Preparation and properties of chromium Dacromet coating solution
|School||Kunming University of Science and Technology|
|Keywords||Chrome-free Dacromet Acid system Coating solution Corrosion resistance|
The Dacromet technology is a high corrosion resistance to hydrogen embrittlement and environmental pollution, metal surface corrosion of new technologies, since its inception in they will have a very wide range of applications. However it still exist certain shortcomings and deficiencies, the need for further research and improvement. From the environmental perspective, hexavalent chromium is the biggest problem, because it's highly toxic and carcinogenic effects, so many brand vehicles in the automotive industry in the industrial countries in the world take the lead in developing technical standards using chromium coating Dacromet applications in other industries are beginning to develop in the direction to the low chromium and chromium-free, looking for chrome-free alternative to the various aspects of performance are more excellent dacromet technology development direction. The purpose of this study is the acid system through experiments looking for a chrome-free, instead chromium Dacromet coating liquid of chromic acid was prepared by a water-soluble chromium Dacromet coating liquid, the use of this coating liquid Preparation The coating has a certain anti-corrosion properties. The main contents of the thesis Dacromet coating solution preparation the chromate system selection and chrome. No the chromate System Selection is based on chromium acids or salts of the same family as the base, adding organic or inorganic acid formulated as a chromium-free acid system. Acid system compatibility and stability test study to determine the acid system; using orthogonal experiment method to determine the formula of the acid system. The results show that the aqueous solution consisting of sodium molybdate, boric acid, formic acid, on the ground without chromate system. The best formula is sodium molybdate 10wt%, boric acid 1wt%, formic acid 8wt%. The sodium molybdate acid system the greatest impact on coating performance, boric acid, followed by formic acid minimum. Orthogonal test chrome-free Dacromet coating liquid formulations and processes. The acid system, zinc powder, aluminum powder, polyethylene glycol, and the sintering temperature and time as a factor to consider the appearance of the coating adhesion and 5% NaCl immersion test as an index. Designed the orthogonal experiment Table L 27 (3 13 sup>) test to determine chromium Dacromet coating liquid formulations and processes. Research component of the coating of the coating solution by orthogonal experiment sintering process, and detected by coating performance, no chromium coating and chrome coating study comparing the results showed that the prepared chromium Dacromet coating solution The optimal value: zinc powder 300g / L, aluminum powder, 70g / L, the mixed acid 40g / L, polyethylene glycol, 180g / L, the process is the sintering temperature of 300 ° C, sintering time 30 minutes. Chrome-free coating system 5% NaCl soaked red rust 1500h, neutral salt spray test 720h. Coating surface morphology and cross-section morphology using optical microscope and scanning electron microscopy (SEM), the results showed that the coating is uniform, continuous matrix close. Coating elemental composition and the phase composition, by a spectrum analyzer and an X-ray diffraction analysis, the results showed that: there are a large number of Zn and Al in the coating, their total amount exceeds 70%, the coating plays a sacrificial anode protective effect of corrosion effects of Zn. Coating still exist in the mass percentage is about 20% of the oxygen element, and Zn, Al is formed between the oxide effective passivation. In summary, the present experimental system got excluding acid system and a water-soluble chromium chromium Dacromet coating liquid to obtain a coating of the coating liquid with a certain corrosion resistance. Through this study, chromium Dacromet the preparation of the coating solution to provide a new method for further research and improved chromium Dacromet coating solution has a certain reference value.