Arc Melted High Temperature Oxides: Recent Developments, Opportunities and Challenges

Reference Presenter Authors
(Institution)
Abstract
14-040 Paschoal Bonadia Bonadia, P.(RHI Magnesita); Gelbmann, G.(RHI Magnesita); The allure of the arc melting of oxides is based on the extreme temperatures that this process can reach combined with its flexibility to melt a virtually infinite number of raw material combinations. The melting process, as opposed to the sintering one, leads to materials with outstanding properties for refractory use, mainly high bulk densities and large primary crystal sizes The oxide arc furnaces have not evolved as much as those for steel melting and for ferroalloys. Therefore, a significant room still exists for improvement, like the use of chemical energy and the recovery of the thermal energy that is lost during the ingots cooling, not mention the size of the furnaces, which should grow in order to enable simpler and more productive plants. A number of different chemistries can be found for electrofused materials in the refractories area. The most traditional ones are the fused magnesias, fused magnesia-chromites and fused aluminas, white and brown, and other alumina based materials like mullite, mullite-zirconia, magnesium spinel and calcium aluminates. More recent advances have led to the development of magnesium spinel with zirconia additions, alumina-chromia with high Cr2O3 content and the so-called active spinels based on hercynite and galaxite phases. Besides allowing numerous combinations of oxides, and sometimes carbides, the arc melting process also enables the design of different microstructures depending on the arc length used, the cooling rate, the volatilization of high vapor pressure impurities and the using of additives. In this context, this lecture presents the basics of the EAF functioning, the effects of some of the process variables on the product microstructures and the characteristics of some materials developed more recently. Moreover, an outlook is given on the future developments expected for the refractories industry.
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