DESIGN, ASSEMBLY AND CHARACTERIZATION OF COMPOSITE ...

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at a reasonable rate in CO2, with a calculated activation energy Ea of 165.80 kJmol -1 in the temperature range from 895 °C to 1038 °C. 2. Development of the aqueous colloidal Ni ink: i. The optimal dispersant concentration for the specific Ni powder ENP 800 is determined. Viscometry indicates that a 2 mg/(g Ni powder) concentration for a cationic polyelectrolyte polyethylenimine (MW=25k) yields lowest viscosity for high solid volume fraction aqueous suspensions of Ni at pH=8.2. ii. A solid volume fraction φsolids=0.472 aqueous Ni gel is developed. iii. Rheological properties of aqueous colloidal Ni gels are characterized. Oscillatory measurement indicates a 300 kPa shear elastic modulus for the Ni gel used for Robocasting; and the Ni gel has a decreasing shear elastic modulus when flocculant (Darvan 821A) addition decreases. iv. Thermal degradation of polymer additives for Ni ink preparation is characterized by thermogravimetric analysis. Residual carbonaceous content in a Ni green structure is estimated to be less than 0.364% by weight after binder removal in air. v. Temperature profile for reducing atmosphere sintering of Ni in 5%H295%N2 is determined. A 700 °C, 2 hours isothermal hold is used to ensure complete reduction of surface NiO; and a subsequent isothermal hold for 2 hours at 900 °C sinter Ni structure to >99.0% of theoretical density. vi. Microstructure and hardness of Ni sinter are examined. The microstructure has an ASTM grain size number of G = 12.6 (Planimetric Procedure, ASTM E112 Section 9) and nominal grain diameter of 4.6 µm, and a Vickers hardness VPN120. 208
3. Development of aqueous colloidal composite inks for solid state sintering: i. Various aqueous colloidal Ni(m) composite inks with different BT:Ni ratios (i.e. 1:4, 2:3, 3:2, and 4:1 by solid volume ratio) have been developed, as well as a pure BT ink. A solid volume fraction of φsolids=0.43 is used for all inks. ii. Rheological properties of aqueous colloidal Ni(m) gels and BT gel are characterized. The Ni(m) gels have shear elastic moduli in the range from 163 kPa to 280 kPa; and the BT gel has a shear elastic modulus of 99 kPa. iii. Sintering strain data of each composite ink in the temperature range from 1100 °C to 1350 °C are determined. Sintering strain increases as Ni volume fraction increases in the Ni(m) ink; and the BT:Ni=4:1 Ni(m) ink has least sintering shrinkage difference from pure BT. iv. Processing conditions are determined for co-sintering. Co-sintering is achieved only with the BT:Ni=4:1 Ni(m) ink for the pure BT ink in a reducing atmosphere at 1350 °C. Re-oxidation is carried out in nitrogen at 800 °C for 24 hours to diminish oxygen vacancies in the reducing-atmosphere sintered BT phase. v. Hardness and density of sintered Ni(m) specimens are examined. A linear relationship exists between the hardness of a Ni(m) specimen and its BT volume fraction. Extrapolated BT and Ni hardness are VPN99 and VPN 387 respectively. And the density of sintered Ni(m) specimens is between 91% and 96% of theoretical. 209
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DESIGN, ASSEMBLY AND CHARACTERIZATI
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ACKNOWLEDGEMENTS First and foremost
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CHAPTER 5 BARIUM TITANATE NICKEL CO
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Table 6.1 Formulations of aqueous c
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Figure 2.12 Schematic illustrations
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Figure 2.35 Schematic of the SHS pr
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Figure 4.9 Sintered nickel lattices
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Figure 6.12 Optical image of the cr
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1.1. Motivation CHAPTER 1 INTRODUCT
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and characterizing rheological prop
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2.1. Materials System CHAPTER 2 BAC
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2.2. Reentrant Structures and Ceram
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devices would provide self-sustaini
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a) b) Figure 2.4 Schematic illustra
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production of concept models, injec
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Fused Deposition Modeling (FDM) was
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Laser Engineered Net Shaping (LENS)
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Inkjet printing (IP) 27 is based on
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Table 2.1 Comparisons of various SF
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Figure 2.11 Processing steps involv
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2.4.1 Colloidal Inks The printing i
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Robocasting has lacked a well-desig
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Table 2.2 Example polymers that dep
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2.6. Sintering In robocasting, sint
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Figure 2.15 Sphere and plate model
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where
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2.5.3 Solid State Sintering In this
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Figure 2.18 Illustration of neck gr
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2.5.3.4 Final Stage During this sta
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Figure 2.23 Schematic diagram of th
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2.5.4.2 Rearrangement With the form
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2.5.4.6 Spreading of Sintering Aid
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Driven by reduction of free energy,
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2.5.5 Sintering Atmosphere Sinterin
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2.7. Composite Materials In this re
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Figure 2.29 Types of composite mate
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Table 2.6 Examples of composite mat
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Table 2.7 Examples of FGM applicati
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2.7.3 Processing For the fabricatio
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prepared discrete layers of uniform
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Powder densification processes gene
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The specific volume fraction beyond
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a) b) Figure 2.34 a) Volume fractio
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When the powders are densified in s
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Various FGM coating processes are a
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of FGMs, such as partially reactive
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leading to a characteristic time τ
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3.1 Introduction CHAPTER 3 AQUEOUS
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occurs in a multi-step process: fir
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a) b) Figure 3.1 a) SEM image of as
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3.2.3 Preparation of Carbon Black C
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3.2.5 Drying Shrinkage Characteriza
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the optimized surfactant concentrat
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The storage modulus of a colloidal
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For HA ink, yield stress
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In the case of the aqueous carbon b
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PPO units of Pluronic F-127 may ads
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a) b) Figure 3.6 A carbon black lat
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a) b) Figure 3.7 SEM images of a) c
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TGA plot is in agreement with previ
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a) b) Figure 3.9 Thermogravimetric
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3.3.8 Fabrication of Complex Cerami
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c) d) 109
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3.4 Conclusion A fugitive support m
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metal inks have been reported for R
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Midland, MI) 5% by weight stock sol
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4.2.5. Thermal Degradation of Binde
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4.3. Results and Discussion 4.3.1.
