**3. Electrodeposition of Zn and Zn–Mn alloy coatings**

To carrying out the electrodeposition of Zn and Zn–Mn Alloy coatings from electrolytic baths obtained from leaching of spent batteries is important to know the metallic composition and concentration of the solution. Table 2 shows the typical composition obtained by an acid leaching with diluted HCl, of the carbon paste obtained from Zn-C spent batteries manufac‐ tured in Brazil [28]. This quantitative analysis of the metal content was performed by atomic absorption spectrometry and indicated that in addition to Zn2+ and Mn2+ traces of other species such as Fe2+, Cu2+ and Pb2+ were present in solution.


**Table 2.** Composition of the Electrolytic Bath Obtained from Recycling of Zn-C Batteries.

tech) have been gradually replacing hydrometallurgical ones due to their higher efficiency, lower cost and few industrial requirements [25]. Bioleaching was characterized by efficient release of metals from solid phase into aqueous solution under the mild conditions of room temperature and pressure by contact and/or non-contact mechanisms in the presence of

Another alternative method developed for Zn-Mn batteries recycling is the electrodeposition of Zn and Zn–Mn alloy coatings over different kinds of steel to corrosion protection [28, 29]. Electrodeposited coatings of zinc are extensively employed in the protection of steel against corrosion. However, this protective effect is not very effective under aggressive atmospheric conditions [30]. In recent years, several materials have been investigated to improve the durability of these coatings. Electrodeposited alloys of Zn, such as Zn–Ni, Zn–Co and Zn–Fe, present higher corrosion resistance than pure zinc coatings. Also, it has been reported in the literature that Zn–Mn alloys show even better corrosion resistance properties [31–34]. The high corrosion resistance of these alloys is likely due to the dual protective effect of manganese: on the one hand Mn dissolves first because it is thermodynamically less noble than Zn, thereby protecting Zn; and on the other hand Mn ensures the formation of compounds with a low solubility product over the galvanic coating. Depending on the aggressivity of the environment to which the Zn–Mn alloy is exposed, various compounds may be found in the passive layer, including oxides such as MnO, MnO2, Mn5O8 and *γ−*Mn2O3, or basic salts like Zn4(OH)6SO4.*x*H2O and Zn5(OH)8Cl.2H2O [31, 35, 36]. The protective effect of Zn–Mn is dependent on the Mn content of the alloy. Although it has been reported that among the Zn alloys those of Zn–Mn show the highest corrosion resistance, their deposition process presents some drawbacks related to the bath instability and current efficiency. Among the various electrolytic baths and additives proposed to obtain Zn–Mn alloys, the use of a chloride-based acid bath with polyethylene glycol (PEG) as the additive seems very promising [31–33].

The mainly practical application in produce a protective Zn-Mn layer over steel is related to the substitution of the primary painting process on metallic parts produced in foundries. Furthermore it is important to note that beside the great interest in recycling Zn-C batteries the use solution produced by the acidic leaching of these exhausted batteries to obtaining

Considering the concepts described above this chapter brings some highlighting on the development of a methodology to recover zinc and manganese present in exhausted zinc– carbon batteries through chloride acidic leaching of the solid material. The leaching solution is then used as an electrolytic bath for the electrodeposition of the galvanic coating on AISI 1018 steel. Polyethylene glycol is used as the additive in the bath to obtain both Zn and Zn–

To carrying out the electrodeposition of Zn and Zn–Mn Alloy coatings from electrolytic baths obtained from leaching of spent batteries is important to know the metallic composition and

protective Zn-Mn films were described only in two papers[28,29].

**3. Electrodeposition of Zn and Zn–Mn alloy coatings**

Mn alloys.

acidophilic sulfur-oxidizing and/or iron-oxidizing bacteria [26, 27].

214 Modern Surface Engineering Treatments

It could be seen from the Table above that the batteries used containing Pb as heavy metal in their composition, however this quantity found corresponds to 0.18% by weight of the battery electrolytic paste that was in agreement with the limits established by CONOMA (0.20%).

To prepare the electrolytic bath from this solution the pH is adjusted to 5.0. During this step occurs the hydrolysis of some metallic ions forming a gelatinous brown material, possibly due to the formation of iron hydroxide that was removed by filtration. From this filtrated solution it was prepared four electrolytic baths used in obtaining the Zn-Mn alloy coatings. These baths were prepared to the addition of boric acid and different quantities of additives (ammonium isocyanate - NH4SCN and polyethylene glycol – PEG10.000) as showed in Table 3.


