Coated cathodes

Corrosion prevention (liners, coatings, cathodic protection)... 

The preparation of the metal surface to receive the protective coating is of prime importance since a coating which is not bonded to the metal surface can allow electrolytes to contact the metal, with resultant corrosion. If water films develop between the metal and the electrically non-conductive coating, cathodic protection becomes ineffective. 

Rating the results of corrosion tests on electroplated coatings cathodic to the substrate Guidance on stationary outdoor exposure corrosion tests... 

Electrodeposited chromium coatings. Electrolytic corrosion testing Coatings cathodic to the substrate-rating of electroplated test specimens subjected to corrosion tests... 

Coatings, cathodic protection, and chemical additives are used extensively to prevent internal and external pipeline corrosion. The excessive use of incompatible chemical additives has caused severe problems in gas-transporting systems. Costs arising from these problems often exceed the costs of the chemicals themselves. The careful evaluation and selection of chemical additives can minimize these problems and reduce operating costs [I860]. 

Zinc electrowinning takes place in an electrolytic cell and involves running an electric current from a lead-silver alloy anode through the aqueous zinc solution. This process charges the suspended zinc and forces it to deposit onto an aluminum cathode (a plate with an opposite charge) that is immersed in the solution. Every 24 to 48 h, each cell is shut down, the zinc-coated cathodes removed and rinsed, and the zinc mechanically stripped from the aluminum plates. The zinc concentrate is then melted and cast into ingots, and is often as high as 99.995% pure. 

Cold rolling, Raney-nickel-coated cathodes, 40 114... 

Although at least four different technologies [cold rolling, flame spraying, Zn and A1 melt dipping, cathodic deposition of Ni/Zn precursor alloys (76)] have been described, only cold rolling and cathodic deposition of precursor alloys are used for commercial production of Raney-nickel-coated cathodes. 

Fig. 12. Morphology of Raney-nickel-coated cathodes for hydrogen evolution from caustic electrolytes (a) surface of Ni-Zn precursor coatings, (b) surface of Raney-nickel coating prepared by caustic leaching of the Zn content of the precursor, (c) cut through a Raney-nickel coating.

Fig. 14. Comparison of the current-voltage curves of a smooth nickel cathode and two different Raney-nickel-coated cathodes posessing comparable loading and effective surface (a) smooth nickel. Raney nickel prepared from two different precursors (b) plasma-sprayed NiAh, (c) NiAU cold rolled together with Mond nickel.

Fig. 15. Ru and RuOi-coated cathodes cyclic voltammogram of (a) RuO coating, (b) Ru-metal cathode, (c) semilogarithmic cnrrenl voltage curve of the cathodic hydrogen evolution at a Ru-coated and a RuO >-coated cathode in 30 wt% KOH at 80°C.

The cost of building a pipeline is usually divided into four categories materials (line pipe, fittings coatings, cathodic protection, etc), right-of-way... 

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). 

In the case of alkyl-substituted aromatics, the predominant reaction path very often is side-chain acyloxylation. By using Pd-coated cathodes in an undivided cell, it is possible to avoid the formation of the side chain-substituted products, because under these conditions the benzyl ester undergoes cathodic cleavage into the starting compounds 161) ... 

Chlorobenzene, 1,2,3,5-tetrachlorobenzene and lindane (y-hexachlorocyclo-hexane) were dechlorinated in different solvents on plain and metal-modified carbon cloth cathodes. In dimethylsufoxide and ACN, chlorobenzene was dechlorinated even on plain carbon materials, while Pd-coated and Zn-coated cathodes were necessary to perform degradation in methanol and water, respectively (Kulikov etal. 1996). 

Fig. 14.5 Effect of preparation temperature on phenol degradation, phenol 100 mg L-1 electrolyte 0.25MNa2SO4 anode Sn02 with nanometer coating cathode stainless steel...

Figure 15.22 Effect of the system pressure in anode magnetron argon DC discharge with TMS coated cathode CRS plate, 76 mm interelectrode distance, and 180G.

Fig. 1 shows one of the first electrolytically deposited alumimun coatings to be obtained from this type of electrolyte. Since electrolytic aluminum deposition from this system has no true smoothening effect, thick layers become even rougher, as illustrated by the thickly coated cathode plate shown in Fig. 1. The cathodic deposition and the anodic dissolution of aluminum corresponded to almost 100 <7o of the amount expected according to the Faraday rule, which is an important prerequisite for even considering using this electrolysis technique for technical applications. Independently of the layer thickness, the deposited aluminum layers are found to be ectraordinarily pure. Spectroscopic investigations have revealed purities of up to 99.999%. Even when relatively impure raw aluminum with purities of 99.7% functions as the anode, very pure aluminum can be deposited. Therefore, obviously not only a technique of electroplating aluminum was discovered, but also a method of...

---