Effects of Pore Forming Additives on Microstructures and Mechanical Properties of Aluminium Titanate Ceramics

Abstract

Aluminium titanate (Al₂TiO₅, AT) has a large uniaxial anisotropy of thermal expansion on the crystallographic orientation, which generates microcracks in the ceramics. Owing to microcraks, which buffer thermal expansion, AT shows especially low thermal expansion. On the other hand, microcracks remarkably decrease a mechanical strength and sometimes induce the destruction of specimens due to crack growth. In this study, AT ceramics containing various amounts of pore forming additives of different particle diameter were prepared by firing at various temperatures. The effects of contents and particle sizes of pore forming additives on microstructures and mechanical properties of AT ceramics were examined. In the case of lower contents of pore forming additives, visible large cracks causing the destruction were observed on the surfaces of the specimens and bending strengths decreased with increasing firing temperature. On the other hand, the bending strength of the specimens containing higher amounts of pore forming additives scarcely depended on firing temperatures. The pore spacings decreased with increasing additives content and decreasing particle size of additives. Therefore, large cracks causing decline of bending strength were difficult to occur in the specimens containing higher amounts of additives because crack growth was effectively prevented around pores, resulting in less decline of bending strength with firing temperature. The inhibition of crack growth was effective in the case of the additive with small particle size. As a result, the bending strength of the specimen containing the additive with small particle size was higher than that of the specimen with the large size additive.