**Table 3.** Composition of the Obtained Electrolytic Bath through Recycling of Cells Used to Obtain Mn-Zn Alloys.

The behavior of AISI 1018 carbon steel electrodes in the presence of the electrolytic baths prepared from recycled batteries could be investigated by measurements of cyclic voltamme‐ try. The Figure 2 shows the voltammetric curves obtained on 1018 carbon steel immersed in the proposed electrolytic baths (see Table 3). It could be seen from Figure 2a that with no additive on the bath the voltammogram showed two regions of reduction. The first region present a peak current with maximum current in -1.4 V and is related to the electrodeposition of zinc on the electrode. The second region present a continuous increase on reduction current starting on E = -1.5 V, this region can be related to the formation of Mn-Zn alloy, but tis increase in cathodic current has an important contribution of the process of hydrogen evolution. This former observation is the reason of the needing of usage of additives that could be a hindrance for this reaction on the surface. When the potential is swept in the positive direction no peak of current is observed, just a constant increase on anodic current starting in almost E = -1.2 V, this current increase is related to the dissolution of metal layer deposited on the steel during the cathodic scan.

**Figure 2.** Voltammetric Curves Obtained on 1018 Carbon Steel Immersed in the Proposed Electrolytic Baths (see Table 3) (a) S0, (b) S1, (c) S2 and (d) S3 with scan rate = 20 mV s-1.

No significant changes are observed with the addition of the addictive PEG10,000 and with the addition of a mixture of NH4SCN and PEG10,000 (see Figures 2b and 2d), except by a slight diminishment on the current density, this loss in current density could be assigned to the presence of the additives. As discussed by Diaz-Arista et al. [31] the PEG10,000 can adsorb on the steel surface blocking of the active sites for hydrogen evolution, but the isocyanate, according to these authors has the function of complexing with the ions Zn2+ decreasing the competition with the reduction of ions Mn2+. However, in the presence of NH4SCN the voltammetric curves are considerably different from the others conditions, as could be seen in Figure 2c. This figure shows that the process of Zn2+ electrodeposition, that occurred with a peak current at ca. -1.4 V in the other conditions, is now linked to the Mn2+ electrodeposition process as could be observed by the continuous increase in the cathodic current with the augment of the potential forward negatives values. This behavior was assigned to the fact that

**8**

the NH4SCN has complex interactions with Zn2+ and Mn2+ decreasing the difference between the reduction potential of these two metallic species on the steel surface. The characterization of the coatings obtained with NH4SCN as addictive showed films with bad quality as weak adherence to the surface, inhomogeneity, and with no increase in the Mn proportion related to the presence of Zn. For this reason this additive was not used in the others experiments

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After determining the potential range for reduction of the metallic ions Zn2+ and Mn2+ presented in the prepared electrolytic baths, the coating were obtained in the potentiostatic mode in two situations: first by application of -1.2 V and the second by application of -1.6 V during 15 min. The conditions used during the potentiostatic electrodeposition using the S0 and S1 solutions were chosen in agreement with previous studies carried out by other authors on the electro‐ deposition of Zn–Mn alloys [31]. The resulting current–time curves are shown in Figure 3. At -1.2 V, in the absence of additive, the current density stabilized at around -4.5 mA cm-2. In the presence of PEG, the current density is slightly less negative (-3.6 mA cm-2). When electrode‐ position was carried out at -1.6 V the current densities with and without the additive were -17.6 mA cm-2 and -10.8 mA cm-2, respectively. It is important to note that the presence of additive during the electrodeposition at more negative potentials makes the current density more stable. The instability observed in the electrodepositions carried out with S0 solution, particularly at -1.6 V, may be attributed to hydrogen evolution. In a study on the effect of additives on the hydrogen evolution reaction during Zn electrodeposition, Song et al. [37] suggested that PEG acts as an inhibitor of hydrogen absorption in the electrodeposited Zn.

