Patent GB-568232-A (GB)
Title: Titanium oxide pigment production
IPC: C01G23/053
Filed: 1943-01-26
Abstract: 568,232. Titanium oxide pigments. DU PONT DE NEMOURS & CO., E. I. Jan. 26, 1943, No. 1320. Convention date, Jan. 9, 1942. [Classes 1 (iii) and 95] A nucleating agent for titanium salt solution hydrolysis is prepared by mixing alkali with a titanium chloride solution to produce an alkaline suspension of hydrous titanium oxide, and activating the hucleating characteristics thereof by admixing a mineral acid until the suspension is acid in reaction. Preferably, a titanium chloride solution containing up to 125 g./l. TiO2 is mixed with alkali such as caustic soda, at not more than about 50‹ C., to produce a hydrous titanium oxide suspension of alkalinity about .2-.8 N, e.g..4 N NaOH, determined by titration with .1 N H2SO4 and brom thymol blue. After a relatively short time, usually 1-5 mins., the suspension is brought to an acidity of about .05-2.5, preferably .1-1 N, determined by titration with .4 N NaOH and the same indicator. This may be effected by adding further titanium chloride solution. The acid mixture is preferably heated to about 75-90‹ C., for from 5 mins. to 3 hrs., to produce a secondary ripening and, if desired, a peptization. The resulting suspension or peptized sol is used in amounts of about 1-5 or even 10 per cent on the TiO2, basis for seeding titanium salt solution, especially the sulphate, or it may be cooled to below 60‹ C. and stored for future use. Prior to use, coagulation of the nuclei may be effected as described in Specification 1824/43. The hydrolysate obtained, particularly in the anatase form, calcines to a rutile pigment at below about 1000‹, e.g. 850-975‹ C. Calcination may be effected in the presence of potassium or sodium salts, especially sulphates, as in Specification 360,436, or of an alkali metal salt and a compound of a polyvalent metal as described in Specification 580,734. The nucleating agent is very finely divided and exhibits the rutile X-ray diffraction pattern on heating above 100‹ up to, say, 550‹ C. The rutile pigments obtained with its use have a particle size of about .2-.5 microns. In producing the nucleating agent, the titanium chloride solution is preferably added to the alkali,. whereby alkaline conditions are first obtained, continued addition converting to the desired acid normality. The alkalinity is at least that indicated by phenol phthalein, and generally about .05-2.5 N, and may be maintained for up to 30 mins. or longer. The subsequent ripening is effected at about .05- 2.5 N acid, preferably using a strong acid free from sulphate ions such as acid titanium chloride solution or monobasic acids such as hydrochloric or nitric, whereby peptization is induced. In place of or together with caustic soda, alkali metal or ammonium hydroxides or carbonates, alkaline earth hydroxides or other alkali may be used. The product may be applied to the production of mixed or extended titanium oxide pigments containing, for example, zinc sulphide or oxide, lithopone or metal titanates, or such extenders as calcium or barium sulphate, calcium carbonate and magnesium silicates. In examples : (1) caustic soda and titanium chloride solutions are mixed to give a suspension of titanium dioxide of about .8 N NaOH. Hydrochloric acid is added to give a .5 N HC1 suspension which is heated to 85‹ C. for 25 mins. 5 per cent of the sol produced is used for hydrolysis of a titanium sulphate solution by boiling for 3 hrs., the washed precipitate being calcined with .5 per cent sodium sulphate at 950‹ C. to give a rutile pigment; (2) titanium chloride solution is added to caustic soda to give 1 N NaOH, further additions giving a suspension which is .45 N HC1. This is heated to 90‹ C. for 20 mins. and the sol obtained coagulated with cold caustic soda to give a pH of 7, the washed precipitate being used for seeding a titanium sulphate; (3) caustic soda is added over 5 mins. to titanium chloride solution to give a suspension in .5 N NaOH which, after ageing for 3 mins., is acidified with further chloride solution, heated to 90‹ C. for 15 mins., and further treated as in (2) ; (4) titanium chloride and caustic soda solutions are added simultaneously to a mixer to give a suspension in .6 N NaOH. This is added to more chloride solution to give an acidity of .5 N HCI and the mixture treated as in (2) ; (5) mixing is effected as in (4) to give .2 N NaOH, HC1 then being added to a value of .52 N ; (6) orthotitanic acid is precipitated by adding the chloride solution to caustic soda, the precipitate being maintained in an alkaline environment until further chloride gives a pH of 6.7. The precipitate is mixed with HC1 to give a normality of .35, and heated to 80‹ C. for 20 mins. The seed is used for titanium sulphate hydrolysis. Specification 275,672, [Class 1 (iii)], also is referred to. The Specification as open to inspection under Sect. 91 comprises also the use of other titanium salts such as the nitrate, iodide or sulphate in the preparation of the nucleating agent. In the case of the sulphate, soluble polyvalent ions must be removed from the precipitate. The alkaline precipitation followed by acid ripening may be effected by adding alkali rapidly or without sitrring to produce alkaline zones where the hydrate precipitates, acid conditions then being produced by stirring. An additional example (6) describes the rapid addition of caustic soda to give local alkalinity, the final suspension being In .45 N HC1. This subjectmatter does not appear in the Specification as accepted.