Effect of Phosphorus on Viscosity-Temperature Behavior of High-Sodium Coal Ash Slag

Co-gasification of P-rich fuels and coal would reduce the large-scale usage of fossil fuels and pollution emissions, and fit the "carbon neutrality" goal in 2060. However, the effect of phosphorus on the viscosity-temperature behavior and structure of high-sodium coal ash slag is not yet completely characterized. In this work, the ef-fect of phosphorus on the viscosity and structure of slag was investigated, and the crystallization tendency was also elevated. Results indicate that the high-sodium coal ash slag has a low viscosity as the Na2O can provide O2 -ions and break Si-O-Si bonds, leading to decreasing the slag viscosity. The slag viscosity gradually increases as the PO43-/Na molar ratio increases because the phosphorus acts as a network former and enhances the slag viscosity. The temperature of critical viscosity rises from 1206 degrees C to 1305 degrees C and 1127 degrees C to 1207 degrees C, respec-tively, for Group 1 and Group 2 when the PO43-/Na molar ratio rises from 0/0 to 2/1. With the addition of phosphorus, the cations of Na are removed from the silicate network and form Na phosphate complexes and Si-O -Si linkages, and the content of Q3(Si) and Q4(Si) units increases while the contents of Q0(Si), Q1(Si), and Q2(Si) units decrease, increasing the slag viscosity. In addition, the Si-O-P and P-O-P linkages are formed due to the phosphorus atoms being introduced into the slag structure. Resulting in decreases the content of non-bridging oxygen and rises the degree of polymerization of slag. Furthermore, the viscous flow activation energy of slag increases while reducing the crystallization tendency after the application of phosphorus.