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An arc spectroscopic method was developed on the analogy of thermogravimetry. Using spectrographic recording, line intensity vs. arcing time relations were determined and transformed to weight loss vs. time curves for the components evaporated from a carbon electrode cavity. The temperature of a spot 3 mm below the bottom of the cavity was followed with a thermocouple and temperature of the bottom was calculated. As a first attempt the decomposition of tricalcium phosphate was investigated. It was estimated that in the reductive surroundings of the cavity the temperature at which the rate of decomposition was maximum, was about 2000°.

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Aluminum sulphate hydrates

Kinetics of the thermal decomposition of aluminum sulphate using different calculation methods

Journal of Thermal Analysis and Calorimetry
Authors: H. Moselhy, J. Madarász, G. Pokol, S. Gál, and E. Pungor


Three different calculation methods of deriving kinetic parameters (activation energy and preexponential factor) from dynamic TG data have been applied for the sulphate decomposition stage of the aluminum sulphate octadecahydrate. The constant rate experiments were carried out by Derivatograph and DuPont thermobalances. The three parameters estimation methods included a simple differential method, the classical Coats-Redfern and a new direct integral method. The fits of the curves obtained by these procedures were compared both graphically and numerically. It was found that the direct integral method gave the most satisfactory results. With the order type reaction models this method in each case produced the smallest residual deviation values and the best fitting curves compared to those obtained by the other two methods. The activation parameters calculated by the differential method were not acceptable at all, for the estimated curves were very far from the measured ones.

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The thermal decompositions of lithium, sodium, potassium, rubidium and caesium formates were investigated by a complex dynamic thermoanalytical method. The ratio of the products in reactions resulting in alkali metal carbonates and oxalates depended variously on the atmosphere used. Differences were found compared to isothermal investigations, in that the catalytic effects of bases could not be observed and the oxalate-conversion was lower. The formation of oxalate did not occur in the cases of lithium and caesium formates; the order for the other salts was sodium formate < potassium formate > rubidium formate.

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Reactions of binary and ternary alkali metal carbonate mixtures with aluminium oxide were studied by means of a derivatograph under different conditions. Reaction products were identified by X-ray diffraction.

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