**Figure 3.** Potentiostatic curves obtained during electrodeposition onto an AISI 1018 steel electrode from S0 and S1

The characterization of the coating obtained potentiostatically was performed by measure‐ ments of Scan Electronic Microscopy (SEM), Energy Dispersion Spectroscopy (EDS) and X Ray Diffraction (XRD). The Figure 4 shows the morphology of the deposit obtained potentiostati‐ cally at -1.2 V from the base solution (S0). The SEM image shows that the deposit is comprised

described in this text.

baths.

the NH4SCN has complex interactions with Zn2+ and Mn2+ decreasing the difference between the reduction potential of these two metallic species on the steel surface. The characterization of the coatings obtained with NH4SCN as addictive showed films with bad quality as weak adherence to the surface, inhomogeneity, and with no increase in the Mn proportion related to the presence of Zn. For this reason this additive was not used in the others experiments described in this text.

in cathodic current has an important contribution of the process of hydrogen evolution. This former observation is the reason of the needing of usage of additives that could be a hindrance for this reaction on the surface. When the potential is swept in the positive direction no peak of current is observed, just a constant increase on anodic current starting in almost E = -1.2 V, this current increase is related to the dissolution of metal layer deposited on the steel during

> 1 ciclo 2 ciclo 3 ciclo 4 ciclo

\_\_\_\_\_\_1 Cycle \_\_\_\_\_\_2 Cycle \_\_\_\_\_\_3 Cycle \_\_\_\_\_\_4 Cycle


 1 ciclo 2 ciclo 3 ciclo 4 ciclo

\_\_\_\_\_\_1 Cycle \_\_\_\_\_\_2 Cycle \_\_\_\_\_\_3 Cycle \_\_\_\_\_\_4 Cycle


**Figure 2.** Voltammetric Curves Obtained on 1018 Carbon Steel Immersed in the Proposed Electrolytic Baths (see Table

No significant changes are observed with the addition of the addictive PEG10,000 and with the addition of a mixture of NH4SCN and PEG10,000 (see Figures 2b and 2d), except by a slight diminishment on the current density, this loss in current density could be assigned to the presence of the additives. As discussed by Diaz-Arista et al. [31] the PEG10,000 can adsorb on the steel surface blocking of the active sites for hydrogen evolution, but the isocyanate, according to these authors has the function of complexing with the ions Zn2+ decreasing the competition with the reduction of ions Mn2+. However, in the presence of NH4SCN the voltammetric curves are considerably different from the others conditions, as could be seen in Figure 2c. This figure shows that the process of Zn2+ electrodeposition, that occurred with a peak current at ca. -1.4 V in the other conditions, is now linked to the Mn2+ electrodeposition process as could be observed by the continuous increase in the cathodic current with the augment of the potential forward negatives values. This behavior was assigned to the fact that

**d**


**j / mA.cm-2**

**b**

**j / mA.cm-2**

**IIc**

**Ic**


**E/V (Ag/AgCl)**

**Ic**


**E/V (Ag/AgCl)**

**8**

 1 ciclo 2 ciclo 3 ciclo 4 ciclo

\_\_\_\_\_\_1 Cycle \_\_\_\_\_\_2 Cycle \_\_\_\_\_\_3 Cycle \_\_\_\_\_\_4 Cycle

 1 ciclo 2 ciclo 3 ciclo 4 ciclo

\_\_\_\_\_\_1 Cycle \_\_\_\_\_\_2 Cycle \_\_\_\_\_\_3 Cycle \_\_\_\_\_\_4 Cycle

the cathodic scan.

216 Modern Surface Engineering Treatments


**c**


**j / mA.cm-2**

**j / mA.cm-2**

**a**


**Ic**

**E/V (Ag/AgCl)**

**Ic**

3) (a) S0, (b) S1, (c) S2 and (d) S3 with scan rate = 20 mV s-1.


**E/V (Ag/AgCl)**

After determining the potential range for reduction of the metallic ions Zn2+ and Mn2+ presented in the prepared electrolytic baths, the coating were obtained in the potentiostatic mode in two situations: first by application of -1.2 V and the second by application of -1.6 V during 15 min. The conditions used during the potentiostatic electrodeposition using the S0 and S1 solutions were chosen in agreement with previous studies carried out by other authors on the electro‐ deposition of Zn–Mn alloys [31]. The resulting current–time curves are shown in Figure 3. At -1.2 V, in the absence of additive, the current density stabilized at around -4.5 mA cm-2. In the presence of PEG, the current density is slightly less negative (-3.6 mA cm-2). When electrode‐ position was carried out at -1.6 V the current densities with and without the additive were -17.6 mA cm-2 and -10.8 mA cm-2, respectively. It is important to note that the presence of additive during the electrodeposition at more negative potentials makes the current density more stable. The instability observed in the electrodepositions carried out with S0 solution, particularly at -1.6 V, may be attributed to hydrogen evolution. In a study on the effect of additives on the hydrogen evolution reaction during Zn electrodeposition, Song et al. [37] suggested that PEG acts as an inhibitor of hydrogen absorption in the electrodeposited Zn.

