Topotactic growth of α-alumina platelets on 2/1 mullite single crystal surfaces upon thermal decomposition of mullite in dry and wet atmospheres

Short-term wet annealing of 2/1 mullite at 1650 °C characterized by a low gas flow rate and a water partial pressure of PH2O=0.2Ptotal had no effect on the general platelet formation processes and the prevalent orientation relationships as the mullite decomposition rate was distinctly higher than the silica volatilization rate. Topotactic growth of α-alumina (0 0 · 1) platelets influenced by vapor phase impurity doping has been recognized as a widespread phenomenon in numerous other high-temperature investigations of 2/1 mullite single crystals.