Kinetics of electrodeposition of NiP, CoP and NiCoP coatings depending on sodium hypophosphite concentration
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2018-01-01
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Abstract
The effect of NaH2PO2 concentration in the electrolyte (pH = 2) on the kinetics of NiP, CoP and NiCoP alloys electrodeposition at room temperature was studied. It was established that at concentration of NaH2PO2 about 0,2 M the deposition rate of NiP alloys decreases; the deposition rate of CoP alloys increases but at the same time the quality of the coating becomes bad. In both cases it was observed a depolarizing effect on the deposition. With increasing of the content of NaH2PO2, the phosphorus content in NiCoP alloys increases to approximately 7 % and the current efficiency of electrodeposition (CEE) goes over 100 %. The comparison of the kinetic data with those of CEE of NiCoP coatings showed that the mechanism of deposition is mixed chemical-electrochemical.