Method for preparing polycrystalline fibrous TiO2 pigment

Claim 1

Process for producing a fibrous, polycrystalline, rutile TiO 2 composition wherein the individual fibers have a cross-section dimension in the range of from 0.04 to 0.3 millimicrons and a ratio of length to cross-section in the range of from 1.5 to about 25 comprising the steps of: hydrolyzing a titaniium sulfate-iron-sulfate solution to form a titania hydrate, filtering, bleaching and washing said hydrate to remove the soluble iron salts therefrom, said bleached hydrate being substantially iron-free but containing from 5% to 15% H 2 SO 4 associated with said hydrate, slurrying said hydrate and treating said hydrate with a sufficient amount of an ammoniacal agent selected from the group consisting of ammonia, ammonia hydroxide and ammonium carbonate to neutralize the titania hydrate slurry to a pH of from 5 to 11, washing said titania hydrate to remove the soluble salts therefrom and retaining no more than about 2% SO 3 in said hydrate, calculated on a TiO 2 basis, adding to the washed substantially sulfate-free TiO 2 hydrate a mineralizing complex consisting essentially of a potassium salt in an amount from 0.0 to 2.0% calculated as K 2 O, and calcium salt in an amount from 1.0 to 6.0% calculated as CaO, a compound of boron in an amount from 0.5 to 2.0% calculated as B 2 O 3 and rutile promoter sol in an amount of about 6.0%, all percentages based on the weight of TiO 2 , calcining the treated hydrate at temperatures in the range of from 812° to 865° C., washing the calcine to remove calcium ions, milling the calcine and optionally hydroclassifying and finishing the milled calcine.