Electrodeposited Alloy Powders

All abovementioned methods are expensive in comparison with the electrodeposition of Mo-Ni alloy coatings. Although molybdenum cannot be separately electrodeposited from aqueous solutions, it can be codeposited with the iron-group metals (Fe, Co, Ni) in the presence of appropriate complexing agents, by the type of alloy electrodeposition defined by Brenner [13] as induced codeposition. 

It should be emphasized here that only two papers concerning electrodeposition of Mo-Ni alloy powders (actually powders of the system Mo-Ni-O) and their characterization are published so far [14-16]. 

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Jovic VD, Jovic BM, Maksimovic VM, Pavlovic MG (2007) Electrodeposition and morphology of Ni, Co and Ni-Co alloy powders part II. Ammonium chloride supporting electrolyte. Electrochim Acta 52 4254—4263... 

Anomalous Codeposition of Alloy Powders 8.2.1 Electrodeposited Co-Ni Powders... 

Polarization Curves for Co-Ni Alloy Powder Electrodeposition from the Sulfate-Containing Supporting Eiectroiyte... 

In Fig. 8.1a are shown polarization curves corrected for IR drop for the processes of Co, Ni, and Co-Ni alloy powder electrodeposition from 1 M (NH4)2S04 + 0.7 M NH4OH containing supporting electrolyte. Their shape of aU polarization curves is identical, characterized with two inflection points, A and B. For Co electrodeposition, sharp increase of current occurs at about —1.19 V versus Ag/AgCl, while for Ni electrodeposition, this phenomenon is moved to more negative potentials... 

Fig. 8.1 (a) Polarization curves for the electrodeposition of cobalt (Co), nickel (Ni), and Co-Ni alloy powders after IR drop correction recorded for different Ni /Co ions ratios 4.00, 1.50, 0.67, and 0.25 (marked in the figure), (b) The same polarization curves after hydrogen evolution current density subtraction, (c) Corresponding rji vs. E curves for (b) (Reprinted from Ref. [1] with kind permission from Springer)... 

The Morphology of the Co-Ni Alloy Powders Electrodeposited from the Sulfate-Containing Supporting Electrolyte... 

As the Ni /Co ions ratio in the electrolyte decreases from 4.00 to 1.50, the composition of the Co-Ni alloy powder changes from about 78 at.% Ni - 22 at.% Co to about 56 at.% Ni - 44 at.% Co, and this change influences the morphology of the powder. All powder agglomerates electrodeposited at Ni /Co = 1.50 are covered with the fem-like dendrites (Fig. 8.3b). Only few of agglomerates are bigger (about 200 pm), and the number of cavities observed on them is significantly... 

Considering all detected types of agglomerates in electrodeposited Co-Ni alloy powders of different compositions, one can conclude that only one powder (with 78 at.% of Ni) contains very small amount of cauliflower-like agglomerates typical for pure Ni powder, but slightly different, while the rest of them contain some of the agglomerates detected in pure Co powder. The difference between the agglomerates detected in pure Co powder and in Co-Ni alloy powder (except for the... 

Polarization curves corresponding only to the processes of electrodeposition of pure metals and alloy powders (after subtracting hydrogen evolution current density) are shown in Fig. 8.6b. Corresponding t][ vs. E curves for pure metals and alloy powder electrodeposition are presented in Fig. 8.6c [1]. 

As in the case of sulfate-supporting electrolyte (Fig. 8.1b), diffusion limiting current density (in this case not represented with the plateau) for Co is higher than that for Ni (Fig. 8.6b). At the same time, all polarization curves for Co-Ni alloy powder electrodeposition are characterized with higher values of current densities. 

From all solutions, Fe-Ni alloy powders were electrodeposited at a constant current density corresponding to the slightly lower value (/pinflection point B (marked with ( )) on the polarization curves (see Fig. 8.14) [1, 8]. 

Polarization Curves for Fe-Ni Alloy Powder Electrodeposition from Chloride Citrate-Supporting Electrolyte... 

The polarization curves corrected for IR drop for the processes of Fe, Ni, and Fe-Ni alloy powder electrodeposition from ammonium chloride-sodium citrate containing supporting electrolyte in the presence of Fe(ll) and Ni(II) species are shown in Fig. 8.14. In the case of Fe(II) salts, polarization curve for iron electrodeposition (Fe) was placed at more positive potentials than that for nickel (Ni) as it is expected from the values of their reversible potentials. The polarization curves for Fe-Ni alloy powder electrodeposition are placed in between, and all of them were placed at more positive potentials than expected from the Ni/Fe ratio, indicating anomalous codeposition. 

A low current efficiency for the Fe-Ni alloy powder electrodeposition from the solution containing Fe(III) salt is the consequence of the first step in the overall reaction being reduction of Fe(III) species into Fe(II) species, taking place at all potentials more negative than —0.2 V versus AglAgCl. Nevertheless, some experiments were performed in the solution of Fe(III) ions and the morphology of electrodeposited Fe-Ni alloy powders was investigated. 

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