Konrad G. Weil

Copper ion reduction catalyzed by chloride ions

Abstract The cathodic reduction of copper(II) is studied in the absence and in the presence of chloride ions (1×10−3≤cCl≤8×10−3 M) in an electrolyte that is comparable to galvanic copper baths (2.2 M H2SO4+0.3 M CuSO4). Experiments conducted with the electrochemical quartz-microbalance, largely under conditions of cyclic voltammetry, demonstrate the formation and reduction of CuCl on the copper surface. A mechanism of Cu(II) reduction with intermediate formation of CuCl is postulated. Its rate is comparable to that of chloride-free Cu(II) reduction. The enhancement of the reduction current observed in the presence of chloride is proposed to result from the fact that the mechanism involving CuCl mediation proceeds in parallel with the chloride-free path.

Influence of the Surface Microstructure on the Coupling Between a Quartz Oscillator and a Liquid

A quartz oscillator, operated with one of its faces in contact with a liquid, can be used as a highly sensitive microbalance. When use together with an electronic driver circuit, frequency changes will not only reflect changes of vibrating rigid mass but also detect changes of the surface microstructure. Using impedance spectroscopy we have analyzed the influence of the surface microstructure on the frequency changes. A liquid that is rigidly coupled to the surface by inclusion into voids or narrow channels can be discerned from a liquid that is viscously coupled to the surface

An EQCM Study of the Electrochemical Copper(II)/Copper(I)/Copper System in the Presence of PEG and Chloride Ions

The charge-transfer reaction between copper(II) and copper electrodes is studied in electrolytes that are similar to galvanic copper baths, 2.2 M H 2 SO 4 + 0.3 M CuSO 4 + chloride ions (c C1 ≤ 1 × 10 -2 M), and polyethyleneglycol 1500 (PEG, c PEG ≤ 4 X 10 -3 M). Electrochemical quartz crystal microbalance (EQCM) measurements are conducted, mainly under conditions of cyclic voltammetry. The formation and dissolution of CuCI on the electrode surface at c C1 ≥ 2 mM is demonstrated, a notable shift of the pseudo-equilibrium potential associated with CuCI deposition is analyzed, and the inhibition of the charge-transfer reaction by the PEG/Cl - surface layer is characterized. It is shown that the inhibiting layer forms by reaction between the adsorbate-covered copper electrode and PEG, i.e., neither Cu + nor Cu ++ from the electrolyte are required. Numerical simulations of the processes as well as parallel experiments conducted with electrolytes not containing Cu(II) support the proposed mechanisms, in particular the role of the intermediate Cu + .

Application of a quartz crystal microbalance to the study of copper corrosion in acid solution inhibited by triazole-iodide protective films

When one uses one side of a quartz crystal microbalance as the working electrode in electrochemical experiments, mass changes can be monitored continuously with a sensitivity of a few nanograms per square centimeter. In this study the working electrode consisted of electrolytically deposited copper, exposed to 0.1M sodium sulfate at pH 3, open to the atmosphere and in some cases containing H{sub 2}O{sub 2}. Upon addition of one of the inhibitors, benzotriazole (BTA), tolyltriazole (TTA), carboxy-benzotriazole (CBT), or these inhibitors plus potassium iodide, the rate of frequency change decreases markedly. After removal of the inhibitors from the corrosive medium by fast solution exchange there is a marked continuing protective effect of the inhibitor films in the cases of BTA + KI and TTA + KI with the latter being the most stable and protective of all of the films. The results were qualitatively the same in the more corrosive solution containing H{sub 2}O{sub 2}.

EQCM studies of the electrodeposition and corrosion of tin–zinc coatings

Abstract A 70% Sn–30% Zn layer is deposited from a neutral non-cyanide bath. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) show that it is composed of Sn and Zn phases. By use of an electrochemical quartz crystal microbalance (EQCM), the plating current efficiency is determined. When the plated sample is exposed to a 0.5 M Na2SO4 (pH 3.6) solution at open circuit potential (OCP), the EQCM measures the corrosion rate. The open circuit potential shows that the Zn dissolution reaction is the major reaction occurring at OCP. A linear potential scanning experiment shows that the anodic polarization current of this system is rather small in a wide range of potentials until it reaches the anodic dissolution potential of pure Sn in the same solution.

