Electrodeposition difficulty

One potential difficulty with CF-EF is the electrodeposition of the particles at the electrode away from the filtration medium. This phenomenon, if allowed to persist, will result in performance decay of CF-EF with respect to maintenance of the electric field. Several approaches such as momentaiy reverses in polarity, protection of the electrode with a porous membrane or filter medium, and/or utilization of a high fluid shear rate can minimize electrodeposition. 

A major advantage of the electroless nickel process is that deposition takes place at an almost uniform rate over surfaces of complex shape. Thus, electroless nickel can readily be applied to internal plating of tubes, valves, containers and other parts having deeply undercut surfaces where nickel coating by electrodeposition would be very difficult and costly. The resistance to corrosion of the coatings and their special mechanical properties also offer advantages in many instances where electrodeposited nickel could be applied without difficulty. 

On account of the fact that the electrode potential of molybdenum is more negative than the discharge potential of hydrogen, principle difficulties arise to cathodically electrodeposit molybdenum chalcogenide films from aqueous solutions. Theoretically, the deposition of pure molybdenum by electrolytic reduction of molybdates in acidic aqueous solutions is possible according to the reaction... 

In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

The difficulties include the inconvenience of handling radioactivity and the necessity for obtaining an accurate radiochemical analysis of two phases containing several elements (which often involves complicated spectra). Highly sensitive instrumentation is required for the analysis e.g. a Li-Si surface barrier detector for a particles, a 2 r gas counter for (3-radiation and a Li-Ge detector for 7-radiation. Great care is required during source preparation, which is best done by electrodeposition. 

Reactions in which the nature of the substrate is vital (e.g., as in electrocatalysis, corrosion, electrodeposition) do not offer opportunities for application of a technique in which the substrate is regarded essentially as an electron source or sink, rather than as an electrocatalyst. The very large field of bioelectrochemistiy (which involves concepts such as enzymes as electrodes and even offers electrochemical mechanisms for metabolism) would offer difficulties for potential sweep applications because of the very high resistance of the substrate.21... 

SIMS analysis of electrodeposited Th alpha-particle sources gives rise to higher signals for the ThO and ThO/ than for Th. This leads to difficulties in quantitation as the oxide to atomic ion ratios will be sensitive to local oxygen concentrations. Isobaric... 

There are no reports on spin valve structures built by electrodeposition. One possible difficulty of the use of electrodeposition is the ultrathin thickness of metal layers in these structures. 

Taylor et al.8 were the first to report an electrochemical method for preparation of MEAs for PEMFCs. In their technique, Pt was electrochemically reduced and deposited at the electrode membrane interface, where it was actually utilized as an electrocatalyst. Nation, which is an ion exchange polymer membrane, is first coated on a noncatalyzed carbon support. The Nafion-coated carbon support is then immersed into a commercial acidic Pt plating solution for electrodeposition. Application of a cathodic potential results in diffusion of platinum cations through the active Nation layer. The migrated platinum species are reduced and form Pt particle at the electrode/membrane interface only on the sites which are both electronically and ionically conductive. The deposition of Pt particles merely at the electrode/membrane interface maximizes the Pt utilization. The Pt particles of 2-3.5 nm and a Pt loading of less than 0.05 mg cm-2 were obtained employing this technique.8 The limitation of this method is the difficulty of the diffusion of platinum... 

In summary, this study shows the great possibility of generating Cu/n-Si junctions with a nearly perfect rectifying behavior from CuCN solutions. Diode characteristics are comparable to those reported for contacts prepared by physical methods and are not appreciably subject to modification with time. The second promising point is the high adherence of Cu films, which was exploited to electrodeposit adherent Ni films from a modified Watts bath. This two step procedure seems to solve the major difficulty encountered upon growing thick metal layers onto H-Si surfaces from acidic solutions and enables to prepare stable electrical junctions with defined electrical properties. 

In this process, oxide fuel is dissolved in a molten chloride salt mixture through which Q2-HCI gas is flowing. Dissolved uranium and plutonium are then recovered as oxides by cathodic electrodeposition at 500 to 700°C. The process was demonstrated with kilogram quantities of irradiated fuel, with production of dense, crystalline UO2 or UO2-PUO2 reactor-grade material. Difficulties were experienced with process control, off-gas handling, electrolyte regeneration, and control of the plutonium/uranium ratio. Development has been discontinued. 

The mechanical properties of sintered apatites has limited their application to low stress areas in the body. To overcome this difficulty, apatites are applied as coatings on the surface of metallic implants where high loads on the implant are expected. Various coating options are available including thermal spraying, sputter deposition, pulsed laser deposition, sol-gel deposition, electrophoretic coating, electrodeposition, and biomimetic deposition. These are discussed in turn. 

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