Process for the production of carbides such as titanium carbide, boron carbide or zirconium carbide

摘要

PICT:0777013/III/1 Hard carbides are produced from a mixture of carbon and the oxide of the element the carbide of which is to be produced, by electric arc heating in an electric furnace comprising two electrodes capable of up and down movement and a carbon or graphite bridge, each electrode making arcing contact initially with the carbon bridge and then with carbide which builds up on the bridge in the form of two ingots, with little or no formation of liquid, as the reaction proceeds. The ratio of the cross sectional area of the bridge to the diameter or equivalent diameter of the electrodes may be 2:12. The applied voltage may be 50-160 volts. The production of titanium, zirconium and boron carbide, and proportions of carbon to oxide of 1-2 to 1, 0.7-1.5 to 1, and 0.6-1 to 1 respectively are specified. The oxide may be in the form of ore, e.g. rutile, zircon or baddeleyite. Unconverted or partially converted oxide from a previous operation may be mixed with fresh oxide. As shown, the furnace comprises two electrodes 80 and an oval-shaped shell 20 supported on a base 66 around an inner container 67 and cooled by sprays of water supplied at inlets 57-60. A concave layer of fine carbon and pitch is formed in the inner container 67 and refrectory non-electrically conducting oxide material is packed between the container 67 and the shell 20. A layer of oxide material is then added to a height of ca. 4 inches above the top of container 67. The oxide material may be the same as is used in the reduction process, unconverted or partly converted material from a previous operation or other oxide material, e.g. alumina (in the production of boron carbide). In a trough in the oxide material is then placed a bridge of graphite or carbon of length equal to the distance between the electrodes. The furnace is wheeled beneath the electrodes which are then lowered into position. A layer of mixture to be heated is then placed in the furnace to a depth of 1-3 inches and a current passed through the electrodes. In operation automatic control mechanism raises and lowers the electrodes, maintaining arcs with a current flow of ca. 8,000 amps., and additional mixture is introduced as carbide is formed. The layer of mixture may be maintained 1-3 inches deep in the area of the electrodes, measured from the bottom of the electrodes. After completion of a run the electrodes are raised, the furnace wheeled away, allowed to cool while the water spray is maintained, and the shell lifted. Three phase power may be used instead of single phase power, using three electrodes and a round or trilobed furnace shell. Specification 747,834 [Group XXXVI] is referred to.