The coal ash fusibility is an important parameter that affects the boiler design and operation significantly. Superfine pulverized coal is beneficial to the alleviation of fouling and slagging problems due to its distinctive properties in the aspects of multiphase flow, heat transfer and combustion atmosphere. In this work, the size related ash fusion propensity were emphasized from the point of view of the chemical and mineralogical morphology of coal ash. A comprehensive study on the chemistry and thermal behavior of superfine pulverized coal ash was conducted combining multiple analytical methods such as XRF (X-ray fluorescence), XRD (X-ray diffraction), TGA (thermo-gravimetric analysis), slagging indices, AFT (ash fusion temperatures) tests and phase diagrams. Besides, a quantitative analysis method was proposed to eliminate the subjective judgments in AFT tests through a numerical image-processing platform, which could depict a complete deformation profile of the whole ash fusion process with high precision and reproducibility. The results from this work are helpful for understanding the size dependence of ash thermal behavior, and predicting the ash fusion propensity in the future application of superfine pulverized coal. (C) 2016 Elsevier Ltd. All rights