Using a derivatograph, fluorination of corundum with ammonium fluoride vas round to take place in three distinot steps with the formation of aluminium fluoride. The DТA curves indicate the formation of ammonium aluminium hexafiluoride at 180°C. The andothermic peak at 225°C rep-manents the dissociation of the resulted ammonium bifluo-ride & some decomposition of ammonium aluminium hexafluo-ride. The endothermic peak at 300°C represents the intensive formation of ammonium aluminium ttetrafluoride, which dissociates at 360°C to aluminium fluoride.
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