Reaction-bonding behavior of mullite ceramics with Y2O3 addition

Mullite ceramics were fabricated by a reaction-bonding technique from powder mixtures of Al2O3 and Si, with an Y2O3 addition. The mullitization and densification behavior was investigated as a function of Y2O3 content, heating rate, processing temperature and holding time as well as mullite seeds. It has been shown that mullite formation occurs by nucleation and growth within an aluminosilicate glass, but lattice and grain-boundary diffusion becomes important at the later stage of mullite growth. The addition of Y2O3 can decrease the glass viscosity and thus enhance the mullitization reaction, while the incorporation of mullite seeds may reduce the grain size and consequently allow pore elimination under conditions of shorter-range diffusion. After heating at 1400°C for 5 h or 1450°C for 2 h, an almost fully dense state was achieved for 15 mol% Y2O3-doped and 5 mol% mullite-seeded specimens.