Abstract: A simple process for preparing acicular calcium sulphate dihydrate is provided in which a slurry of calcium carbonate containing 100 to 800 grams per liter calcium carbonate is mixed with a solution of sulphuric acid containing 80 to 500 grams per liter sulphuric acid in proportions which produce a calcium sulphate slurry having a pH from 0.5 to 1.5. The process can be used to neutralise by-product sulphuric acid from the preparation of titanium dioxide with crushed limestone. Preferably the calcium sulphate slurry is stirred after formation to reduce the level of unreacted carbonate. The calcium sulphate produced has an aspect ratio of at least 4:1 and has excellent properties for use in paper. The process enables the production of acicular calcium sulphate without employing special crystallisation procedures.

Abstract: A new process for preparing a composite pigment from titanium dioxide and calcium sulphate is provided in which the calcium sulphate is milled to a particle size less than 10 microns, mixed with titanium dioxide and the mixed particulates are coated with an oxide or hydrous oxide of a metal or silicon. The process can particularly be employed in conjunction with a sulphate-process titanium dioxide plant in which by-product sulphuric acid is converted to gypsum. The composite pigment shows improved optical properties in comparison to a mixture of titanium dioxide and gypsum.

Abstract: A process for coating particulate zirconia for use in ceramics is claimed. The particulate zirconia is coated with a hydrous oxide of a stabilizing metal such as yttrium, an alkaline earth metal or a rare earth metal by hydrolysis of a salt of the metal. An initial dispersion of the zirconia is prepared at a pH above 7.5 and, preferably, in the presence of an organic dispersing agent.The coated zirconia produced according to the process has been shown to form ceramic bodies with a higher strength than those prepared from particulate zirconia coated by prior known processes.

Abstract: A composition suitable for use in the manufacture of ceramics comprises particulate zirconia the particles of which are coated with a hydrous oxide of yttrium and a hydrous oxide of manganese, iron, cobalt, nickel, copper or zinc. Preferably the particles also have an inner coating of titania, zirconia, hafnia or alumina.Ceramics prepared from the particulate zirconia of the invention are resistant to degradation by water at temperatures above 100.degree. C.

Abstract: A process for the decomposition of photocatically degradable organic material includes exposing the organic material to ultraviolet light as the material is passing across the surface of a spinning disc. The surface of the disc carries anatase titanium dioxide adhering to the disc. The anatase titanium dioxide acts as a catalyst in the degradation process and preferably has a high surface area.Organic materials such as hydrocarbons alcohols, acids, esters and others are destroyed by this environmentally acceptable process.

Abstract: Titanium dioxide carries an ester or a partial ester of an hydroxy compound containing 1 to 6 OH groups and an aliphatic saturated C.sub.10 to C.sub.22 monocarboxylic acid. The product is easily dispersible in plastics compositions, particularly masterbatches. The titanium dioxide can also be coated with one or more hydrous oxides.The product is prepared by milling the titanium dioxide in a fluid energy mill in the presence of the ester or partial ester.

Abstract: A quench system which can be used to quench a continuous reaction such as the continuous digestion of titaniferous ores with sulphuric acid is provided. The quench system comprises a pressure vessel (1) equipped with a full bore outlet valve (5) connected to a reaction vessel (7) which may require quenching. The pressure vessel is partly filled with a liquid (18) and the ullage is occupied by a gas under pressure, the pressure being sufficient to discharge the liquid through the outlet valve (5) when open. The reaction vessel is equipped with means to detect cessation of stirring therein or power failure and the full bore valve is equipped with means (19) to open when cessation of stirring or power failure is detected.Operation of the quench system enables a reaction to be rapidly cooled and diluted to prevent solidification and the problems associated therewith in the event of the reactants being unstirred.

Abstract: A composition suitable for the production of ceramics is provided. The composition comprises a particulate material which is a nitride, carbide, carbonitride or boride of Ti, Zr, Al, Si or B having a coating on the particle comprising 5 to 75 wt % with respect to particulate material of an oxide or hydrous oxide of zirconium.The composition can be used to produce a tough zirconia/non-oxide ceramic without the need to co-mill the ingredients.A stabilising agent for the zirconia may also be present in the coating although the invention is designed to avoid the necessity for such agents.Coating usually is effected by a wet treatment process in which the particles are dispersed in a solution of a hydrolysable zirconium salt and the oxide or hydrous oxide is coated on the particles by adjusting the pH of the dispersion.

