Differential Thermal Analysis of Clays and Carbonates

Abstract

Differential thermal analysis (DTA) began soon after the development of the thermocouple. It has progressed through the systematic development of better equipment and the cataloguing of typical DTA curves for a variety of materials until good technique now requires control of the composition and pressure of the furnace atmosphere as well as consideration of the thermodynamics and kinetics of the reactions involved. Although differential thermal analyses have been made for many materials, the major applications have been concerned with clay and carbonate minerals.In DTA curves for clay minerals the low-temperature endothermic loop associated with the loss of water, and the high-temperature exothermic loop accompanying the formation of new compounds, are changed in shape, temperature, and intensity by the kind of exchange cations. The midtemperature-range endothermic loop has a temperature dependence on the partial pressure of water in the furnace atmosphere. For the anhydrous normal carbonates the dissociation temperature and its dependence on the partial pressvire of CO 2 are in the decreasing order Ca, Mg, Mn, Fe, and Zn. The lower temperature loop of dolomite, the reaction for which must be preceded by an internal rearrangement, is independent of the pressure of CO 2 but may be shifted to a lower temperature by prolonged fine grinding which accomplishes a similar rearrangement.