The thermal conductivity of mold flux is crucial for optimising the productivity and quality of steels.
This study investigates the thermal conductivity of molten oxides, including CaO-BO1.5-AlO1.5 (CBA),
CaO-BO1.5-AlO1.5-SiO2 (CBAS), and CaO-MgO-BO1.5-AlO1.5 (CMBA) melts, using a hot wire method.
Additionally, their structure is examined using Raman spectrometry and magic angle spinning
nuclear magnetic resonance (MAS-NMR) to explore their relationship. Furthermore, first-principles
calculations are employed to assess the covalency of each bond in the melts for a more quantitative
analysis of their relationship. The study confirms that an increase in the CaO concentration of the
CaO-BO1.5-AlO1.5 melts reduces the amount of bridging oxygen and consequently decreases thermal
conductivity. The covalency of the B[4]-O bond is highest, especially when the second-nearestneighbour
Al atoms transition from Al[6] to Al[4], forming the AlB3O7 structure with B[4]. The
relationship between thermal conductivity and the structure of CaO-BO1.5-AlO1.5-SiO2 melts can be
quantitatively assessed using the degree of polymerisation of the network structure and the variation
of covalency as indicators.
Furthermore, replacing CaO with MgO in the CaO-MgO-BO1.5-AlO1.5 melts reveals a mixed alkaline
earth effect on thermal conductivity.