Studies On The Improvement Of Synthetic Process Of Zinc Phosphate Pigment And Its Anti-Corrosive Properties

As an environment-friendly anti-corrosive pigment, Zinc phosphate shows good water and corrosion resistant properties as well as chemical resistant and flash effect. Because Lead and Chromium based anti-corrosive pigments cause severe environmental pollution problem, more and more attentions have been paid on Zinc Phosphate pigment and a large number of researchs have been made since 1990s. After reviewing these published papers within the last ten years, the processes of mirconization, Ammonium Carbonate leaching method and microwave synthesis of Zinc phosphate had been investigated. For the first process, industrial grade zinc oxide was predissolved in acetic acid. Then phosphoric acid was added under the existence of surfactant to prepare fine Zinc Phosphate. The mechanical disintegrator operation is not required compared to the traditional technology. The wetting angles of Zinc phosphate with different surfactants were measured and the corresponding wetting Gibbs free energy change AG were calculated, and showed that OP-10 is the best wetting agent. It was concluded from the adsorption of OP-10 on Zinc Phosphate that the surfactant was helpful to diminish the size of Zinc Phosphate particals. For the second technics, Ammonia/Ammonium Carbonate mixing solvent was used to dissolve low grade Zinc Oxide to produce Zinc ammonium complex, which reacted with phosphoric acid to make Zinc Phosphate. Such a method had a remarkble decrease in product cost (less cost 1301/t). In the microwave process, the microwave radiation took as a heater. Comparing with the direct electric heating, the percent conversion of Zinc oxide was remarkably increased. The unreaction of Zinc Oxide down from 16% to 1% with 48.8% energy saving.All products were analyzed with X-ray diffraction, DTA, IR and chemical analysis.The results showed the products of micronization process and Ammonium Carbonate leaching method are the mixture of Zinc Phosphate dihydrate and tetrahydrate. The product of microwave process is pure Zinc Phosphate dihydrate. The chemical analysis indexes accorded with the standard of anti-corrosion pigment. The improved processes present here solved the both problems of high unreaction rate of Zinc Oxide and big particle in product from traditional technology.The test methods for commercial solvent type paint were introduced in the test of prepared Zinc Phosphate. Comparing with the traditional pigment such as Lead red, Zinc chrome yellow and lead-containing Zinc Oxide, the anti-corrosion performance of all prepared products were better than Zinc oxide and similar to the other two pigments. While the fine Zinc phosphate was used to prepare the water base paint, a better storage stability was obtained. As a result, the non-toxic water base paint can be produced with fine Zinc Phosphate in the case of not any toxic Zinc chrome or lead red pigment.