**Figure 3.** Potentiostatic curves obtained during electrodeposition onto an AISI 1018 steel electrode from S0 and S1 baths.

The characterization of the coating obtained potentiostatically was performed by measure‐ ments of Scan Electronic Microscopy (SEM), Energy Dispersion Spectroscopy (EDS) and X Ray Diffraction (XRD). The Figure 4 shows the morphology of the deposit obtained potentiostati‐ cally at -1.2 V from the base solution (S0). The SEM image shows that the deposit is comprised of hexagonal plates with pyramidal clusters grouped into nodules of several sizes, as is normal for pure zinc electrodeposits [37]. The EDS analysis (inset on Figure 4) showed the presence of zinc as the predominant element in the coating.

Although differences were observed in the morphology of the deposited coatings obtained with and without the use of the additive, the XRD analysis exhibited in Figure 6 showed the characteristics diffraction peaks for the coating obtained on AISI 1018 steel electrode at −1.2 V vs. (Ag/AgCl), t = 15 min, using the solution S0 (without additive). A similar composition was obtained with the bath S1 in the same electrodeposition condition. As can be seen, the formation of a Zn-Mn alloy could not be obtained from this potentiostatic experiments carried

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**Figure 6.** X-ray diffraction (XRD) pattern of the deposit obtained on AISI 1018 steel electrode at −1.2 V vs. (Ag/AgCl), t

**Figure 7.** SEM image of the deposit formed on AISI 1018 steel electrode at −1.6 V vs. (Ag/AgCl), t = 15 min, from

out at -1.2 V.

= 15 min.using the solution S0 (without additive).

solution S0. The results for the EDS analysis are shown in the inset.

In the presence of PEG, the deposit obtained is comprised of hexagonal crystals oriented perpendicularly to the substrate surface (Figure 5) and the zinc also was the predominant element (inset on Figure 5). This type of morphology was also observed by Ballesteros *et al.* [30] who studied the influence of PEG as an additive on the mechanism of Zn deposition and nucleation.

**Figure 4.** SEM image of the deposit formed on AISI 1018 steel electrode at -1.2V vs. (Ag/AgCl), polarization time = 15 min, using solution S0 as electrolytic bath. The results for the EDS analysis of the film are shown in the inset.

**Figure 5.** SEM image of the deposit formed on AISI 1018 steel electrode at -1.2V vs. (Ag/AgCl), polarization time = 15 min, using solution S1 as electrolytic bath. The results for the EDS analysis of the film are shown in the inset.

Although differences were observed in the morphology of the deposited coatings obtained with and without the use of the additive, the XRD analysis exhibited in Figure 6 showed the characteristics diffraction peaks for the coating obtained on AISI 1018 steel electrode at −1.2 V vs. (Ag/AgCl), t = 15 min, using the solution S0 (without additive). A similar composition was obtained with the bath S1 in the same electrodeposition condition. As can be seen, the formation of a Zn-Mn alloy could not be obtained from this potentiostatic experiments carried out at -1.2 V.

of hexagonal plates with pyramidal clusters grouped into nodules of several sizes, as is normal for pure zinc electrodeposits [37]. The EDS analysis (inset on Figure 4) showed the presence

In the presence of PEG, the deposit obtained is comprised of hexagonal crystals oriented perpendicularly to the substrate surface (Figure 5) and the zinc also was the predominant element (inset on Figure 5). This type of morphology was also observed by Ballesteros *et al.* [30] who studied the influence of PEG as an additive on the mechanism of Zn deposition and

**Figure 4.** SEM image of the deposit formed on AISI 1018 steel electrode at -1.2V vs. (Ag/AgCl), polarization time = 15

**Figure 5.** SEM image of the deposit formed on AISI 1018 steel electrode at -1.2V vs. (Ag/AgCl), polarization time = 15

min, using solution S1 as electrolytic bath. The results for the EDS analysis of the film are shown in the inset.

min, using solution S0 as electrolytic bath. The results for the EDS analysis of the film are shown in the inset.

of zinc as the predominant element in the coating.

218 Modern Surface Engineering Treatments

nucleation.

**Figure 6.** X-ray diffraction (XRD) pattern of the deposit obtained on AISI 1018 steel electrode at −1.2 V vs. (Ag/AgCl), t = 15 min.using the solution S0 (without additive).

