Preparation of nanocrystalline aluminium phosphate as an anticorrosive pigment

AlPO(4) was synthesized in reaction of H(3)PO(4), NH(4)H(2)PO(4) or (NH(4))(2)HPO(4) with solid Al, Al(2)O(3) and Al(OH)(3) or aq. soln. of Al(2)(SO)(3) optionally in presence of citric acid at 20-90 degrees C and pH 3.7-10 (Al:PO(4)(3-) ratio 1:1 or 1:3) with following calcination of the ppts. at 100-1000 degrees C. Chem. purity of the AlpO(4) crystals, their size and crystallinity were detd. Neither pH, nor raw material concn. nor reaction temp. influenced the product quality. The av. size of AlpO(4) crystallites calcinated at 200 degrees C was 28-45 nm. The particle size was 0.14 to 0.31 mu m.