Thermal conductivity of Na2O-B2O3-SiO2 melts

Borosilicate glasses are candidate materials for the immobilization of high-level radioactive waste. The values of thermal conductivity of different borosilicate melts are thus indispensable information when optimizing the temperature distribution in a glass melting furnace. In this study, the thermal effusivity of Na2O-B2O3-SiO2 melts was measured using a front heating-front detection laser-flash method. The thermal conductivity, which can be obtained by combining the measured thermal effusivity with the specific heat capacity and density, was calculated using the least-squares method; the values for the Na2O-B2O3-SiO2 melts either slightly decreased linearly with increasing temperature or remained almost constant over the investigated temperature range. The values of thermal conductivity of the Na2O-B2O3-SiO2 melts were higher than those of B2O3-SiO2 melts and lower than those of CaO-B2O3-SiO2 melts. Furthermore, the thermal conductivity of the Na2O-B2O3-SiO2 melts was compared with those of the B2O3-SiO2 and CaO-B2O3-SiO2 samples.