Papers by Keyword: Gel-Casting

Abstract: In order to research the toughening effects of carbon nanotubes on 3Y-ZrO₂ via different moulding methods. 3Y-ZrO₂ and 3Y-ZrO₂ with two kind of carbon nanotubes were prepared by compression moluding forming and gel-casting. And all of the green bodies were sintering at 1600°C in high temperature furnace. The X-ray diffraction and density of sintered bodies, microstructural of fracture surface and fracture toughness were characterized and analyzed. Results shown that gel-casting is better than compression about toughening 3Y-ZrO₂ by carbon nanotubes. For gel-casting, the density is nearly the same and fracture toughness has been improved which is form 5.17MPa·m^1/2 to 5.63 MPa·m^1/2_. For compression moulding forming, the density was reduced by the aggregation of carbon nanotubes. The fracture toughness can’t improve by carbon nanotubes.

Abstract: Silicon carbide possess high performances such as high hardness and strength, oxidation and high temperature resistance, high thermal conductivity and low thermal expansion coefficient. Widely used methods of molding green body for sintered pressureless bonded silicon carbide comprise dry pressing molding and casting molding. The former fails in preparation of complex shapes, while those prepared by casting molding are prone to have defects such as nonuniformity of density and easy cracking. Gel-casting is a net-shape modeling technology caused by the polymerization of organic monomer (acrylamide). The green bodies molded by gel-casting have uniform structure, high density, high strength and machinability. In this study, gel casting molding and pressureless sintering were used to prepare silicon carbide. The effect of the parameters of gel casting and sintering on the microstructure of the obtained silicon carbide was examined

Abstract: High alumina foam ceramics products with low density, high specific surface area, low thermal conductivity, corrosion resistance and other excellent physical and chemical properties are suitable for chemical, metallurgy and other related fields ^[1-4]. Alumina foam ceramics that compression strength increased by 200%, was prepared by Rizwan Ahmad through impregnation process using foamed rubber ^[5]. However foamed rubber was expensive and could be decomposed creating poisonous gases at high temperature. Zhou l z ^[6] prepared mullite porous ceramics with high strength by gel-casting method. Gel-casting is an effective method for preparation of ceramics products with large size and complicated shape. Fiber reinforced dense ceramics composite materials with excellent performance have been studied widely ^[7-10], it is also an important issue to adequately investigate the reinforcement of porous ceramics with fiber.

Abstract: Si₃N₄-BN composites were prepared by die-pressing and precursor infiltration and pyrolysis (PIP) route using borazine as the precursor. The composition, microstructure, mechanical, and dielectric properties of the composites with different porosities were investigated. With the adoption of starch as pore forming substance, drawn the Si₃N₄ preform from the liquid precursor borazine and decrease the pressure during curing, the porosity of the Si₃N₄-BN composites were effectively increased. Along with the increase of the porosity of the composites, the mechanical properties were decreased and the dielectric properties were improved. With 20 wt.% starch and drawn Si₃N₄ preform from borazine before curing, the density, porosity, flexural strength and elastic modulus of the composites were 1.70 g·cm^-3, 29.78%, 48.05MPa and 32.45GPa, respectively. The dielectric constants and loss tangents were 4.20~4.44 and 0.48~3.42×10^-3 at the frequency 7~ 18GHz. Composites with various dielectric and mechanical properties can be designed and prepared according to the application needs.

Abstract: Gel-casting is promising in fabricating uniform and complex-shaped ceramic body, but it is confined in industrial application for the neurotoxic acrylamid (AM) gel system. Ether-contained oligomer poly(ethylene glycol)(200) dimethacrylate (PEG(200)DMA) with methacrylate end-group on either side of the long chain can act as cross-linking agent in free radical polymerization to form branchy gel network structure, which improves the green body strength. In this study, low-toxic PEG(200)DMA was chosen as the main binder and crosslinker and small dosage AM was applied to adjust the viscosity of the ceramic slurry to gel-cast 3YSZ (PEG(200)DMA: AM = 4:1, mass ratio). Influence of monomer concentration, dispersant concentration and solid loading on the rheological behavior of the slurry and the flexural strength of the green body were investigated using aqueous PEG(200)DMA/AM gel system to gel-cast 3YSZ. The results show that the flexural strength of green bodies notably increases with the increasing of monomer concentration and reaches high up to 14.4 MPa when gel-cast 3YSZ ceramics using PEG(200)DMA/AM gel system with appropriate amount of PAA-NH₄, monomer and solid loading. This gel system obviously reduces the toxicity of the conventional AM system and, at the same time, ensures high flexural strength of green bodies.

