Analysis of the transformation behaviors of a Chinese coal ash using in ‐/ ex‐situ XRD and SEM‐EXD

Crystal and phase transitions of a Chinese Datong coal ash were evaluated using room temperature X‐ray diffraction (RT‐XRD), in‐situ high temperature (HT)‐XRD, and scanning electron microscope combining energy dispersive X‐ray analysis (SEM‐EDX) as temperature varied from 300 °C to 1600 °C. The transforming behaviors of ash were related to its melting properties. Results revealed that the transforming behavior of minerals from in‐situ HT‐XRD was different with that from routine RT‐XRD. Low‐temperature Datong ash contained quartz and clays (such as kaolinite); the changes in minerals at low‐temperature region (300–1000 °C) were mainly due to the minerals decomposition and partial phase transition. Significant transition of quartz to cristobalite occurred at ca. 1100 °C; the continuous transition and reaction of silica and alumina at ca. 1200 °C accelerated the softening of the ash (ST ≈ 1290 °C). An X‐ray amorphous liquid phase was formed mainly by the eutectic solution of silica and mullite at ca. 1400 °C, which obviously affected the hemisphere temperature (HT ≈ 1490 °C) of ash; meanwhile, ultra fine alumina solid particles, which were probably derived from kaolinite, were found in the melted ash. Virtually, the fusing (FT > 1500 °C) of Datong ash was considered to be determined by the formation of solid particles and eutectic solution. Eventually, the semi‐quantitative evaluation of transformations of ash was successfully obtained through the combined methods. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.