Direct current deposition

Several studies were published in recent years on electrodeposition of W-Co alloys. Donten and Stojek used pulse electrodeposition to increase the tungsten content in amorphous Co-W alloys. These alloys contained, in addition, small amounts of boron or phosphorous. They showed that, if a symmetrical current pulse was used, the tungsten content in the alloys reached a maximum value of 41.4 at.%, which is higher than in the case of direct current deposition. However, when using any asymmetrical... 

High-concentration (40 weight percent [wt%]) ternary Pt alloy samples prepared using the carbothermal technique have yielded surface area and activity values comparable to commercial Pt samples. Platinum/Carbon (Pt/C) prepared by pulse-electrodeposition showed superior surface area and activity when compared to direct current deposited Pt/C electrodes. 

Figure 5.15 shows that the corrosion current is one order of magnitude smaller for the pulse current-deposited (pc) Zn-Ni-Cd (7% Cd) sacrificial coatings when compared to the direct current-deposited (dc) Zn-Ni-Cd with 22% Cd in the alloy [36]. The corrosion rates of pulse current-deposited Zn-Ni-Cd sacrificial coatings that contain 7% and 3% Cd were 0.49 and 1.03 mpy, respectively much lower than the 2.87 mpy observed for the direct current-deposited Zn-Ni-Cd alloy with 22% Cd in the alloy. 

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... 

Cr/Co alloys can be deposited on a cathode composed of brass and mild-steel plates in ChCl/EG mixtures. By using the direct current deposition method (DCD) an alloy composed of 80.04% of Co and 34.56% of Cr was obtained. ... 

Plasmas can be used in CVD reactors to activate and partially decompose the precursor species and perhaps form new chemical species. This allows deposition at a temperature lower than thermal CVD. The process is called plasma-enhanced CVD (PECVD) (12). The plasmas are generated by direct-current, radio-frequency (r-f), or electron-cyclotron-resonance (ECR) techniques. Eigure 15 shows a parallel-plate CVD reactor that uses r-f power to generate the plasma. This type of PECVD reactor is in common use in the semiconductor industry to deposit siUcon nitride, Si N and glass (PSG) encapsulating layers a few micrometers-thick at deposition rates of 5—100 nm /min. 

A large number of CVD diamond deposition technologies have emerged these can be broadly classified as thermal methods (e.g., hot filament methods) and plasma methods (direct current, radio frequency, and microwave) [79]. Film deposition rates range from less than 0.1 pm-h to 1 mm-h depending upon the method used. The following are essential features of all methods. 

Different ways of the structural classification of deposits exist. In one system, the following structures are distinguished arbitrarily (1) fine-crystalline deposits lacking orientation, (2) coarse-crystalline deposits poorly oriented, (3) compact textured deposits oriented in field direction (prismatic deposits), and (4) isolated crystals with a predominant orientation in the field direction (friable deposits, dendrites). The structure of metal deposits depends on a large number of factors solution composition, the impurities present in the solntion, the current density, surface pretreatment, and so on. 

In addition to microwave plasma, direct current (dc) plasma [19], hot-filament [20], magnetron sputtering [21], and radiofrequency (rf) [22-24] plasmas were utilized for nanocrystalline diamond deposition. Amaratunga et al. [23, 24], using CH4/Ar rf plasma, reported that single-crystal diffraction patterns obtained from nanocrystalline diamond grains all show 111 twinning. 

Although the sputter deposition technique can provide a cheap and directly controlled deposition method, the performance of PEM fuel cells with sputtered CLs is still inferior to that of conventional ink-based fuel cells. In addition, other issues arise related to the physical properties of sputtered catalyst layers, such as low lateral electrical conductivity of the thin metallic films [96,108]. Furthermore, the smaller particle size of sputter-deposited Ft can hinder water transport because of the high resistance to water transport in a thick, dense, sputtered Ft layer [108]. Currently, the sputter deposition method is not considered an economically viable alternative for large-scale electrode fabrication [82] and further research is underway to improve methods. 

Selective synthesis of acetylene (>90%) from methane was accomplished by microwave plasma reactions.568 Conversion of methane to acetylene by using direct current pulse discharge was performed under conditions of ambient temperature and atmospheric pressure.569 The selectivity of acetylene was >95% at methane conversion levels ranging from 16 to 52%. In this case oxygen was used to effectively remove deposited carbon and stabilize the state of discharge. Similar high... 

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. 

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). 

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