The difference of corrosion resistance between aluminum tripolyphosphate and zinc phosphate
As an anti-rust pigment, aluminum tripolyphosphate has the characteristics of good water resistance and strong corrosion resistance, but also can enhance the properties of flame retardant, shock absorption, pressure resistance, etc., so it is used in different resins made of metal sheet protection with anti-corrosion coatings, is the current application prospect of anti-rust pigments. However, since aluminum tripolyphosphate is a kind of weak acid strength and high acidity Lewis solid acid, and most of the resins used in water-soluble paint are carboxylic acid, which is neutralized by ammonia before being dissolved in water, so it is a more alkaline polymer, if the selected pigment is acidic, it is often possible to promote the acidification of water-soluble paint, resulting in condensation and destruction. So aluminum tripolyphosphate can't be used directly as a pigment. At present, aluminum tripolyphosphate products have some disadvantages, such as large particle size, wide particle size distribution, irregular morphology, high raw material cost and bad production process. In addition, due to the aluminum tripolyphosphate anti-rust pigments slightly soluble in water and poor hydrolysis, aluminum tripolyphosphate root ion dissociation speed is slow, the effect delay, although it is a long-term anti-rust pigment, but can not overcome the problem of "flash rust", can not replace the traditional toxic chromium, lead anti-rust pigments. In order to improve the actual anti-rust properties of aluminum tripolyphosphate anti-rust pigments, it is necessary to modify the particle size and morphology; It is a chemical modification, that is, increasing Zn2+, Ca2+ cations; Third, the preparation of composite phosphate pigments, using the synergistic effect between different kinds of pigments, to enhance the strengths and avoid weaknesses, purposefully improve the performance of the single system anti-rust pigments, not only overcome the problem of "flash rust", but also reflect the long-term anti-rust effect of aluminum tripolyphosphate. Firstly, the intermediate aluminum tripolyphosphate was prepared and reacted with ZnO and Ca(OH)2 under ultrasonic environment to prepare the modified aluminum tripolyphosphate fine powder. The effects of factors such as zinc-calcium ratio, reaction temperature and ultrasonic radiation on the reaction process and the final product were investigated. Finally, the conditions for preparing aluminum tripolyphosphate with good dispersibility were determined. After years of research and development, the researchers analyzed and discussed the rust prevention mechanism of the pigment. In the early stage of immersion, the current density changed greatly, which indicates that in the early stage of immersion, aluminum tripolyphosphate just began to decompose slowly and gradually diffused to the metal-coating interface. In order to react with Fe2+ and Fe3+ to form a protective film, its dissociation and expansion of II II need a certain time. As the aqueous solution passes through the coating, zinc phosphate, zinc calcium phosphate, etc., gradually hydrate, and miscible with the alkyd resin to form a complex phase, thus reducing the gap of the coating film, further improving the shielding and protection effect of the coating, and the current density tends to be flat. In the later stage, the current tends to be stable, and the tripolyphosphate ion P3010 u000E, which has a strong ability of water dissolving 5-exit complexation, has a strong complexation ability with Fe2+ and Fe3+, and forms a complex and dense MxFey(PO4)z passivation protective film on the steel surface. Thus passivating the metal. The application experiment shows that the modified aluminum tripolyphosphate has better anti-rust performance than the commercial anti-rust pigment. The experimental results show that the modified water-based aluminum tripolyphosphate can be used as an ecological anti-rust pigment in the coating industry, and the synergistic effect with zinc phosphate has a wide range of application, and the anti-rust effect has a greater improvement.