Effects of Adding Form of Additives on the Structure and Properties of High-Purity Alumina Ceramics

Abstract

High-purity alumina ceramics was prepared using high-purity α-Al2O3 powder as raw material, nitrates or oxides of magnesium, chromium and copper as additives by a wet ball milling with a later dry pressing forming and normal pressure sintering process. The influence of additives on the sintering temperature, microstructure and bending strength of the prepared alumina ceramics was studies. The results showed that the additive doped with nitrate can be dispersed uniformly in the body with molecule scale, and the oxides obtained by decomposing of nitrates have the higher reactivity. Thus, the nitrate additives have better capacity than oxide additives in reducing the sintering temperature and inhibiting the abnormal grain growth, and the alumina ceramics prepared by adding of nitrate additives have higher density and bending strength.

Influence of Silicon-Modified Al Powders (SiO2@Al) on Anti-oxidation Performance of Al2O3-SiO2 Ceramic Coating for Carbon Steel at High Temperature

“…To sum up, the Al powders in SiO 2 @Al melted at 662.85 • C and reacted with SiO 2 on its surface, which generated local high temperature and the sintering of ceramic raw materials, thus contributing to its excellent anti-oxidation performance, which was consistent with the non-isothermal kinetics. Besides, mullite and cristobalite formed at 1150 • C could further enhance the coating compactness and improve the anti-oxidation performance above 1150 • C [19]. However, ceramic raw materials just sintered above 1150 • C within AS, and thus showed an unobvious anti-oxidation effect below this temperature.…”

“…Silicates with low melting points are always added into Al 2 O 3 -SiO 2 coating to accelerate the sintering under low temperature. However, a eutectic crystal of Fe-2FeO·SiO 2 is formed over 1170 • C, which is harmful to the anti-oxidation performance of the protective coating at high temperature [18,19]. In order to accelerate the sintering of Al 2 O 3 -SiO 2 coating under low temperature and avoid the formation of Fe-2FeO·SiO 2 over 1170 • C, silicates with low melting point should be replaced by other additives [20,21].…”