Electrical Conductivity and Structure of CaO–MgO–SiO₂–Al₂O₃–BaO Slag with Different BaO/Al₂O₃ Molar Ratios

This study investigated the impact of BaO/Al₂O₃ molar ratio on the electrical conductivity and Al coordination state of CaO–MgO–SiO₂–Al₂O₃–BaO slag using four-electrode technique and ²⁷Al MAS-NMR spectroscopy, respectively. With an increasing BaO/Al₂O₃ molar ratio from 0.14 to 0.36, BaO preferentially participated in charge compensation of Al³⁺, which facilitated the transition from AlO₅ and AlO₆ structures to AlO₄ structure and increased the stability of AlO₄ tetrahedra, thus enhancing the slag’s polymerization and reducing its electrical conductivity. However, once the compensation achieved equilibrium, remaining BaO was involved in depolymerizing the tetrahedral structure and promoting the formation of AlO₅ and AlO₆ structures. Consequently, the decreased degree of polymerization and increased concentration of free ions together led to an increase in electrical conductivity. However, the increased migration resistance due to the large radius of Ba²⁺ ion is responsible for the electrical conductivity minimum near the molar ratio of 0.43.