Decomposition of Mullite

Free surfaces of 2:1 mullite (2Al 2 O 3 ·SiO 2 ) specimens decomposed with the evolution of SiO and O 2 when they were heated at high temperatures under low partial pressures of O 2 ; this reaction was analyzed thermodynamically. In addition, bubbles were observed at internal interfaces between mullite and fused‐SiO 2 diffusion couples. These bubbles, when formed at 1 atm ambient pressure between 1650° and 1800°C, resulted from reaction of Si particles and residual SiO 2 ‐rich glass in the fused cast mullite.