Chemical and thermal etching of magnesium orthosilicate single crystals

Abstract

(010) cleavage surfaces of magnesium orthosilicate crystals were chemically etched in concentrated HCl solution, in HCl vapour at room temperature and in NaOH and KOH melts at 400 °C. These cleavage surfaces were also thermally etched at various temperatures ranging from 1100 to 1200 °C, and the chemical and thermal etch patterns were compared. It was found that the two types of etch pit had different origins. It is believed that the chemical etch pits reveal the sites and the nature of linear defects in the crystals while the thermal etch pits probably nucleate at the sites of impurities or defect segregations. Evidence for the existence of an indentation process in thermal decomposition was obtained. A mechanism for the formation of the thermal etch pits is proposed and its implications are discussed.