Thermal Dissociation of CdO and CdFe 2 O 4

Knudsen effusion mass spectrometry has been applied to two identical alumina cells inside a revolving molybdenum cylinder. The one cell was filled with cadmium ferrite and the other with cadmium oxide, and the ionic current intensities of Cd + and O 2 + were measured above both samples. The ratio between the intensities above the ferrite and above the oxide was found to be approx. 0.6, for both Cd + and O 2 + . From this ratio and from calorimetric data the Gibbs energy of the reaction CdO + Fe 2 O 3 → CdFe 2 O 4 could be derived. The endothermic ferrite is stable above 677 K. Its normal enthalpy, H° 298 is ‐ 1 065 kJ/mol, and its normal entropy, S° 298 is 168 J/K mol. The non‐stoichiometry of CdO is discussed.