Dacromet Coating Technology Formulation Research

As a metal corrosion technology, DACROMET technology was derived from foreign country in 1960 and introduced into china in 1990. Because of its advantages in high corrosion resistance, no hydrogen brittle, less pollution, high temperature resistance and uniform coat, it has been used widely in many fields. In this paper, the origin of this technology, development, present research situation and developing direction was reviewed. The performance character of film, technical process and equipment of this technology was introduced too. It is significant to study the compositions of coating solution and mechanism of coat formation and corrosion resistance for DACROMET technology.Main compositions in coating solution and operation conditions that influence DACROMET technology were studied with systemic experiment in this article. Meanwhile, the element composition, phase composition and structure of the coat were analyzed systematically using XRD, SEM, EDS and XPS. Based on this work, the mechanisms of film formation and corrosion resistance for DACROMET technology were preliminary discussed. The results showed:1. The finer zinc powder in coat solution and more uniform coat will lead to a higher corrosion resistance. The corrosion resistance of coat prepared with flake zinc powder was higher than that prepared with grainy zinc powder. The optimal content of zinc powder in coating solution was 270~330g/L. Aluminum powder, whose optimal content in coating solution was 30g/L, mainly played a role in improving outward appearance of coat.2. Mixed chromic acid in coat solution had a better effect than sole chromic acid in coat solution. Meanwhile, when the mass ratio of chromic acid to boric acid was 4, not only the appearance of coat was improved, the bonding force and corrosion resistance of coat were greatly enhanced. The optimal reducing agent was acrylic acid whose optimal content range in coating solution is 40ml/L~60ml/L.3. The pH of coating solution adjusted by ZnO should be controlled between 3.5-5.5. The optimal preliminary baking condition was 20-25 minutes of baking time under 80℃-90℃ of baking temperature. The optimal sintered condition shouldbe 20-40 minutes of solidifying time under 300°C of solidifying temperature.4. The color of prepared uniform andsmooth DACROMET coat appeared from silvery white to silver gray. The experiment time of corrosion resistance for ammonium nitrate can reach 120 minutes and 1000 hours for salt fog without appearing rust. Meanwhile, the bond strength between coat and substrate is very well. These excellent performances which were slightly better than alike production reached the requirement of international standard. The content of chromium in coat is 3.5.%-4.5% which was decreased greatly compared with that of alike production which can reach 8%. This was according with the international trend of environment protection.5. The structure of coat was systematically analyzed from many sides. The main elements in coat were chromium which existed with the form of oxide, zinc and aluminum which existed with the form of elementary substance. The oxide of chromium with amorphous form is nCr2O3*mCrO3 which plays a role as bonding agent tightly combining flake zinc powder, aluminum powder and substrate. Based on all of the work illustrated above, the mechanisms of coat formation and corrosion resistance for DACROMET technology were successfully explained.