Dynamic and controlled rate thermal analysis (CRTA) has been used to characterise alunites of formula [M(Al)3(SO4)2(OH)6] where M+ is the cations K+, Na+ or NH4+. Thermal decomposition occurs in a series of steps: (a) dehydration, (b) well-defined dehydroxylation and (c) desulphation.
CRTA offers a better resolution and a more detailed interpretation of water formation processes via approaching equilibrium
conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter
on the process of decomposition. Constant-rate decomposition processes of water formation reveal the subtle nature of dehydration