The quality of molten aluminum is dependent on the methods used for its treatment, and the rigid media tube filter RMF is the most reliable means of removing inclusions from molten aluminum. In the present study, we examined the effects of adding SiO 2 to alumina filters bound by aluminum borate 9Al 2 O 3 · 2B 2 O 3 : 9A2B to improve the penetration of molten aluminum into the filter. With the addition of SiO 2 , although the amount of 9A2B crystal was decreased by formation of borosilicate

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... s and 9A2B crystal shape became short and small, the penetration ratio for adding 10 mass% SiO 2 was substantially improved and the amount of Si outflow and corrosion resistance were reduced. The degrees of thermal expansion of alumina filters with 10 mass% SiO 2 were similar to those of non-SiO 2 -bound filters. In conclusion, alumina filters with bound 9A2B crystals including 10 mass% SiO 2 showed improved penetration of molten aluminum and reduced both Si outflow and corrosion resistance. As the thermal expansion of the filter was similar to that of filters containing no SiO 2 , this material is suitable for bonding of RMF heated to 800°C under restriction.