Electrodeposition electrodes

The H and OH" ions are supplied by the simultaneous electrolysis of water during electrodeposition. Electrode reactions involving the resins are of little significance. However, oxidation of the metal substrate does play a role in anodic electrocoating. 

An algorithm was developed that keeps the boundary closed in all circumstances of electrodeposition, electrode dissolution, electrochemical machining and levelling. 

The development of scanning probe microscopies and x-ray reflectivity (see Chapter VIII) has allowed molecular-level characterization of the structure of the electrode surface after electrochemical reactions [145]. In particular, the important role of adsorbates in determining the state of an electrode surface is illustrated by scanning tunneling microscopic (STM) images of gold (III) surfaces in the presence and absence of chloride ions [153]. Electrodeposition of one metal on another can also be measured via x-ray diffraction [154]. 

Markovic N M, Gasteiger H A and Ross P N 1995 Copper electrodeposition on Pt(111) in the presence of chloride and (bi)sulphate Rotating ring-Pt(111) disk electrode studies Langmuir 11 4098-108... 

In electrogravimetry the analyte is deposited as a solid film on one electrode in an electrochemical cell. The oxidation of Pb +, and its deposition as Pb02 on a Pt anode is one example of electrogravimetry. Reduction also may be used in electrogravimetry. The electrodeposition of Cu on a Pt cathode, for example, provides a direct analysis for Cu +. 

After the plates have been washed and dried thoroughly, they are pressed ia a preliminary operatioa to the desired thickness. Iadividual electrodes are thea cut from the sheets and a secondary pressing operation to final thickness is done. Often a secondary operation is required to remove sharp edges of electrodeposited 2iac electrodes. 

One potential difficulty with CF-EF is the electrodeposition of the particles at the electrode away from the filtration medium. This phenomenon, if allowed to persist, will result in performance decay of CF-EF with respect to maintenance of the electric field. Several approaches such as momentaiy reverses in polarity, protection of the electrode with a porous membrane or filter medium, and/or utilization of a high fluid shear rate can minimize electrodeposition. 

Section 6.2.1 offers literature data on the electrodeposition of metals and semiconductors from ionic liquids and briefly introduces basic considerations for electrochemical experiments. Section 6.2.2 describes new results from investigations of process at the electrode/ionic liquids interface. This part includes a short introduction to in situ Scanning Tunneling Microscopy. 

Germanium In situ STM studies on Ge electrodeposition on gold from an ionic liquid have quite recently been started at our institute [59, 60]. In these studies we used dry [BMIM][PF<3] as a solvent and dissolved Gel4 at estimated concentrations of 0.1-1 mmol 1 the substrate being Au(lll). This ionic liquid has, in its dry state, an electrochemical window of a little more than 4 V on gold, and the bulk deposition of Ge started several hundreds of mV positive from the solvent decomposition. Furthermore, distinct underpotential phenomena were observed. Some insight into the nanoscale processes at the electrode surface is given in Section 6.2.2.3. 

They form a monolayer that is rich in defects, but no second monolayer is observed. The interpretation of these results is not straightforward from a chemical point of view both the electrodeposition of low-valent Ge Iy species and the formation of Au-Ge or even Au Ge h compounds are possible. A similar result is obtained if the electrodeposition is performed from GeGl4. There, 250 20 pm high islands are also observed on the electrode surface. They can be oxidized reversibly and disappear completely from the surface. With Gel4 the oxidation is more complicated, because the electrode potential for the gold step oxidation is too close to that of the island electrodissolution, so that the two processes can hardly be distinguished. The gold step oxidation already occurs at -i-lO mV vs. the former open circuit potential, at h-485 mV the oxidation of iodide to iodine starts. 

In the reductive regime, a strong, apparently irreversible, reduction peak is observed, located at -1510 mV vs. the quasi reference electrode used in this system. With in situ STM, a certain influence of the tip on the electrodeposition process was observed. The tip was therefore retracted, the electrode potential was set to -2000 mV, and after two hours the tip was reapproached. The surface topography that we obtained is presented in Figure 6.2-14. 

Ruthenium, iridium and osmium Baths based on the complex anion (NRu2Clg(H20)2) are best for ruthenium electrodeposition. Being strongly acid, however, they attack the Ni-Fe or Co-Fe-V alloys used in reed switches. Reacting the complex with oxalic acid gives a solution from which ruthenium can be deposited at neutral pH. To maintain stability, it is necessary to operate the bath with an ion-selective membrane between the electrodes . 

Electrodeposition This method of paint application is basically a dipping process. The paint is water-based and is either an emulsion or a stabilised dispersion. The solids of the paint are usually very low and the viscosity lower than that used in conventional dipping. The workpiece is made one electrode, usually the cathode, in a d.c. circuit and the anode can be either the tank itself or suitably sized electrodes sited to give optimum coating conditions. The current is applied for a few minutes and after withdrawal and draining the article is rinsed with de-ionised water to remove the thin layer of dipped paint. The deposited film is firmly adherent and contains a minimum of water and can be stoved without any flash-off period. This process is used for metal fabrications, notably car bodies. Complete coverage of inaccessible areas can be achieved and the corrosion resistance of the coating is excellent (Fig. 14.1). 

In the case of an electrochemical cell with a negative electrode consisting of an elemental metal, the process of recharging is apparently very simple, for it merely involves the electrodeposition of the metal. There are problems, however. 

One of these is the "shape change" phenomenon, in which the location of the electrodeposit is not the same as that of the discharge (deplating) process. Thus, upon cycling, the electrode metal is preferentially transferred to new locations. For the most part, this is a problem of current distribution and hydrodynamics rather than being a materials issue, therefore it will not be discussed further here. 

Poly crystalline silver layer electrodeposited on a polycrystalline platinum electrode. 

A series of Be-Pt intermetallic compounds arc prepared during the electrodeposition of Be on Pt from a solution of BeCl2 in an equimol NaCl-KCl mixture at 710°C. X-Ray diffraction of the electrode surface shows the presence of BePt, BcjPt. Electrolytic methods are also used to extract single crystals of Be,V from alloys prepared by arc melting Be and the transition metal in the proportion 15 1. 

As noted earlier, the kinetics of electrochemical processes are inflnenced by the microstractnre of the electrolyte in the electrode boundary layer. This zone is populated by a large number of species, including the solvent, reactants, intermediates, ions, inhibitors, promoters, and imparities. The way in which these species interact with each other is poorly understood. Major improvements in the performance of batteries, electrodeposition systems, and electroorganic synthesis cells, as well as other electrochemical processes, conld be achieved through a detailed understanding of boundaiy layer stracture. 

Cattarin S, Furlanetto E, Musiani MM (1996) Cathodic electrodeposition of Se on H electrodes. J Hectroanal Chem 415 123-132... 

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