Heats of Transformations in Bismuth Oxide by Differential Thermal Analysis

DTA was chosen as a convenient method for resolving differences in the reported heat of transition and heat of fusion of Bi₂O₃. The heat of the low to high transition of K₂SO₄ (at 583 °C) and the heat of fusion of Ag (at 960.8 °C) were used as internal standards. These standards were mixed directly with the Bi₂O₃ in three weight ratios. The heating schedule for each weight ratio was 3°/min, 9°/min, and 3°/min. For evaluating internal consistency, DTA determinations were made for mixtures of the two standards. Linearity was obtained within limits between the weight ratio of Bi₂O₃ and standard and the corresponding ratio of peak areas. The heat of transition of Bi₂O₃ $$ cubic was found to be 9.9 ± 0.5 kcal/mole and the heat of fusion $$ 3.9 ± 0.2 kcal/mole. The uncertainties are estimated limits of error, based on internal consistency and on the values of the standards.