Abstract: Provided herein is a device useful for measuring the fineness of a dispersion of particles in a liquid vehicle. A device according to the invention includes a light source, a means for mounting a film of said vehicle of increasing thickness, and a means for producing an electronic image of said film, in which these elements are positioned relative to one another so that the light the imaging means receives is predominantly light reflected from regions of the surface of said film which are disrupted by protruding particles. This is achieved by configuring the device so that the image producing means is aimed into the dark field below the light source, with the image producing means being directed generally at an angle below the angle of reflection of any light reflected from undisrupted regions of the surface of the film.

Abstract: A process is provided for increasing the concentration of sulfuric acid in a waste solution of sulfuric acid previously used to produce titanium dioxide. The waste solution of sulfuric acid is fed into a first heat exchanger/evaporator stage that operates at a sulfuric acid concentration of less than 30%. A portion of the solution discharged from the first heat exchanger/evaporator is fed into a heat exchanger/evaporator that uses waste heat and operates at a sulfuric acid concentration that is greater than 40%, while the remainder of the solution discharged from the first heat exchanger/evaporator and the solution discharged from the heat exchanger/evaporator using waste heat is fed into a second heat exchanger/evaporator that operates at a sulfuric acid concentration that is greater than 50%.

Abstract: A process for producing chlorine and iron oxide from iron chloride (which may be generated as a by-product of the direct chlorination of titaniferous ores) comprises the steps of converting ferrous chloride to ferric chloride by reaction with chlorine, separating the solids from the gaseous products, reacting the gaseous ferric chloride with oxygen, condensing unreacted ferric chloride onto iron oxide particles, separating the gaseous products from the iron oxide particles and recycling the iron oxide particles to the oxidation or condensation step.

Abstract: Provided herein is a device useful for measuring the fineness of a dispersion of particles in a liquid vehicle. A device according to the invention includes a light source, a means for mounting a film of said vehicle of increasing thickness, and a means for producing an electronic image of said film, in which these elements are positioned relative to one another so that the light the imaging means receives is predominantly light reflected from regions of the surface of said film which are disrupted by protruding particles. This is achieved by configuring the device so that the image producing means is aimed into the dark field below the light source, with the image producing means being directed generally at an angle below the angle of reflection of any light reflected from undisrupted regions of the surface of the film.

Abstract: Provided herein is a process for treatment of solutions which contain ferrous, ferric and soluble manganese species which process comprises addition of an oxidizing agent to such a solution to cause formation of manganese dioxide particles and adding manganese dioxide seed particles so as to cause nascent manganese dioxide agglomerates formed from the action of the addition of the oxidizing agent on the soluble manganese species to adhere to the manganese dioxide seed particles. By a process according to the invention, it is possible to effectively remove the soluble manganese species as solid manganese dioxide by having effective control over the size of the manganese dioxide particles to enable their subsequent removal using ordinary filtration techniques.

Abstract: A process for production of titanium oxide comprises digesting an ilmenite ore in which at least 92% by weight of the iron which is present is in the ferrous form, if necessary adding a reducing agent and subsequently precipitating hydrous titanium oxide. When a reducing agent is added the amount used is equivalent to less than 4.0% by weight metallic iron calculated with respect to ilmenite ore. The process enables an increased throughput on a pigment plant and less co-product in the form of iron compounds is produced.

Abstract: An aqueous gloss emulsion paint comprises a dispersion of structured composite particles, said structured particles comprising an association of particles of inorganic pigment and polymeric particles. The polymeric particles are formed from a polymer or copolymer having a minimum film forming temperature not greater than 50.degree. C. The component particles of the composite particles are held in association as a result of surface charges on the particles said surface charges on the polymeric particles being of opposite sign to the surface charge on the particles of inorganic pigment. The ratio of polymeric particles to particles of inorganic pigment in the composite particles is from 0.5:1 to 6:1 by volume.

Abstract: A pigmentary material comprises particulate titanium dioxide the particles of which have been treated with a polymeric hindered amine stabiliser. The stabiliser is a polymer having a main chain substantially free of acidic groups and having hindered amine stabilising groups. The stabilising groups comprise at least 35 per cent by weight of the polymer. Preferably, the titanium dioxide particles are also treated with an organic compound such as a polyhydric alcohol, an alkanolamine, a polysiloxane or a fatty acid.

Abstract: A structured composite pigmentary material comprises composite particles consisting of an association of at least one titanium dioxide particle and at least one non-film-forming organic polymer particle wherein the particles are held in association as a result of a positive surface charge on the titanium dioxide particles and a negative surface charge on the polymeric particles, the composition of the composite being such that the ratio by volume of polymeric particles to titanium dioxide particles is in the range 0.3:1 to 0.6:1. An aqueous paint composition and a method of preparing the structured composite pigmentary material are described.

