Effect of alkaline oxides on aluminate slag structure by first principles calculation

•With alkaline oxides adding, the proportion of CN for Al were AC > MAC > LAC > BAC > NAC.•The depolymerization ability of alkaline cations was ranked as NAC > BAC > MAC > LAC.•The charge compensation ability of alkaline cations was ranked as Na+ > Li+ > Ba2+ > Mg2+.•A small number of electrons were localized between O atoms, which surrounded Al to form a closed structure. To guide the research and development of CaO-Al2O3-based mold fluxes, the influence mechanism of 8 mol% alkaline oxides (Na2O, Li2O, BaO, MgO) on the multi-scale structure characteristics of aluminate slag (CaO/Al2O3 = 1.3) at 1873 K was analyzed by first-principles calculation. With the addition of alkaline oxides, the stability of Al-O and Ca-O bonds in slag system was Na2O-Al2O3-CaO (NAC) ≈ BaO-Al2O3-CaO (BAC) > Li2O-Al2O3-CaO (LAC) ≈ Al2O3-CaO (AC) > MgO-Al2O3-CaO (MAC), and the proportion of average coordination number for Al were AC > MAC > LAC > BAC > NAC. The alkaline cations played two roles of structure depolymerization and charge compensation, as the ability was ranked as NAC > BAC > MAC > LAC, and Na+ > Li+ > Ba2+ > Mg2+, respectively. At the electronic level, a small number of electrons were localized between O atoms, which surrounded Al to form a closed structure. Adding appropriate amount of Na2O/BaO was necessary to effectively regulate the low/non-reactive mold flux.