Calorimetric and spectrophotometric studies of selected lanthanide and actinide compounds in the solid state

Author

Jerry Brock Burns

Date of Award

8-1995

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

J. R. Peterson

Abstract

The enthalpies of solution in 1.000 N HCl of Eu, Gd, and Lu oxychlorides were measured using samples on the milligram and submilligram scale. The standard enthalpies of formation for these compounds have been calculated. The compounds were prepared from treatment of the corresponding sesquioxides with anhydrous HG. Single crystals were grown from a 1:10 (Eu, Gd) or 1:1 (Lu) mixture of sesquioxide-in-trichloride flux. Europium oxychloride was chosen for study due to the lack of reported experimental values. Gadolinium oxychloride was used as the tie point to a well-known literature value. Lutetium oxychloride was studied in order to clarify significant discrepancies among the reported values. Factors considered in assessing the derived enthalpy values included: (1) effect of crystal structure on the enthalpy of formation; (2) degree of crystallinity upon the observed dissolution rate; (3) effect of sample preparation method (e.g., on characteristics of sample's surface and stoichiometry) on experimental result. In preparation for these thermodynamic studies, estimations were made regarding the enthalpies of formation of the compounds to be studied. Predictions were based upon the thermodynamic similarities of LnCl₃ and LnOCl, with respect to the Ln(III) ionic radii and to the electronic ground state term symbol of the Ln(III) ions. Both predictive methods yielded values of ΔH^{°>_f(EuOCl) in good agreement with the ΔH°>_f(EuOCl) determined in this work, -903.5 ± 0.4 kJ mol-1. The ΔH°>_f(GdOCl) determined in this work (-981.4 ± 0.4 kJ mol-1) was in good agreement with the accepted literature value (-979 kJ mol-1). A wide range of values for ΔH°>_f(LuOCl) have been reported in the literature (-950 to -990 kJ mol-1). This work (ΔH°>_f(LuOCl) = -987.2 ± 0.8 kJ mol-1) confirmed the more negative values in this range and suggests that the more positive values could result from oxide contamination. In addition, the standard enthalpy of formation of Pm oxychloride was also predicted to be -996 ± 3 kJ mol-1 but was not confirmed in this work due to its unavailability. Polarized Raman studies were performed on an aligned single crystal of Lutetium oxychloride. The spectra obtained were used to assign the symmetries of the Ramanactive bands of the rhombohedral lanthanide oxychlorides (Er→Lu). Previous assignment of these vibrations in LuOCl, made without benefit of a single-crystal and polarized Raman spectra, were corrected. The enthalpy of solution in 1.000 N HCl of Cf oxychloride was measured using samples of mass comparable to those in the lanthanide experiments. This measurement extended the range of available experimental thermodynamic data for the actinide elements. Although the number of experimental dissolutions was less than desired, ΔH°>_f(CfOCl) was calculated to be -927 ± 8 kJ mol-1. Given this value for CfOCl, ΔH°>_f(BkOCL) was interpolated to be -936 ± 6 kJ mol-1}

Recommended Citation

Burns, Jerry Brock, "Calorimetric and spectrophotometric studies of selected lanthanide and actinide compounds in the solid state. " PhD diss., University of Tennessee, 1995.
https://trace.tennessee.edu/utk_graddiss/9937