Kinetics of the Decomposition of Freeze‐Dried Aluminum Sulfate and Ammonium Aluminum Sulfate

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Abstract
Conventional thermoanalytical techniques confirmed earlier studies on the stoichiometry of the decomposition of aluminum sulfate and ammonium aluminum sulfate (alum). The kinetics of the sulfate decomposition of freeze‐dried aluminum sulfate, of sieve fractions of reagent grade aluminum sulfate, and of freeze‐dried alum were studied isothermally at several temperatures between 635 and 770°C. The activation energy, a preexponential term, and a degree‐of‐fit parameter are presented. The calculations are based on several kinetic models for each data set. The freeze‐dried aluminum sulfate fits a contracting area model with an activation energy of 69 kcal/mol, and the reagent grade aluminum sulfate fits the contracting volume model with an activation energy of 74 kcal/mol. Both were calculated using a fraction reacted (alpha) of 0.15 to 0.90. The freeze‐dried alum was fitted with less precision to a first order model with an activation energy of 83 kcal/mol over the range of alpha 0.3 to 0.9.

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