Effect of impurity elements on displacement reaction between molten Al and SiO₂ designed for utilization of Al scrap

It is difficult to purify Al scrap by means of the general refining process, because of iron impurity, so they are diluted with new Al metal and reused. In the author's previous report, attempts were made to utilize the Al scrap for fabrication of the composite materials by displacement reaction between molten scrap and vitreous silica (SiO₂). In this study, influence of impurities (Fe, Cu, Mg, Si, Sn) on the displacement reaction rate was investigated, the elements of which are present in the Al scraps derived from window frames. It was shown that the reaction rate was not decreased very much by addition of the elements within the composition range of the Al scrap. However, Mg addition to Al decreased the rate more than the other elements. A composite body consisting of Al and Al₂O₃ phases is formed by displacement reaction between molten pure Al and SiO₂, but when molten scrap is reacted with SiO₂, Mg was contained in Al ₂O₃ phase, and the other impurities were contained in the metal (Al) phase. Fe and Cu have interaction with Si (by-product of the reaction), resulted in the higher Si content in the metal phase. On the contrary, this tendency was not obvious in Al-Sn reaction case.