GB842726A - Improvements in or relating to the production of aluminium - Google Patents

Abstract

842,726. Extracting aluminium. PECHINEY COMPAGNIE DE PRODUITS CHIMIQUES ET ELECTROMETALLURGIQUES. Oct. 31, 1956 [Nov. 4, 1955], No. 33267/56. Class 82(1) Aluminium is produced by decomposition of aluminium nitride at a pressure equal to or less than 40 mm. of mercury in the range 1500‹C.- 2000‹C., while substantially preventing any contact between carbon in the apparatus and the nitride and its decomposition gases, the carbon-containing by products of the reaction being formed and retained in a zone siutated before that in which aluminium is condensed to the liquid state. Preferably the carbon (c%) and aluminium oxide (a%) contents of the starting material are restricted by the formula a + 7.5c # 6.8. In the apparatus shown in Fig. 2 aluminium nitride in crucible 4 is heated to the decomposition temperature by induction coil 15, the trap 14 is heated to within the range 1400‹C.- 1500‹C. by coil 16 to retain carbide-containing by-products, the top of condenser 10 is maintained at a temperature in the range 1200‹C.-1300‹C. to condense aluminium in liquid form which is collected at 13, and the walls 11 of the vapour duct are maintained at a temperature in the range 1000‹C.-1200‹C.to condense oxide-containing impurities in the vapours. At least those parts of the apparatus which operate at a temperature above 1500‹C. have their surfaces made of or covered with a nitride or carbide of tungsten, molybdenum, tantalum, titanium or zirconium or a mixture of these compounds. The coating may be formed by painting on the surfaces a mixture of metal powder in an organic medium and firing under vacuum at a temperature over 1000‹C., e.g. 1500- 1800‹C., to convert the metal to carbide.