GB930605A - Preparation of refractory products by arc melting - Google Patents

Abstract

In a process of preparing a compact cast refractory product a charge containing at least one refractory mineral oxide is fused in an electric arc furnace by means of an arc striking between the charge and at least one carbon electrode positioned above the charge, and the molten charge is subjected to agitation while maintaining an oxidising atmosphere in contact therewith, the distance of the or each said electrode above the surface of the molten charge being sufficient to ensure that carbon given off by a said electrode along the path of the arc will be oxidised before reaching the charge. The reduction of any constituent of the charge by carbon from the electrode is thus avoided. The agitation may be produced by bubbling an oxidizing gas through the bath, by adding sodium peroxide or other oxygen liberating bodies to the bath, by electro-magnetic means, or by the arc itself, provided suitable conditions of arc length and current are maintained. The furnace atmosphere is preferably constantly renewed to remove carbon monoxide, and may be ionized by adding carbonate of soda to the charge. Refractory products obtained by the process are characterised by freedom from detectable elemental carbon and metallic iron and are particularly suitable for use in glass furnaces where they do not give rise to bubbles in the molten glass. Particular mineral oxides mentioned are alumina, zirconia, magnesia and chrome oxide. The products may contain alumina or alumina and zirconia in a total proportion exceeding 63%, zirconia from 0 to 90%, and silica in a proportion lower than 30%. An example specifies .ZrO2.33 to 54% .SiO2.13 to 2% .Na2O.1,5 to 0,28% .Al2O3.50 to 36% .Fe2O3 \sB TiO2.<1,5%