Electrodeposition behavior of zinc-nickel-iron alloys from sulfate bath.

Abstract The present work is directed at collecting the properties of Zn-Ni and Zn-Fe alloys in one alloy via the electrodeposition of Zn-Ni-Fe ternary alloy. Electrodeposition of ternary Zn-Ni-Fe alloy was investigated and compared with the characteristics of Zn-Ni electrodeposits. The electrodeposition was performed from a sulfate bath onto a steel substrate. Structural analysis by X-ray diffraction (XRD) method revealed that the Zn-Ni-Fe alloys consisted of a mixture of zinc, and ([gamma]-[Ni.sub.2][Zn.sub.11]) and ([Fe.sub.3][Ni.sub.2]) phases. The study was carried out using electrochemical methods such as cyclic voltammetry and galvanostatic for electrodeposition, while anodic linear polarization resistance and anodic linear sweeping voltammetry techniques were used for the corrosion study. Surface morphology and chemical composition of the deposits were also examined by using scanning electron microscopy and atomic absorption spectroscopy, respectively. It was found that the obtained Zn-Ni-Fe alloy exhibited more preferred surface appearance and better corrosion resistance without adding any organic brighteners to the plating bath in comparison to Zn-Ni alloy that electrodeposited at similar conditions. Results obtained revealed that the increase in corrosion resistance of ternary deposits is not only attributed to the formation of ([gamma]-[Ni.sub.2][Zn.sub.11]) phase, but also to iron codeposition and formation of ([Fe.sub.3][Ni.sub.2]) phase.

Keywords Electrodeposition, Phase structure. Surface morphology, Corrosion resistance, Ternary Zn-Ni-Fe alloy

Introduction

Zn-Ni alloy coatings have attracted much attention because they possess higher corrosion resistance and better mechanical characteristics in comparison with zinc and other zinc alloy coatings. (1-10) Although the literature concerning ternary alloys is very limited in comparison with that of binary alloys, it has been found that Zn-Ni-Fe alloys are valuable for their leveling action. (11) It has been observed that the addition of Fe to Zn-Ni alloy led to the formation of a ternary Zn-Ni-Fe alloy, which, when deposited from a chloride bath, improved both the appearance of the alloy and its corrosion resistance. (12) In addition. Zn-Ni-Fe alloy has been found to be useful as a source in a hydrogen evolution reaction. (13) Electrodeposition of these alloys has attracted considerable attention because they exhibit the phenomena of "anomalous codeposition." This term, introduced by Brenner, (14) is used to describe the preferential deposition of the less noble metal (i.e., Zn) to the more noble metal (Ni or Fe). In other words, the reduction of Ni or Fe is inhibited while the deposition of Zn is enhanced when compared with their individual deposition rates. Several theories have been forwarded by various researchers, (15-21) but the most widespread one, and subject of controversy, is the so-called "hydroxide suppression mechanism" (HSM). This model, initially proposed by Dahms and Croll (15) for the Ni-Fe alloys, suggests that the discharge of more noble ions (i.e., [Ni.sup.2+]) is hindered by the formation of Fe[(OH).sub.2] in respective electrolytes, due to local pH rise, on the catalyst surface and. therefore, inhibits the codeposition of Ni. Tsuru el al. (22) have supported HSM theory by producing a normal deposition from a methanol bath and showed that anomalous behavior occurs when water is added to the electrolyte. Recently, the hydroxide oscillation concept was proposed, (23) according to which the thickness of the hydroxide layer changes periodically and the hydrogen reduction and cobalt deposition takes place when the hydroxide layer is depleted.

In contrast, Gomes and Valles (24) have disagreed and objected to the HSM theory. They observed that an increase in the solution pH promotes the normal codeposition of Zn-Co alloys. However, Chassaing and Wiart (25) and Miranda et al. (26) found high Ni deposition at higher pH values during Zn-Ni electrodeposition in chloride and sulfate medium and suggest that the deposition of Ni is activated with an increase in solution pH of the Zn-Ni system, which is in contradiction with HSM.

Two other papers on NiFe electrodeposition propose different mechanisms. The mechanism of Lieder and Biallozor (27) assumes that [Ni.sup.2+] discharges first to form a thin layer which chemisorbs water to form adsorbed Ni[(OH).sup.+], and competition between the [Ni.sup.2+] and [Fe.sup.2+] to occupy active sites leads to the preferential deposition of Fe. Matlosz (28) uses a two-step reaction mechanism involving adsorbed monovalent intermediate ions for both electrodeposition of iron and nickel, as single metals, and combines the two to develop a model for codeposition. Anomalous effects are assumed to be caused by preferential surface coverage due to differences in Tafel rate constants for electrodeposition.

