Electrodeposition cationic

Solvent for Electrolytic Reactions. Dimethyl sulfoxide has been widely used as a solvent for polarographic studies and a more negative cathode potential can be used in it than in water. In DMSO, cations can be successfully reduced to metals that react with water. Thus, the following metals have been electrodeposited from their salts in DMSO cerium, actinides, iron, nickel, cobalt, and manganese as amorphous deposits zinc, cadmium, tin, and bismuth as crystalline deposits and chromium, silver, lead, copper, and titanium (96—103). Generally, no metal less noble than zinc can be deposited from DMSO. 

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. 

Zinc is electrodeposited from the sodium zincate electrolyte during charge. As in the zinc/bromine battery, two separate electrolytes loops ("posilyte" and "nega-lyte") are required. The only difference is the quality of the separator The zinc/ bromine system works with a microporous foil made from sintered polymer powder, but the zinc/ferricyanide battery needs a cation exchange membrane in order to obtain acceptable coulombic efficiencies. The occasional transfer of solid sodium ferrocya-nide from the negative to the positive tank, to correct for the slow transport of complex cyanide through the membrane, is proposed [54],... 

Cathodic electrodeposition of microcrystalline cadmium-zinc selenide (Cdi i Zn i Se CZS) films has been reported from selenite and selenosulfate baths [125, 126]. When applied for CZS, the typical electrocrystallization process from acidic solutions involves the underpotential reduction of at least one of the metal ion species (the less noble zinc). However, the direct formation of the alloy in this manner is problematic, basically due to a large difference between the redox potentials of and Cd " couples [127]. In solutions containing both zinc and cadmium ions, Cd will deposit preferentially because of its more positive potential, thus leading to free CdSe phase. This is true even if the cations are complexed since the stability constants of cadmium and zinc with various complexants are similar. Notwithstanding, films electrodeposited from typical solutions have been used to study the molar fraction dependence of the CZS band gap energy in the light of photoelectrochemical measurements, along with considerations within the virtual crystal approximation [128]. 

The UPD and anodic oxidation of Pb monolayers on tellurium was investigated also in acidic aqueous solutions of Pb(II) cations and various concentrations of halides (iodide, bromide, and chloride) [103]. The Te substrate was a 0.5 xm film electrodeposited in a previous step on polycrystalline Au from an acidic Te02 solution. Particular information on the time-frequency-potential variance of the electrochemical process was obtained by potentiodynamic electrochemical impedance spectroscopy (PDEIS), as it was difficult to apply stationary techniques for accurate characterization, due to a tendency to chemical interaction between the Pb adatoms and the substrate on a time scale of minutes. The impedance... 

Figure 14.1a shows aj vs. U curve in Cu + Sn + H2SO4 with (solid curve) and without (dashed curve) cationic surfactant. The addition of the surfactant causes a drastic change in they vs. U curve. Namely, an NDR appears in a narrow potential region of about 5 mV near —0.42 V, where the Cu-Sn alloy is electrodeposited. Another notable point in the surfactant-added solution is that a current oscillation appears when the Uis kept constant in (and near) the potential region of this NDR, as shown in Figure 14.1b. It was also revealed that both the NDR and current oscillation appeared only in the presence of cationic surfactant and not in the presence of anionic surfactant.

Applications Electrodeposition of cationic paint resin on automobiles (connected to the cathode) provides a uniform, defect-free coating with high corrosion resistance, but carries with it about 50 percent excess paint that must be washed off. UF is used to maintain the paint concentration in the paint bath while generating a permeate that is used for washing. The spent wash is fed back into the paint path (Zeman et al., Microjiltration and UltrajUtration, Marcel Dekker, New York, 1996). 

The composition of the electrolyte is quite important in controlling the electrolytic deposition of the pertinent metal, the chemical interaction of the deposit with the electrolyte, and the electrical conductivity of the electrolyte. In the case of molten salts, the solvent cations and the solvent anions influence the electrodeposition process through the formation of complexes. The stability of these complexes determines the extent of the reversibility of the overall electroreduction process and, hence, the type of the deposit formed. By selecting a suitable mixture of solvent cations to produce a chemically stable solution with strong solute cation-anion interactions, it is possible to optimize the stability of the complexes so as to obtain the best deposition kinetics. In the case of refractory and reactive metals, the presence of a reasonably stable complex is necessary in order to yield a coherent deposition rather than a dendritic type of deposition. 

Air Filter wet ashed in HNO3/HF, purified with cation and anion exchange columns and electrodeposition a -Spectroscopy No data No data Knab1979... 

Sea water Co-precipitation with iron hydroxide, purified by anion exchange, coprecipitation with BiP04, cation exchange, electrodeposition a -Spectroscopy No data 64-79% Lovette et al. 1990... 

The electrodeposited Bi2Sr2CaiCu2Ox (BSCCO) precursor films were obtained by co-electrodeposition of the constituent metals using nitrate salts dissolved in DMSO solvent. The electrodeposition was performed in a closed-cell configuration at room temperature ( 24°C). The cation ratios of the electrodeposition bath were adjusted systematically to obtain BSCCO precursor compositions. A typical electrolyte-bath composition for the BSCCO films consisted of 2.0-g Bi(N03)3-5H20,1.0-g Sr(N03)2, 0.6-g Ca(N03)2-4H20, and 0.9-g Cu(N03)2-6H20 dissolved in 400 mL of DMSO solvent. The substrates were single-crystal LAO coated with 300 A of Ag. 

Electrodeposition of Dieiectrics—Separators and Cation-Conductive Eiectroiytes... 

Ferrocenyl dendrimers also afford electroactive films on indium tin oxide (ITO) electrodes in the same manner as described above. UV-visible spectroelectro-chemical measurements of this modified electrodes on oxidation show changes characteristic for the formation of fenocenium cations. Thus, Figure 8 shows the UV-visible absorption spectrum of a film of 2 electrodeposited on a transparent ITO electrode, which exhibits a strong band at 260 nm and a weak absorption band centered at 600 nm, which agree with those observed for the cationic dendrimer [2 KPF j ]g in solution described above. 

ADTECHS Corporation (ADTECHS) has developed the radionuclides separation (RASEP) process for the removal and stabilization of radionuclides from liquid waste streams. The process uses filtration, selective adsorption, and electrodeposition fixation followed by cement sohdifi-cation. According to the vendor, the technology is commercially available. 

Rodriguez-Torres etal. [235] have used ammonia-containing baths for Zn-Ni alloy electrodeposition on Pt. Zinc and nickel species exist in the form of [Zn(NH3)4] + and [Ni(NH3)6] " complexes in such solutions. The deposition at pH 10 was investigated and compared with deposition from ammonium chloride baths at pH 5. The Ni content in the alloys was found to be 40-60% higher from the ammonia-containing bath than from the acidic baths. The deposition mechanism was found to be affected by complexation of the metal cations by ammonia. 

The nse of complexation to allow codeposition of alloys is well known in electroplating. The best-known example is that of brass (Cu/Zn) plating, where cyanide, which is a stronger complex for Cu than it is for Zn, brings the deposition potentials of the two metals, originally far apart, to almost the same value. There is a direct connection between this effect and the equivalent one for CD. This arises from the fact that, for both CD and electrodeposition of alloys (we in-clnde mixed metal compounds in the term alloy), the effect of the complexant is to lower the concentration of free cations. For CD this affects the deposition throngh the solnbility product, while for electrodeposition it affects the deposition potential through the Nemst equation ... 

Electrodeposition of metal oxide thin films in aqueous solutions is made possible by promoting hydrolysis of metal cations with electrochemically... 

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