**Figure 7.** SEM image of the deposit formed on AISI 1018 steel electrode at −1.6 V vs. (Ag/AgCl), t = 15 min, from solution S0. The results for the EDS analysis are shown in the inset.

Figure 7 shows the morphology of the deposit obtained potentiostatically at -1.6 V without the use of the additive. In the SEM image an amorphous and porous deposit covering some parts of the substrate can be observed. The EDS analysis (inset on Figure 7) indicated that the manganese content of this deposit is around 8% wt.

The XRD analysis of the coating obtained at −1.6 V vs. (Ag/AgCl) from solution S0 is showed in Figure 8. This XDR measurement also indicated that these experimental conditions did not favor the formation of a Zn-Mn alloy. This result may be related to the formation of Mn(OH)2(s) species on the substrate surface due to the hydrogen formation under these experimental conditions, resulting in an increase in the pH in the vicinity of the working electrode [38]. In addition, the formation of Mn(OH)2 in high alkaline conditions agrees well with the Eh x pH (Pourbaix) diagrams [39].

**Figure 8.** X-ray diffraction (XRD) pattern of the deposit obtained on AISI 1018 steel electrode at −1.6 V vs. (Ag/AgCl), t = 15 min.using the solution S0 (without additive).

In comparison with the morphology observed for the deposit obtained without PEG, the deposit formed in the presence of this additive is very different. The SEM image and EDS analysis for this coating are showed in Figure 9.

**Figure 10.** X-ray diffraction (XRD) pattern of the deposit obtained on AISI 1018 steel electrode at −1.6 V vs. (Ag/AgCl),

**Figure 9.** SEM image of the deposit formed on AISI 1018 steel electrode at −1.6 V vs. (Ag/AgCl), t = 15 min, from

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As it was not possible to obtain films containing Zn-Mn alloy through potentiostatic electro‐ deposition, coatings were obtained by galvanostatic deposition. As the current density stabilized at around -10 mA cm-2 with the presence of PEG in the electrolytic bath during potentiostatic electrodeposition at -1.6 V, this current density was chosen for the attempted galvanostatic electrodeposition of the Zn-Mn alloy. Figure 11 shows the chronopotentiometric

t = 15 min, using the solution S1 (with PEG10,000 as additive).

solution S1. The results for the EDS analysis are shown in the inset.

curves obtained.

This figure shows that the deposit formed is compact and homogeneous with a cauliflowerlike morphology; however, once again, the presence of manganese in the deposit could not be detected. The change in the morphology of the deposit may be associated with the partial adsorption of the additive on the electrode surface during the electrodeposition of Zn2+ [40]. In addition, the XRD analysis exhibited in Figure 10 revealed that the deposit is comprised principally of Zn crystals in the plane (101), corroborating the EDS results.

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Figure 7 shows the morphology of the deposit obtained potentiostatically at -1.6 V without the use of the additive. In the SEM image an amorphous and porous deposit covering some parts of the substrate can be observed. The EDS analysis (inset on Figure 7) indicated that

The XRD analysis of the coating obtained at −1.6 V vs. (Ag/AgCl) from solution S0 is showed in Figure 8. This XDR measurement also indicated that these experimental conditions did not favor the formation of a Zn-Mn alloy. This result may be related to the formation of Mn(OH)2(s) species on the substrate surface due to the hydrogen formation under these experimental conditions, resulting in an increase in the pH in the vicinity of the working electrode [38]. In addition, the formation of Mn(OH)2 in high alkaline conditions agrees well with the Eh x pH

**Figure 8.** X-ray diffraction (XRD) pattern of the deposit obtained on AISI 1018 steel electrode at −1.6 V vs. (Ag/AgCl), t

In comparison with the morphology observed for the deposit obtained without PEG, the deposit formed in the presence of this additive is very different. The SEM image and EDS

This figure shows that the deposit formed is compact and homogeneous with a cauliflowerlike morphology; however, once again, the presence of manganese in the deposit could not be detected. The change in the morphology of the deposit may be associated with the partial adsorption of the additive on the electrode surface during the electrodeposition of Zn2+ [40]. In addition, the XRD analysis exhibited in Figure 10 revealed that the deposit is comprised

principally of Zn crystals in the plane (101), corroborating the EDS results.

the manganese content of this deposit is around 8% wt.

(Pourbaix) diagrams [39].

220 Modern Surface Engineering Treatments

= 15 min.using the solution S0 (without additive).

analysis for this coating are showed in Figure 9.

