VAPORIZATION OF THALLIUM (III) OXIDE AND THALLIUM ACTIVITIES IN THALLIUM SUPERCONDUCTORS

Vaporization reactions for both Tl2O3(s) and a Tl superconductor sample, primarily Tl2Ba2Ca2Cu3Oy(S) (Tl-2223), were determined. The vapor species were examined by Knudsen effusion mass spectrometry at temperatures in the range 657 to 773 K for Tl2O3(S) and 672 to 836 K for Tl-2223. Additional experiments with thermogravimetric analysis (TGA) equipment were performed. In both cases of vaporization of Tl2O3 and Tl-2223, the vapor species were concluded to be Tl2O(g) and O2(g). Vapor pressures were measured. For Tl2O3(S), DELTA-vapH0 (298.15 K) was measured as 320.4 +/- 6 kJ/mol. The activity of Tl2O3 in the Tl-2223 superconductor was measured as 0.0044 +/- 0.001 at 750 K. A measure of the stabilization of Tl2O3 in the Tl-2223 superconductor is given by mu(Tl2O3,SC) - mu(Tl2O3,pure) = -33.84 +/- 3.0 kJ/mol.