Development of Ni-based coatings for corrosion protection

Abstract

Zn, Ni, and Mn are commonly in various industries for their unique properties. The present study, investigation the electrodeposition of Ni−Mn and Zn−Ni−Mn coatings onto a Cu substrate using a sulfate bath at ambient temperature, with a special focus on the effect of deposition potential and [Mn2+], on the coatings' nucleation, chemical composition, surface morphology, crystalline structure, and corrosion resistance. The coatings have been prepared and characterized using various techniques, including, CV and, CA. The nucleation and growth processes were investigated based on Scharifker and Hills' (S-H) model. The investigation demonstrates that the deposition potential and [Mn2+] had significant effects on the nucleation mode of Ni−Mn and Zn−Ni−Mn alloys. (EDX) analysis of Ni-Mn coatings indicates that an increase in [Mn2+] led to changes in the weight fractions of Ni and Mn in the coatings. The Ni content decreased from 96.9 to 94.1 wt.%, while the Mn content increased from 1.5 to 4.6 wt.%. Sulfur content remained constant at approximately 1.5 wt.%. For Zn−Ni−Mn coatings, the co-deposition behavior was anomalous, with Zn as the major element and its content ranging from 55.7 to 69.7 wt.%. Ni content varied from 37.7 to 22.2 wt.%, while the Mn content increased from 1.6 to 4 wt.%, and the S content decreased slightly from 5 to 3.4 wt.%. (SEM) showed that Ni−Mn coatings were uniform with a cauliflower-like morphology, globular-shaped particles, and a porous cracked surface, while the ternary Zn−Ni−Mn coatings had a compact and dense morphology with good uniformity, no cracks, and pyramidal-shaped particles. The crystal structure of XRD is primarily composed of Ni-Mn solid solution and nickel, exhibiting preferred orientations in the FCC structure, specifically along the (111), (200), and (220) planes. The phase diagrams ofZn−Ni−Mn alloysrevealed the presence of both η-Zn and NiZn3 phases in Zn−Ni−Mn coatings, which enhance their corrosion resistance. Corrosion resistance was studied using LTP and (EIS). The optimized chemical composition for the most corrosion-resistant Ni-Mn coating was estimated as Ni 96.9 and Mn 1.6. In contrast, the optimized composition for the Zn-Ni-Mn coating included55.7 wt.% Zn, 37.7 wt.% Ni, and 1.6 wt.% Mn. After 2 weeks of immersion in saline solution, SEM and XRD investigations reveals that the coatings offer effective cathodic protection through the formation of a protective oxide layer consisting of MnO2 oxide and Ni (OH)Cl2hydroxide. exhibiting a non-uniform, with highly porous microstructure, and Zn−Ni−Mn coating showed the formation of Zn5(OH)8Cl2, ZnO, and ZnMn2O4 oxide and hydroxide chloride phases with a non-homogeneous highly porous morphology.