Impact of the phosphorus concentration on the morphological and corrosion behaviour of Ni-P, Co-P and Co-Ni-P electrodeposits

This work reports the results of a study on the effect of NaH2PO2 concentration as a phosphorus source on the properties of the Ni-P, Co-P and Co-Ni-P electrodeposits compared to Ni, Co and Co-Ni deposits. Binary and ternary alloys were electrodeposited from sulphate baths without additives at room temperature. The elementary analysis of the alloys determined by X-ray fluorescence spectroscopy (XRF) confirms the induced deposition type of the P with Ni and Co; where the P content depends strongly on the operational conditions. Morphological investigation conducted by atomic force microscopy (AFM) and scanning electron microscopy (SEM) shows that the addition of P has a smoothing effect on the Ni-based deposits and a magnification effect on the Co-based deposits. X-ray diffraction (XRD) analysis reveals that the deposits have a crystalline structure for deposits with low P content (< 11 wt-%) and amorphous structure for deposits with high P content. The incorporation of P atoms into the deposits has significantly improved their corrosion resistance according to the corrosion parameters determined by Tafel plot analysis.