Thermal Conductivity of Molten B2O3, B2O3–SiO2, Na2O–B2O3, and Na2O–SiO2 Systems
With the aid of the transient hot‐wire method, the thermal conductivity of molten B2O3, B2O3–SiO2, Na2O–SiO2, and Na2O–B2O3 systems was measured along with their temperature and composition. It was observed that the thermal conductivity of pure B2O3 increased with temperature, until about 1400 K, and then decreased subsequently. Using the MAS‐NMR, 3Q‐MAS, and Raman spectroscopy, the structure of B2O3 and SiO2 in the B2O3–SiO2 system was confirmed. Findings show that an addition of B2O3 into the pure SiO2 system causes a significant decrease in thermal conductivity, due to the formation of boroxol rings. The thermal conductivity of the Na2O–SiO2 system was measured and its phonon mean free path was calculated. In addition, a positive linear relation between viscosity and thermal conductivity was observed. In the Na2O–B2O3 system, it was found that a change in the relative fraction of 4‐coordinated boron has an influence on the thermal conductivity when the concentration of Na2O is between 10 and 30 mol%, in which case the tetraborate unit is dominant.
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Document Type: Research Article
Publication date: May 1, 2015