Phillip G. Wahlbeck

DFT models of molecular species in carbonate molten salts

Raman spectra of high temperature carbonate melts are correlated with carbonate species modeled at 923 K using B3LYP/(6-311+G(2d,p)) density functional calculations. Species that are theoretically stable at 923 K include O(2-), O(2)(-), O(2)(2-), CO(3)(2-), C(2)O(6)(2-), CO(4)(-), CO(4)(2-), CO(4)(4-), CO(5)(2-), KCO(4)(-), LiCO(4)(-), KO(2)(-), LiO(2)(-), NaO(2)(-), KO(2), LiO(2), NaO(2), KCO(3)(-), LiCO(3)(-), and NaCO(3)(-). Triangular, linear, and bent forms are theoretically possible for KO(2)(-) and NaO(2)(-). Triangular and linear forms may exist for LiO(2)(-). Linear and triangular versions are theoretically possible for LiO(2)(-) and KO(2). A triangular version of NaO(2) may exist. The correlation between measured and theoretical Raman spectra indicate that monovalent cations are to be included in several of the species that produce Raman spectra.

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), ΔvapH0 (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 μ(Tl2O3,sc)−μ(Tl2O3,pure)=−33.84±3.0 kJ/mol.

Activities of copper in the Y-Ba-Cu-O system

The vapor pressures of Cu in equilibrium with YBa2Cu3O6.24 were measured as a function of temperature by the Knudsen effusion method using a quadrupole mass spectrometer as the detector. The data were fitted to ln [P(Cu)/bar]=(−66104±4485)(1/T)+(35.360±3.869). The activity of Cu [in YBa2Cu3O6.24(s) ] was calculated as the ratio of the above equilibrium pressure divided by the vapor pressure of pure Cu(s). From the activities, relative chemical potentials were calculated. The vapor pressure of Cu from the superconductor intersects the vapor pressure of Cu from pure Cu(s) at 1290±20 K, which indicates that the superconductor decomposes to metallic Cu at temperatures greater than 1290 K.

THERMODYNAMICS OF THE TL-O SYSTEM AND TL-SUPERCONDUCTORS

Experiments have been performed to determine vaporization reactions in the Tl–O system. When the starting sample was pure Tl2O3(c), the vapor was initially rich in oxygen compared to the starting Tl2O3(c) composition. When the extent of vaporization of the sample was between 30% and 80%, the residue composition was Tl4O3(c). The congruently vaporizing composition was concluded to be in the Tl4O3(c) single phase region. This conclusion supports the thermodynamic data for thallium oxides which was published by Holstein. Vapor pressure data for the two phase region with Tl-superconductors Tl-2223(c) and Tl-1223(c), which we measured previously and reported as activities, have been reevaluated.