Fine electrodeposition

In the field of electrowinning and electrorefining of metals, titanium has an advantage as a cathode, upon which copper particularly can be deposited with finely balanced adhesion that allows the electrodeposited metal to strip easily when required. Titanium anodes are also being employed as a replacement for lead or graphite in the production of electrolytic manganese dioxide. 

Chromium is also a very hard metal with excellent wear resistance, and so is widely used as a coating material for engineering applications. For these purposes, coatings are applied by electrodeposition which may be several millimetres thick. These hard engineering chromium coatings invariably contain fine cracks and fissures which can allow corrodents to attack the... 

Single-phase ZnS films of a fine grain size (no XRD shown) and a band gap of 3.7 eV were electrodeposited from aqueous alkaline (pH 8-10) solutions of zinc complexed with EDTA, and thiosulfate as a sulfur source [101]. The voltammet-ric data implied that deposition occurred either by S-induced UPD of Zn or by a pathway involving both Zn " and thiosulfate concurrently. 

It was reported recently [216] that optical-quality PbTe thin films can be directly electrodeposited onto n-type Si(lOO) substrates, without an intermediate buffer layer, from an acidic (pH 1) lead acetate, tellurite, stirred solution at 20 °C. SEM, EDX, and XRD analyses showed that in optimal deposition conditions the films were uniform, compact, and stoichiometric, made of fine, 50-100 nm in size, crystallites of a polycrystalline cubic structure, with a composition of 51.2 at.% Pb and 48.8 at.% Te. According to optical measurements, the band gap of the films was 0.31 eV and of a direct transition. Cyclic voltammetry indicated that the electrodeposition occurred via an induced co-deposition mechanism. 

The SHE is depicted in Figure 7.12, and shows the electrode immersed in a solution of hydrogen ions at unit activity (corresponding to 1.228 mol dm-3 HC1 at 20 °C). Pure hydrogen gas at a pressure of 1 atm is passed over the electrode. The electrode itself consists of platinum covered with a thin layer of platinum black , i.e. finely divided platinum, electrodeposited onto the platinum metal. This additional layer thereby catalyses the electrode reaction by promoting cleavage of the H-H bonds. 

As can be seen in Fig. 4.14a, the metallic deposit obtained after application of a reductive electrodeposition step in Zr02 plus ZnO mixtures consists of large irregularly-shaped grains of Zn accompanied by fine Zn column-shaped grains—as indicated by the SEM/EDX analysis depicted in Figs. 4.14b and 4.14c [234]. 

The electrodeposition offer the advantage of a fine control of the thickness of the catalytic layer, thus optimizing the electroactive area and the transparency of the cathode. A cathode that possesses both a remarkable catalytic activity and a partially porous structure with a large active area is important for limiting the concentration... 

It would be quite correct to state that fine grain size, in the last analysis, is the main reason for the higher strength of electrodeposited metal as compared to their wrought forms. 

In this book a broad-church of ionic liquids will be assumed, encompassing all of the above types because, in the discipline of electrodeposition, it is the resultant deposit that is important rather than the means. As will be seen later there is also a very fine line between a concentrated electrolyte solution and an ionic liquid containing diluents. 

---