The Sasaki and Talbot proposed model (29) extends the one-dimensional diffusion modeling of Grande and Talbot, (30) a supportive or interpretive, rather than a predictive, model of electrodeposition. A main contribution of this model is the inclusion of hydrogen adsorption and its effects on electrodeposition. Zech et al. (31) concluded that codeposition of iron group metals leads to a reduction of the reaction rate of the nobler component and an increase of the reaction rale of the less noble component compared to single metal deposition.

In the present work, it was felt that it would be interesting to collect the properties of Zn-Ni and Zn-Fe alloys in one alloy via the electrodeposition of Zn-Ni-Fe ternary alloy. The electrodeposition of ternary Zn-Ni-Fe alloy from sulfate electrolytes as well as surface morphology and corrosion resistance were studied. In addition, a comparison was made between Zn-Ni and Zn-Ni-Fe alloys obtained under the same conditions. The results of the experimental approach were based essentially on the analysis of the cyclic voltammograms and galvanostatic measurements during the electroplating. For corrosion study, the anodic linear sweep voltammetry and linear polarization resistance were used.

Experimental

The standard bath compositions for Zn-Ni-Fe deposits are given in Table 1. The sulfate salt concentrations in the baths for separate deposits, (a) Zn, (b) Ni, (c) Fe, and (d) Zn-Ni alloy, are (a) 0.10 M Zn[SO.sub.4]. (b) 0.10 M NiS[SO.sub.4] (c) 0.10 M Fe[SO.sub.4], and (d) 0.10 M Zn[SO.sub.4], and 0.10 M NiS[SO.sub.4], respectively. The electrolytes used for electrodeposition of different deposits were freshly prepared using Analar grade chemicals without further purification and dissolved in appropriate amount of doubly distilled water.

Table 1: Basic bath composition of ternary Zn-Ni-Fe alloy
electrodeposition

Bath composition  Concentration (M)

Zinc sulfate           0.1
Nickel sulfate         0.1
Ferrous sulfate        0.1
Sodium sulfate         0.2
Boric acid             0.2
Sulfuric acid          0.01

The electrolytic cell was used for the present work as detailed in reference (32). Before each run, the cell was cleaned with chromic/sulfuric mixture, washed with single and doubly distilled water, and filled with the 50 [cm.sup.3] of the electroplating solution. The electrodeposition process was performed on pure steel rod of cross-sectional area 0.196 [cm.sup.2] at pH = 2.5 and current density 5.0 mA [cm.sup.-2] for 10 min at 30[degrees]C.

For electrochemical methods (cyclic voltammetric behavior, galvanostatic measurements, linear polarization resistance, and anodic sweeping voltammetry techniques), an EG&G Potentiostat/Galvanostat Model 273A, controlled by a PC using Corrosion Analysis Software Model 352, was used. All cyclic voltammetry experiments were initiated at 0 V in a negative direction, and reversed at -1.2 V in a positive direction at 0 V at a scan rate of 5 mV [s.sup.-1].

Anodic sweeping voltammetry analysis is employed effectively for the in situ characterization of the electrodeposition process and products of the galvanostalically obtained electrodeposits on the steel substrate. For anodic sweeping voltammetry, the galvanostatic deposition was carried out for 10 min to obtain a thin deposit. The analysis was performed right after the galvanostatic depositions in 0.5 M [Na.sub.2][SO.sub.4] + 0.05 M EDTA solution.

The surface morphology of the deposit was evaluated by a Scanning Electron Microscope (JSM-5500 LV, SEM, JEOL. Japan). X-ray diffractometry (XRD). X'Pert Pro PANalytical, was used to identify the phases of Zn-Ni-Fe alloys deposited. Steel and copper sheets cathodes, of widths 1.0 cm and 1.0 cm in length, were used for XRD and SEM analysis, and chemical and EDX analysis, respectively. To steel and copper sheets provided with a narrow strip of about 1 [cm.sup.2] area, clamp terminals were attached for electrical contact. To determine its composition, the deposit (32) was stripped in 30% (v/v) HCl solution, then diluted with doubly distilled water up to 100 [cm.sup.3] and analyzed to ascertain the Zn, Ni, and Fe contents in the deposited alloy using Atomic Absorption Spectroscopy (Variian SpectrAA 55).

