Lead alloy electrodeposition

Consequently, ions such as BF4 and PFf), which might be expected to complex or solvate an electroactive metal species, are not expected to be reduced and to influence alloy composition, unlike AICI4 and A ECU. In principle, this should lead to better control of alloy composition since the concentrations of the electroactive species may be controlled independently. For example, one can avoid an electroactive species such as [Ti(AlCl4)3] which is likely responsible for the limited composition range found in Ti-Al alloys electrodeposited from chloroaluminates. 

Terneplate is a tin-lead alloy coated sheet steel, and is produced either by hot dipping or electrodeposition. The hot dipping process with a chloride flux is used to produce most temeplates. The coating layer, whose electrode potential is more noble than that of the steel substrate, contains 8-16% Sn. Since the electrode potential of the coating layer is more noble than the steel substrate, it is necessary to build a uniform and dense alloy layer (FeSn2) in order to form a pinhole free deposit. 

When the electrolyte contains more than one cation, their simultaneous discharge becomes possible. This will occur if their deposition potentials (under the conditions used) are close to one another, and it can lead to alloy electrodeposition (q.v.). The most general case, however, is of course where hydrogen ion is the second cation, and the simultaneous evolution of hydrogen is a common accompaniment of metal deposition. The amount of current that will be dissipated in this way can be calculated if the current-potential curves for the two processes are known. It must be remembered that the curve for H2 evolution depends on the nature of the cathode surface as well as on the pH of the solution. Figure E.4 illustrates the deposition of zinc from a neutral solution of zinc sulphate. At the point at which the curves intersect the current efficiency for zinc deposition is 50%, but at high current densities it is much greater. 

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]. 

Relatively little attention has been devoted to the direct electrodeposition of transition metal-aluminum alloys in spite of the fact that isothermal electrodeposition leads to coatings with very uniform composition and structure and that the deposition current gives a direct measure of the deposition rate. Unfortunately, neither aluminum nor its alloys can be electrodeposited from aqueous solutions because hydrogen is evolved before aluminum is plated. Thus, it is necessary to employ nonaqueous solvents (both molecular and ionic) for this purpose. Among the solvents that have been used successfully to electrodeposit aluminum and its transition metal alloys are the chloroaluminate molten salts, which consist of inorganic or organic chloride salts combined with anhydrous aluminum chloride. An introduction to the chemical, electrochemical, and physical properties of the most commonly used chloroaluminate melts is given below. 

Chronopotentiometry. Paunovic and Oechslin (8) measured the adsorption of peptone on lead-tin alloy electrodes using chronopotentiometric and double-layer measurements. This case is different from the adsorption of HCOOH because peptone is not an electroactive species in the conditions smdied but only blocks the surface used for the electrodeposition of lead-tin alloys from solutions containing Sn and Pb ions. Chronopotentiometric analysis is based on the following principles (7). In the absence of adsorption, the relationship between the transition time r (for reduction of Sn and Pb in this case), the bulk concentration c° of the substance reacting at the electrode, and the current I is given by the equation... 

Electrodeposition of lead-tin alloy films is usually performed in the presence of peptone as an additive. Peptone is adsorbed on the metal surface during the electrodeposition process. The fractional surface coverage Q of the lead-tin electrode may be determined from the double-layer capacitance C measurements, and/or chronopotentiometric measurements. For a solution containing 9.0 g/L of tin and 13.0 g/L of lead, the following relationship between the concentration of peptone, the double-layer capacitance C, and the transition time At is observed (8). 

Bismuth-film electrodes (BiFEs), consisting of a thin bismuth-film deposited on a suitable substrate, have been shown to offer comparable performance to MFEs in ASY heavy metals determination [17]. The remarkable stripping performance of BiFE can be due to the binary and multi-component fusing alloys formation of bismuth with metals like lead and cadmium [18]. Besides the attractive characteristics of BiFE, the low toxicity of bismuth makes it an alternative material to mercury in terms of trace-metal determination. Various substrates for bismuth-film formation are reported. Bismuth film was prepared by electrodeposition onto the micro disc by applying an in situ electroplating procedure [19]. Bismuth deposition onto gold [20], carbon paste [21], or glassy carbon [22-24] electrodes have been reported to display an... 

The electrodeposition of antimony [77] and indium-antimony [78] alloys has been reported in a basic EMICI-EMIBF4 ionic liquid. Antimony trichloride, SbCl3, dissolves in the ionic liquid and forms SbQ, the same as in the basic chloro-aluminate ionic liquid. Metallic Sb can be obtained by the cathodic reduction of SbCl4, as shown in Eq. (9.14). The formal potential of Sb(III)/Sb is reported as —0.27 V vs. AI/Al(in) in the ionic liquid containing Cl at 0.11 M. In addition the oxidation of SbCl4 leads to the formation of a pentavalent antimony species, SbClg ... 

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