The effect of alkali halides on the thermal hydrolysis of magnesium chloride and magnesium bromide

DTA, TG and DTG curves were recorded for ground mixtures of hydrated MgCl₂ and MgBr₂ with NaCl, NaBr, KCl, KBr, CsCl and CsBr. Infrared spectra of the ground mixtures were recorded after they had been heated to several temperatures. Substitutional solid solutions of hydrated magnesium in potassium and cesium salts were formed during grinding of the salt mixtures. However, a solid solution of MgCl₂ is always obtained with KCl and CsCl, as a result of grinding the alkali chloride either with MgCl₂ or with MgBr₂. Also, a solid solution of MgBr₂ is always obtained with KBr and CsBr, either from MgCl₂ or from MgBr₂. Cesium halides form stable solid solutions with the magnesium halides, and thermal hydrolysis of the hydrated magnesium is prevented. The solid solutions formed with potassium halides are less stable than those formed with cesium salts and hydrated Mg is thermally hydrolyzed. The temperature at which this hydrolysis occurs in the presence of potassium halide is above 300 °C, whereas in its absence this reaction occurs at temperatures below 250 °C. No hydrated solid solution of Mg is formed with sodium halides during the grinding process and the thermal behavior of magnesium chloride or bromide in sodium chloride or bromide, respectively, is similar to the thermal behavior of the pure magnesium salt. The thermal behavior of MgBr₂ in NaCl is similar to that of pure MgCl₂ but the thermal behavior of MgCl₂ ground with NaBr shows some similarities with each of the two pure magnesium salts, the chloride and the bromide.