The high-temperature thermal conductivity of CaO-Al2O3-B2O3 melts was measured using the hot-wire method between 1550 and 1850 K. From the structural analysis of the as-quenched melts based on Raman spectra, X-ray photoelectron spectroscopy (XPS), magic-angle spinning nuclear magnetic resonance (MAS-NMR) and molecular dynamics simulation, the relationship between thermal conductivity and melt structure was discussed. When the Al2O3/B2O3 ratio was fixed at unity, the CaO increments from 40 to 60 mol pct lowered the thermal conductivity. The three-dimensional network structures were depolymerized, resulting in more orthoborates and fewer bridging oxygens. Al population increased with the CaO addition, while the fraction of B species decreased relative to B species. When the CaO content was fixed at 50 mol pct, the thermal conductivity initially decreased with B2O3 increments up to 25 mol pct. The proportion of Al-O-Al linkages dropped, while the borate units mostly remained in two-dimensional forms. Greater addition of B2O3 over 25 mol pct enhanced the thermal conductivity mainly due to the conversion of BO3 triangular units to BO4 tetrahedral units. The structural changes are consistent with the topological network connectivity evaluated from the ring statistics.
Bibliographical noteFunding Information:
This work was supported by the Ministry of Science and ICT (MSIT) through the National Research Foundation of Korea (NRF) grant ( 2018R1A2B2006609 ).
© 2020 The Author(s).
All Science Journal Classification (ASJC) codes
- Ceramics and Composites
- Surfaces, Coatings and Films
- Metals and Alloys