Anodic methods

Two methods of providing cathodic protection for minimizing corrosion of metals are in use today. These are the sacrificial-anode method and the impressed-emf method. Both depend upon making the metal to be protected the cathode in the electrolyte involved. 

Examples of the sacrificial-anode method include the use of zinc, magnesium, or aluminum as anodes in electrical contact with the metal to be protected. These may be anodes buried in the ground for protection of underground pipe lines or attachments to the surfaces of equipment such as condenser water boxes or on ship hulls. The current required is generated in this method by corrosion of the sacrificial-anode material. In the case of the impressed emf, the direct current is provided by external sources and is passed through the system by use of essentially nonsacrificial anodes such as carbon, noncor-rodible alloys, or platinum buried in the ground or suspended in the electrolyte in the case of aqueous systems. 

A comprehensive work on the electrodeposition chemistry and characterization of anodically synthesized CdTe thin films has been presented by Ham et al. [98]. In this work, along with the electrolytic anodic synthesis of CdTe by using Cd anodes in alkaline solutions of sodium telluride, an electroless route of anodizing a Cd electrode held at open circuit in the same solution was also introduced. The anodic method was expected to produce CdTe with little contamination from Te on account of the thermodynamic properties of the system the open-circuit potential of Cd anodes in the Te electrolyte lies negative of the Te redox point, so... 

This method of corrosion protection consists of (i) the sacrificial anode method and (ii) impressed current cathodic protection. The other related impressed current protection method is anodic protection. 

The configuration of the products obtained by the anodic method 0/a = 13.9) shows a remarkable similarity with the microsomal oxidation products (P/a = 14.1), whereas peroxybenzoic acid oxidation exhibits poor stereospecificity (P/a = 3). ... 

Tetramethylcyclopit ane (2 equation 7) is the simplest strained hydrocarbon which is easily oxidized by the anodic method in methanol to give two products widi a total yield of 71%. ... 

Enolic alkenes, i.e. alkenes bearing electron-donating substituents such as alkoxy, acyloxy and dialkyl-amino groups, are easily oxidizable by the anodic method. 

The relatively low oxidation potentials of simple aliphatic amines indicate that they should be easily oxidized by the anodic method. 

As the oxidation potential clearly shows, carbanions may easily be oxidized by the anodic method. The most typical process of the anodic oxidation of carbanions is the formation of radical species (equation 52). 

The anodic method, which often gives superior yields, has been effectively used in the total synthesis of a number of natural products, as in the preparation of Aniba neolignan (LII) in 81% yield [52] ... 

While anodic oxidation of simple alcohols is of limited utility, direct oxidation of vicinal diols and related compounds is an excellent method for achieving oxidative cleavage to the corresponding carbonyl or carbonyl-acetal products, as in Eqs. (53) and (54). Unlike certain chemical glycol cleavage reactions, the anodic method is not limited by the stereochemistry of the substrate oxygens [132]. 

Over the past two decades, enormous progress has been achieved in the synthesis, characterization and device applications of nanostructured Ti02. Among the various types of nanostructured Ti02, the quasi-one-dimensional nanostructure has attracted particular attention. This chapter will give a comprehensive review on the synthesis of this quasi-one-dimensional Ti02 nanostructure by electrochemical anodization method, the characterization of its properties, and its potential for applications. 

There exist a variety of methods to synthesize quasi-one-dimensional nanostructured materials, which include but not limited to vapor phase growth, template-assisted synthesis, sol-gel deposition, surfactant-assisted growth, sonochemical method, hydrothermal method, and electrochemical deposition [21], Among the various methods, the electrochemical anodization method is one of the simplest and cheapest methods to synthesize ordered quasi-one-dimensional nanostructure. 

The electrochemical anodization method to synthesize nanostructured metal oxide has been known for more than 50 years [22], However, it was only until quite recently that highly ordered A12C>3 nanostructure was obtained by anodization [23], Thereafter, self-assembled anodic Ti02 nanostructure with a certain degree of ordering became a hot area of research partly due to the attractive properties of Ti02, which are promising for various applications. 

The effectiveness of anodic methods can vary considerably and is mainly determined by the protective nature of the passive layer formed. 

Chen XJ, Shen ZM, Yuan T, Zheng SS, Ju BX, Wang WH. (2006). Enhancing electrokinetic remediation of cadmium-contaminated soils with stepwise moving anode method. Journal of Environmental Science and Health Part A 41 2517-2530. 

In contrast, the anodic oxidation technique relies on the metal cation exhibiting a low oxidation state that is anodically oxidized to a higher oxidation state [6], Here the pH of the electrolyte is often critical and has to be chosen such that the lower oxidation state is stable while the higher oxidation state readily undergoes hydrolysis to yield the metal oxide or hydroxide. Another anodic method exploits the fact that the desired metal compound is precipitated on lowering the pH close to the electrode achieved by reduction of water or other additives. 

The sacrificial anode method is the practical in-service application of galvanic cell. Hence, the corrosion potential for a sacrificial anode material must be lower than that of the structure to be protected. 

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