Abstract: A treated inorganic solid comprises particulate inorganic material the particles of which are coated with an alkylphosphonic acid or ester thereof, the alkylphosphonic acid containing 6 to 22 carbon atoms. The particulate material is usually a pigment, extender or filler which is treated by mixing with the alkylphosphonic acid or ester for example in an aqueous dispersion or during a process step such as milling. The treated inorganic solid is particularly useful for preparing polymer compositions such as masterbatches.

Abstract: A method for the manufacture of a titanium dioxide pigment comprises mixing a suspension of titanium dioxide with a reagent formed by reacting concentrated phosphoric acid with aluminium or an aluminium compound at elevated temperature and adding an alkaline compound to the suspension until a pH value of at least 3.5 is achieved. A novel pigment which can be prepared by the method of the invention comprises titanium dioxide, the particles of which have a surface coating of aluminium phosphate in which the molar ratio of aluminium to phosphorus lies in the range 1.8:1 to 1:1.4 Al:P. The pigments prepared according to the invention are useful in the preparation of paper laminates.

Abstract: A process for preparing a structured composite pigmentary material comprises forming a dispersion of uncoated particles of titanium dioxide at a pH value at which the particles have a surface charge and subjecting the dispersion to cross-flow filtration until the dispersion contains more than 50% by weight titanium dioxide. The concentrated dispersion is mixed with a dispersion of chemically distinct particles having a surface charge of opposite sign under conditions which ensure that the sign of the surface charge on either of the particulate materials is not reversed. In the resultant composite pigmentary material the titanium dioxide particles are held in association with the chemically distinct particles as a result of said surface charges.

Abstract: A process for the production of a structured composite pigmentary material in the form of a dispersion comprises mixing an aqueous dispersion of inorganic pigmentary particles and an aqueous dispersion of polyvinyl chloride (PVC) particles. The inorganic pigment particles carry a positive surface charge and the PVC particles carry a negative surface charge and the particles in the composite are held in association as a result of these charges. The inorganic pigment particles and PVC particles are mixed in the presence of a surfactant system which provides both anionic and steric stabilisation.

Abstract: A process for preparing anatase titanium dioxide by precipitating hydrous titanium oxide in the absence of added nuclei from a solution of titanium sulphate containing the equivalent of 200 to 300 grams TiO.sub.2 per liter and having an acid to titanium ratio in the range 1.6:1 to 2.2:1, the precipitation being induced by the addition of 5 to 35 parts water per 100 parts titanium sulphate solution. The hydrous titanium oxide is calcined in the presence of an amount of potassium compound equivalent to between 0.20 and 0.60 weight percent calculated as K.sub.2 O based on TiO.sub.2 and between 0.15 and 0.55 weight percent phosphorus calculated as P.sub.2 O.sub.5 based on TiO.sub.2. The hydrous titanium oxide is subjected to calcination in a process having a specified thermal profile. The product of the process is anatase titanium dioxide having an average crystal size larger than conventionally prepared anatase. Said product is easily milled to form a product with a high single crystal fraction.

Abstract: An improved kiln for the calcination of a powder comprises a directly heated rotary kiln in which at least a part of the inner circumferential wall is equipped with a plurality of protrusions. The protrusions are shaped so that the powder is substantially not lifted during operation of the kiln. In a preferred embodiment the protrusions have the shape of a triangular prism and are positioned within the kiln so as to pass through the powder in the manner of a plough. Preferably the top face of the prism is an isosceles triangle in which the equal angles are greater than the angle of repose of the powder for which the kiln is designed.

Abstract: A novel method for the production of titanium dioxide slurries having a high solids content comprises subjecting an aqueous slurry of titanium dioxide to cross-flow filtration to produce a slurry containing at least 50%, preferably 60 to 80% titanium dioxide by weight. The slurry can be washed during filtration to reduce the concentration of soluble ions. The process can produce concentrated slurries of titanium dioxide having remarkably low viscosities.

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: A composite particulate pigmentary material is disclosed which comprises an association of at least two chemically distinct materials in which the particles of one material carry a positive surface charge and the particles of the second material carry a negative surface charge and particles are held in association as a result of these surface charges. Also disclosed is a method for preparing composite particulate pigmentary material comprising forming aqueous dispersions of two particulate materials under conditions in which the surface charges of the particles of the two materials are of different signs and mixing the dispersions. Typical materials useful for preparing the composite include inorganic pigments, fillers and extenders and organic polymeric microspheres. The product is useful as a pigment in, for example, paints, inks, paper and plastics.

Abstract: A novel inorganic particulate powder coated with an organic polymer is claimed. The product is obtainable by dispersing in water inorganic particles at a pH higher than their isoelectric point in the presence of a polymeric polybasic acid as a dispersing agent to produce particles having a modified isoelectric point. The pH of the dispersion is then adjusted to a value below 9 but above the modified isoelectric point and an ethylenically unsaturated monomer is polymerized in the presence of the dispersion so as to coat the inorganic particles with polymerized monomer. A method for forming the particles is also claimed.The particles prepared by the method have been shown to be uniformly and discretely coated with an organic polymeric coating and can be used in many applications where it is desired to disperse inorganic particles in organic media such as paints, inks and plastics compositions.

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.