Improvements in or relating to a process for the preparation of cadmium yellow pigments

摘要

A cadmium yellow pigment, viz.: a mixed sulphide of Cd and Zn, is prepared by calcining in a non-oxidizing atmosphere a mixture of (a) zinc sulphide, (b) cadmium sulphide and (c) an oxide of cadmium and/or of zinc or a material capable of yielding such oxide(s) on calcination, the mixture having incorporated therein either before or during the calcination a quantity of uncombined sulphur. The oxide (c) and the uncombined sulphur preferably constitute from 3 to 47 mol. per cent of the calcination mixture, and the molar ratio of oxide or oxide forming material, (c) to uncombined sulphur is in the range of from 1: 1 to 1.5: 1. The mixture which is calcined is preferably prepared by reacting in aqueous solution a water-soluble zinc salt, a water-soluble cadmium salt, a water-soluble sulphide of an alkali metal or alkaline earth metal or ammonium sulphide, an aluminate, silicate hydroxide or carbonate of an alkali metal, alkaline earth metal or ammonium, and sulphur, and separating the precipitated solids from the solution to form said mixture. The water-soluble sulphide is preferably the molar equivalent of the cadmium sa and the uncombined sulphur and the aluminate, silicate, hydroxide or carbonate are together the molar equivalent of the zinc salt. The specified sulphides are those of sodium, barium or ammonium, and sodium hydroxide, barium hydroxide, sodium carbonate, ammonium carbonate, sodium aluminate and sodium silicate are also specified reagents. A specific reaction mixture is given as zinc nitrate, cadmuim nitrate, barium sulphide, barium hydroxide, and sulphur. The zinc salt and the aluminate, silicate, hydroxide of carbonate may be replaced by an amount of zinc oxide equivalent to the zinc salt. The uncombined sulphur maybe added after the commencement of the calcination, and the mixture may be calcined at a temperature of 800 DEG to 1000 DEG F. before the addition of sulphur, and at 500 DEG to 800 DEG F. after the addition. These pigments are alleged to be much stronger than those previously known, and they show an increased gloss which makes them advantageous for use in printing inks and increased transparency which is advantageous in applications to such materials as plastics and synthetic fibres. The preferred Zn/Cd ratio is from 0.428: 1 to 0.018: 1.ALSO:A cadmium yellow pigment, viz. a mixed sulphide of Cd and Zn, is prepared by calcining in a non-oxidizing atmosphere a mixture of (a) zinc sulphide, (b) cadmium sulphide, and (c) an oxide of cadmium and/or of zinc or a material capable of yielding such oxide(s) on calcination, the mixture having incorporated therein either before or during the calcination a quantity of uncombined sulphur. The oxide (c) and the uncombined sulphur preferably constitute from 3 to 47 mol. per cent of the calcination mixture, and the molar ratio of oxide or oxide forming material (c) to uncombined sulphur is in the range of from 1:1 to 1.5:1. The mixture which is calcined is preferably prepared by reacting in aqueous solution a water-soluble zinc salt, a water-soluble cadmium salt, a water-soluble sulphide of an alkali metal or alkaline earth metal or ammonium sulphide, an aluminate, silicate hydroxide or carbonate of an alkali metal, alkaline earth metal or ammonium, and sulphur, and separating the precipitated solids from the solution to form said mixture. The water-soluble sulphide is preferably the molar equivalent of the cadmium sa and the uncombined sulphur and the aluminate, silicate, hydroxide or carbonate are together the molar equivalent of the zinc salt. The specified sulphides are those of sodium, barium or ammonium, and sodium hydroxide, barium hydroxide, sodium carbonate, ammonium carbonate, sodium aluminate and sodium silicate are also specified reagents. A specific reaction mixture is given as zinc nitrate, cadmium nitrate, barium sulphide, barium hydroxide, and sulphur. The zinc salt and the aluminate, silicate, hydroxide or carbonate may be replaced by an amount of zinc oxide equivalent to the zinc salt. The uncombined sulphur may be added after the commencement of the calcination, and the mixture may be calcined at a temperature of 800 DEG to 1000 DEG F. before the addition of sulphur, and at 500 DEG to 800 DEG F. after the addition. These pigments are alleged to be much stronger than those previously known, and they show an increase gloss which makes them advantageous for use in printing inks and increased transparency which is advantageous in applications to such materials as plastics and synthetic fibres. The preferred Zn/Cd ratio is from 0.428:1 to 0.018:1.