Abstract: A novel process for the preparation of titanium dioxide comprises reacting titanium tetrachloride with oxygen at an elevated pressure and a temperature above 700.degree. C. The titanium tetrachloride is introduced into the reactor in at least two points and that portion introduced in the first inlet point is admixed with aluminium chloride and has been heated to a temperature of at least 450.degree. C. by utilizing the heat of reaction of aluminium and chlorine. The process provides an energy efficient method for producing titanium dioxide and avoids the need for auxiliary heating of the reactor by, for example, hydrocarbon combustion or electric discharge, which auxiliary heating can introduce impurities into the product titanium dioxide.

Abstract: An improved method of milling a particulate material in a jet mill is described. The material is fed from a holding vessel to be entrained by a gas, the holding vessel having an ullage which is maintained at a pressure of at least 0.05 MPa but less than the pressure at which gas is introduced to the jet mill. The method is particularly usefully employed in an impact jet mill in which the entrained particles impinge upon a surface, are reflected into another jet and passed into a cylindrical separation chamber. The method enables such an impact mill to be operated under more energy-efficient conditions.

Abstract: A mill for grinding powder material is disclosed having a cylindrical separation chamber into which the powder material is fed as a dispersion in a gas stream. Powdered material initially is supplied through two spaced powder inlets each located between a jet and a venturi throat assembly so that milling fluid introduces the powder material through the venturis and the venturis are mounted in opposition so that the gas streams carrying the powder impinge on one another to impart grinding. The impinged material passes to a third venturi to be entrained in a gas fed from a third jet nozzle and introduced through the venturi into the separation chamber. The mill is of particular use for milling pigmentary powders.

Abstract: The invention relates to an improved mill that achieves excellent milling with a reduced consumption of milling gas. The mill incorporates an impact plate in-line with a first jet and venturi and a second jet and venturi to entrain the milled particles from the plate to feed into a separation/milling chamber.