Fabrication of rigid media tube filter bound with aluminum borate using Al2O3–B2O3–MgO frit for filtration of molten aluminum

We performed a study of a tube filter binding agent for molten aluminum (rigid media tube filter, RMF). In this study, we examined the formation mechanism of aluminum borate (9Al2O3·2B2O3; 9A2B) from Al2O3–B2O3–MgO frit composition, which used MgO instead of CaO in the Al2O3–B2O3–CaO frit in our previous report. The results indicated that crystallization of 9A2B is easier in Al2O3–B2O3–MgO compared to Al2O3–B2O3–CaO, in that crystals are formed with only a heating process, and the amount of crystallization increases depending on the calcination temperature and the heat load over the retention time. A tube filter made of Al2O3–B2O3–MgO frit contained a larger amount of 9A2B crystals and therefore its strength did not deteriorate until a very high temperature of 1200 °C was reached, and its coefficient of thermal expansion was low. This is an advantageous property for RMF used under constraints and high temperatures. In addition, when the amount of 9A2B crystal formation increases, the wettability of molten aluminum decreases, and it becomes more difficult for molten aluminum to impregnate the filter material, but we found that corrosion resistance was high.