In this study, the thermal behavior of ash components in three types of Vietnam coals, anthracite (Quang Ninh, QN), bituminous coal (Thai Nguyen, TN), and lignite (Lang Son, LS), were analyzed by XRD and TEMs. In order to obtain ash components, these coals were calcined in air or Ar atmosphere at different temperatures. From the analysis of QN ash, the peak of anhydrite was observed by XRD measurement even though the CaO content of the ash was very low, suggesting that anhydrite is a mineral that easily crystallizes. From the results of XRD measurements of QN and LS, it was found that calcination in an air atmosphere causes a change from kaolinite to andalusite to mullite. From the results of XRD measurement and TEM observation, the needle-shaped crystals observed by QN and LS calcined at 800°C and 1000°C in an air atmosphere may be andalusite. It was found that crystal ash components in Vietnam coal behave differently depending on the processing temperature and atmosphere.
