Production of an anticorrosive pigment on phosphate basis

摘要

The invention relates to the production of phosphorus- containing anticorrosive pigments with a particle size of at most 20 microns by reacting one or more calcium or magnesium compounds with phosphoric acid or acid alkali metal or ammonium phosphates by intimately mixing an aqueous suspension or solution of the reactants inside a dispersing means rotating at a speed of 3000 to 10,000 rpm. More particularly, fine pulverulent calcium and magnesium compounds are converted, with agitation, together with water and, if desired, a water- soluble alkanol to a homogeneous suspension or solution. The suspension or solution is intimately mixed, inside the dispersing means at 0 to 40 C. and in an approximately stoichiometric ratio, with the phosphoric acid or acid phosphate solution. Resulting and precipitated pigment is separated and dried under mild conditions while maintaining its content of water of crystallization. The anticorrosive pigment is comprised of a homogeneous mixture and/or mixed crystals of which 10 to 95 mol % is calcium hydrogen phosphate dihydrate, the balance being magnesium hydrogen phosphate trihydrate. An at least 55 weight % proportion consists of particles with a size of up to 5 microns with a BET-surface of at least 1 m.sup.2 /g.