**Figure 9.** SEM image of the deposit formed on AISI 1018 steel electrode at −1.6 V vs. (Ag/AgCl), t = 15 min, from solution S1. The results for the EDS analysis are shown in the inset.

**Figure 10.** X-ray diffraction (XRD) pattern of the deposit obtained on AISI 1018 steel electrode at −1.6 V vs. (Ag/AgCl), t = 15 min, using the solution S1 (with PEG10,000 as additive).

As it was not possible to obtain films containing Zn-Mn alloy through potentiostatic electro‐ deposition, coatings were obtained by galvanostatic deposition. As the current density stabilized at around -10 mA cm-2 with the presence of PEG in the electrolytic bath during potentiostatic electrodeposition at -1.6 V, this current density was chosen for the attempted galvanostatic electrodeposition of the Zn-Mn alloy. Figure 11 shows the chronopotentiometric curves obtained.

Figure 12 shows the SEM image of the deposit obtained galvanostatically at -10 mA cm-2 in the absence of PEG. The deposit formed is porous and with grains of diverse dimensions ir‐ regularly distributed on the substrate surface. The EDS analysis (inset in Figure 12) revealed

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In addition, the XRD patterns of the film showed above were very similar as those obtained during the potentiostatic deposition at -1.2 V from solution S0n (see Figure 6) indicating only

The results obtained in the presence of PEG indicated the formation of the Zn-Mn alloy during galvanostatic electrodeposition. Figure 13 shows the SEM micrograph of the deposit obtained under these conditions. The results indicate that the PEG decreased the mean size of grains inducing the formation of a smooth deposit. Although the EDS analysis did not clearly indicate

**Figure 13.** SEM image of the deposit formed on AISI 1018 steel electrode at −10 mA cm-2, t = 15 min, from solution S1.

The XRD results, exhibited in Figure 14 showed a diffractogram characteristic of a mixture of Zn and ε-phase Zn-Mn with different crystallographic. This finding may be related to the low manganese content, around 2% wt in the deposit. Ballesteros *et al.*[30] have reported that the presence of additives such as PEG can shift the potential of Zn deposition to very negative values. Such behavior is associated with the partial adsorption of PEG onto the substrate surface. The authors related that in the presence this additive the electrodeposition of zinc can occurs in two different ways. First, the zinc is electrodeposited onto the active sites on the electrode surface that are not blocked by adsorbed PEG molecules. In second, the zinc is electrodeposited onto the active sites that are liberated when PEG molecules are desorbs from electrode surface. This occurs in potential very more negative than the first. The effect of displacement of the zinc reduction potential to more negative values is known as cathodic polarization. Accordingly, potentials as negative as -1.6V vs. SCE could be used to obtain deposits of zinc alloys with metals such as Mn. Similar XRD results were observed by Sylla *et*

that there is no manganese present in the coating.

the presence of the Zn crystals in different planes.

the presence of Mn in the deposit.

The results for the EDS analysis are shown in the inset.

**Figure 11.** Chronopotentiometric curves obtained during electrodeposition of the deposits on AISI 1018 steel elec‐ trode from base solution S0 and solution S1.

In the absence of PEG the potential changed during the electrodeposition, resulting in a rough and irregular deposit, as evidenced in the SEM analysis. On the other hand, when the additive was added to the base solution, the deposition potential stabilized at around -1.68 V at the beginning of the electrodeposition. Additives such as PEG can shift the potential of Zn deposition to more negative values, enabling Zn alloys to be obtained with metals for which the deposition potentials are very negative [30]. In addition, the use of PEG as an additive allowed a compact and homogeneous deposit to be obtained.

**Figure 12.** SEM image of the deposit formed on AISI 1018 steel electrode at −10 mA cm-2, t = 15 min, from solution S0. The results for the EDS analysis are shown in the inset.

Figure 12 shows the SEM image of the deposit obtained galvanostatically at -10 mA cm-2 in the absence of PEG. The deposit formed is porous and with grains of diverse dimensions ir‐ regularly distributed on the substrate surface. The EDS analysis (inset in Figure 12) revealed that there is no manganese present in the coating.

In addition, the XRD patterns of the film showed above were very similar as those obtained during the potentiostatic deposition at -1.2 V from solution S0n (see Figure 6) indicating only the presence of the Zn crystals in different planes.

