Viscosity and phase transformation in coal ash slags near and below the temperature of critical viscosity

The phase transformation of multicomponent aluminosilicates on liquidus curves becomes an important parameter in the prediction of the slag behavior upon cooling. Three major factors are taken into consideration: (1) thermodynamic driving forces for a selection of stable phases on liquidus curves, such as free energies of components at various temperatures, (2) the effect of free energy of mixing on the tendency to phase segregation in liquid solution on cooling, and (3) free energy change at the solid-melt interface and entropy of fusion and their effects on the morphology of the crystalline phase(s). In order to identify the solid phase(s) crystallized from ash slag it is proposed, first, to calculate major binary free energy composition diagrams based on major oxides in ash and, second, to select phase(s) with the free energy and composition constrained by free energy diagrams.