b'Table 1. Polycrystalline moduli of uranium borides (average of two samples) calculated by correcting forporosity from RUS and NI.Material G (GPa) K (GPa) E (GPa) H (GPa) D(K)UB2 (RUS) 145.526.48 127.7011.18 316.3126.96 0.1 490.429.4UB2 (NI) - - 32018 22.02.9 - -UB4 (RUS) 191.606.93 194.211.95 432.5012.85 0.15 686.427.2UB4 (NI) - - 48429 28.41.4 - -tested specimens was calculated fromis higher throughout the temperature the reduced modulus using the equa- range and only returns to values tion in [8]. The values for the shear,obtained for heating at the 370-470 bulk, and Youngs moduli, from bothK range. The thermal conductivity RUS and NI, as well as Poissons ratioof UB4 increases linearly with and Debye temperatures, from RUS,temperature throughout the measured averaged for the two measured samplestemperature range and the values are summarized in Table 1. From theobtained for heating and cooling comparison of Youngs moduli in Tablecoincide. The thermal conductivity of 1, it is observed that there is generallyUB 2can be expressed in the following good agreement between RUS and NIform:measurements from this work. The thermal conductivities of UB 2and UB 4were calculated, on cooling andwhere the first term, commonly used heating, and the results are shown into describe the thermal conductivity Figure 1 along with literature data forof UO 2[10], represents the phonon UO 2[9]. The conductivity for UB 2iscontributions in terms of A, a significantly higher than that of UB 4 temperature independent scattering throughout the measured temperatureterm and B, a temperature dependent range. However, both materials havephonon-phonon scattering term. thermal conductivities significantlyThe second term represents the higher than that of UO 2 . On heating,electron contributions to the thermal the thermal conductivity of UB 2 conductivity. By fitting Equation 1 to decreases with a minimum at 874 K,the UB 2heating data, the following above which the conductivity starts tovalues were obtained: A=7.23010-3 increase. As was expected, based onmKW-1, B=9.00010-5 mW-1 the thermal diffusivity results for UB 2 ,and C=1.32710-2 Wm-1K-2, the thermal conductivity on coolingproviding an R2=0.9923. Based on 2019|AFC ACCOMPLISHMENTS 61'