GB708970A - Process for the preparation of finely divided metal oxides and silicon dioxide - Google Patents

Abstract

<PICT:0708970/III/1> In the production of metal or silicon oxides by decomposing a mixture of metal or silicon chloride vapour and oxygen - containing gases, in which the mixture is ignited to a flame with the aid of an auxiliary flame produced by separately introduced gases, the moisture content of the gas current which first comes into contact with the outflowing reaction mixture is maintained below the limit above which a crust formation takes place at the contact zone within 12 hours. The permissible moisture content varies with the nature of the chloride being decomposed, the discharge velocity of the gases, their temperature &c. but is always less than 1 per cent. by volume, and may be 0.01 per cent. Suitable combustible gases are hydrogen, carbon monoxide, coal gas, petroleum or oil vapour, or mixtures thereof. Carbon monoxide is especially suitable, yielding no hydrochloric acid, but its combustion can only be effected in the presence of 0.01 per cent. water vapour, or more depending on the gas velocities, the burner area etc.; to this end water vapour, or hydrogen, or hydrogen-containing combustible material is added to the carbon monoxide or oxygen-containing gas, whichever is not led into immediate contact with the chloride reaction mixture. The latter is produced by introducing oxygen-containing gases into the distillation or sublimation chamber, the mixture being then preheated, or by atomizing heated liquid metal chloride under pressure with the oxygen-containing gas. Pure oxygen may be used, or it may be admixed with nitrogen, carbon dioxide &c. The inert gas may alternatively be introduced into the reaction chamber between the chloride-oxygen mixture and the flame-producing gas, its moisture content being subject to the above considerations. The reaction may contain from a deficiency up to 20-50 per cent. of oxygen for the combustion of the chloride. Suitable burners consist of concentric tubes, the chloride-oxygen mixture passing through one tube and the combustible gases passing through outer, and in some cases also inner, concentric tubes. In a modification shown in Fig. 5, oxygen with a hydrogen and moisture content of 0.1 per cent. by volume each passes through the central tube 13, a mixture of titanium chloride, oxygen and nitrogen with a small content of aluminium and silicon chlorides through all of the tubes 14, carbon monoxide with a moisture content of 0.001 per cent. by volume through the free space between tubes 15, 13, and oxygen through the space between tubes 16, 15. The temperature of the reaction chamber is maintained at 1200 DEG C. The decomposition of titanium, zirconium, iron, aluminium and silicon chlorides, is indicated. Specification 661,685 is referred to.