Verfahren und Vorrichtung zur Herstellung feinstteiliger anorganischer Oxyde

摘要

A process of producing very finely-divided mineral powders in dispersed form is carried out in two stages in separate chambers, the first stage comprising the volatilisation of the mineral in an enclosed arc furnace 1, the output of which is controlled by introducing into the furnace an inert gas the rate of flow of which is automatically varied as a function of current intensity, and the second stage comprising the combustion in a chamber 10 of the powders produced in the chamber 1. The oxides of silicon, aluminium, titanium, magnesium, beryllium, zirconium or zinc may be thus produced, or fluorspar. The furnace may be supplied with two or more minerals, with or without coke. When coke is added, reduction as well as volatilization takes place in the first stage. Raw material, e.g. silica sand and coke, is fed through screw conveyers 11 to tubes 13 and graphite tubes 14 into the furnace adjacent but not into the arc, at such a speed that a pool of molten charge remains on the furnace floor 10-20 mm. below the electrode ends. The furnace floor 3 may be of fine sand surrounded by walls 4 of silicon carbide and surmounted by a graphite roof 5 with a central outlet 2 formed by a graphite tube 9. Nitrogen is fed into the furnace through the charge tubes 13 and through tubes 7 (Fig. 1, not shown) surrounding the graphite electrodes 6, which may be longitudinally adjusted by a screw to keep the tips 8-15 cms. apart. The nitrogen entraining the vaporized mineral passes through the outlet 2 into a sheet-metal chamber 10, where the product which comprises carbon monoxide, silicon monoxide and silicon is immediately cooled by an inert gas introduced through a tube 27. Cold nitrogen is used or a part of the gases from which the dispersed powder has been removed is cooled and recycled. The walls of the chamber 10 may further be cooled by water. Air or oxygen is introduced through inlets 29 in the upper part of the chamber to burn the product to form a white dispersed silica powder which is drawn through the top of the chamber 10 by a fan and passed through one or more cyclone separators, any silica then remaining being removed by passing the gas through filter bags. The silica powder is spherical with a diameter of 10-100 mm. and is suitable as a filler for rubber and plastics. Turbulent flow of the combustion air may be ensured by adjustable baffles in the chamber adjacent the inlets 29, over which a slide may move to adjust the amount of entering air or oxygen. The impedance of the arc varies according to the amount of mineral vapour therein and as this vapour is removed by the nitrogen, the flow of nitrogen is controlled to keep the arc intensity constant (see Group XXXV), and ensure a regular flow of volatilized product to the chamber 10.