Metal cathode

The emission spectrum from a hollow cathode lamp includes, besides emission lines for the analyte, additional emission lines for impurities present in the metallic cathode and the filler gas. These additional lines serve as a potential source of stray radiation that may lead to an instrumental deviation from Beer s law. Normally the monochromator s slit width is set as wide as possible, improving the throughput of radiation, while being narrow enough to eliminate this source of stray radiation. 

Fused-salt electrolysis of K2NbFy is not an economically feasible process because of the low current efficiency (31). However, electrowinning has been used to obtain niobium from molten alkaU haUde electrolytes (32). The oxide is dissolved in molten alkaU haUde and is deposited in a molten metal cathode, either cadmium or zinc. The reaction is carried out in a ceramic or glass container using a carbon anode the niobium alloys with the cathode metal, from which it is freed by vacuum distillation, and the niobium powder is left behind. 

In this process, uranium metal is electrodeposited at the cathode, while plutonium and other transuranium elements remain in the molten salt as trichlorides. Plutonium is reduced in a second step at a metallic cathode to produce Cd—Pu intermetallics. The refined plutonium and uranium metals can then be refabricated into metallic fuel (137). 

It has been claimed that the D-D fusion reaction occurs when D2O is electroly2ed with a metal cathode, preferably palladium, at ambient temperatures. This claim for a cold nuclear fusion reaction that evolves heat has created great interest, and has engendered a voluminous titerature filled with claims for and against. The proponents of cold fusion report the formation of tritium and neutrons by electrolysis of D2O, the expected stigmata of a nuclear reaction. Some workers have even claimed to observe cold fusion by electrolysis of ordinary water (see, for example. Ref. 91). The claim has also been made for the formation of tritium by electrolysis of water (92). On the other hand, there are many experimental results that cast serious doubts on the reahty of cold fusion (93—96). Theoretical calculations indicate that cold fusions of D may indeed occur, but at the vanishingly small rate of 10 events per second (97). As of this writing the cold fusion controversy has not been entirely resolved. 

Galvanic Corrosion Galvanic corrosion is the corrosion rate above normal that is associated with the flow of current to a less active metal (cathode) in contact with a more active metal (anode) in the same environment. Tables 28-1 7 and 28-li show the galvanic series of various metals. It should be used with caution, since exceptions to... 

Note that zinc anodes are often used to protect steel and other relatively noble metals cathodically. In this case, the fasteners were acting as unintentional sacrificial anodes, protecting the stainless steel. Simple solutions to the problem would be to insulate the fasteners from the stainless steel electrically or to use stainless steel fasteners. 

It is apparent (Fig. 1.21) that at potentials removed from the equilibrium potential see equation 1.30) the rate of charge transfer of (a) silver cations from the metal to the solution (anodic reaction), (b) silver aquo cations from the solution to the metal (cathodic reaction) and (c) electrons through the metallic circuit from anode to cathode, are equal, so that any one may be used to evaluate the rates of the others. The rate is most conveniently determined from the rate of transfer of electrons in the metallic circuit (the current 1) by means of an ammeter, and if / is maintained constant it can eilso be used to eveduate the extent. A more precise method of determining the quantity of charge transferred is the coulometer, in which the extent of a single well-defined reaction is determined accurately, e.g. by the quantity of metal electrodeposited, by the volume of gas evolved, etc. The reaction Ag (aq.) -t- e = Ag is utilised in the silver coulometer, and provides one of the most accurate methods of determining the extent of charge transfer. 

Environment Reduce kinetics of cathodic reaction Lower potential of metal Cathodic inhibition Reduce a , reduce O2 concentration or concentration of oxidising species lower temperature, velocity agitation Cathodically protect by sacrificial anodes or impressed current sacrificially protect by coatings, e.g. Zn, Al or Cd on steel Formation of calcareous scales in waters due to increase in pH additions of poisons (As, Bi, Sb) and organic inhibitors to acids... 

Amperometry at inert metal cathodes is the most important approach to p02 measurements known today The subject of experimental investigations since 1945 the... 

D ions oxidized from the fork (anode) and depositing on the silver metal (cathode)... 

Electrolytic recovery (ER) is the oldest metal recovery technique. Metal ions are plated-out of solution electrochemically by reduction at the cathode.34 There are essentially two types of cathodes used for this purpose a conventional metal cathode and a high surface area cathode (HSAC). Both cathodes can effectively plate-out metals, such as gold, zinc, cadmium, copper, and nickel.22... 

Nitro groups attached to a primary and secondary alkyl group in a highly basic (pH > 13) medium exist as the nitronate (enolate) anions. These anions must be very difficult to reduce by electron transfer and are surely much more difficult to reduce than water. Since the electrohydrogenation of such nitro compounds to the corresponding amines is veiy efficient at Raney metal cathodes in 0.1 to 0.15 M KOH (or NaOH) aqueous alcohol (pH > 13) (12), as... 

The reduction of C02 can be driven electrochemically at metallic cathodes, however, it requires large overpotentials (<—1.5 V) and electrode poisoning often occurs.65 Those problems can be addressed by adding catalysts. Metal complexes are a priori good candidates as electrocatalysts. It is expected that their reduction will be accompanied by the appearance of a vacant coordination site able to bind C02 and thus activate its reduction in the metal coordination sphere.1... 

Three-dimensional Cu or Ni foam and reticulated carbon (for the recovery of noble metals) cathodes are used. Between each pair of cathodes an inert,... 

Synchotron based techniques, such as surface X-ray scattering (SXS) and X-ray absorption spectroscopy (XAS), have found increased use in characterization of electrocatalysts during electrochemical reactions.37 These techniques, which can be used for characterization of surface structures, require intricate cell designs that can provide realistic electrochemical conditions while acquiring spectra. Several examples of the use of XAS and EXAFS in non-precious metal cathode catalysts can be found in the literature.38 2... 

Research on alternative catalysts for the ORR for use in PEM fuel cell cathodes is an exciting and growing field of research. Several classes of materials show potential for replacing precious metal cathodes, especially for automotive power applications and direct methanol systems. Increasing the understanding of active sites in alternative catalysts, the mechanisms for oxygen reduction, and optimization of full fuel cell preparation using alternative materials, will lead to further improvements in performance. 

T.M. Brown, R.H. Friend, I.S. Millard, D.J. Lacey, T. Butler, J.H. Burroughes, and F. Cacialli, Electronic line-up in light-emitting diodes with alkali-halide/metal cathodes, J. Appl. Phys., 93 6159-6172 (2003). 

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