Patent GB-1108425-A (GB)
Title: Production of metal oxides
IPC: C01G23/07
Filed: 1965-03-24
Abstract: <PICT:1108425/C1/1> A method for the vapour phase oxidation of halides of metals boron, silicon and phosphorus, particularly titanium tetrachloride, comprises passing elemental oxygen introduced at an inlet 6 in a reactor through a plasma are A struck between two electrodes 1 and 8 where it is heated to a temperature exceeding that required for reaction between the oxygen and metal halide, passing the oxygen into a burner 10 where it is mixed and cooled with secondary oxygen to give an overall temperature in excess of 1900 DEG C., and passing the stream into a reaction chamber 17, the stream being externally surrounded by a concentric stream of inert gas e.g. chlorine, carbon dioxide, argon, nitrogen, helium, krypton or xenon and an external concentric stream of metal halide e.g. TiCl4; at least one of the electrodes 1 and 8 being formed of at least one metal, or at least one compound of a metal which will form a white metal oxide on oxidation and from which particles of metal are controllably emitted as nucleating agents under the conditions of the discharge and are fed into the reaction zone with the oxygen.  The electrodes may be made of aluminium, arsenic, barium, beryllium, boron, calcium, gadolinium, germanium, hafnium, lanthanum, lithium, magnesium, phosphorus, potassium, samarium, scandium, silicon, sodium, strontium, tantalum, tellurium, terbium, thorium, thalium, tin, titanium, yttrium, ytterbium zinc, zirconium niobium, gallium, or antimony or of Al4C3, TiC or ZrC.  To add more than one nucleating agent to the reaction zone the anode and cathode are constructed out of different metals.  A small amount of metal halide e.g. SiCl4 or TiCl4 can be included in the oxygen stream passing through the arc to augment the nucleating agents generated by the electrodes and may provide different nucleating agents to those coming from the electrode.  Metal powders may alternatively be added and carbonates are also referred to.  In a modification the reactants may be mixed and introduced into the reactor and a temperature below the reaction temperature and an inert gas heated above the reaction temperature by passage through a plasma arc and which has been charged with nucleating agents, is introduced into the reaction zone thereby causing pigmentary metal oxide to form.  The inert gas can be introduced in a direction transverse or perpendicular to the direction of the feed stream of mixed reactants.  The rate at which metal particles are emitted from the electrodes is determined by magnetic coils or cooling means.  Radio frequency and induction heating means can be used as an additional source of heat energy. When TiO2 is prepared it is removed by a bag filter or cyclone separator and the chlorine gas and unreacted titanium tetrachloride are sent direct to a chlorinator in which rutile is being chlorinated to TiCl4 for use in the vapour phase oxidation.  In a modification the electrodes 1 and 8 are constructed out of a material which does not form a white oxide upon oxidation e.g. copper, graphite, silver alloy and are used in conjunction with an auxillary electrode (not illustrated) located upstream or downstream of the electrodes 1 and 8 and which is supplied with a current sufficient to vaporise the metal of the electrode.  The electrode is preferably constructed from aluminium.