Coated anodes

The second form consists of Pt metal but the iridium is present as iridium dioxide. Iridium metal may or may not be present, depending on the baking temperature (14). Titanium dioxide is present in amounts of only a few weight percent. The analysis of these coatings suggests that the platinum metal acts as a binder for the iridium oxide, which in turn acts as the electrocatalyst for chlorine discharge (14). In the case of thermally deposited platinum—iridium metal coatings, these may actually form an intermetallic. Both the electrocatalytic properties and wear rates are expected to differ for these two forms of platinum—iridium-coated anodes. 

Miscellaneous. Ruthenium dioxide-based thick-film resistors have been used as secondary thermometers below I K (92). Ruthenium dioxide-coated anodes ate the most widely used anode for chlorine production (93). Ruthenium(IV) oxide and other compounds ate used in the electronics industry as resistor material in apphcations where thick-film technology is used to print electrical circuits (94) (see Electronic materials). Ruthenium electroplate has similar properties to those of rhodium, but is much less expensive. Electrolytes used for mthenium electroplating (95) include [Ru2Clg(OH2)2N] Na2[Ru(N02)4(N0)0H] [13859-66-0] and (NH 2P uds(NO)] [13820-58-1], Several photocatalytic cycles that generate... 

An XPS spectrometer schematic is shown in Figure 7. The X-ray source is usually an Al- or Mg-coated anode struck by electrons from a high voltage (10—15 kV) Alka or Mgka radiation lines produced at energies of 1486.6 eV and 1256.6 eV, with line widths of about 1 eV. The X rays flood a large area (-I cm ). The beam s spot size can be improved to about lOO-jim diameter by focusing the electron beam... 

There are obviously situations which demand considerable over-design of a cathodic protection system, in particular where regular and efficient maintenance of anodes is not practical, or where temporary failure of the system could cause costly damage to plant or product. Furthermore, contamination of potable waters by chromium-containing or lead-based alloy anodes must lead to the choice of the more expensive, but more inert, precious metal-coated anodes. The choice of material is then not unusual in being one of economics coupled with practicability. 

Studies suggested that under certain conditions platinum would become mechanically detached from titanium anodes owing to attack of the substrate through pores in the coating. Anodes became available with a... 

Fig. 2. Performance curve of (a) pure Ni-lOCr and (b) Ce02 coated anode.

VFD tubes operate by the same principle as CRTs but use low-energy electrons (10-100 V) to excite the phosphor. The electrons are emitted from a cathode (wire) and are accelerated and controlled so that they bombard a phosphor-coated anode, causing the phosphor to emit light. ZnO Zn (green-emitting) phosphors were used in early VFD devices, but as the application range expanded, demand developed for multicolored displays.29... 

Fig. 5.10. Schematic diagram of a simple phototube circuit. Photons (hv) strike the CdS-coated anode and electrons are ejected and attracted toward the positive cathode and return through the circuit. The ammeter monitors the flow of electrons that are proportional to the intensity of the photons.

Another example is the very slight delamination that occurs when a thin copper layer is overcoated with an organic coating such as a photoresist and the system is made anodic. The rate of disbonding is a function of the applied potential and hence the rate of dissolution of the copper beneath the coating. Anodic delamination occurs very slowly relative to cathodic delamination at equal potential differences from the corrosion potential. 

Fig. 5.17 Real time observation of anodization behavior of a 400 nm Ti thin film anodized at lOV in the HF - aqueous electrolyte (acetic acid and 0.5 vol.% HF mixed in ratio of 1 7). Inset shows a typical current density versus time response observed for a titanium foil (with one face protected with polymer coating) anodized at the same potential and electrolyte.

