Electrochemical deposition cathodic reaction

Other corrosion inhibitors also enhance passivity without electrochemical reduction, by depositing insoluble oxidation products into the passivating film. For example benzoate ions cause deposition of ferric benzoate into the oxide, but do not provide any cathodic reaction. 

The electrolyte is made by in situ chlorination of vanadium to vanadium dichloride in a molten salt bath. Higher valent chlorides are difficult to retain in the bath and thus are not preferred. The molten bath, which is formed by sodium chloride or an equimolar mixture of potassium chloride-sodium chloride or of potassium chloride-lithium chloride or of sodium chloride-calcium chloride, is contained in a graphite crucible. The crucible also serves as an anode. Electrolysis is conducted at a temperature about 50 °C above the melting point of the salt bath, using an iron or a molybdenum cathode and a cathode current density of 25 to 75 A dnT2. The overall electrochemical deposition reaction involves the formation and the discharge of the divalent ionic species, V2+ ... 

For forced-convection studies, the cathodic reaction of copper deposition has been largely supplanted by the cathodic reduction of ferricyanide at a nickel or platinum surface. An alkaline-supported equimolar mixture of ferri- and ferrocyanide is normally used. If the anolyte and the catholyte in the electrochemical cell are not separated by a diaphragm, oxidation of ferrocyanide at the anode compensates for cathodic depletion of ferricyanide.3... 

One important type of complex mechanism in electrode reactions is a series of consecutive reactions. One example of this type is electrochemical deposition from complexed ions. In this case the electrochemical reaction is preceded by a chemical reaction. Another example is that of inclusion of cathodic hydrogen evolution. We discuss these two cases next. 

The anodic reaction is an oxidation reaction producing electrons in the anode, while the cathodic reaction is a reduction reaction consuming electrodic electrons at the cathode interface. We shall consider, as an example, an electrochemical cell consisting of a metallic zinc electrode and a metallic copper electrode, in which the anodic reaction of zinc ion transfer (zinc dissolution) is coupled with the cathodic reaction of copper ion transfer (copper deposition) as shown in the following processes ... 

Electrochemical deposition is the method of forming a thin layer on a substrate via an electrochemical reaction. It can be used to obtain either cathodic films, such as... 

This observation would at first seem to defy thermodynamics. To make an electrochemical reaction occur, one has to apply an overpotential. If a cathodic reaction such as metal deposition is involved, the overpotential should be negative (i.e., the potential applied should be negative with respect to the reversible potential). In Fig. 61, metal... 

The Birch and Benkeser reactions of some unsaturated organic compounds [318 and references therein], which consist of a reduction by sodium or lithium in amines, can be mimicked electrochemically in the presence of an alkali salt electrolyte. The cathodic reaction is not the deposition of alkali metal on the solid electrode but the formation of solvated electrons. Most of the reactions described were performed in ethylenediamine [319] or methylamine [308,320]. A feature of these studies is variety introduced by the use of a divided or undivided cell. In a divided cell, the product distribution appears to be the same as that in the classic reduction by metal under similar conditions. In contrast, in an undivided cell the corresponding ammonium salt is formed at the anode it plays the role of an in situ generated proton donor. Under such conditions, the proton concentration... 

Electrodeposition or electrochemical deposition (of metals or alloys) involves the reduction of metal ions from electrolytes. At the cathode, electrons are supplied to cations, which migrate to the anode. In its simplest form, the reaction in aqueous medium at the cathode follows the equation ... 

The auxiliary electrode used is usually electrochemically inert, yet capable of maintaining rapid cathodic reactions to maintain the desired polymerization rate at the working electrode surface. During deposition at anodic potentials, the auxiliary electrode is exposed to (sometimes extreme) negative potentials. The increase in pH (due to the reduction of dissolved oxygen in the solution and to the reduction of water itself) may interfere with the polymerization process hence, the positioning of the auxiliary electrode is of paramount importance. To prevent an increase in pH, easily reduced species such as copper or silver salts may be added. This provides a more facile electrode reaction at the cathode and prevents electrode reactions that result in a change in pH. 

Chemical reactions can be initiated and sustained by a corona discharge. Boron has been deposited on a tungsten wire substrate in a corona discharge at relatively low temperatures. The deposition process is electrochemical in nature, the boron being deposited cathodically, and the mechanism for the reaction is indicated to be of the form ... 

Electroplating is the most widely used electrochemical surface treatment process, involving the electrochemical deposition of a layer of metal or alloy onto a substrate by means of one or more cathodic metal ion reduction reactions of the form... 

The electrochemical monolayer deposition in cathodic reactions above the Nemst potential, the underpotential deposition (UPD), is one of the most promising instruments for assembling of nanostructures from atoms and atomic monolayers [1], Though the UPD phenomenon has been known for decades [2], its technological application is still hindered, because of insufficient knowledge of the dynamics and mechanisms of reactions in the monolayers. 

Tatapudi and Fenton [17] explored the synthesis of ozone in a proton exchange membrane (PEM) electrochemical flow reactor as a part of an overall scheme to study the paired synthesis of ozone and hydrogen peroxide in the same PEM reactor. A mixture of commercially available lead dioxide powder and Teflon deposited on a Nafion" 117 membrane was used as the anode. Current efficiencies ranged from 2.5% at an applied potential of 3.0 V to 5.5% at 4.0 V. The corresponding cathodic reaction was hydrogen evolution. 

Atmospheric corrosion is electrochemical corrosion in a system that consists of a metallic material, corrosion products and possibly other deposits, a surface layer of water (often more or less polluted), and the atmosphere. The general cathodic reaction is reduction of oxygen, which diffuses through the surface layer of water and deposits. As shown in Section 6.2.5, the thickness of the water film may have a large effect, but it is more familiar to relate atmospheric corrosion to other parameters. The main factors usually determining the accumulated corrosion effect are time of wetness, composition of surface electrolyte, and temperature. Figure 8.1 shows the result of corrosion under conditions implying frequent condensation of moisture in a relatively clean environment (humid, warm air in contact with cold metal). 

Electroplating is the process of electrochemically depositing a layer of metal onto a surface. The object to be plated is made the cathode in an electrolyte bath containing the metal ion, M"", so that the reaction at the cathode is... 

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