Silane Gas Production Through Hydrolysis of Magnesium Silicide by Hydrochloric Acid

Abstract

Monosilane (SiH₄) is a common precursor for the production of high-purity silicon for solar PV applications. As an alternative to carbothermic reduction of silica to produce metallurgical grade silicon with subsequent conversion to silane, an alternative route over magnesiothermic reduction of silica to Mg₂Si has been explored in our earlier work. In the current work, silane gas production through hydrolysis of Mg₂Si in HCl acid solution was studied. Two sources of Mg₂Si were chosen: a commercial Mg₂Si source and a Mg₂Si source produced through magnesiothermic reduction of high-purity natural quartz. Effects of various parameters on the hydrolysis of Mg₂Si, including different experimental setups, temperature of the acid solution, acid concentration, reaction time, and relative amounts of reactants were studied. The evolution of produced gases was determined by two different methods: firstly, by passing the produced gas through a KOH solution to capture Si with subsequent analysis of the Si content in the KOH solution by inductively coupled plasma mass spectrometry and secondly, on-line gas analysis by GC–MS. The silane distribution between different silane species with reaction time was evaluated and the activation energy of silane formation was calculated. The results indicated comparable silane yields obtained from the on-line GC–MS method and KOH solution analysis method, as well as for commercial Mg₂Si and the Mg₂Si–MgO mixture produced through magnesiothermic reduction. Furthermore, adding HCl acid to Mg₂Si in water led to higher SiH₄ formation yield than adding Mg₂Si to acid. However, the total silane yield for the two methods was similar at approximately 32%.

Graphical Abstract