| 摘要 |
Metal oxides and silica are prepared by a process comprising introducing streams of metal halide vapour and oxidizing gas separately into a fluidized bed through the base of a reactor containing the bed, there being at least one metal halide vapour stream and at least one oxidizing gas stream the directions of whose paths as they enter the bed intersect in the bed and whose velocities as they enter the bed are such that the two streams impinge upon each other within the bed. The oxides may be titanium dioxide, alumina, ferric oxide, zirconia and silica. The oxidizing gas may be oxygen or free-oxygen containing gases such as air, and also water, hydrogen peroxide or oxides of nitrogen. The bed may be of particles of size 50-2000 microns and may consist, of silica, alumina, zirconia, zircon sand, titanium dioxide or mixtures thereof. Other gases, e.g. nitrogen may be employed to assist fluidization of the bed. The bed may be heated with an external source such as by burning a fuel, e.g. propane within the bed or by preheating one or both of the reactants. The reactants are introduced at a velocity of at least five feet per second. Additives may be introduced with the reactants, e.g. in the case of titanium dioxide, aluminium halides, silicon halide, water vapour or a hydrogen-containing gas which is converted to water within the bed, zirconium halides, lower halides of titanium, a source of an alkali metal such as potassium, rubidium or caesium and/or thorium. Particles of weight media crystal size below 0.25 microns or 0.20 microns may be produced. The hot gases leaving the bed containing oxide particles are passed to an upper zone maintained at at least 600 DEG C. into which additional amounts of the metal halide and/or oxidizing gas may be introduced as described in Specification 991,318. |