Measurement of pH Gradients in the Crevice Corrosion of Iron Using a Palladium Hydride Microelectrode

The study of localized corrosion is hindered by the inability to characterize electrolyte compositions inside crevices and pits during the corrosion process. This paper describes the development of a microelectrode systemfor in situ monitoring of the pH in artificial crevices and small recesses. This system permits determination of the pH gradient inside a crevice, even in the presence of a pronounced potential drop. The pH sensor, consisting of a palladium hydride electrode, can be positioned at any desired depth into the crevice while observing the position of the passive to active transition. With increasing time of crevice corrosion, one finds a pronounced pH change in the crevice electrolyte. This work lends further insight toward understanding of crevice corrosion and other localized corrosion phenomena.

The influence of halide ions on the kinetics of electrochemical copper(II) reduction

Abstract The cathodic reduction of copper(II) in an electrolyte comparable to technical conditions (2.2M H2SO4 + 0.3M CuSO4) is markedly affected by the presence of small concentrations of halide ions. Chloride ions accelerate the reaction, while it is slowed down by bromide. Experiments in which cyclic voltammetry is combined with an electrochemical quartz-crystal microbalance reveal the deposition and dissolution of crystalline CuCl or CuBr, respectively, on the copper surface. At the technically relevant more negative electrode potentials bulk CuCl and CuBr are unstable, however halide ions are adsorbed on the copper electrode. Although there is evidence for adsorption of the reacting Cu(II) species at the electrode surface, up to a concentration of 0.3M CuSO4 in presence as well as in absence of adsorbed halogenide, there is no evidence for limiation of the reaction rate caused by a limited coverage of the surface with this species.

Absolute rate constants for some reactions of ethylene and cyclopropane with iron-cluster ions

Abstract The absolute rate constants for the consecutive binding of ethylene and cyclopropane to Fe + 4 ions under hydrogen abstraction are reported. It is evident from these data that the formation of cluster ions with Fe 4 C 6 H + 6 stoichiometry takes place at an unexpected high reaction rate. In addition, we report on chemical reactions of Fe 4 (C 2 H 2 ) + m ions ( m =0–3) with ammonia. These experiments show that cluster ions with m =0–2 bind NH, releasing simultaneously H 2 , while cluster ions with m =3 adsorb intact ammonia molecules.

Intermetallic species in the vapour above alkali metal-antimony mixtures

Abstract The equilibrium vapour above mixtures of antimony with one of the alkali metals Na or K was studied using Knudsen effusion mass spectroscopy. The results are discussed together with data from the literature on the Li-Sb and Cs-Sb systems. In addition to the homonuclear species Me, Me2, and Sbn (1 ⩽ n ⩽ 4) the following heteronuclear particles were observed: LiSb, NaSb, Me2Sb, MeSb2, Me2Sb2, Me2Sb4, K4Sb4, and Na6Sb4. From the ionization efficiency curves, the appearance potentials, and the apparent enthalpies of evaporation conclusions could be drawn on fragmentation pathways in these systems. On comparing the measured systems with each other, characteristic differences as well as similarities are found which indicate variations in the bond nature of the different species. The latter can be correlated with electronegativity differences. Of particular interest is the compound Na6Sb4. It seems likely that the sodium atoms are oriented octahedrally around an antimony tetrahedron. The ionization energy of this species is very close to that of sodium atoms. Under electron impact it fragments according to Na6Sb4 + e− → Na5Sb+4 + Na + 2e−. These properties can be understood when Na6Sb4 is described as a metallic cluster.

The electrochemical quartz crystal microbalance (EQCM) in the studies of complex electrochemical reactions

Many electrochemical processes contain more than one charge transfer step. If one of these steps leads to a mass change of the working electrode one can use the electrochemical quartz crystal microbalance (EQCM) in situ to determine the rate of this process as a function of the applied potential. Examples for the use of the EQCM for the elucidation of complex electrochemical reaction, which are discussed in this paper are the electrodeposition of alloys with simultaneous hydrogen evolution, the corrosion of alloys, and the autocatalytic reduction of hydrogen peroxide on silver electrodes in acidic solution.