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4.3.2. Preparation of Nickel Ink Su
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260 °C for 8 hours, the residual c
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Table 4.1 Calculated residual carbo
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a) b) Figure 4.6 Sintered Ni struct
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temperature 138, 139 lead to 92-95%
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Figure 4.8 Scanning electron microg
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c) Figure 4.9 Sintered nickel latti
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5.1. Introduction CHAPTER 5 BARIUM
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materials within the overall struct
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40:60, 60:40, 80:20 are separately
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5.2.3. Rheological Characterization
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5.2.5. Co-sintering and Re-oxidatio
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mixing, BT and Ni phases appear uni
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The combined use of PAA and PAA-90K
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To quantify this difference in sint
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As the BT and Ni particles used in
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The reducing atmosphere used in the
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Figure 5.7 Vickers hardness number
Page 173 and 174: 5.3.6. Fabrication of BT-Ni composi
Page 175 and 176: modify the sintering kinetics of th
Page 177 and 178: a) b) Figure 5.10 Co-sintered compo
Page 179 and 180: 5.4. Conclusions Freeform fabricati
Page 181 and 182: Liquid phase sintering involves usi
Page 183 and 184: (pH=4.4, 31.5% by weight) (Adva Flo
Page 185 and 186: concentration of 7 mg/mL in the aqu
Page 187 and 188: Table 6.1 Formulations of aqueous c
Page 189 and 190: thickness. Each layer of the struct
Page 191 and 192: 6.2.6. Hardness Test Microindentati
Page 193 and 194: micrographs for these two powders.
Page 195 and 196: Second, the added LiAC∙2H2O is am
Page 197 and 198: Figure 6.3 Oscillatory behavior for
Page 199 and 200: a) b) Figure 6.4 Sintering strain c
Page 201 and 202: mass transport in LFBT network. 167
Page 203 and 204: The above discussion is mainly focu
Page 205 and 206: Figure 6.8 shows the bowtie-shaped
Page 207 and 208: Figure 6.10 A NPR composite of para
Page 209 and 210: etween BT and Ni phases. But Zn ele
Page 211 and 212: Figure 6.13 Scanning electron micro
Page 213 and 214: Figure 6.15 shows the mapping of Ti
Page 215 and 216: Figure 6.17 and Figure 6.18 show el
Page 217 and 218: Figure 6.19 shows element mapping f
Page 219 and 220: 6.3.7. Piezoelectricity and Dielect
Page 221 and 222: 6.4. Conclusions Aqueous colloidal
Page 223: geometric features, including non-s
Page 227 and 228: 7.2. Recommendations In the context
Page 229 and 230: gelation behavior. κ-carrageenan i
Page 231 and 232: REFERENCES 1. Larsson 9301647, 1993
Page 233 and 234: 29. Simchi, A.; Petzoldt, F.; Pohl,
Page 235 and 236: 61. Bouvard, D., Acta Metallurgica
Page 237 and 238: 92. Morissette, S. L.; Lewis, J. A.
Page 239 and 240: 120. Boehm, H. P., Some Aspects of
Page 241 and 242: 150. Atkinson, A., Growth of Nio an
Page 243 and 244: APPENDICES A. Mathematical Modeling
Page 245 and 246: and
Page 247 and 248: conditions: Equation A.12 is solved
Page 249 and 250: and with
Page 251 and 252: a) b) Figure B.1 a) Freeze-dried st
Page 253 and 254: a) Figure C.1 Cr-Ni lattices of 5Cr
Page 255 and 256: E. Binary Phase Diagram of ZnO-B2O3
Page 257 and 258: References A.1. Du, Z., Sarofim, A.
Page 259: Name: Jian Xu Date of Degree: May,
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