Isothermal DTA Research Articles

A simple method of determining the activation energy of an isothermal solid-state decomposition reaction

A simple approach to determine the activation energy (E) of solid-state decomposition reactions is described. The activation energy is calculated from the slope of the logarithm of the maximum peak height of the isothermal DTA trace versus the reciprocal of the absolute temperature. The proposed method is applied in the study of the kinetics of thermal decomposition of cadmium carbonate. The activation energy calculated from this method (90.8±2.2 kJ mole−1) is in very good agreement with the value (87.5±2.5 kJ mole−1) obtained by the conventional method.

Measurement of oxidation stability of polyolefins by thermal analysis

AbstractDifferential thermal analysis (DTA) is well known for measuring temperatures and heats of physical and chemical transitions in materials. Recent development work on improved stabilization systems for polyolefin wire insulations has required fast procedures for measuring the performance of stabilization systems. Isothermal DTA procedures have been developed into routine tools for measuring stability of polyolefins by determining the oxidative induction time at elevated temperatures.Oxidative induction time has been used to study the stability of polyethylene and polypropylene in raw material form and on wire. The dependence on temperature and antioxidant concentration have been measured. Effects of oxidation catalysts, catalyst deactivators and various environmental exposures are readily observed. Techniques and apparatus have been developed for simultaneous testing of a multiplicity of samples, providing for economical large scale use of the method.

Thermal expansion characteristics and stability of pseudobrookite-type compounds, Me 3O 5

Thermal expansion measurements on various oxide compounds crystallizing with the orthorhombic pseudobrookite structure are reported. The unusual expansion anisotropy appears to be a structure-related property. It was observed for all pseudobrookites including the new phases MgTi 1.6Zr 0.4O 5, MgFeNbO 5 and MgFeTaO 5. The highest thermal expansion coincides with the direction of the double chains of strongly distorted (MeO 6)-octahedra. This is in the direction of the c-axis where the shortest 0–0 distances are also found. The smallest, or even “negative”, expansion always occurs in the direction of the a-axis. This is the shortest axis, its length corresponds to the height of the distorted (MeO 6)-octahedra. Isothermal heat treatment and DTA runs proved the instability of Al 2TiO 5, MgFeNbO 5 and, especially, Ga 2TiO 5. Stable compounds like Fe 2TiO 5 and MgTi 2O 5 are formed at much lower temperatures than the unstable compounds Al 2TiO 5 and Ga 2TiO 5 (strongly endothermic reactions at 1360 °–1370 °C). Ga 2TiO 5 decomposes spontaneously and strongly exothermically into the component oxides at about 980 °C. All pseudobrookite compounds are mechanically very weak due to their strong expansion anisotropy.