Structure-thermal properties relationship of borosilicate glasses containing MoO3

The effect of MoO₃ incorporation on structure and thermal properties (e.g., thermal diffusivity, heat capacity, and thermal conductivity) of a borosilicate glass with a composition of 59.76 SiO₂–14.46B₂O₃–2.90 Al₂O₃–11.46 Na₂O-11.42 CaO (mol%) was investigated systematically. MoO₃ incorporation induced phase separation and crystallization of CaMoO₄ and Na₂MoO₄ in borosilicate glass. CaMoO₄ phases with grain size of about 200 nm in diameter were homogenously dispersed in the glass matrix, while, Na₂MoO₄ as a second phase formed on the surface. In addition, MoO₃ incorporation resulted in re-polymerization of the glass network. These structural changes have obvious influence on thermal properties. MoO₃ additions up to 6 wt% decreased thermal diffusivity by 7.5 %, heat capacity by 27.8 % and thermal conductivity by 30.2 %. Correlations between the structure, microstructure and thermal properties were proposed. It is speculated that the decrease of thermal conductivity mainly results from the decrease of mean free path of phonons caused by interface scattering. The understanding of the linkages between structure, microstructure, and thermal properties should provide insights for the design of borosilicate glass compositions for vitrification of MoO₃-rich high-level waste.