Exploratory evaluation of experimental methods for heat capacity and transition temperature assessment for strontium and barium molybdates at the Royal Military College of Canada

Evaluations of the transition properties of strontium and barium molybdates (Sr-Mo-O and Ba-Mo-O) are required for the development of accurate thermodynamic models of such chemical systems. Although methods have previously been established for the determination of heat capacity and transition temperature, high-temperature (e.g., above 1273 K) chemical interactions between these materials and measurement crucibles limit the application of current methods. Differential Scanning Calorimetry (DSC) analysis using standard alumina crucibles show unsatisfactory results at high temperatures (e.g., >1300 K) as secondary processes occur between the crucible and materials under study. This paper presents: (i) low to moderate temperature (e.g., 223 – 473 K) measurements of heat capacity for BaMoO₄, which benchmark the method that is applicable to other strontium and barium molybdates; and (ii) the preliminary development of a novel high temperature (e.g., >1300 K) method that uses boron nitride and platinum liners in standard alumina crucibles for the evaluation of melting temperatures (T_m) of strontium and barium molybdates, with potential application for assessment of enthalpies of melting (ΔH_m). Preliminary high temperature studies show consistent results for the assessment of the transition temperature of SrMoO₄. Although this paper presents work in progress, possible limitations and improvements are also examined for future work to increase the accuracy of these techniques. (author)