The crystalline and microstructural transformations of two coal ashes and their quenched slags with similar chemical compositions during heat treatment

The crystalline and microstructural transformations of two laboratory ashes and their quenched slags (from a gasifier) with similar chemical compositions [one with high silicon dioxide (SiO2) concentrations and the other with high aluminum oxide (Al2O3) concentrations] were systematically characterized using X-ray diffraction, multinuclear solid-state nuclear magnetic resonance, and a high-temperature viscometer. The results show that the content of SiO2 and Al2O3 in ash has significant influence on the crystal types and size of cristobalite clusters in the liquid slag during heat treatment. Consequently, the formed cristobalite clusters were crucial to the viscosities and rheological properties of liquid slags.