Studies on slag deposit formation in pulverized coal combustors. 2. Results on the wetting and adhesion of synthetic ash drops on different steel substrates

Abstract

A simple sticking apparatus has been further developed to study the comparative wetting and adhesion properties of a synthetic coal ash slag on boiler steels. Both the wetting and adhesion behaviour appears to be affected by the physical nature of the oxide layer on the steel surface (i.e., thickness and microporosity). The adhesion force is also found to be a function of the chemical nature of the surface oxide layer on the steel (i.e., whether the layer is predominantly ferrous (FeO) or ferric (Fe 2O 3) oxide). The presence of a sodium salt (either sulfate or carbonate) on the steel surface enhances both the wetting and adhesion properties by dissolution in the molten drop creating a less viscous glass with a lower liquidus temperature at the drop-surface interface. At this time it is difficult to establish whether the bonding between the slag and steel oxide layer is mechanical, chemical, or a combination of both.