a study on fine grinding process in jet mill - ePrints@USM

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Rj Rj Ch Cl Ch Gr Gr Figure 2.4: Fragmentation scheme for gibbsite ground in jet mill. Rj – rupture of joints, Ch – chipping, CI – cleavage, Gr – ultimate grinding (Frances et al., 2001). Quantitative morphology analysis allows one to better evaluate the fragmentation processes (Lecoq et al., 1999). There are several methods of particle quantification. Pons et al. (1999) classified three different levels of shape descriptors which are macroscopic descriptor, mesoscopic descriptors and pseudo-3D shape. The macroscopic descriptors are calculated from size measurements made on the particle silhouette. The basic macro-shape descriptors are equivalent circular diameter, elongation and circularity. Equivalent circular diameter is the diameter of a disc having the same area as the projected silhouette. The calculation for equivalent circular diameter is shown in Equation 2.1. D eq C1 A = 2 Equation 2.1 π 22
The circularity (C) is a measure of both rugosity of the silhouette contour and its elongation as shown in Equation 2.2. Circularity is equal to 1 for a disk and increases when the silhouette departs from this reference shape, either because it gets elongated or its roughness increases. Circularity of a square is 1.27 (Marrot et al., 2000) It should be used in conjunction with another shape factor such as elongation (Frances et al., 2001). C 2 P 4πA = Equation 2.2 The choice of the number of particles chosen for shape quantification is a critical issue as it will greatly influence the final remarks regarding shape (Faria et al., 2003). Large number of particle need to be characterized to gain statistical validity and this process is very time consuming especially with sample preparation. This process will be more time consuming if the image capturing process is done in scanning electron microscope (Belaroui et al., 2002). Therefore it is necessary to determine the number of particles to be examined to obtain statistically valid results. The effect of sample size on the morphological characteristics can be assessed by considering the changes of the descriptors average values and standard deviation versus number of particles. The average value of the descriptor is very essential to avoid the possibilities of shape orientation effect of the descriptors value as particle in the samples contains variety of values (Molina-Boisseau et al., 2002). Belaroui et al., (2002) determine the changes of the descriptors average values and standard deviation versus number of particles as shown in Figure 2.5. Belaroui et al. (2002) finally considered that 80 particles were sufficient enough to assess the morphology based on scanning electron microscopy photomicrograph. 23
Page 1 and 2: A STUDY ON ULTRA FINE GRINDING OF S
Page 3 and 4: CONTENTS Page Number ACKNOWLEDGEMEN
Page 5 and 6: Chapter 3 METHODOLOGY 3.1 Introduct
Page 7 and 8: REFERENCES 178 APPENDIX 1 : Volume
Page 9 and 10: Table 4.4 Table 4.5 Table 4.6 Table
Page 11 and 12: (●), 9000 rpm unsteady (○), 110
Page 13 and 14: Figure 3.4 Schematic diagram of gri
Page 15 and 16: Figure 4.24 Figure 4.25 Figure 4.26
Page 17 and 18: Rj rupture of joints CI cleavage Ch
Page 19 and 20: ψ span values di Kα βf βh βg D
Page 21 and 22: LIST OF PUBLICATION Samayamutthiria
Page 23 and 24: A Study on Ultra Fine Grinding of S
Page 25 and 26: 1.0 Introduction CHAPTER 1 The scop
Page 27 and 28: Although fine grinding will induce
Page 29 and 30: on the particle should be higher th
Page 31 and 32: eakage mechanism are controlled by
Page 33 and 34: operating parameters will be studie
Page 35 and 36: particles and it takes place simult
Page 37 and 38: Table 2.1: Key physical properties
Page 39 and 40: grinding soft materials such as sof
Page 41 and 42: Nozzle Nozzle Classifier Nozzle Mov
Page 43 and 44: Table 2.3: Application of jet mill
Page 45: (Berthiaux and Dodds, 1999; Tasirin

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