a digital image technique. For this purpose, three slagging tests were carried out in a pilot scale furnace. An oil-cooled probe was used to collect the slags which formed at about 1523 K. The corresponding probe surface temperatures were in the ranges of 758-617, 693-597, and 669-560 K with deposit growth. The results show that the deposition surface temperature has an evident effect on the deposition rates and morphology. The stable thickness of deposit decreases with the increasing deposition surface temperature. The electron micrographs reveal that the higher deposition surface temperature results in the occurrence of a more compact morphology and more macro pores in the slag layer. Furthermore, the low deposition surface temperature can facilitate the formation of sulfates in the initial layer.