Thermophysical Properties of NbAlO4 and TaAlO4

Abstract

Thermophysical properties of the ternary oxides NbAlO₄ and TaAlO₄ are experimentally determined. For NbAlO₄, the molar heat capacity is 98.9 J (mol\(\cdot\)K)⁻¹ at 0 \(^{\circ }\)C up to 155.6 J (mol\(\cdot\)K)⁻¹ at 950 \(^{\circ }\)C and for TaAlO₄ 97.1 J (mol\(\cdot\)K)⁻¹ at 0 \(^{\circ }\)C up to 154.2 J (mol\(\cdot\)K)⁻¹ at 950 \(^{\circ }\)C, respectively. Maier-Kelley polynomials are provided for the molar heat capacities. Thermal diffusivities in the range from 20 \(^{\circ }\)C to 700 \(^{\circ }\)C (\(\alpha _{NbAlO_{4}}\): from 0.009 to 0.004 cm²·s⁻¹ and \(\alpha _{TaAlO_{4}}\): from 0.017 to 0.005 cm²·s⁻¹), bulk densities at 25 \(^{\circ }\)C (\(\rho _{NbAlO_{4}}\)= 3.94 g\(\cdot\)cm⁻³ and \(\rho _{TaAlO_{4}}\)= 6.07 g·cm⁻³) and melting points of the oxides are measured, and the thermal conductivities are calculated from these properties. The thermal conductivity from 20 \(^{\circ }\)C to 700 \(^{\circ }\)C of NbAlO₄ \(\lambda _{ NbAlO_{4}}\) is in the range from 0.020 to 0.013 W·cm⁻¹·K⁻¹ and of TaAlO₄ \(\lambda _{TaAlO_{4}}\) in the range from 0.039 to 0.015 W·cm⁻¹·K⁻¹, respectively. A porosity correction for thermal conductivities is applied, and with that, data for perfectly dense material are provided.