Study On The Novel Process And Cathodic Process Of Nickel Composite Electrodeposition

Corrosion is one of the main forms which disable the function of meterials. Meterial Corrosion caused great harm, namely it bring economic losses and many serious accidents, consume a large amount of valuable resources and energy and pollute environment. The process of Composite electrodeposition is one of surface protection technology and only need simple equipment that is operated easily, low temperature. Which Composite coatings not only can improve corrosion resistance, wear resistance, oxidation resistance at high temperature and other properties of metal surface, but also can save materials, energy and manufacturing cost, it is widely used in the machinery, electronics, and other fields. The goal of this article is to obtain the nickel sealing process of good corrosion resistance of coatings and high stability of nickel sealing bath. The specific research contents and conclusions are as follows:1. Select the appropriate nickel sealing particles. Composite plating ((also called as nickel sealing) that were done in bright nickel plating bath that that were added nano-Al2O3 powder, nano-Al2O3 emulsion, nano-TiO2 powder and SN-B respectively can be prepared bright nickel-based composite coating, leading to multilayer nickel/chromium composite coatings featuring a micropore density above 1×104 numbers/cm2. SN-B particles have good suspension and stability in the bath, the obtained multilayer nickel/chromium composite coating has the maximum micropore density, the most uniform distribution of micropore on plane surface and the best corrosion resistance. Micropore of the obtianed chrorium coating from the nickel sealing bath containing transparent nano-Al2O3 liquid and nano-SiO2 powder are very few. It is results that SN-B is the best nickel sealling particles.2. Choose the suitable dispersant. Different dispersants were added to nickel sealing bath respectively and were studied effect on the appearance of the composite coating, Micropore density of chromium coating and stability of nikel sealing. the results showed: small organic molecules dispersants can disperse particles and improve the stability of the plating solution hardly; most of polymer dispersant can make the appearance of composite coatings become worse and the number of micropore of the chromium coating is reduced;, although micropore density of chromium coating reduced slightly, SN-A can improve the uniformity of the miropore distribution of chromium coating in complex parts surface and the stability of nickel sealing bath. It is results that SN-A is the best dispersant.3. Single factor experiment determined the appropriate compositions of nickel sealing bath consist of NiSO4·6H2O 250～350 g/L, NiCl2·6H2O 30～70 g/L, H3BO335～45 g/L, the blight agent HN-TP10.08～0.2 mL/L, the auxiliary agent HN-TP25～10 mL/L, the wetting agent HN-191-2 mL/L, the dispersant SN-A 0.1-0.3 g/L, the nickel sealing particles SN-B 0.02-0.08 g/L; the optimum conditions of the nickel sealing process are as follows:cathode current density 4-8 A/dm2, pH 3.8-4.2, temperature 45-55℃, plating time 2 min, complex parts can be increased plating time.4. By studying adhesion, hardness, corrosion resistance and other properties of composite coating can be found that adhesion between brass and composite coating, composite coating and the bright nickel layer is very good, the hardness of composite plating, bright nickel layer and brass substrates were 445.2 HV,408.8 HV and 141.1 HV respectively that show composite coating embedded SN-B particles can increase the hardness. SEM and EDS analysis can know nickel composite coatings and the surface composite coatings and bright nickel coating is roughness, bright and fine structure, and composite coatings are uniformly dispersed a large number of particles and composite coatings have some pore. Tafel curves and electrochemical impedance spectroscopy that were obtained in different solutions show that corrosion resistance of composite coating in acidic and neutral media is better than bright nickel coating, and composite coating slightly worse than the bright nickel in alkaline medium, multilayer nickel/micropore chrome composite coating are easier corrosion in neutral, acidic and alkaline media, but because of the presence of large number of micropores of chromium coating that can disperse corrosion current and reduce corrosion rate, corrosion resistance of multilayer nickel/micropore chrome composite coating are better than multilayer nickel/chrome composite coating in the three corrosion medium.5. Studying cathodic process of nickel electrodeposition by Electrochemical Workstation found cathodic polarization curves show that the blight agent can increase the nickel electrodeposited cathodic polarization, and can accelerate coating nucleation rate, reduce the grain size and increase the surface smooth and bright of coating, SN-B and SN-A have no influence on nickel electrodeposited cathodic polarization and Electrochemical impedance spectroscopy show that the blight agent can increase electrochemical impedance of the reduction of nickel ions and cause the coating becomes bright; SN-B and SN-A have little effect on electrochemical reaction resistance of nickel electrodeposition, but SN-B can increase the resistance of the solution. Cathodic polarization curves and electrochemical impedance spectroscopy analysis results are consistent.6. A simple, economical and novel process of nickel sealing of new technology was explored on the basis of previous study of the nickel sealing particles of commercially available nanoparticles, namely the bath containing barium sulfate particles for nickel composite plating (nickel sealing) was prepared by dropping barium complexant solution directly to normal bright nickel plating bath, and multilayer nickel/chromium composite coatings featuring a micropore density above 6×104 numbers/cm2 can be obtained after nickel seal plating. By single factor experiment results the optimal process conditions of preparing nickel sealing bath are as follows:dosage 10 mL/L, dropping rate 30 s/mL, stirring intensity grade 4, and temperature 40℃. The results of CASS salt spray test showed that multi-layer nickel/micropores chrome have good corrosion resistance. Although this process of nickel sealing have many advantage, such as briefness, low cost, maintenance and so on, microporous density is less than 1×104 numbers/cm2 when the bath stand three days and the stability of nickel sealing bath is very bad, so it is difficult for the novel process of nickel sealing to be used in actual production.