Abstract: Green bodies suitable for use in manufacturing ceramic articles are provided. The bodies comprise a coherent mass of particles of aluminium oxide free of organic binder and having a fracture stress measured by a biaxial disc flexure test of at least 10 MPa. The particles of aluminium oxide are coated with at least one inorganic oxide or hydrous oxide.The green body can be shaped by drilling, sawing etc. to a desired shape approximating to that of the ceramic article which it is used to produce. Generally such shaping is considerably easier than shaping the finished ceramic article.

Abstract: A polymeric bead has now been developed to act as a support for other entities having a volume mean diameter of up to 250 microns and having a surface provided with pores which form at least 10% by area of the surface. At least one third of the total area of the pores is provided by pores having a larger size of at least 0.4 micron. A method for the manufacture of such polymeric beads involves using a water-in-oil-in-water emulsion technique in which the amount of water used in the preparation of the aqueous phase is not greater than 125 parts by weight per 265 parts by weight of the mixture of the polyester resin and monomer which is used.The porous beads provide an excellent base for carrying enzymes, bacteria and catalysts species useful in a wide range of applications.

Abstract: A method for preparing pigmentary titanium dioxide is claimed. An aqueous solution of a titanium halide is mixed with 0.1 to 1.0% by weight titanium dioxide nuclei and the resultant mixture is heated in a sealed vessel to 150.degree. to 300.degree. C. at which temperature it is maintained for at least 15 minutes. The mixture is subjected to ultrasonic vibrations for at least a part of the heating process.The product of the process is useful as a white pigment without need for further treatment to optimise its particle size.

Abstract: Green bodies suitable for use in manufacturing ceramic articles are provided. The bodies comprise a coherent mass of particles of titanium dioxide free of organic binder and having a fracture stress measured by a biaxial disc flexure test of at least 5 MPa. The particles of titanium dioxide are coated with at least one inorganic oxide or hydrous oxide.The green body can be shaped by drilling, sawing etc. to a desired shape approximating to that of the ceramic article which it is used to produce. Generally such shaping is considerably easier than shaping the finished ceramic article.

Abstract: Chemical waste is burned in oxygen using an electric plasma flame to heat a stream of gas which contains at least 70% by weight oxygen. Liquid waste in fine droplet form is introduced into the gas stream via a two-fluid atomizer using a carrier gas also preferably oxygen. The total amount of oxygen present is at least 30% more than required for complete combustion of the liquid waste. The reaction mixture is maintained at a temperature of at least 1450.degree. C. for a time of at least 2 milliseconds prior to cooling rapidly of the reaction products to a temperature below 300.degree. C.

Abstract: The invention provides a form of particulate zirconia suitable for forming zirconia ceramics in which the zirconia is stabilized in the cubic and/or tetragonal phase.The particles of zirconia are coated with a hydrous oxide of cerium and at least one hydrous oxide of lanthanum, neodymium or praseodymium. In a preferred embodiment a mixture of hydrous oxides of lanthanum and neodymium is used.Preferably the particles are also provided with an inner coating comprising hydrous titania, zirconia or alumina.The products of the invention can be converted into ceramics having a greater strength than ceramics produced from zirconia coated with a similar amount of ceria alone or those produced by physically mixing similar quantities of stabilizing oxides with the particulate zirconia.

Abstract: A process for forming ceramics comprises mixing titanium nitride with an average particle size less than 0.2 micron, zirconia having a particle size less than 1 micron and a stabilizing agent for stabilizing the zirconia in the tetragonal or cubic phase forming the mixture into a desired shape and firing at between 1300.degree. and 1700.degree. C.Preferably the stabilizing agent is in the form of coating on the zirconia.The process is suitable for forming hard and tough ceramics which are electroconducting and can be shaped by electro-discharge machining. It is particularly suitable for forming ceramics containing between 70 and 90% by weight titanium nitride.

Abstract: A process for the decomposition of photocatalytically decomposable organic material includes exposing the organic material to ultraviolet light as the material is passed across the surface of a spinning disc. The organic material is in the form of a liquid dispersion, preferably an aqueous dispersion and the dispersion also contains anatase titanium dioxide which acts as a catalyst in the decomposition process. Preferably the anatase titanium dioxide has a high surface area.Organic materials such as hydrocarbons, alcohols, acids, esters and others are destroyed in this environmentally acceptable process.

Abstract: A process for the production of a suspension of nuclei has been developed in which an aqueous mixture of titanium tetrachloride, aluminium ions and hydroxyl ions is cured at at temperature of from 50.degree. to the boiling point. The pH of the suspension before or after curing has a value of from 6.5 to 10.5. The aqueous mixture is prepared by mixing a solution of titanium tetrachloride with a solution of a base, e.g. sodium hydroxide and aluminium hydroxide.When used to nucleate hydrolysis in the "sulphate" process a large crystal size anatase pigment is produced.