Lactose/tannin-based calcium aluminate coatings for carbon-bonded alumina foam filters: A novel approach in environment-friendly steel melt filtration

In this paper, a new approach in the development of calcium aluminate (CA) coatings for ceramic foam filters for steel melt filtration is presented. This approach is based on applying an environmentally friendly binder system based on lactose and tannin. The use of such a binder was previously demonstrated for the matrix of carbon-bonded alumina filters. In this research, the influence of the total solid content, the binder content, and the centrifugation speed on the coated ceramic foam filters’ final properties was studied. All of the prepared coating slips were analyzed in terms of their rheology. The most promising slips were applied on carbon-bonded alumina filters, which were prepared using a lactose- and tannin-based binder system. For the selected coating slips, three different centrifugation speeds (600, 1000, and 1400 rpm) were used to optimize the coating layer thickness and the overall amount of the coating material applied to the filter. The coated and thermally treated filters were tested in terms of their cold crushing strength. Furthermore, the microstructure of the filters and mainly the coating layer thickness were studied. It was observed that both the centrifugation speed and the total solid content in the coating slip have a major impact on the filter properties. The most promising results were obtained for a coating containing 72.5 wt% of total solids applied at 1000 rpm centrifugation speed. This batch of coated samples showed a cold crushing strength of more than double the value obtained for the uncoated reference, while having a uniform coating layer with the thickness of ∼177 μm.