Ceramic Filter Materials and Filter Structures with Active and Reactive Functional Pores for the Aluminum Melt Filtration

The application of ceramic foam filters is state of the art in the casting of aluminum melt. Despite their industrial use since the 1960s, the filtration mechanisms are not fully understood. The Collaborative Research Center 920 investigated the influence of the filter surfaceFilter surface chemistry and wetting between filter and melt on the filtration efficiencyFiltration efficiency. The investigated filter surfaces based on Al2O3AlO, MgAl2O4MgAlO, 3Al2O3·2SiO23AlO·2SiO and TiO2TiO showed differences in the filtration efficiency and the wetting behavior whereby a good correlation for inclusions smaller than 110 µm was found–the larger the contact angleContact angles the higher the filtration efficiency. The results raised the question whether the intrinsic contact angle or the different roughnessRoughness of the materials caused the changes in the filtration efficiency. A filtration trial at the Hydro pilot filtration line revealed a strong influence of the filter surface roughness on the filtration efficiency. A filter coated with Nano-Al2O3, with a divergent intrinsic contact angle compared to be Al2O3 reference filter, showed no improvement of the filtration behavior indicating no influence of the intrinsic contact angle on the filtration.