The values of electrochemical corrosion measurements of the coatings. [E.sub.corr], the corrosion potential, [I.sub.corr], the corrosion current, [R.sub.p], the polarization resistance, and corrosion rate, were obtained and represented in Table 2.

Table 2: Values of Zn, Ni, and Fe amount in the deposit, total mass of
the deposit, content (Zn, Ni, and Fe), current efficiencies (Zn, Ni,
Fe, Zn-Ni, and Zn-Ni-Fe deposits), thickness, and electrochemical
corrosion measurements of the deposit on copper (2 [cm.sup.2]) deposited
galvanostatically from a bath containing (a) 0.10 M Zn[SO.sub.4],
(b) 0.10 M Ni[SO.sub.4], (c) 0.10 M Fe[SO.sub.4], (d) 0.10 M Zn
[SO.sub.4] and 0.10 M Ni[SO.sub.4], (e) 0.10 M Zn[SO.sub.4], 0.10 M
Ni[SO.sub.4], and 0.1 M Fe[SO.sub.4], with 0.01 M [H.sub.2][SO.sub.4],
0.20 M [Na.sub.2][SO.sub.4], and 0.20 M [H.sub.3]B[O.sub.3] at 5 mA
[cm.sup.-2] for 10 min at 30[degrees]C

Parameter                                     Deposit

                          (a) Zn   (b) Ni   (c) Fe    (d)        (e)
                           only     only    only      Zn-Ni     Zn-Ni-Fe
                                                       alloy     alloy

Zn amount in the deposit  183         0        0      130       126
([10.sup.5] g)

Ni amount in the deposit    0        56.6      0       18.3      16.5
([10.sup.-5] g)

Fe amount in the deposit    0         0      129         0        2.4
([10.sup.5] g)

Total mass of the         183        56.6    129       148.3    144.9
deposit ([10.sup.-5] g)

Zn content (%)            100         0        0       87.8      86.9

Ni content (%)              0       100        0       12.2      11.3

Fe content (%)              0         0      100        0         1.7

Zn current efficiency      90.02      0        0       63.9      61.9
([e.sub.zn]) (%)

Ni current efficiency       0        31.02     0        9.9       9.0
([e.sub.Ni]) (%)

Fe current efficiency       0         0       74.3      0         1.38
([e.sub.Fe]) (%)

Zn-Ni deposit current       0         0        0       73.8       0
efficiency
([e.sub.[Zn-Ni]]) (%)

Zn-Ni-Fe deposit current    0         0        0        0        72.4
efficiency
([e.sub.[Zn-Ni-Fe]]) (%)

Thickness of the deposit    1.3       0.32     0.83     1.0       1.1
([mu]m)

[R.sub.p] (k[omega])        0.131     2.24     0.117    0.127     0.194

[I.sub.corr] (A             2.88      0.08     0.87     1.48      1.27
[cm.sup.-2] x
[10.sup.-5])

[E.sub.corr] (mV)         997      -169     -334      986      -608

Results and discussion

Figure 1 shows the cyclic voltammetry for the electro-deposition of Zn, Ni, and Fe alone, and the Zn-Ni and Zn-Ni-Fe alloys on steel rod in the bath solutions at 30[degrees]C. From the figure, the potential jumps were performed from 0.0 V ([E.sub.i]) to more negative potentials -1.2 V ([E.sub.f]); in the negative scan, the deposition of Zn alone starts at about -1110 mV and close to Zn-Ni and Zn-Ni-Fe codeposition potential (at about -1050 mV and -1038 mV, respectively). On the other hand, from the same figure, it is obvious that the deposition of Ni and Fe alone starts at about -900 and -950 mV, respectively, and the growth of deposited layer increases gradually when the potential was shifted to more negative values. Although, the polarization curve of Zn-Ni and Zn-Ni-Fe alloy deposition lies between the polarization curves of each deposition Zn and Ni and/or Fe, but Zn-Ni-Fe alloy deposition potential is nobler than Zn-Ni deposition potential; this may be due to codeposition of Fe into the alloy. This position suggested that the codeposition enables Zn to deposit at more positive potential (i.e., shifts the deposition potential of Zn to less negative values) due to the presence of [Ni.sup.2+] and [Fe.sup.2+], which facilitates Zn deposition. However, the codeposition of Ni and Fe shifted negatively in the presence of [Zn.sup.2+].

