Papers by Keyword: Gelcasting

Abstract: Fused Quartz crucible with large scale was formed by gelcasting processing in this paper. Effects of dispersant, pH values and particle grading on solids content of slurries were discussed to increase the volume density of the green compacts and decrease the shrinkage and deformation during sintering. Effects of acrylamide content and the ratio of acrylamide to coupling agent on bending strength of the green compacts were investigated. Effects of the amount of initiator and curing temperature on the gelcasting processing were studied as well. The green compacts with solids content of 80% was obtained when the addition ratio of dispersant to Quartz powders was 0.3wt %, the ratio of Quartz powders in D50 of 1.9μm and 7.6μm was adjusted to 3:7, the addition ratio of acrylamide to Quartz powders was 1.0wt % and the ratio of acrylamide to coupling agent was 16:1. The bending strength of the sinterred produts was found to be 76.0MPa with volume density of 1.94 g/cm2. Fused Quartz crucible prepared under conditions mentioned above was 800mm in length, 800mm in width and 400mm in height.

Abstract: In this paper, gel casting process of RBSC was deeply studied. The rheological property of C/SiC slurry was analyzed, high solid loading (67%) slurry with low viscosity was produced. Also the properties of green body and sintered body were studied. Finally, through optimizations of process parameters, a large-sized (650mm), complex-shaped (with thin ribs about 2.5mm) was fabricated through gel casting process with no cracks and deformation. It was showed that gel casting process is suitable for producing large-sized, complex-shaped RBSC components.

Abstract: Porous yttria-stabilized zirconia (YSZ) ceramics were fabricated by tert-butyl alcohol (TBA)-based gelcasting method using high solid loading slurry. Micron pores were generated by using low-cost carbon powder as the pore-forming agent. The TBA-based slurries of 50% solid loading appropriate for gelcasting were successfully prepared by using commercial dispersant BYK-163. The rheological behavior of the slurries were measured and discussed. The porosity, microstructure, compressive strength and thermal conductivity of the porous ceramics were tested and analyzed. The results show that this low-cost technology is significant for fabricating porous ceramics with both high compressive strength and low thermal conductivity.

Abstract: Ti-6Al-4V alloy was prepared by gelcasting. Plasma rotating electrode and hydrogenation-dehydrogenation Ti-6Al-4V powders were mixed used to meet both high performance and low cost objectives. The morphological properties were investigated by SEM. The results showed that the gelcasting green body with mixed powders has advantages of high solids loading and excellent sinterability. After sintered at 1400°C for 2h, the relative density reached 98%. The bending strength and hardness were 313MPa and 49.8(HRC).

Abstract: Ti-6Al-4V green body was processed by gelcasting. Effects of the powder morphology, dispersant and pH on the solids loading were investigated. The morphological properties were investigated by SEM. The results show that the powder morphology is the overriding factor in slurry processing. Slection of dispersant and pH are another two critical factors affecting the solids loading by a percentage of 2 to 4. With optimum conditions: spherical powders, 1.5 wt.% ammonium citrate as the dispersant and pH=11, the green body with high solids loading of 59.4% was prepared.

Abstract: The gelcasting technique was used to fabricate 95 alumina ceramics green bodies. The gel system based on MAM-MBAM was low-toxicity in this study. The green bodies and the sinter obtained with solid content of 55vol% had high strength, density and quality. The influences of the monomers mole ratio (MAM/MBAM) and the monomers content (MAM and MBAM) on the compressive strength of green bodies, the solid content on the density, compressive strength and the shrinkage rate of green bodies were also discussed. The experimental results showed that the best mole ratio of MAM/MBAM was 12/1. Compressive strength increased with the increase of monomers content (MAM and MBAM). The microstructure of the green bodies indicated that the ceramic powders were connected by polymeric networks, and the ceramic powders in the green body distributed homogeneously and compactly.

Abstract: Gelcasing has been recognized as a very high-potential method in fabricating complex-shaped ceramic products. In this contribution, the gelcasting process was applied to manufacture green body of dental zirconia-toughened alumina (ZTA) ceramic base crowns. As one of a series studies, this study was conducted to investigate the influence of initiator and catalyst concentrations on idle and processing time of gelcasting system and the strength of green and sintered body of ZTA ceramic base crowns. Six different groups were divided basing on different proportion of initiator (1-6 vol.%), and with different proportion of catalyst correspondingly. The results showed that when the initiator was 4vol.% and the catalyst was 8vol.% at room temperature, the time of solidified reaction and bisque properties were optimum and it also met the requirement of practical running time for shaping dental all-ceramic crown in lab.

Abstract: Reaction-bonding sintering silicon carbide (RB-SiC) toughened by 10vol% short carbon fibers were produced by Gel-casting method using water soluble epoxy as gel former and then reaction sintering at 1750°C under vacuum atmosphere for 2 h . SEM showed that short carbon fibers could disperse uniformly in the preforms and sintered carbon fiber reinforced silicon carbide composites (C_f/SiC). The mechanical test results showed that the strength decrease from 286 MPa for RB-SiC to 231 MPa for C_f/SiC, however, the fracture toughness of Cf/SiC increased from 3.65 MPa m^1/2 to 5.28 MPa m^1/2 compared with RB-SiC. The strength decrease of the C_f/SiC should be ascribed to the chemical reaction between the addition of short fibers and matrix, and the increase of the fracture toughness could be attributed to fiber debonding, fiber pull-out and crack deflection .

Abstract: In the present work, porous HA scaffolds with well controlled pore size, porosity and high compressive strength were prepared by aqueous gelcasting. PMMA beads with different size were used as the pore forming agent. The compositions, microstructure and properties of porous HA bioceramics were analyzed by XRD, SEM, Hg porosimetry etc. The mechanical properties were also tested. For scaffolds with the porosity as 70%, the average compressive strength was 11.9±1.7 MPa. Results showed that glecasting process can be used for the preparation of porous HA biomaterials with well controlled pore size and improved mechanical properties.

Abstract: In this paper, an indirect solid freeform fabrication (ISFF) process was developed to rapidly fabricate ceramic casting molds by combining stereolithography with gelcasting technology. To realize this method, the stereolithography apparatus was used to fabricate a resin mold, and then aqueous ceramic slurry was cast into the resin mold and in situ polymerized to form a wet green body of ceramic casting mold. Freeze drying, pyrolyzing and sintering completed the manufacturing route. Finally, the ceramic casting mold with complex ceramic cores was obtained, and a car radiator with deep grooves was produced to verify the validity and feasibility of the method.