Microstructure And High Temperature Oxidation Behavior Of Mn-Ni Coatings Fabricated By Electrodeposition

In this paper, electroposition of Mn–Ni alloys on stainless steel surface hasbeen studied. The effects of different agent concentrations, current densities, saltconcentrations on the coating morphology and composition have been carried out.The morphology and composition were analyzed via Scanning electron microscopeand Energy spectrum characteriation. To increase the content of manganese ofcoating, double–complexing agents were applied. The optimized parameter wasachived by subsequent pre-oxidation. In this optimized process, content ofmanganese is up to30%. Oxidation performance test was done by weight gaincharacterization and the mechanism of oxidation was studied.The results showed that, to get homogeneous alloy coating, the concentration ofcomplexing agent must be higher than metal cation. Once the contentration is belowgoal concentration, the bath will be of instability. A substantial increase ofmanganese content in coatings can be got via the increase of intensity. As theincrease of current density, the manganse content will increase too.Electrodeposition process parameters were optimized through morphology andcomposition after the pre-oxidation experiment. In this process, this technology canget30%manganese content in the alloy coating. Then the coating sufferedsubsequent cycle high–temperature oxidation. This paper studied their oxidationresistances and their conductivities at high temperatures, and found that theoxidation resistances were significantly improved with the oxidation rate constant of3.2631×10^–8g²·cm^–4·h^–1, SEM and X–ray diffraction analysis of oxide morphologyand micro–structure after cyclic oxidation were applied, the results suggested theoxide coating was mainly composed of the outside nickel–manganese spinel layerand the inner chromium oxide layer, The cross–section spectrum analysis of oxideshowed that the outside oxide did not contain chromium, this double oxide layer canprevent the volatilization of chromium to the surface, The area specific resistance ofoxide coating after200h oxidation was13Ω·cm², and it was less than the fuel cellconnection material requirement under the high temperature oxidation. Ultimately,the studies above proved the Ni–Mn alloy coating by electrodeposition system canbe used as a connection material of the fuel cell.