DESIGN, ASSEMBLY AND CHARACTERIZATION OF COMPOSITE ...

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5.2.6. Hardness of Composites Microindentation Vickers test (0.5 kgf load, 5 seconds) is used to measure hardness of Ni(m) composites. For each Ni(m) composition, cylindrical rod specimens are sintered in moist H2/N2 gas at 1350 °C for 1 hour. In preparation for hardness testing, these specimens are cross-sectioned using a diamond saw (Labcut 1010, Extec, Enfield, CT), embedded in epoxy resin, and then polished using a polisher (Labpol 8-12, Extec, Enfield, CT) with diamond pastes at 3 to 0.25 µm particle size (DiaDuo, Struers, Denmark). For comparison purposes, density of each sample is determined by Archimedes method. 5.3. Results and Discussion 5.3.1. Preparation of Colloidal Inks Despite the dissimilar surface chemistries of BT and Ni particles, Ni(m) gel may be prepared by directly blending polyelectrolyte stabilized BT and Ni suspensions. The initial gel strength depends on the mixing ratio of BT to Ni, and may require adjustment by appropriate polyelectrolyte addition to achieve proper gel strength for use in Robocasting. Pure BT ink is prepared using a dispersant containing the predetermined amount of PAA and PAA-90K followed by flocculation using PEI, so that its solid volume fraction and drying behavior become compatible to Ni(m) inks. The surface chemistry of nickel and barium titanate as colloidal particles are 135, 137, 142-144, complex and disagreement exists in the literature about their isoelectric point, 162, 163 Nevertheless anionic PAA stabilized BT and cationic PEI stabilized Ni suspensions may be directly blended to form the Ni(m) colloidal gel ink. After rigorous 144
mixing, BT and Ni phases appear uniformly blended and remain stable without observable phase separation. This is expected behavior since the affinity of PAA for the surface of BT and PEI for Ni are not likely to cause dispersant displacement; rather, it is expected that hetero-flocculation will occur. This process is illustrated in Figure 5.3. Hetero-flocculation of BT and Ni particles occurs through reversible electrostatic “bridging” between adsorbed oppositely charged polymer molecules. At this point, the gel strength (i.e., magnitude of yield stress and shear elastic modulus) depends on the interaction strength between adsorbed PEI and PAA, and the density of those bridging points (i.e. volume ration of BT and Ni particles). The mixing process is thus of utmost importance to homogenize the blended ink and set the initial structure of the colloidal gel. For a thoroughly-blended composite gel with a BT:Ni volume ratio around 80:20, the ink rheology at φsolids=0.43 after HPMC and DI water addition is satisfactory for printing and no further addition of PEI or PAA is needed. However, for a blend with a higher BT volume fraction, an addition amount of PEI is needed to achieve acceptable rheology at φsolids=0.43. Conversely, for an ink with higher Ni volume fraction, an additional amount of PAA is needed. In either direction, it seems the appropriate ratio of total PAA to PEI is of the order 3:2. The extreme cases represent pure component ink formulations: a PAA stabilized aqueous BT suspension is flocculated by PEI; and a PEI stabilized aqueous Ni suspension is flocculated by PAA. 145
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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
Page 109 and 110: For HA ink, yield stress
Page 111 and 112: In the case of the aqueous carbon b
Page 113 and 114: PPO units of Pluronic F-127 may ads
Page 115 and 116: a) b) Figure 3.6 A carbon black lat
Page 117 and 118: a) b) Figure 3.7 SEM images of a) c
Page 119 and 120: TGA plot is in agreement with previ
Page 121 and 122: a) b) Figure 3.9 Thermogravimetric
Page 123 and 124: 3.3.8 Fabrication of Complex Cerami
Page 125 and 126: c) d) 109
Page 127 and 128: 3.4 Conclusion A fugitive support m
Page 129 and 130: metal inks have been reported for R
Page 131 and 132: Midland, MI) 5% by weight stock sol
Page 133 and 134: 4.2.5. Thermal Degradation of Binde
Page 135 and 136: 4.3. Results and Discussion 4.3.1.
Page 137 and 138: 4.3.2. Preparation of Nickel Ink Su
Page 139 and 140: 260 °C for 8 hours, the residual c
Page 141 and 142: Table 4.1 Calculated residual carbo
Page 143 and 144: a) b) Figure 4.6 Sintered Ni struct
Page 145 and 146: temperature 138, 139 lead to 92-95%
Page 147 and 148: Figure 4.8 Scanning electron microg
Page 149 and 150: c) Figure 4.9 Sintered nickel latti
Page 151 and 152: 5.1. Introduction CHAPTER 5 BARIUM
Page 153 and 154: materials within the overall struct
Page 155 and 156: 40:60, 60:40, 80:20 are separately
Page 157 and 158: 5.2.3. Rheological Characterization
Page 159: 5.2.5. Co-sintering and Re-oxidatio
Page 163 and 164: The combined use of PAA and PAA-90K
Page 165 and 166: To quantify this difference in sint
Page 167 and 168: As the BT and Ni particles used in
Page 169 and 170: The reducing atmosphere used in the
Page 171 and 172: 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
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Figure 6.13 Scanning electron micro
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Figure 6.15 shows the mapping of Ti
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Figure 6.17 and Figure 6.18 show el
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Figure 6.19 shows element mapping f
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6.3.7. Piezoelectricity and Dielect
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6.4. Conclusions Aqueous colloidal
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geometric features, including non-s
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3. Development of aqueous colloidal
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7.2. Recommendations In the context
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gelation behavior. κ-carrageenan i
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REFERENCES 1. Larsson 9301647, 1993
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29. Simchi, A.; Petzoldt, F.; Pohl,
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61. Bouvard, D., Acta Metallurgica
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92. Morissette, S. L.; Lewis, J. A.
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120. Boehm, H. P., Some Aspects of
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150. Atkinson, A., Growth of Nio an
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APPENDICES A. Mathematical Modeling
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and
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conditions: Equation A.12 is solved
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and with
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a) b) Figure B.1 a) Freeze-dried st
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a) Figure C.1 Cr-Ni lattices of 5Cr
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E. Binary Phase Diagram of ZnO-B2O3
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References A.1. Du, Z., Sarofim, A.
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Name: Jian Xu Date of Degree: May,
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