The fuel cell in Figure 13.9 can be conceptually viewed as a combination of a Nafion film-coated cathode and a Nafion film-coated anode. Hence, the fuel cell is, in essence, a combination of two chemically modified electrodes. This idea is, in fact, more than just a concept, because electrochemical investigations of Nafion film-coated electrodes have been used to obtain fundamental chemical and electrochemical information that is relevant to the operation of such devices [93]. For example, the kinetics of 02 reduction in fuel cells can be investigated at such modified electrodes the solubility and diffusion coefficient for 02 in Nafion and the proton conductivity of this membrane material can also be determined. Chemically modified electrodes have made analogous contributions to battery development. 

Takahashi and co-workers (69,70,71) reported both cathodic and anodic photocurrents in addition to corresponding positive and negative photovoltages at solvent-evaporated films of a Chl-oxidant mixture and a Chl-reductant mixture, respectively, on platinum electrodes. Various redox species were examined, respectively, as a donor or acceptor added in an aqueous electrolyte (69). In a typical experiment (71), NAD and Fe(CN)g, each dissolved in a neutral electrolyte solution, were employed as an acceptor for a photocathode and a donor for a photoanode, respectively, and the photoreduction of NAD at a Chl-naphthoquinone-coated cathode and the photooxidation of Fe(CN)J at a Chl-anthrahydroquinone-coated anode were performed under either short circuit conditions or potentiostatic conditions. The reduction of NAD at the photocathode was demonstrated as a model for the photosynthetic system I. In their studies, the photoactive species was attributed to the composite of Chl-oxidant or -reductant (70). A p-type semiconductor model was proposed as the mechanism for photocurrent generation at the Chi photocathode (71). 

Matsui, K., Kyotani, T., and Tomita, A. Hydrothermal synthesis of single crystal Ni(OH)2 nanorods in a carbon-coated anodic alumina film. Adv. Mater. 14, 2002 1216-1218. 

The electrocatalytic behavior of olefins was studied by Zanta et al. (2000) at thermally prepared ruthenium-titanium- and iridium-titanium-dioxide-coated anodes. The aliphatic olefins were shown to be inactive in the region before oxygen evolution, while aromatic ones showed one or two oxidation peaks, and the catalytic activity seemed to be the same for both substrates. However, as for platinum anodes, voltammetric studies and FTIR analyses have also shown the formation of a polymeric film that blocks the surface of the electrode and decreases its activity. 

Komori and Nonaka [499] reported the first example of an electrochemical enantiomer-differentiating reaction When racemic 2,2-dimethyl-1-phenyl-1-propanol was oxidized at a poly(L-valine)-coated anode, 43% optically pure (S)-(—)-2,2-dimethy 1-1-phenyl-1-propanol was recovered as an unreacted part. Yamagishi and Aramata [500] also found electrooxidative optical resolution of a racemic Co(l,10-phenathroline)3 complex by a chiral clay-coated anode, and Yoshinaga and coworkers [501] electrore-ductively resolved racemic Co(acetylacetonato)3 by using optically active supporting electrolytes. 

The DSA-type anodes are inert , coated anodes made of a valve metal (titanium, niobium, or tantalum) base coated with an electrochemically active coating. The active coating is made either of noble metals or of mixed metal oxides. Noble metals in active coatings are usually platinum or platinum alloys. Mixed metal-oxide coatings contain active oxides and inert oxides the active components are usually ruthenium dioxide (R.UO2) and iridium dioxide (IrC>2) and the inert components are mostly titanium dioxide (TiC>2) and other oxides such as tantalum... 

PAn-nitrilic rubber composites76 have been prepared using rubber-coated anodes for electyropolymerization. The resultant material has the mechanical properties of a crosslinked elastomer with the electrical and electro-optical properties... 

The exposure cell is constructed of aluminum. The back plate has channels to provide for circulation of cooling water. The side piece has nozzles which provide entrance and exit ports for the exposure atmospheres. The face plate is made from 1/8 in. quartz. All aluminum parts were subjected to a "hard-coat" anodizing process to minimize corrosion. The back plate was covered with a one mil thick sheet of teflon to protect the samples from contamination. 

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