Topological understanding of thermal conductivity in synthetic slag melts for energy recovery: An experimental and molecular dynamic simulation study

Blast furnace slag stores a massive amount of thermal energy which commonly dissipates during cooling. To lay the foundation for the development of heat retrieval technique, it is vital to realize the thermophysical properties of the slags. In this work, thermal conductivity of CaO-SiO ₂-Al ₂O ₃-MgO melts with 0–15 mol% Al ₂O ₃ was investigated using the hot-wire method. The compositional dependence of thermal conductivity was discussed with respect to the structure characterized by Raman spectroscopy, MAS-NMR (magic angle spinning-nuclear magnetic resonance) and MD (molecular dynamics) simulation in short- and intermediate-range order. The additions of Al ₂O ₃ up to 9 mol% notably promote the thermal conductivity. The formation of Al-O-Si linkages is greatly enhanced, establishing a polymerized aluminosilicate network. The significant reduction of NBO/T _real contributes to a higher thermal conductivity. Further additions of Al ₂O ₃ up to 15 mol% do not significantly increase or reduce the thermal conductivity. Although NBO/T _real still decreases, the decremental rate becomes less rapid. The topological ring size of aluminosilicate network becomes smaller since the formation of Al-O-Al linkages is greatly facilitated at higher Al ₂O ₃ content, which reduces the mean free path of phonon vibrations. It may counteract the enhancement of thermal conductivity by the reduction of network modifying oxides.