Techniques direct oxide reduction

This technique of forming semiconducting films by direct oxidation-reduction is used to grow highly microcrystalline films directly on the copper or silver substrate. These films show a metallic sheen and can be grown to a thickness of 10 ym in a... 

Direct electrochemical reduction and oxidation treatment of pollution involving a mass-free reagent - the electron - is a very attractive idea, because it is a uniquely clean process, as (1) the reduction and oxidation take place at inert electrodes and (2) there is no need to add chemicals. The techniques of cathodic reduction/anodic oxidation of wastewaters containing dyes are relatively new and have drawn the attention of investigators in Japan, China, USA and Russia [55]. 

Moreover, despite the many advances in electrochemical measurement and modeling, our understanding of SOFC cathode mechanisms remains largely circumstantial today. Our understanding often relies on having limited explanations for an observed phenomenon (e.g., chemical capacitance as evidence for bulk transport) rather than direct independent measures of the mechanism (e.g., spectroscopic evidence of oxidation/reduction of the electrode material). At various points in this review we saw that high-vacuum techniques commonly employed in electrocatalysis can be used in some limited cases for SOFC materials and conditions (PEEM, for example). New in-situ analytical techniques are needed, particularly which can be applied at ambient pressures, that can probe what is happening in an electrode as a function of temperature, P02, polarization, local position, and time. 

The first electrochemical studies of Mb were reported for the horse heart protein in 1942 (94) and subsequently for sperm whale Mb (e.g., 95) through use of potentiometric titrations employing a mediator to achieve efficient equilibriation of the protein with the electrode (96). More recently, spectroelectrochemical measurements have also been employed (97, 98). The alternative methods of direct electrochemistry (99-102) that are used widely for other heme proteins (e.g., cytochrome c, cytochrome bs) have not been as readily applied to the study of myoglobin because coupling the oxidation-reduction eqiulibrium of this protein to a modified working electrode surface has been more difficult to achieve. As a result, most published electrochemical studies of wild-type and variant myoglobins have involved measurements at eqiulibrium rather than dynamic techniques. 

The fluoride reduction technique is being replaced in production plants by the metallothermic reduction of an oxide (24). Direct oxide... 

Energetics of oxidation-reduction (redox) reactions in solution are conveniently studied by arranging the system in an electrochemical cell. Charge transfer from the excited molecule to a solid is equivalent to an electrode reaction, namely a redox reaction of an excited molecule. Therefore, it should be possible to study them by electrochemical techniques. A redox reaction can proceed either by electron transfer from the excited molecule in solution to the solid, an anodic process, or by electron transfer from the solid to the excited molecule, a cathodic process. Such electrode reactions of the electronically excited system are difficult to observe with metal electrodes for two reasons firstly, energy transfer to metal may act as a quenching mechanism, and secondly, electron transfer in one direction is immediately compensated by a reverse transfer. By usihg semiconductors or insulators as electrodes, both these processes can be avoided. 

A very useful extension of the voltammetric technique is cyclic voltammetry (Adams, 1969 Cauquis and Parker, 1973) in which one scans the potential of the working electrode in an unstirred electrolyte solution in the anodic (cathodic) direction and records one or several peaks due to oxidation (reduction) of the substrate. At some suitable potential, the direction of the scan is reversed and peaks due to reduction (oxidation) of intermediates and/or products formed during the forward scan are observed. In the simplest case a linear increase (decrease) of the potential with time is employed (triangular cyclic voltammetry) with scan rates in the range 0 01-1000 V s 1. It should be noted that cyclic voltammetry at scan rates above 1 Vs"1 requires the use of a differential cell to reduce the residual current due to charging of the electrified interface (see, for example, Peover and White, 1967). The theory of cyclic voltammetry has been... 

Cyclic voltammetry (CV) is an important and widely used electroanalytical technique. Although CV is infrequently used for quantitative analysis, it finds wide applicability in the study of oxidation/reduction reactions, the detection of reaction intermediates, and the observation of follow-up reactions of products formed at electrodes. In CV, the applied potential is swept in first one direction and then the other while the cunent is measured. A CV experiment may use one full cycle, a partial cycle, or several cycles. 

As any method of anion analysis may be applied if isolation techniques such as evaporation, precipitation, ion exchange, or solvent extraction are employed, we shall limit the discussion to direct methods and admit isolation techniques only if they are simple and rapid. The methods apparently best suited to the direct analysis of trace amounts of anions therefore are limited to selective membrane potentiometric, atomic absorption, fluorescence, and spectrophotometric methods following oxidation-reduction or complexometric reactions, or solvent extraction. Most of the traditional analytical methods—gravimetric, titrimetric, emission spectrometric, and electrical methods involving oxidation and reduction are less suitable, as are most radioactive procedures including neutron activation analysis, except in special cases. 

In the aqueous solutions of metal salts commonly used for the preparation of oxides, metal ions are present mostly in the form of hydrated ions [M(H20)/0H)J + or complexes with other compounds occurring in the solution. Using radiation, in the process of their conversion to oxides two basic simultaneous reactions are employed—change of the metal oxidation state (most often radiation reduction) and/or precipitation of insoluble compounds due to the formation of the precipitant. Both reactions are initiated and controlled by the radiation absorbed in the aqueous solution as a result of the process, solid phase is formed in the solution. According to the solid phase composition, the preparations may be classified into two main categories—direct and indirect formation of oxides. Direct oxide formation means that after drying the solid phase consists of (nano)crystalline oxide phase, whereas indirect formation encompasses the formation of precursors to oxide(s). These precursors include amorphous or crystalline hydroxides, oxide hydroxides, carbonates, or basic carbonates. Oxides are obtained by calcination of the precursors in the oven, similar to other oxide preparation techniques. 

Chlorination. Direct chlorination has been the preferred technique for regeneration of cupric etchant because of its historically low cost, high rate, efficiency in recovery of copper, and pollution control. The cupric chloride-sodium chloride system (Table 34.1, no. 3) is suitable. Figure 34.2 shows a generalized process. Chlorine, hydrochloric acid, and sodium chloride solutions are automatically fed into the system as required. Sensing devices include oxidation-reduction instruments (Cu oxidation state), density (Cu concentration), level sensors. 

---