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The high-temperature ablation properties of nano zirconia reinforced fused silica ceramics were tested using an ultra-high-temperature oxyacetylene ablation equipment. The results show that the linear recession rate and the mass loss rate of the composite ceramics containing 10 wt% zirconia are 0.087 mm/s and 0.016 g/s at 40 s ablation time, respectively, both much lower than that (0.106 mm/s and 0.028 g/s) of the pure fused silica ceramics, indicating superior ablation resistance properties of the composite ceramics. The depth of the melting area along with the flame direction of the composite ceramics is much shallower than that of the pure samples. Moreover, the composite ceramics show excellent heat shielding properties. [ABSTRACT FROM AUTHOR]

Abstract: Silica ceramics with low porosity, high strength, low dielectric constant and loss were fabricated by gelcasting using a low-toxicity N′N-dimethyl acrylamide (DMAA) gel system. Effect of solid loading on rheological properties of slurries, properties of green bodies and sintered ceramics were investigated. The solid loading of suspension that can meet requirements for casting is as high as 68vol%. However, it is found that the highest flexural strength of 15.4MPa for green bodies and 67.4MPa for sintered ceramics is obtained at the solid loading of 64vol% and 66vol%, respectively. Ceramics with dielectric constant of 3.27 and the lowest dielectric loss (1MHz) of 7.82×10–4 are obtained at the solid loading of 64vol%. Solid loading has a critical effect on properties of green and sintered silica bodies. [Copyright &y& Elsevier]

A low-toxicity and water-soluble monomer N, N-dimethylacrylamide (DMAA) was used as gelling agent in gelcasting of silica ceramics. In order to prepare high solid loading and low viscosity gelcasting slurries, effects of various parameters such as zeta potential, pH value, dispersant dosage and solid loading on rheological behaviors of the suspensions were investigated. The results suggest that the best conditions are pH 7.7 and dispersant dosage 0.1wt%. The maximum flexural strength of green bodies with only 2wt% organics in the slurry could be up to 15.3MPa. The sintering shrinkage, bulk density, coefficient of linear expansion and flexural strength of sintered ceramics are 5.2%, 1.95g/cm3, 0.58×10−6 k−1 (200°C) and 67.4MPa, respectively. The dielectric constant and loss (1MHz) are 3.26 and 7.8×10−4, respectively. [ABSTRACT FROM AUTHOR]