The results obtained in the presence of PEG indicated the formation of the Zn-Mn alloy during galvanostatic electrodeposition. Figure 13 shows the SEM micrograph of the deposit obtained under these conditions. The results indicate that the PEG decreased the mean size of grains inducing the formation of a smooth deposit. Although the EDS analysis did not clearly indicate the presence of Mn in the deposit.

**Figure 11.** Chronopotentiometric curves obtained during electrodeposition of the deposits on AISI 1018 steel elec‐

In the absence of PEG the potential changed during the electrodeposition, resulting in a rough and irregular deposit, as evidenced in the SEM analysis. On the other hand, when the additive was added to the base solution, the deposition potential stabilized at around -1.68 V at the beginning of the electrodeposition. Additives such as PEG can shift the potential of Zn deposition to more negative values, enabling Zn alloys to be obtained with metals for which the deposition potentials are very negative [30]. In addition, the use of PEG as an additive

**Figure 12.** SEM image of the deposit formed on AISI 1018 steel electrode at −10 mA cm-2, t = 15 min, from solution S0.

trode from base solution S0 and solution S1.

222 Modern Surface Engineering Treatments

The results for the EDS analysis are shown in the inset.

allowed a compact and homogeneous deposit to be obtained.

**Figure 13.** SEM image of the deposit formed on AISI 1018 steel electrode at −10 mA cm-2, t = 15 min, from solution S1. The results for the EDS analysis are shown in the inset.

The XRD results, exhibited in Figure 14 showed a diffractogram characteristic of a mixture of Zn and ε-phase Zn-Mn with different crystallographic. This finding may be related to the low manganese content, around 2% wt in the deposit. Ballesteros *et al.*[30] have reported that the presence of additives such as PEG can shift the potential of Zn deposition to very negative values. Such behavior is associated with the partial adsorption of PEG onto the substrate surface. The authors related that in the presence this additive the electrodeposition of zinc can occurs in two different ways. First, the zinc is electrodeposited onto the active sites on the electrode surface that are not blocked by adsorbed PEG molecules. In second, the zinc is electrodeposited onto the active sites that are liberated when PEG molecules are desorbs from electrode surface. This occurs in potential very more negative than the first. The effect of displacement of the zinc reduction potential to more negative values is known as cathodic polarization. Accordingly, potentials as negative as -1.6V vs. SCE could be used to obtain deposits of zinc alloys with metals such as Mn. Similar XRD results were observed by Sylla *et* *al.* [32]. They reported a Mn content of 1% wt in a Zn-Mn alloy deposit obtained from a chloridebased acidic bath containing PEG as an additive. The authors postulated that the presence of PEG allowed the formation of a compact and homogeneous deposit with cauliflower-like morphology. However, the presence of PEG in the solution hindered manganese deposition and inhibited the formation of the ζ-phase Zn-Mn. It is important to note that the peaks observed in our study for Zn and the phases of Zn-Mn alloy are very close and some overlap may have occurred.

The evaluation of the corrosion resistance of the coating obtained could be performed by measurements of polarization curves. Figure 15 shows the polarization curves of the produced

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**17**

coatings in a solution containing NaCl 3% (w/v).


**c**


galvanostaticly at -10mA.cm-2.

**ln j (mA.cm-2**

**)**


**ln j (mA.cm-2)**


**a**


**Steel Surface without protection** 

**substrato sem proteçao**

> **S0 S1 S2 S3**





**ln j (mA.cm-2**

**E/V (Ag/AgCl)** 

**Figure 15.** Potentialdynamic Polarization Curves (a) steel surface without protection (b) coating obtained potentiosta‐ ticly at -1.2 V vs (Ag/AgClsat.); (c) coating obtained potentiostaticly at -1,6 V vs (Ag/AgClsat.) and (d) coating obtained

The results showed above include the measurements of the coatings obtained using NH4SCN as additive to illustrate the poor protection of the coating produced with this additive due to the lack of homogeneity as described above (see Table 3). The curves showed in Figure 15 indicate that in general, all coatings shift the corrosion potential value (Ecorr) to negative regions when compared with the Ecorr of the substrate (-0.77 V), this behavior is characteristic for the formation of cathode coatings. It could be also noted from Figure 15 that the corrosion current density (*i*corr) is relatively higher for the coating that presented more negative values of Ecorr. This fact could be seen as divergences but it needs to take in account that the coating that presented more negative values for Ecorr presented also higher roughness, fact that increase

Almost at the same time that the work described in this text was done, others experiments using a very similar approach were done by Brito *et al.* [29]. These authors used H2SO4 solution to leaching spent Zn-C and used methylamine as addictive. They found that the quality of deposits produced from lixiviation depends strongly on the magnitude of the electrodeposi‐ tion current; homogeneous and uniform deposit layers with good anticorrosive properties were obtained, preferentially, at low current densities. The Mn/Zn mass ratios in the produced deposit layers are influenced by electrodeposition currents and the electrodeposition duration.

