The Chemical Polishing of Sapphire and MgAl Spinel

Based on air annealing studies at 1500°C, it appears that bulk and surface mechanical damage in sapphire and spinel may be greatly minimized. Such annealed surfaces can then be effectively polished chemically leaving essentially featureless surfaces. Preannealed sapphire orientations can be polished at 285°C in a mixture for 15 min while spinel orientations may be treated in a mixture at 250°C for the same length of time. (111) spinel and sapphire cannot be chemically polished by the procedures described but are presumably amenable to removal of most surface and mechanical saw and polish induced bulk damage via the high‐temperature annealing process.