Verfahren zum Herstellen von feinverteiltem Titandioxyd

Finely divided titanium dioxide is obtained by vaporizing solid material containing titanium dioxide by contacting it with a substantially inert gas heated to a temperature above the boiling point of titanium dioxide and condensing the vaporized material. The heated gas may be in the form of a plasma and may be e.g. argon, oxygen or free-oxygen containing gas such as air, nitrogen, helium, neon, krypton, carbon dioxide or oxides of nitrogen. a minor proportion of a gas which has a high thermal conductivity, e.g. hydrogen, may be included. The heating may be in the form of an arc between electrodes preferably arranged as a central electrode and an annular electrode both of which may be cooled by means of a circulating liquid coolant. The current may be direct or alternating. Induction heating may be employed by passing the gas through a space surrounded by a confining tube of e.g. silica and around which is wound electrically conducting material, e.g. copper tubing carrying an alternating current of, say, 200 kilocycles to 10 megacycles. A gaseous or liquid coolant, e.g. water, may be passed through the coil. The gas may be in helical or laminar flow or a mixture of both. The first and last turns of the coil may be in a direction opposite to that of the remainder. The particles of titaniferous material may be of 30-100 microns and may be added to the gas stream as described in Specification 1,093,442. The condensed material may be subjected to a magnetic or electric field. A rutilizing agent, e.g. an aluminium halide or zirconium tetrachloride may be added before vaporization and other modifying agents, e.g. compounds of silicon or boron such as the halides, or lower halides of titanium, water or alkali metal ions may be added before or after vaporization. An apparatus as shown comprises two silica tubes (1) and (2), around (1) are wound coils of copper tubing (3) connected to a radio-frequency generator. A silica tube (4) provides an annular space (5) through which gas may be passed. Silica tube 6 with orifice (7) is attached to a supply of particulate material and feed gas. The lower end of (2) is connected through a filter to a source of reduced pressure. Tube (2) is cooled with air through pipes 8.