**)**


**d**

**ln j (mA.cm-2**

**)**

**b**


**E/V (Ag/AgCl)**



**E/V (Ag/AgCl)**

**S0 S1 S2 S3**

http://dx.doi.org/10.5772/56438

225

**S0 S1 S2 S3**

**E/V (Ag/AgCl)**



their superficial area causing this increase in current.

**E/V (Ag/AgCl)**

**Figure 14.** X-ray diffraction (XRD) pattern of a deposit obtained on AISI 1018 steel electrode at -10 mA cm-2, t = 15 min from solution S1 (with PEG10,000 as additive)

Table 4 shows a summary of all parameters used in the electrodeposition and some charac‐ teristics of the deposits obtained.


**Table 4.** Electrodeposition parameters and characteristics of the deposits obtained

The evaluation of the corrosion resistance of the coating obtained could be performed by measurements of polarization curves. Figure 15 shows the polarization curves of the produced coatings in a solution containing NaCl 3% (w/v).

*al.* [32]. They reported a Mn content of 1% wt in a Zn-Mn alloy deposit obtained from a chloridebased acidic bath containing PEG as an additive. The authors postulated that the presence of PEG allowed the formation of a compact and homogeneous deposit with cauliflower-like morphology. However, the presence of PEG in the solution hindered manganese deposition and inhibited the formation of the ζ-phase Zn-Mn. It is important to note that the peaks observed in our study for Zn and the phases of Zn-Mn alloy are very close and some overlap

**Figure 14.** X-ray diffraction (XRD) pattern of a deposit obtained on AISI 1018 steel electrode at -10 mA cm-2, t = 15

Table 4 shows a summary of all parameters used in the electrodeposition and some charac‐




**Table 4.** Electrodeposition parameters and characteristics of the deposits obtained



w/t Mn)

may have occurred.

224 Modern Surface Engineering Treatments

min from solution S1 (with PEG10,000 as additive)

teristics of the deposits obtained.

**Without additive Deposit**

**With additive Deposit**

**Figure 15.** Potentialdynamic Polarization Curves (a) steel surface without protection (b) coating obtained potentiosta‐ ticly at -1.2 V vs (Ag/AgClsat.); (c) coating obtained potentiostaticly at -1,6 V vs (Ag/AgClsat.) and (d) coating obtained galvanostaticly at -10mA.cm-2.

The results showed above include the measurements of the coatings obtained using NH4SCN as additive to illustrate the poor protection of the coating produced with this additive due to the lack of homogeneity as described above (see Table 3). The curves showed in Figure 15 indicate that in general, all coatings shift the corrosion potential value (Ecorr) to negative regions when compared with the Ecorr of the substrate (-0.77 V), this behavior is characteristic for the formation of cathode coatings. It could be also noted from Figure 15 that the corrosion current density (*i*corr) is relatively higher for the coating that presented more negative values of Ecorr. This fact could be seen as divergences but it needs to take in account that the coating that presented more negative values for Ecorr presented also higher roughness, fact that increase their superficial area causing this increase in current.

**17** Almost at the same time that the work described in this text was done, others experiments using a very similar approach were done by Brito *et al.* [29]. These authors used H2SO4 solution to leaching spent Zn-C and used methylamine as addictive. They found that the quality of deposits produced from lixiviation depends strongly on the magnitude of the electrodeposi‐ tion current; homogeneous and uniform deposit layers with good anticorrosive properties were obtained, preferentially, at low current densities. The Mn/Zn mass ratios in the produced deposit layers are influenced by electrodeposition currents and the electrodeposition duration. Lower electrodeposition currents and shorter electrodeposition duration improve the depo‐ sition of Mn in relation to Zn. The presence of the methylamine, also benefit the deposition of Mn and that the addition of methylamine to the electrodeposition baths contributes to the establishment of deposit coatings, with better anticorrosive properties.

**Author details**

Paulo S. da Silva1

**References**

, Jose M. Maciel2

, Karen Wohnrath2

Electrodeposition of Alloys Coatings from Electrolytic Baths Prepared by Recovery of Exhausted Batteries for…

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