Direct current, deposition with

The created ions, electrons, and neutral fragments participate in complex surface reactions that form the basis of the film growth. Positive-ion bombardment of surfaces in contact with the plasma plays a key role by modifying material properties during deposition. A direct-current (dc) bias potential may be applied to the excitation electrode to increase the ion energy and enhance the desired effects of ion bombardment (30). 

The industrial manufacture of aluminum is ba.sed on the Hall-Heroult process developed in 1886. In this process aluminum oxide (see Section 3.2.4.2 for the production of aluminum oxide from bauxite) is dissolved in a cryolite (Na3AlF5) melt and electrolyzed at 940 to 980°C with direct current. Molten metallic aluminum is deposited at the carbon electrode (cladding of the bottom) and taken off as a liquid. Oxygen is formed at the anode, also of carbon (presintered or Soederberg-electrode), with which it reacts forming carbon dioxide and carbon monoxide. 

After a steady state is established, there exists a stable concentration profile from a point close to the electrode surface (where the concentration is half of that in the bulk) toward the bulk of solution,- which determines a diffusion layer similar to that obtained with direct current deposition at the... 

Fire Refining. The impurities in bhster copper obtained from converters must be reduced before the bUster can be fabricated or cast into anodes to be electrolyticaHy refined. High sulfur and oxygen levels result in excessive gas evolution during casting and uneven anode surfaces. Such anodes result in low current efficiencies and uneven cathode deposits with excessive impurities. Fite refining is essential whether the copper is to be marketed directly or electrorefined. 

Using pulse plating techniques with a duty cycle of 50%, it is also possible to produce crack-free chromium deposits from a sulphate- or silicofluoride-catalysed solution with a hardness similar to deposits obtained by direct currenf . A high frequency (2 000-3 000 Hz) is required to give the hardest deposits at a current density of 40 A/dm and a temperature of 54°C. It is important to avoid conditions that will co-deposit hydrides. 

Fuel cells incorporating lithographic methods and masking/deposition/etching protocols have been fabricated on Si wafers and thereby satisfy two critical needs in a standard fuel cell collection of electrons (current collectors) and controlling the flow field of fuel and oxidant. Kelley et al. produced a miniature direct methanol fuel cell (DMFC) with a current— voltage and fuel utilization performance that matched standard-sized DMFCs prepared in-lab.A working volume for the miniature DMFC of 12 mm was reported, with an operational performance of 822 W h kg at 70 °C. ... 

Electroless Deposition of Copper. The basic ideas of the mixed-potential theory were tested by Paunovic (10) for the case of electroless copper deposition from a cupric sulfate solution containing ethylenediaminetetraacetic acid (EDTA) as a complexing agent and formaldehyde (HCHO) as the reducing agent (Red). The test involved a comparison between direct experimental values for and the rate of deposition with those derived theoretically from the current-potential curves for partial reactions on the basis of the mixed-potential theory. 

The most popular method of silver recovery is electrolytic deposition. In an electrolytic recovery unit, a low voltage direct current is created between a carbon anode and stainless steel cathode. Metallic silver plates onto the cathode. Once the silver is removed, the fixing bath may be able to be reused in the photographic development process by mixing the desilvered solution with fresh solution. Recovered silver is worth about 80% of its commodity price. Used silver films also constitute a significant quantity of waste. The film can be sold for silver recovery to many small recyclers. 

A plant for this purpose comprises a vacuum chamber with ancillary equipment. The articles to be plated are mounted on a water-cooled cathode and, following evacuation of the chamber and filling with argon to a pressure of 0.002 Torr, direct current from a supply in the range 2000 to 5000 V is applied—to give a glow discharge in the area of the cathode. The article or articles mounted there thus are cleaned by ionic bombardment. Next, the evaporation source is excited, and the atoms of source material are deposited on the work pieces. 

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