GB1107506A - The preparation of zircon pigments - Google Patents

Abstract

A blue pigmentary zirconium silicate (zircon) is prepared by heating to at least 700 DEG C. in a non-oxidizing or reducing atmosphere a mixture of sodium silicozirconate, and a basic zirconium sulphate of formula SO32ZrO2.nH2O, where "n" is small but variable, with a vanadium compound and sufficient silica to provide an overall SiO2: ZrO2 molar ratio of approximately 1:1. The reaction mixture preferably contains sodium silicozirconate, Na2O.ZrO2.SiO3, a basic zirconium sulphate of formula SO3.2ZrO2, and silica in the molar ratio of 1:1:2, together with 2 to 4.5% preferably 2.5% by weight of a vanadium compound (as V2O5 based on the sum of zirconia and silica in the mixture). The preferred vanadium compound is ammonium vanadate. The preferred atmosphere is an inert or reducing gas, and the calcination is preferably performed in a graphite saggar. Specified atmospheres are nitrogen and carbon dioxide. Sodium sulphate may be added to the mixture before calcination, in an amount such that the calcined product contains for example 10 to 50%, preferably 32-34%, by weight of sodium sulphate, and the calcined product is washed free from sodium sulphate with water.ALSO:A blue pigmentary zirconium silicate (zircon) is prepared by heating to at least 700 DEG C. in a non-oxidizing or reducing atmosphere a mixture of sodium silicozirconate, and a basic zirconium sulphate of formula SO3.2ZrO2.nH2O where "n" is small but variable, with a vanadium compound and sufficient silica to provide an overall SiO2:ZrO2 molar ratio of approximately 1:1. The reaction mixture preferably contains sodium silicozirconate, Na2O. ZrO2.SiO2, a basic zirconium sulphate of formula SO3.2ZrO2, and silica in the molar ratio of 1:1:2, together with 2% to 4.5% preferably 2.5% by weight of a vanadium compound (as V2O5 based on the sum of zirconia and silica in the mixture). The preferred vanadium compound is ammonium vanadate. The preferred atmosphere is an inert or reducing gas, and the calcination is preferably performed in a graphite saggar. Specified atmospheres are nitrogen and carbon dioxide. Sodium sulphate may be added to the mixture before calcination, in an amount such that the calcined product contains for example 10% to 50%, preferably 32-34% by weight of sodium sulphate, and the calcined product is washed free from sodium sulphate with water. The above pigments may be used, e.g. in a proportion of 10% by weight, in a fritted enamel of composition by weight, 39.0% orthoclase, 5% English kaolin, 26% ground quartz, 5.0% CaCO3, and 7% ZnO, 0.5% BaCO3, and 16.3% sodium silicozirconate which is fired at a temperature of 1120 DEG C. to give a blue enamel facing on an earthenware tile.