Abstract: A method of operating an aluminum smelting cell during the start-up phase of the cell is described. The method includes forming a layer of boron oxide on the exposed surface of the cathode of the cell, forming a layer of aluminum on the boron oxide layer, and starting the cell. This melts the boron oxide layer to form a barrier impervious to oxygen at a temperature from about 400.degree. C. to about 650.degree. C., and the aluminum layer is melted to form a barrier to oxygen at temperature above about 600.degree. C. to about 1000.degree. C. to reduce the development of oxidation products.

Abstract: A filter medium suitable for hot liquid and gaseous materials, more particularly molten metals, for example aluminium and its alloys, is characterized by the use of sintered ultrafine bauxite granules. Filter media according to the invention exhibit superior thermal shock resistance, may be used repeatedly and are much cheaper than filter media of the prior art.