Abstract: In order to study the influence of fabrication accuracy on the transmission performance of photonic cystals, the resin molds with inverse diamond structure with the same size were fabricated in different forming angle (30°,60°,90°) by stereolithography (SL). The alumina PCs with diamond structure were obtained combining the molds and gel-casting. The results showed that different forming angle of three kinds molds resulted in the change of the size and relative angle of their cells, and the PCs fabricated were also. The transmission properties of PCs had an obvious change in the width and smoothness of the band gap, which displayed that the resin molds by SL resulted in fabrication errors would affect the transmission properties of PCs. In the practical fabrication of diamond-structure PCs, fabrication errors caused in the different forming angle needed to be considered when SL technology was utilized to fabricate the molds, which also fit complex molds.

Abstract: To compare the influence of porosity on bending strength, density, viscosity of slurry of dental zirconia-toughened alumina(Ce-TZP/A) ceramic by gel-casting technique. Ce-TZP/A composite ceramic powder was made from a Al2O3 of micron grade and 3Ce-ZrO2 of nanometer grade, with sintering additives of MgO and TiO2. The slurries of 5(v/v), 52%, 54%, 56% ,58% and 60% were prepared separately, and sintered at 1200°C after in situ molding using gel-casting. The properties such as bending strength, density, viscosity of slurry of specimens were measure and compared. Slurry was prepared with optimum solid content, and applied to form dental CeTZP/A basal crown on the plaster die. The marginal fitness of crowns was observed after sintered. The mean viscosity of slurry (PaS) were: 0.27±0.05, 0.31±0.1, 0.33±0.09, 0.96±0.12, 1.01±0.07, 1.21±0.02. The effect of solid loading (P=0.05) were significant. The mean bending strength (MPa) were: 43.15±0.8, 47.9±1.5, 50.09±1.7, 58.12±1.9, 39.17±1.6, 35.08±1.2. The mean toughness (MPa m^1/2) were: 17.6±0.8, 16.9±0.6, 16.1±0.5, 17.8±0.9, 18.6±0.8, 20.5±0.2. The mean density (g/cm) were: 5.32±0.9, 5.43±0.8, 6.13±0.5, 6.01±0.5, 5.13±0.3, 5.05±0.4. The specimen formed from slurry of 52(v/v) had better properties than that of others solid loading after sintered at 1150º. With the solid loading increased, the viscosity of slurry has a significantly improved.

Abstract: h-BN/Si₃N₄ composite ceramics were fabricated by gel-casting method and pressureless sintering using Si₃N₄ and h-BN as raw materials. The effect of h-BN on the microstructure and comprehensive properties of h-BN/Si₃N₄ ceramic were investigated. The results showed that the introduction of h-BN hindered the densification of h-BN/Si₃N₄ ceramic as well as the transformation of α-Si₃N₄ to β-Si₃N₄. The mechanical properties of Si₃N₄ based ceramics decreased with the increase of h-BN content, while the thermal property, dielectric properties and machinability increased.

Abstract: The TiC/Fe steel matrix composites were prepared by gelcasting technology of selecting the appropriate gel system and additives, the reasonable technological parameters. The toluene and 2-hydroxyethyl methacrylate (HEMA) were as gel system, oleic acid as dispersant. The rheological property, curing process and performance of the body were analyzed. The results show that the monomer (HEMA) content of 4.6wt% and oleic acid to 2wt% which increased the solid content from 50 to 54vol.%. The relative density of green body is 59.6%, the intensity is 28MPa. After sintering, the complicated shape was prepared.

Abstract: The porous titanium alloys containing molybdenum elements have been prepared by gel-casting methods. The composite coatings with hydroxyapatite (HAP) and TiO₂ were prepared on the precursor in this study. The microstructure was examined by scanning electron microscopy (SEM) and X-ray diffraction, and part of the coatings was examined by EDS to indicate the linear distribution of HAP and TiO2. The Solid content of gel-casting of water base can reac_{Subscript text}h 35%，and porosity can reduce to 42% after sintering.