The authors have studied thermal properties of refined ammonium hexafluorosilicate obtained by anhydrous fluorine-ammonium scheme. The sublimation stages within the temperature range 20…500 °С were studied by thermogravimetric method. The authors have studied the laws of influence of sample heating rate and evaporator geometry on temperature conditions of heating and sublimation of ammonium hexafluorosilicate. Possible ways of improving the equipment for raising the efficiency of heating and evaporation were proposed.