Verfahren zur Herstellung farbbestaendiger TiO2/Al2O3-Pigmente

1,157,106. Titania-alumina pigment. E. I. DU PONT DE NEMOURS & CO. 18 Oct., 1966 [22 Oct., 1965], No. 46498/66. Heading ON. TiO-Al 2 O 3 pigment is coated with SiO 2 . An aqueous slurry containing 20-40% by wt. TiO 2 -Al 2 O 3 prepared by co-oxidation of TiCl 4 and AlCl 3 (the A1 2 0 3 content ranging from 0 to 10% by wt. of the TiO 2 ) is heated to 40-70‹ C., and a solution of a water-soluble alkali metal silicate is added with agitation in an amount sufficient to provide 1 to 25% of SiO 2 based on the wt. of TiO 2 . The resultant mixture is aged for at least 30 mins. at pH of at least 9 at 40-70‹ C. and the pH is then reduced to not >6.5. Further ageing for at least 20 minutes at 40-70‹ C. is then carried out; the pigment coated with 5i0 2 is recovered, e.g. by filtration, and calcined at 300-1000‹ C. The initial silicate solution may be sodium silicate at 100-400 gms./1.