Electrodeposition of Co powders

Fig. 1.12 Polarization curves for (a) the electrodeposition of Co powder measured without IR drop correction (dot line, ini) and with IR drop correction (solid line, i,ot) and (b) the electrodeposition of Co powder measured with IR drop correction (solid line, i,ot), (O) polarization curve for hydrogen evolution (i(H2)) and (A) polarization curve for Co powder electrodeposition (ico) after subtraction of i(H2). Solution 0.10 M C0SO4 - -1.0 M (NH4>2S04 -I- 0.70 M NH4OH (Reprinted from Ref. [28] with permission from Elsevier and Ref. [29] with kind permission from Springer)...

According to Calusam [55] some information on electrodeposition of Co powder is available in patents [56] as well as in reviews [57]. Unfortunately these references are from 1932 and there are no data about the morphology of powder particles, since then there are no published data about electrodeposition of Co powder. Only two micrographs of Co powder, showing that the particles are very fine agglomerates, are presented in the Metallographic Atlas of Powder... 

Fig. 2.24 Typical polarization curves for the electrodeposition of Co powder from ammonium sulfate-cunmonium hydroxide supporting electrolyte with (1) and without (2) IR drop correction. Polarization curves for hydrogen evolution in different supporting electrolytes are also presented in the figure (curves 3 and 4) (Reprinted from [90, 91] with the permission of Elsevier.)...

Fig. 2.35 Polarization curves for the electrodeposition of Co powder after IR drop correction (/tot) recorded onto GC electrode (/tot(GfC)) and onto Co electrode (/tot(Co))...

The morphology of Co powder electrodeposited at higher current density (/pd(2) = —1.85 A cm ) is much more uniform in comparison with the morphology of Co powder electrodeposited at a lower current density. 

The morphology of Co powder agglomerates electrodeposited at / pd (marked in Fig. 2.35), independently of the substrate (GC or Co), is presented in Fig. 2.36. It is practically the same as that for Co powder electrodeposited at7pd(2) from sulfate electrolyte [90], except that all nodular endings possess flat surface [91] which is actually composed of very thin (about 0.1 pm) and about 1 pm long crystals of Co, as shown in Fig. 2.33. 

Hydrometallurgical processes, i.e. production of Ni, Co, Cu, or similar metals, are well established in practice. Similarly, the electrodeposition of metallic powders has been extensively studied over the last century. A significant portion of this book is devoted to electrodeposition of metallic powders. The study of electroless deposition of metal powders has to a certain extent been neglected. The formation of metallic powders occurring during electroless deposition of metallic powders is considerably less investigated than its electrolytic counterpart. 

Reisse and co-workers [147-149] were the first to describe a novel device for the production of metal powders using pulsed sonoelectrochemical reduction. This device exposes only the flat circular area at the end of the sonic tip to the electrodeposition solution. The exposed area acts as both cathode and ultrasound emitter, named by Reisse et al. as sonoelectrode . A pulse of electric current produces a high density of fine metal nuclei. This is immediately followed by a burst of ultrasonic energy that removes the metal particles from the cathode, cleans the surface of the cathode, and replenishes the double layer with metal cations by stirring the solution. In [145], a list is given of chemically pure fine crystalline powders, mostly metals or metallic alloys, prepared by this method, with particle sizes varying between 10 and 1000 run depending on deposition conditions. 

Jovic VD, Maksimovic VM, Pavlovic MG, Popov KI (2006) Morphology, internal structure and growth mechanism of electrodeposited Ni and Co powders. J Solid State Electrochem... 

Jovic VD, Jovic BM, Pavlovic MG (2006) Electrodeposition of Ni, Co and Ni-Co alloy powders. Electrochim Acta 51 5468-5477... 

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

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)... 

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... 

With increasing the content of Co " " ions in the solution, as well as Co content in the powder (Ni /Co ions ratio of 1.50, 42 at.% Co in the powder), very few cauliflower-like agglomerates can be detected in the powder electrodeposit (Fig. 8.8a), being of the size of about 100 pm, while most of them are spongy-like... 

With further decrease of the Ni /Co ions ratio in the solution (0.33, 83 at.% Co in the powder), compact agglomerates, typical for pure Co powder, could be clearly detected in the powder electrodeposit, as can be seen in Fig. 8.13a, together... 

The Mo-Ni-O powders were electrodeposited from two supporting electrolytes, as in the case of Co-Ni system 1 M NHjCl-fO. M NH4OH and 1 M (NH4)2S04 -f 0.7 M NH4OH, with the pH of the solutions being 9.0. 

Most of the data concerning Co, Fe and Ni powders electrodeposition are summarized in Chapter XVIII of the book Electrodeposition of Powders from Solutions, by Calusam [55]. 

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