Enhanced mechanical properties of novel Al2O3-based ceramic filter by using microporous corundum-spinel and nano-Al2O3 powders

In this work, the novel Al2O3-based ceramic filter prepared by replacing dense Al2O3 raw material with microporous corundum-spinel raw material is proposed and enhanced. The effects of nano-Al2O3 powder content (0, 2.5, 5 and 7.5 wt%) on the rheological properties of the slurries, microstructures, pore characteristics and mechanical properties of the filters were investigated. When the nano-Al2O3 powder content increased from 0 to 5 wt%, the rheological properties of the slurries were optimized, resulting in a larger thickness diameter and uniform distribution of the filter skeleton. The nano-Al2O3 powder with a high reactivity accelerated the diffusion mass transfer rate of ions and increased the sintering driving force, thus promoting the development and growth of the spinel grains. It also led to the formation of more spinel neck connections between the microporous corundum-spinel particles, which enhanced the cold compressive strength and thermal shock resistance of the filters, while the pore size slightly increased due to the spinel volume expansion between the particles. When the nano-Al2O3 powder content further reached 7.5 wt%, the yield stress of the slurry increased markedly due to the agglomeration phenomenon, leading to an uneven distribution of the filter skeleton and a lower cold compressive strength of the filter. Overall, the mechanical properties of the novel Al2O3-based ceramic filters were greatly enhanced by the addition of 5 wt% nano-Al2O3 powder. The filter skeleton had a bulk density of 2.19 g/cm3 and an apparent porosity of 41.8%. The novel Al2O3-based ceramic filter also exhibited a high cold compressive strength of 2.37 MPa and an excellent thermal shock resistance. It contained a rougher surface structure compared to existing filters and has the potential for better purification efficiency on molten metal in the future.