GB565349A - Titanium oxide pigment production - Google Patents

Abstract

565,349. Titanium oxide. DU PONT DE NEMOURS & CO., E. I. Jan. 12, 1943, No. 587. Convention date, Jan. 9, 1942. [Class 1 (iii)] A rutile titanium oxide pigment is prepared by mixing a previously prepared anatase TiO2 with a separately prepared titanium-oxygen compound which when calcined at a temperature not in excess of about 1000‹ C., shows the rutile X-ray diffraction pattern, and calcining the mixture. The added compounds acts as a promoter for the conversion of anatase to rutile which occurs at a temperature below that normally required. The preferred promoter is a precipitated, raw rutile TiO2 and is added in an amount of 1-33, preferably 2-10 per cent by weight of the anatase, the mixture then being calcined at 750-1000, preferably 900- 1000‹ C. The anatase may be prepared by hydrolysis of a titanium salt such as titanium sulphate solution with colloidal titanium oxide as seeding agent, as in U.S.A. Reissue Specification 18854, and the rutile promoter by hydrolysis of titanium chloride, the two being mixed, preferably while in aqueous suspension, filtered, dried, and calcined until substantially completely in the rutile form, generally for 1-3 hrs. Previously calcined anatase may, however, be treated as well as extended pigments containing, e.g. barium or calcium sulphate, calcium carbonate, magnesium or other silicates. Instead of precipitated raw rutile, prepared by hydrolysis of titanium chloride or nitrate, a promoter may be used which is in the anatase form, but which on calcination is converted to rutile below about 1000, preferably 600-900‹ C. Reduced raw TiO2 products obtained by the mechanical disintegration of the oxide to reduce particle size as described in Specification 566,920, may also be used. In examples : (1) titanium chloride solution is neutralized with ammonia to a pH of 6.0 to precipitate orthotitanic acid which is washed and peptized by slurrying to a concentration of 30 g./l. TiO2 and 0.3 N HCI, and heating to 80‹ C. for 20 mins. The sol produced is added to TiCl4 solution in an amount equivalent to 3 per cent on the TiO2 basis, the concentration adjusted to 110 g./l., zinc added to reduce 0.5 per cent of the Ti to the trivalent state, and the solution heated to 95-98‹ C. for 30 mins. Sulphuric acid is added and the precipitate filtered, washed and slurried to a concentration of 200 g./l. This constitutes the raw rutile promoter. It is mixed in an amount of 10 per cent on a TiO2 basis with anatase raw pigment prepared as above described, and the mixture filtered, dried and calcined at 950‹ C. for 30 mins. giving 98 per cent rutile conversion ; (2) anatase pigment prepared as in (1) is neutralized to pH 6.8-7.0 with ammonia and after washing out sulphate ions, is mixed with the rutile promoter of (1) in a ratio of 3 : 1 and calcined similarly.