Electrochemical treatment of metals

Hertwig K, Bergmann H, Nieber F (1991) Electrochemical treatment of metal containing water in particle electrode cells, 5-20, 42nd ISE Meeting, Montreux, Switzerland, August... 

A System for Support and Trainii of Personnel Working in the Electrochemical Treatment of Metallic Surfaces... 

Electrochemical treatment of metallic surfaces. Example Oxidation of carbon surfaces by imposition of a highly positive potential electrochemical cycling of gold surfaces (the potential is switched periodically between the values for oxygen and for hydrogen evolution in acid solution). 

Chromate conversion coatings are formed by a chemical or an electrochemical treatment of metals or metallic coatings in solutions containing hexavalent chromium (Cr " ") and, usually, other components. The process results in the formation of an amorphous protective coating composed of the substrate, complex chromium compounds, and other components of the processing bath. 

T0235 Electrochemical Treatment of Contaminated Ground Water—General T0279 Environmental Research and Development, Inc., The Neutral Process for Heavy Metals Removal... 

The electrochemical treatment of contaminated groundwater technology uses direct electrical current applied between two immersed electrodes to produce oxidation-reduction reactions in aqueous solutions. Positively charged metal ions are attracted to the negatively charged electrode (the cathode), where they are reduced. 

Observing the variation of electroreflection spectra in the course of electrochemical treatment of electrodes, one may determine qualitatively reversible and irreversible changes in the near-the-surface layer, for instance, partial decomposition of ZnSe under anodic polarization (Lemasson et al, 1980) and deposition of metal atoms on the surface of ZnO under cathodic polarization (Kolb, 1973). 

The heterocontacts between layered compound and noble metals - silver and copper - were studied. The standard chemical and electrochemical treatment of silver and copper electrode surfaces [6] was performed before the experiment. To avoid any selective etching and breaking of the surface layer, the SnNb5Sc(, crystals were not chemically treated. 

Although the author believes that the generalized concept was originally responsible for the electrochemical treatment of corrosion processes by the early workers, it appears that Hammett and Lorch (23) and Frumkin (24) were among the first to specifically describe metallic dissolution according to this concept. Wagner and Traud (16) showed that the electrode kinetics for hydrogen evolution are not affected by the simultaneous dissolution of the metallic ions. 

In general, the benefit of ultrasound upon metal electrodeposition (discussed in length in Section 3) offers promise for the electrochemical removal of metals from solution, although it should be recognized that the systems are somewhat different. Thus, commercial metal electrodeposition requires high concentrations of metal ions in solution while wastewater treatment involves very dilute concentrations of metal ions. However studies are in hand to define the scope of sonication for metal-ion removal [253], and this area offers great promise. 

The cathodes are similarly corroded (chemically or electrochemically) as the anodes but metallurgical factors affect to a lesser degree, that is, the transformation is gradual [69]. However selective attack, such as from electrolyte impurities, often takes place and the production of a homogeneous surface layer of sub-products or crystal metallic impurities produce micro-cracks reducing the durability [70]. In addition, microbial factors produce cathode failure especially in the electrochemical treatment of wastewaters [71]. 

In the present treatment, the fundamental mechanisms involved in aqueous electrochemical corrosion of metals and alloys and the effects of direct chemical and physical processes will be emphasized. 

Fluorination is effective not only for protecting surfaces from impurities but also for giving catalytic function and improving both the chemical and electrochemical characteristics of metal hydrides. For example, the surface of Mg2Ni created by a fluorination treatment was found to be effective as a catalyst for the catalytic generation of hydrogen from an aqueous alkaline solution of NaBH4 by hydrolysis (see Chapter 6.8). 

A selective electrochemical modification of metallic SWNTs that have been wired to electrodes on a surface, has been achieved by Balasubramanian et al. [122]. The authors used, similarly to Strano et al., a diazonium agent to functionalize metallic SWNTs. Here, the reaction is driven by an electrical potential applied between electrodes in contact with tubes and a counter-electrode. The authors found conditions in which primarily metallic SWNTs react, once the semiconducting SWNTs are driven into the nonconducting state by an appropriate gate voltage. An experimental verification of the selective modification is given by transport measurements in which the signature of metallic SWNTs disappears after treatment. 

Conversion coatings, commonly used in Pre-treatment of metals prior to bonding, are formed by a chemical reaction between an aqueous media, usually containing soluble metal salts, and a substrate to produce an insoluble passivating film. They may be chemical or electrochemically produced when produced with an externally applied voltage, an anodic oxide is formed (see Anodizing). 

Electrochemical processes for the pre-treatment of metals include both anodic oxidation, for example, of Cu and A1 in alkali, or Ti in NaF/HF, and cathodic oxidation of Cu in sodium bicarbonate. Electrochemical pre-treatments promote adhesion by producing either a porous surface (Anodizing of Al), or a needle-like dendritic oxide structure. The most suitable surface structure may often be determined by the generic nature of the paint that will be applied subsequently. 

Treatment of metal cyanides. Cyanide is in common use in the extraction of metal from ore and in electroplating, to hold the metal ion in solution to improve the throwing power. Metal cyanides can also be decomposed by electrochemical oxidation. At higher concentrations of cyanide (>1000 ppm) direct oxidation has been used. This, however, can be unsatisfactory if the uncomplexed metal is insoluble and may precipitate, especially if this occurs on the anode. For example ... 

Masa J, Schilling T, Bron M, Schuhmann W (2011) Electrochemical synthesis of metal-polypyrrole composites and their activation for electrocatalytic reduction of oxygen by thermal treatment. Electrochim Acta 60 410-418... 

Elimination of chromate treatment of metal sur ces has spurred the investigation of conducting polymer sur ce protection. Electrochemical polymerization as well as chemical polymerization (37) and a solvent free process... 

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