Transient light emission from the silicothermic reduction of magnesium oxide with potential for monitoring intermediate compound formation and decay

Abstract

Small silicon samples were brought into contact with magnesium oxide substrate plates and heated under vacuum. At heating temperatures above 1400 K, a transient light emission effect in the Si/MgO interface was observed. The changes in sample brightness are likely caused by a thermal effect. Typically the sample temperature decreases gradually by 40–80 K and is followed by a very fast rise in temperature. The light emission effect may be correlated to the transient formation and decomposition of an inhibiting layer of magnesium silicate and the endothermic formation of gaseous silicon oxide. Tempering a silicon sample on a magnesium oxide plate for several hours produced an etch pit in the substrate material from which the silicon sample split off during the cooling phase. The etch pit was investigated via electron microscopy. EDXS analysis of the finely structured surface of the reaction zone reports a composition of 2/1/5 (Mg/Si/O). A cross-section of the same area reveals a thin layer of reaction products on top of the substrate material.