Papers by Keyword: Gelcasting

Abstract: TiAl intermetallic alloy was prepared by gelcasting. The alloy powders were synthesized through reaction diffusion. The microstructure was investigated by XRD and SEM. The results showed that titanium aluminide powders were synthesized from elemental powders under the condition of 600°C for 3h. The solid loading of metal slurry was 45%. After gelcasting, drying and sintering at 1480°C for 2h, TiAl with the relative density of 93% was successfully prepared.

Abstract: Several hydroxyapatite (HAp) synthesis routes, such as solid state reactions, hydrothermal methods, wet procedures have been widely investigated. At the same time, in the last years many alternative methods to produce HAp, exploiting fish, bovine or pig bones, have been developed; among them the most used are thermal processes as well as subcritical water or alkaline hydrothermal routes. This paper deals with a natural HAp nanopowder extracted from pig bones by a treatment with hot NaOH solution. It was demonstrated that the decomposition phenomena were avoided when the extracted HAp powder was calcined in CO₂ atmosphere or by inducing the formation of CaO at 700 °C and then eliminating it through a washing procedure. The washed HAp was then exploited for producing macroporous components having controlled porosity features in terms of pore shape, size and volume percentage. For this aim, a combination of gelcasting and sacrificial template methods was applied as forming procedure, using agar as natural gelling agent and polyethylene (PE) spheres as pore former.

Abstract: The industrialization of gelcasting technique has been prevented because acryamide is a neurotoxin monomer. In this paper, a low-toxicity gel system based on the polymerization of low-toxicity N-hydroxymothl acrylamide was used for the gelcasting PMN-PZT piezoelectric ceramic. The effects of monomer concentration, the dosage of initiator and catalyst, pH value on polymerization were studied. The results showed that the condition suitable for gelcasting PMN-PZT piezoelectric ceramics could be obtained while monomer concentration was 10wt%～15wt%, the dosages of initiator and catalyst were respectively 0.4 vol%～0.5vol% and 0.4vol%, pH value of slurry was about 10. The highest bending strength of PMN-PZT green body prepared at the aboved conditions can reach 19.5Mpa

Abstract: The piezoelectric ceramic of PMN-PZT was prepared by gelcasting using N-hydroxymothl acrylamide(NMAM) as monomer. The green bodies with different microstructure and properties were obtained by changing solid contents of slurry. The effects of solid volume fraction in slurries on properties of PMN-PZT green bodies were investigated. The results that green shrinkage reduced from 5.95% to 1.47%, the green density increased from 3.51g/cm3 to 4.69g/cm³, and green bending strength increased firstly then decreased when solid content of slurry changed from 45vol% to 60vol%. SEM photographs revealed that^{Superscript text} the green body had a uniform microstructure and few agglomerates when the solid loading was 50vol%.

Abstract: It is difficult to fabricate complicated ceramic parts with conventional manufacturing methods such as injection molding and slip casting. In this paper, an indirect solid freeform fabrication process based on Stereolithography (SL) and gelcasting to shape complicated ceramic parts. A lost resin mold with negative image of part was first fabricated by SL. And then aqueous ceramic slurry with high solids loading and low viscosity were prepared and poured into the resin mold, a wet gelcast body was obtained by in-situ polymerized, and the vacuum freeze-drying technology was used to eliminate the deionized water in the gelcast body for improving efficiency and decrease drying shrinkage. Based on the thermogravimetric analysis results of resin mold and gel ceramic body, a sintering process was carried out to remove mold, organic binder and to sinter ceramic. Finally, the desired ceramic part was successfully fabricated to verify the feasibility and effectiveness of the novel process.

Abstract: The paper presents an integral core/shell fabrication of ceramic casting mould for hollow turbine blades by combining SL (Stereolithography) with gelcasting. This method could guarantee the positional accuracy between ceramic cores and shell, thus achieving the rapid fabrication of complex turbine blade castings. The paper focuses on the design of resin mould for gelcasting, the preparation of ceramic slurry, the pyrolysis of resin prototype and the sintering of ceramic green body. The feasibility and effectiveness of above mentioned method were verified through successful manufacturing of hollow turbine blades with double-walled structure.

Abstract: In this paper, gelatin was selected as binder, sodium alginate as dispersant. The slurries with low viscosity and high solid loading were prepared by mixing two types of 316L stainless steel powders with different particle sizes in proper mass ratios. The freeze drying process was adopted to treat the wet green body. The results show that the slurry with a solid loading as high as 58 vol.% can be obtained by mixing 316L stainless steel powders with mass ratio of fine particles to coarse as 4:6, which has better fluidity and densification. The viscosity of the slurry is less than 1Pa•s. After the freeze drying process, the bending strength of green body reaches 11.15MPa, the drying shrinkage is decreased to 0.44%, and the generation of crack can be prevented. The study results provide some helpful references for further research in rapid manufacturing of complex metal part.

Abstract: The growing interesting in the use of silicon carbide in automotive components, biomaterials, energy, among others, which demand the production of parts with complex geometry that are difficult to obtain by conventional compaction techniques, motivates the search for developing new conformation processes. Within this context, this paper investigates the production of pieces of silicon carbide through the gelcasting process and subsequent green machining of these parts. Three systems of monomers were studied: MAM-NVP-MBAM, MAM-PEG (DMA) and MAM-HMAM. The effect of the concentration of monomers, concentration of chemical initiator and the ratio of chain-forming and crosslinker monomers on the cutting force during machining and surface roughness were evaluated. These data are compared with values of flexural strength and hardness of samples produced under the same conditions. Through a statistical analysis it was determined the best formulation for the production of parts of SiC with favorable characteristics of green machining.

Abstract: Silica-based porous bioactive ceramics was prepared by gel-casting method using silica xerogel powder. Xerogel was derived from rice husk ash. 42 vol.% solid containing slurry was prepared in 1:30 (MBAM:AM) monomer cross-linker solution. The srurry was thixotropic. Gel-casted body was machined efficiently. Dired cast body was sintered at 1100oC. Apatite layer was formed on silica body during In vitro bioactivity experiment. The results suggest that the gel-casted silica ceramics can be used as a bioceramics.

Abstract: Aqueous gel-casting of beryllia using polyelectrolyte NH₄PAA as a dispersant has been investigated. The effects of the dispersant amount, pH values on the surface properties of BeO powders in aqueous solvent were studied and high solids loading BeO suspension (45 vol.%) was developed. A premix solution containing 15-20 wt.% of AM monomer can provide enough mechanical strength for the green body obtained from 45 vol.% BeO suspension. SEM photography indicates that BeO ceramics with homogeneous microstructure can be fabricated. The thermal conductivity of sintered green body is 182.1±10 W/(m.K). Gelcasting is a suitable process to form BeO ceramic parts.