Synthesis And Application Of Hydroxyapatite Coated By Nano-oxide Anticorrosive Pigment

As a new-type anti-rust pigment, phosphate is superior to traditional anti-rust pigments inmany features. Besides the excellent resistance against water and corrosion, phosphatepigment also provides other properties, such as enhanced shock absorption, resistance againstcompression, wearing, and flame. To date, the phosphate has been widely applied to variousantirust paints and is considered to be the most promising antirust pigment. At present, mostphosphate antirust pigments are mainly composed of zincate and aluminate. Due to thelimitation of nature of pure phosphate, its antirust performance as a kind of antirust pigmentcannot reach the expectation. After mixed and modified by other inorganic ions, such ascalcium, strontium or iron, the modified phosphate shows ideal antirust properties. Therefore,it can be assumed that the modified zinc phosphate with calcium presents improves antirustperformance, and calcium phosphate as the antirust pigment also has very good performancewhich is proved by practice.First, hydroxyl calcium phosphate was prepared by precipitation method at roomtemperature. As phosphoric acid is a triprotic weak acid, the products are changeful anduncertain. The influence of acid base titration sequence, calcium phosphate proportion,acid-base concentration, titration rate and reaction temperature on final products wereinvestigated, and the optimum conditions for single calcium phosphate was determined. XRD,SEM, and grading analyzer were used to represent the structure and morphology ofas-obtained samples. One can see that a single particle is ball-shaped with30-50mm indiameter and makes up bar shape in regular way. Grading analysis shows that the size ofsecondary particles is400-500nm and distributed evenly. The samples were put into alcoholacid water-based antirust paint and subjected it to anti-salt spray test. It can be found that theanti-salt spray ability of sample is equal to the commercial zinc phosphate, but still has somedistance from ZPA pigment made in Germany.It is found from the production of tradition antirust paint that the mixing and matching ofantirust pigments are very significant to coating performance. The pigment with large particle size and cheap price serves as the main component and another type or several types ofmaterials of small particle are treated as dispersive auxiliary materials. This way can meet thepurpose of “mixing” and “matching of particle size”. The second step of experiment was tomodify the coating property of as-produced hydroxy calcium phosphate. Nano zinc oxide,nano iron oxide, and nano nanometer titania were used to modify the single-element andmulti-element coating property of hydroxy calcium phosphate. Meanwhile, barium sulfate andtalcum powders were added to improve the oil absorption of nano coating pigment. Sampleswere represented by XRD and SEM. XRD analysis indicates that hydroxy calcium phosphateis the main component of sample, together with the characteristic peaks of barium sulfate andsilicate. SEM diagram shows that single particle still has a ball shape and particles form a barshape in regular way. Hydroxy calcium phosphate modified nano coating was put into alcoholacid water-based paint for antirust application. The result shows that the antirust capacity ofsample coated by single oxide is superior to uncoated sample, but inferior to German APZpigment. The antirust capacity of sample coated by multiple oxides is much higher than thecommercial antirust pigments, resistance against salt increased to240h from144h, equal tothe performance of imported ZPA antirust pigment from Germany. The cost is only3000RMB/t, much lower than the zinc phosphate priced8000RMB/t in the market and theGerman imported ZPA priced60000BMB/t.