Thermoanalytical and calorimetric investigations on the formation and decomposition of some alunites

1987 
Abstract Under hydrothermal conditions the formation of oxonium alunite (OxAl) and potassium alunite (KAI) was experimentally determined as a function of temperature. The straight lines In K = f(T) obtained are the result of the experiments described. From the calorimetric determination of the thermal capacity, the standard formation enthalpy and the standard entropy. In K = f( T ) functions could be calculated. Comparison of experimental and calculated results has proved to be satisfactory for KAI, where the non-stoichiometry is the main consideration. The agreement is not very good for OxAl because of foreign phase components. Investigation of the thermal decomposition under quasi-isothermal and quasi-isobaric conditions shows that the alunites have a defined decomposition temperature. Reactions preceding this decomposition are due to the loss of excess water.
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