>on</strong>gated<br />
or its roughness <strong>in</strong>creases. Circularity of a square is 1.27 (Marrot et al., 2000) It should<br />
be used <strong>in</strong> c<strong>on</strong>juncti<strong>on</strong> with another shape factor such as el<strong>on</strong>gati<strong>on</strong> (Frances et al.,<br />
2001).<br />
C<br />
2<br />
P<br />
4πA<br />
= Equati<strong>on</strong> 2.2<br />
The choice of the number of particles chosen for shape quantificati<strong>on</strong> is a critical issue<br />
as it will greatly <strong>in</strong>fluence the f<strong>in</strong>al remarks regard<strong>in</strong>g shape (Faria et al., 2003). Large<br />
number of particle need to be characterized to ga<strong>in</strong> statistical validity and this <strong>process</strong><br />
is very time c<strong>on</strong>sum<strong>in</strong>g especially with sample preparati<strong>on</strong>. This <strong>process</strong> will be more<br />
time c<strong>on</strong>sum<strong>in</strong>g if the image captur<strong>in</strong>g <strong>process</strong> is d<strong>on</strong>e <strong>in</strong> scann<strong>in</strong>g electr<strong>on</strong><br />
microscope (Belaroui et al., 2002). Therefore it is necessary to determ<strong>in</strong>e the number<br />
of particles to be exam<strong>in</strong>ed to obta<strong>in</strong> statistically valid results. The effect of sample size<br />
<strong>on</strong> the morphological characteristics can be assessed by c<strong>on</strong>sider<strong>in</strong>g the changes of<br />
the descriptors average values and standard deviati<strong>on</strong> versus number of particles. The<br />
average value of the descriptor is very essential to avoid the possibilities of shape<br />
orientati<strong>on</strong> effect of the descriptors value as particle <strong>in</strong> the samples c<strong>on</strong>ta<strong>in</strong>s variety of<br />
values (Mol<strong>in</strong>a-Boisseau et al., 2002). Belaroui et al., (2002) determ<strong>in</strong>e the changes of<br />
the descriptors average values and standard deviati<strong>on</strong> versus number of particles as<br />
shown <strong>in</strong> Figure 2.5. Belaroui et al. (2002) f<strong>in</strong>ally c<strong>on</strong>sidered that 80 particles were<br />
sufficient enough to assess the morphology based <strong>on</strong> scann<strong>in</strong>g electr<strong>on</strong> microscopy<br />
photomicrograph.<br />
23
Circularity<br />
Figure 2.5: Variati<strong>on</strong> of the circularity average values and the standard deviati<strong>on</strong><br />
(Belaroui et al., 2002).<br />
2.4.2 Jet <strong>mill</strong> design parameters<br />
The <strong>jet</strong> <strong>mill</strong> design parameters are the angle of nozzles, types of nozzles, distance<br />
between the nozzles <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber diameter and <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber shape.<br />
2.4.2.1 Effect of angle of nozzles<br />
The research work <strong>on</strong> the angle of nozzles is limited. Only Tuunila and Nystrom (1998)<br />
and Midoux et al. (1999) reported the test work <strong>on</strong> angle of nozzles. Tuunila and<br />
Nystrom (1998) varied angle of nozzles ant three levels which were 23 0 , 33 0 and 43 0 .<br />
Tuunila and Nystrom (1998) reported that the angle of nozzles was less significant<br />
effect <strong>on</strong> the product <strong>f<strong>in</strong>e</strong>ness for two different types of gypsum but the maximum<br />
breakage was obta<strong>in</strong>ed at the largest angle which was 43 o as shown <strong>in</strong> Table 2.5.<br />
Midoux et al. (1999) used three types of <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s with two different nozzle angles<br />
which were 63 o and 67 o . The nozzle angle depended <strong>on</strong> the size of the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />
chamber and had an effect <strong>on</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> ratio of the product (Midoux et al., 1999).<br />
Furthermore, this angle affects the penetrati<strong>on</strong> of nozzle <strong>jet</strong>s <strong>in</strong> the gas stream and it<br />
24<br />
Standard deviati<strong>on</strong>