GB530877A - Improvements in and relating to titanium pigments - Google Patents

Abstract

530,877. Titanium pigments; titanium dioxide. DU PONT DE NEMOURS & CO., E. I. June 21, 1939, No. 18121. Convention date, June 22, 1938. [Classes 1 (iii) and 95] In a process of the production of titanium dioxide pigments, a titanium-oxygen compound is calcined to develop pigment properties in the presence of a substance which will inhibit or retard the conversion of the titanium compound into the rutile crystalline form, and the product so obtained is recalcined, in the absence of such a substance, to change the crystalline form of the titanium dioxide to the rutile modification. Suitable inhibiting or retarding substances are alkali-metal compounds such as potassium carbonate, potassium sulphate, sodium sulphate and sodium sulphide, the amount used not exceeding about 2 per cent. by weight of the pigment and the amount of the compound present is reduced below 0.1 per cent. prior to the second calcination step. Temperatures of 800-1100‹C. are mentioned, the second calcination being conducted at a higher temperature than the first. The process may be applied to the production of pigments consisting of titanium dioxide, and also to pigments containing extenders such as alkaline earth metal sulphates, silica and magnesium silicate. According to Examples : (1) hydrated titanium oxide is calcined with 0.5 per cent. of potassium sulphate at 985‹C. The product is dispersed in water with 0.18 per cent. of sodium hydroxide, and ground. The slurry is coagulated with 0.5 per cent of magnesium sulphate, neutralized with sulphuric acid, filtered, dried, pulverized and recalcined at 1000‹C. for several hours to transform it to the rutile modification ; (2) hydrated titanium oxide is calcined with 0.5 per cent. of potassium sulphate at 975‹C. The product is leached with water until the content of soluble salts is well below 0.1 per cent. and is then recalcined ; (3) hydrated titanium oxide, obtained by the hydrolysis of titanium sulphate solution, is calcined with 0.75 per cent. of potassium carbonate at 950‹C. The product is dispersed in water, wet ground and elutriated. The resultant dispersion is coagulated with sulphuric acid and filtered. The filter cake is dried, re-calcined at 1025‹C., and ground.