New Synthesis Methods Of Zinc Phosphate And Properties Evaluation Of Phosphates In Anti-corrosion Coatings

The low/non-toxic phosphate pigments, as an efficient alternative toreplace the toxic heavy metals pigment, have received a great deal ofrecent attention because of their excellent anti-corrosive abilities.However, a lot of problem of these phosphates such as controllablesynthesis, practical application formula still remain to be unsolved.In this paper, both hydrolysis precipitation and organic solventprecipitation were used to synthesize zinc phosphate. The corrosioninhibitions and possible abate mechanisms of five typical pigments inthree typical anti-corrosion coatings system were exposed. The majorstudies and conclusions are as follows:（1）Zinc phosphate was preprared by hydrolysis precipitation ororganic solvent precipitation using ZnO and H₃PO₄as regents, andprocess conditions was obtained through the orthogonal experiments, andcontent of Zn products was determined by EDTA method. The obtainedproducts were characterized by XRD, SEM, Raman and IR. The resultsshow that the technology conditions of hydrolysis precipitation are:reaction temperature90-100℃, reaction30min, ZnO: H₃PO₄=1.8:1（molarratio）, Phosphoric acid of43%. The technology conditions of organicsolvent precipitation are: reaction temperature90-100℃, reaction30minand Phosphoric acid of43%. Both the two mehods can be used to preparelamellar zinc phosphate, which has the same molecular formula ofZn₃（PO₄）₂·4H₂O.（2） In epoxy zinc-rich epoxy paints, composite zinc phosphate wasused to replace the zinc powder by orthogonal design experiment. Zinc phosphate, APW-I, zinc molybdenum, APW-I:molybdenum acid=7:2（mass）, zinc molybdate were:zinc phosphate=7:2:2（mass） were used toreplace composite zinc phosphate. Inhibitions of the coatings containingthe five pigments in3.5%NaCl were investigated by electrochemicalimpedance spectra. The anticorrosion properties of these pigments wereobtained by the combination to the immersing times test in3.5%NaCl.The results show that composite zinc phosphate can replace zinc powderin zinc-rich epoxy paints used to prepare epoxy zinc powder primers.Cooperative of both zinc powder and organic coatings improve theanticorrosion abilities of epoxy zinc powder primers. The anticorrosionproperties of five pigments are superiors than that of composite zincphosphate, and APW-1is the best one.（3） In chlorinated rubber antirust coating, zinc phosphate, APW-I,zinc molybdate, APW-I: molybdenum acid=7:2（mass）, zinc molybdatewere: zinc phosphate=7:2:2（mass） were used to replaces compound zincphosphate. The electrochemical performance test of the coatings in3.5%NaCl was dectected. The results show that the corrosion resistance are indecremental order:APW-I:zinc molybdate:zinc phosphate=7:2:2（mass）,zinc phosphate> APW-I:zinc molybdate=7:2, APW-I> zinc molybdate.（4） In automotive chassis coatings, composite zinc phosphate werereplaced by zinc phosphate, APW-I, zinc molybdate, APW-I:zincmolybdate:zinc phosphate=7:2:2（mass）, APW-I: zinc molybdate=7:2（mass）, and its corrosion resistance was evaluated by electrochemiacaltest. The results show that the anticorrosion property of five antirustpigment better than composite zinc phosphate, stability and corrosionresistance of zinc phosphate and APW-I: zinc molybdate: zinc phosphatein the whole of soaking period is excellent.