ZnNi alloy electrodeposition from acid baths containing sorbitol or glycerol and characterization of ZnNi deposits

Abstract

The influence of sorbitol or glycerol on the electrodeposition of ZnNi alloys and on the morphology, composition and structure of the ZnNi deposits was investigated. The highest current efficiency (CE), around 90%, was obtained in the presence of glycerol in the potential range from approximately −1.30 V to −1.40 V, while in the presence of sorbitol or absence of either polyalcohol the CE was 82-85%, for the same potential range. Scanning electron microscopy (SEM) analysis showed that ZnNi deposition at −1.26 V or −1.40 V from a bath with sorbitol led to the formation of more compact deposits than with glycerol. Energy dispersive X-ray spectroscopy (EDS) analysis showed that the Ni content in the deposit obtained in the presence of sorbitol remained in the range of 7-9.5 wt% Ni, over a large range of deposition conditions. On the other hand, ZnNi deposits with variable Ni content (5.5-19.5 wt% Ni) were obtained from baths with glycerol or without either polyalcohol, by shifting the deposition potential. All ZnNi deposits showed uniform distribution of the elements Zn and Ni. X-ray analysis of ZnNi deposits obtained from plating baths with and without polyalcohol's at −1.26 and −1.40 V presented the γ, γ 1 and Pt 3 -Zn phases.

Study of the influence of the polyalcohol mannitol on zinc electrodeposition from an alkaline bath

“…The Ni content in the ZnNi deposits produced in the presence of mannitol was raised from 6 to 10 wt% in the potential range -1.26 to -1.40 V. It was suggested that the ZnNi deposits obtained in these baths probably offered sacrificial protection to the substrate (steel). Also, these results corroborated those for ZnNi electrodeposition in the presence and absence of glycerol or sorbitol [17].…”

Study of the effect of mannitol on ZnNi alloy electrodeposition from acid baths and on the morphology, composition, and structure of the deposit

“…1 shows that the initial deposition potential (E d,I ), -1.15 V, did not change in any of the baths studied, implying that no complex was formed between zinc or nickel ions and the boric-mannitol anion. This result corroborates those previously obtained in our laboratory [14][15][16]. Figure 2 shows the voltammetric dissolution charge density (q diss ) of ZnNi deposits produced in baths without and with various amounts of mannitol (Table 1), in the same deposition time (40 s), plotted against deposition potential (E d ).…”

“…Thus, the boric-mannitol complex works as a grain refiner and smoother. Also, these results corroborate those for ZnNi electrodeposition in the presence and absence of sorbitol, reported in an earlier study [14].…”

“…Figure 4a-d show the Ni content (wt%) in the ZnNi deposits for various E d and bath compositions. In a previous paper [14], it was reported that the ZnNi deposits obtained from solutions without polyalcohol show an increase from *6 to *20 wt% Ni in the deposits, as E d becomes more negative, from -1.26 to -1.55 V (Fig. 4a).…”

“…Thus, boric acid has been used as a substitute for ammonium chloride, and in addition to this, other compounds have also been added to the bath, viz. sorbitol or glycerol, with good results [14]. Research on the influence of the polyalcohols like sorbitol, glycerol, and mannitol on the electrodeposition of other metals or alloys [15][16][17] has shown excellent results, with the formation of smooth deposits that do not burn, even in the potential region of high hydrogen evolution.…”