[FIGURE 1 OMITTED]

There is a cathodic peak started at about -577 mV and appeared in the presence and absence of Zn, Ni, and Fe ions in the plating bath (Fig. 2). This cathodic peak may be due to the codeposition of sulfur, which liberated from the reduction of sulfate group at the cathode in the presence of [H.sub.2][SO.sub.4]. Figure 3 shows the voltammograms of all the constituents of the bath in absence of ions that form alloy. It could be seen from the figure that the cathodic peak appeared only in the presence of [H.sub.2][SO.sub.4], in spite of the presence of [Na.sub.2][SO.sub.4], which was considered as a source of [SO.sub.4.sup.-2] group in the plating bath. Moreover, the cathodic peak appeared only in the reduction of sulfuric acid alone and reduction of other constituents with sulfuric acid. These results confirm that the cathodic peak attributed to the codeposition of sulfur from the reduction of the sulfate group occurs only in the presence of [H.sub.2][SO.sub.4], which is the source of [H.sup.+] that reduces the sulfate groups. Taking into consideration that this process is composed of several consecutive steps, the overall reaction in the plating bath is as follows:

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[SO.sub.4.sup.2-] + 8[H.sup.+] 6[e.sup.-] [right arrow] S + 4[H.sub.2]O.

These results were in agreement with the results obtained by using XRD and EDX analysis. Figure 4 shows the EDX pattern of the deposit containing Zn-Ni-Fe alloy. It can be seen from the peaks in this figure that there is another peak that corresponds to the presence of sulfur. In addition, Fig. 5 shows the XRD pattern of the deposit in the absence of Zn, Ni, and Fe, and the obtained peaks correspond to the presence of sulfur only, which is in contradiction with Abou-Krisha's research. (32) He explains the appearance of this peak due to hydrogen evolution. Nevertheless, it was concluded here that the hydrogen evolution started after the deposition of sulfur (Fig. 3) and appeared as wobbly in the cyclic voltammograms, which is due to the reduction of [H.sub.2][SO.sub.4] and [H.sub.2][SO.sub.4] + [H.sub.3][BO.sub.3]. Both the hydrogen evolution and the deposition of sulfur decrease in the presence of [Zn.sup.2+] and/or [Ni.sup.2+] and/or [Fe.sup.2+] due to surface effect that occurs with the addition of these cations. This may be ascribed to the start of competitive adsorption between [Zn.sup.2+] and/or [Ni.sup.2+] and/or [Fe.sup.2+] (or its monovalent intermediate), and S, and [H.sup.+]. On the other hand, the addition of these cations could decrease the adsorption of S and [H.sup.+] and consequently their deposition and evolution, respectively. The anodic current peak (Fig. 3), which attributed to the dissolution of the deposited sulfur, appears at -225 mV and its height decreases with the addition of other constituents to sulfuric acid in the bath. Fortunately, the codeposition of sulfur leads to more improvement of the crystallinity of the deposits. (33)

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

From the positive scan of the cyclic voltammogram (Fig. 1), there is only one anodic peak at about -1110 mV, which corresponds to the anodic dissolution of Zn deposited alone in the absence of Ni and Fe. In addition, there are two anodic peaks at -527 and -101 mV, which correspond to the dissolution of separately deposited pure Fe and Ni, respectively. For Zn-Ni voltammogram, there are three peaks that correspond to the dissolution of the constituents of two phases, [delta]-phase ([Ni.sub.3][Zn.sub.22]) and [gamma]-phase ([Ni.sub.5][Zn.sub.21]). The first and second anodic peaks correspond to the dissolution (dealloying) of Zn from [delta]- and [gamma]-phases, respectively. The third peak corresponds to the dissolution of Ni from its phases as reported earlier by Abou-Krisha. (32) However, for the Zn-Ni-Fe curve, there are four anodic current peaks. The first dissolution anodic peak at -1038 mV is attributed to the dissolution of zinc from pure Zn phase, while the second anodic peak at about -704 mV corresponds to dissolution of zinc from ([gamma]-[Ni.sub.2][Zn.sub.11]) phase. The third and fourth anodic peaks at -633 and -318 mV correspond to the dissolution of iron from ([Fe.sub.3][Ni.sub.2]) phase and nickel from the two phases, respectively, which was confirmed by XRD (Fig. 6).

