Ash deposits formed on an air-cooled probe at different temperatures during combustion of coal blends of a Zhundong lignite (ZL) and an Australian bituminous (AB) were studied in the present work. The blends with various AB ratios were combusted in a drop tube furnace in air at 1400 degrees C, and the ash deposits formed on the probe top surface maintained at 500 degrees C, 600 degrees C, 700 degrees C, and 750 degrees C, were collected and characterised using XRD and SEM-EDS for their mineralogy, morphology and elemental composition. The size distributions and sintering temperatures of the ash deposits were also determined. At the probe temperature of 500 degrees C, the ZL ash deposit was dominated by fluxing minerals where significant amounts of fine particles (<10 mu m) and their aggregates existed, leading to low ash sintering temperatures. As the AB ratio increased to 20 wt% and above, the amount of the fluxing minerals in the deposits decreased while the amount of refractory quartz and mullite minerals increased. Morphologically, the refractory ash particles from AB coal diluted the Na-bearing mineral phases and the contacts between fine ash particles, leading to the absence of nepheline and, correspondingly, an increase in the ash sintering temperature. In addition, as the probe temperature increased, mineral interactions and ash sintering were facilitated when the AB ratio was less than 20 wt%, leading to the formation of new mineral phases and an increase in ash particle sizes. However, no significant mineralogical and morphological changes were observed when the AB ratio was higher than 40 wft, indicating that these ash deposits were more refractory and resistant to the temperature change. (C) 2016 Elsevier B.V. All rights reserved.