Effect of P2O5 on the viscosity of yellow phosphorus slag in electric furnace at high temperatures

•As P2O5 content increases, slag viscosity increases at high temperature, while it decreases at low temperature.•The Si-O network structure of slag is polymerized by the increase of P2O5 content.•P-O-Si bonds are formed, which increase the polymerization degree of slag.•nC2S-C3P solid solution is detrimental to crystallization of gehlenite.•The increase of P2O5 content reduces the average particle size of melilite crystals.