[FIGURE 6 OMITTED]

The height of any peak is considered as an indication of the quantity of its phase in the deposit. Therefore, from Fig. 1 the increase in height of the second Zn-Ni-Fe peak and its shift to more noble direction, in comparison with the content of the same phase for Zn-Ni alloy deposition, reflects the high content of ([gamma]-[Ni.sub.2][Zn.sub.11]) phase in the deposit for Zn-Ni-Fe alloy, and consequently means that the corrosion resistance increases. In addition, the height of the third peak, which corresponds to the dissolution of iron from its phase in the Zn-Ni-Fe alloy, is too low in comparison with the height of the peak that corresponds to the dissolution of Fe alone. This may be ascribed to the presence of Zn and/or Ni in the plating bath that inhibits the codeposition of Fe.

The ternary Zn-Ni-Fe deposits exhibit higher corrosion resistance in comparison to Zn-Ni deposits. The data showed a significant change in the preferred crystal orientation for Zn-Ni-Fe deposits compared to Zn-Ni deposits; this may be explained by the adsorption inhibition theory. (34) Some iron atoms adsorb on the active planes or sites, which have relative high energy, and inhibit crystal growth at that location. Through this mechanism, the growth direction of crystals changes due to this inhibition and remaining plane develops preferred orientation.

Changes in the structure can be observed by SEM analysis that is shown in Figs. 7a and 7b. Figure 7a shows the surface morphology for Zn-Ni deposits which had coarse grain size. The ternary Zn-Ni-Fe deposits show bright, smooth, and more homogenous form of crystallites in which the grain size is finer in contrast to that of Zn-Ni deposits, as shown in Fig. 7b. Moreover, it was found that the grain size decreased with increasing iron content in the ternary Zn-Ni-Fe deposits, even though the nickel content in these deposits is lower than that of binary Zn-Ni alloy. (12)

[FIGURE 7 OMITTED]

Figure 8 shows the potential-time dependence for the deposition of Zn, Ni, and Fe alone, and Zn-Ni and Zn-Ni-Fe alloys on steel at 5 mA [cm.sup.-2] for 10 min. It is clear that the deposition of pure Ni and Fe needs low overpotential to create the initial nucleus and the deposit grows at low potentials. However, the deposition of pure Zn takes place with higher nucleation overpotential and grows at high potential. The Zn-Ni and Zn-Ni-Fe alloys are codeposited at moderate overpotential values lying between Zn overpotential and Ni and Fe overpotentials. This is because the deposition of Ni or Fe is strongly inhibited by the presence of [Zn.sup.2+]. while the deposition of Zn is induced by the presence of [Ni.sup.2+] and/or [Fe.sup.2+] On the other hand, Zn-Ni-Fe alloy is codeposited at more noble overpotential than Zn-Ni alloy that deposited at relatively more cathodic overpotential.

[FIGURE 8 OMITTED]

Figure 9 shows the anodic linear sweep voltammograms obtained during the dissolution of the deposits produced galvanostatically by Zn, Ni, and Fe alone, and Zn-Ni and Zn-Ni-Fe alloys. The phase structure was investigated in [Na.sub.2][SO.sub.4] solution containing complex-forming ions, in which a Zn-Ni-Fe alloy completely dissolves. It is well known that pure Zn dissolves but zinc alloys do not dissolve in [Na.sub.2] [SO.sub.4] solution, while in the presence of a small amount of a complex-forming agent (EDTA), both Zn and its alloys dissolve. (35) It is clear from the figure that each of pure Zn, pure Ni, and pure Fe have only single anodic dissolution peaks (-588, -98, and -291 mV, respectively). In addition, the dissolution peaks of Zn and Fe are high but Ni dissolution peak is low, giving rise to more pure Zn deposition and less Ni, which may be due to surface effect. Also from the same figure, it is clear that pure iron is deposited with high content when deposited alone but with low content when alloyed with other metal. There are three anodic dissolution peaks for the Zn-Ni alloy. However, for the Zn-Ni-Fe alloy, there are also three anodic dissolution peaks, but they attribute to dissolution of zinc from pure Zn phase, which is characterized by the first dissolution anodic peak at -987 mV. The second anodic peak represents the dissolution of zinc from ([gamma]-[[Ni.sub.2][Zn.sub.11]) phase, which overlaps with the dissolution of iron from ([Fe.sub.3][Ni.sub.2]) phase. The third anodic peak at more noble potential characterizes the dissolution of nickel from its phases. There is a clear shift for second and third peaks toward the noble direction comparable with the Zn-Ni alloy peaks, giving rise to an increase in corrosion resistance of the ternary Zn-Ni-Fe deposits.

[FIGURE 9 OMITTED]

The corrosion resistance of the electrodeposited Zn-Ni-Fe and Zn-Ni in 0.05 M HCl using galvanostatic technique was investigated (Fig. 10). It is obvious from the obtained data (Table 2) of corrosion behavior that the corrosion potential of these deposits depended on the alloy composition. However, the deposits with iron codeposition have nobler [E.sub.corr] in contrast to these deposits without iron content. It is clear that the corrosion resistance of Zn-Ni-Fe alloy deposits is higher than those of Zn-Ni deposits, when both types of deposits contain approximately the same nickel content as shown from the polarization resistance curve.

[FIGURE 10 OMITTED]

According to the previous work, (12) anomalous code-position behavior is attributed to the formation of zinc hydroxide film on the cathode surface due to hydrogen reduction, which suppresses the discharge of nickel and iron ions in the deposition of Zn-Ni and Zn-Fe alloys. It was (36) concluded previously that the anomalous code-position occurred even at low current densities, where hydrogen formation was unable to cause large alkalinization effects. In the present work, anomalous code-position may be attributed to the Ni and Fe ions (or its monovalent intermediate) adsorbed first; followed by adsorption of [Zn.sup.2+] (or its monovalent intermediate) onto the freshly adsorbed and deposited nickel and iron. The adsorption of zinc ions inhibits subsequent deposition of nickel and iron [i.e., the competitive adsorption between [Zn.sup.2+] and [Ni.sup.2+] and/or [Fe.sup.2+] (or its monovalent intermediate) to occupy active sites leads to the preferential deposition of Zn], although it does not block it completely. In absence of [Fe.sup.2+], as shown in Table 2, the nickel and zinc content was 12.2% and 87.8%. respectively; but after addition of [Fe.sup.2+] to the bath, nickel and zinc contents in the deposit generally decreases, and reaches 11.3% and 86.9%, respectively. This decrease in zinc and nickel contents was replaced by iron in the deposit, which leads to: first, decrease in the alloy current efficiency from 73.8% (i.e., for Zn-Ni alloy) to 72.4% (i.e.,for Zn-Ni-Fe alloy); second, increase in the thickness of the deposit from 1.0 to 1.1 [micro]m: third, a decrease in the corrosion potential and corrosion current with the codeposition of Fe: and finally, the polarization resistance increases from 0.127 to 0.194 k[OMEGA]. According to these results the ternary Zn-Ni-Fe deposits showed higher corrosion resistance in comparison with Zn-Ni deposits.

Conclusions

This work represents the electrodeposition and corrosion of Zn, Ni, and Fe alone, and Zn-Ni and Zn-Ni-Fe alloy at ordinary conditions.

The results revealed that

1. The electrodeposition of Zn-Ni-Fe exhibited the phenomenon of anomalous type codeposition.

2. Bright and smooth Zn-Ni-Fe alloy surfaces were produced from baths containing approximately equimolar ratio of [[Ni.sup.+2]/[Fe.sup.+2]/[Zn.sup.+2]], even without organic brighteners.

3. The ternary Zn-Ni-Fe deposits showed higher corrosion resistance in comparison with Zn-Ni deposits.

4.The increase in corrosion resistance of Zn-Ni-Fe deposits is not only due to the formation of a high nickel ([gamma]-[[Ni.sub.2][Zn.sub.11]]) alloy phase but also due to codeposition of iron and formation of ([Fe.sub.3][Ni.sub.2]) phase, which causes a clear change in crystal orientation and produces a liner grain size.

5. Zn-Ni-Fe alloys formed a mixture of three phases: ([gamma]-[Ni.sub.2][Zn.sub.11]), ([[Fe.sub.3][Ni.sub.2]). and pure Zn.

6. Sulfur was codeposited during the electroplating of the alloys, which results from the reduction of sulfate group in the presence of [H.sub.2][SO.sub.4].

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M. M. Abou-Krisha ([??]), F. H. Assaf, S. A. El-Naby

Faculty of Science, Chemistry Department,

South Valley University, Qena 83523, Egypt

e-mail: [e-mail]