B.M. Jović

Kinetics of chloride ion adsorption and the mechanism of AgCl layer formation on the (111), (100) and (110) faces of silver

Abstract The kinetics of chloride anion adsorption on the (111), (100) and (110) faces of silver are investigated by linear sweep voltammetry, potentiostatic pulse and impedance (admittance) measurements. It is shown that the first voltammetric (capacitive) peak corresponds to the adsorption of randomly arranged chloride anions with complete charge transfer between the anions and the substrate ( l ≈ 1) and a relatively slow rate of adsorption: k s = (8−9) × 10 −6 cm s −1 . The second (third) voltammetric (capacitive) peak is found to be very sharp, representing (according to the earlier findings) the formation of an ordered AgCl adlayer formed with the topmost Ag layer. At more positive potentials a three-dimensional (3D) growth of AgCl takes place, characterized by the anodic “crystallization loop” and the j − t transients typical of 3D nucleation. It is shown that after prolonged polarization in the potential region of 3D AgCl formation, irreversible formation of AgCl takes place on the electrode surface.

Anion absorption on the (111) face of silver

Abstract Differential capacity (admittance-impedance) measurements for a (111) face of silver in supra-pure solutions of NaF, Na 2 SO 4 and NaCH 3 COO are analysed to obtain data on the specific adsorption of the above-mentioned anions. It is shown that the frequency dependence of the impedance of the electrochemical interface cannot be represented by an equivalent circuit consisting of the ohmic resistance ( R OHρ ) and double-layer capacitance ( C dl ) connected in series in the presence of specific adsorption. The addition of a series combination of a resistance ( R ct ) and capacitance ( C ad ) in parallel with C dl gives a reasonable representation of the data. R ct permits the evaluation of some semiquantitative information about the adsorption kinetics.

Corrosion Behavior of Ti3GeC2 and Ti2AlN in 1 M NaOH

In this paper we report on the corrosion behavior of Ti 3 GeC 2 and Ti 2 AlN in a 1 M NaOH solution, investigated by electrochemical impedance spectroscopy (EIS), polarization, and (-potential measurements. The EIS results for Ti 3 GeC 2 and some results for Ti 2 AlN could be fitted to a complex equivalent circuit, where the double layer is represented by a constant phase element. The passive film is represented by a polarization resistance in series with a parallel connection of a resistance of the passive film (R pf ) and its capacitance (C pf ). In both cases passive layers were formed. Based on the ζ-potential measurements, we conclude that the passivating layer that forms on Ti 3 GeC 2 , over a wide pH range, is most likely GeO 2 -based, while the one formed on Ti 2 AlN is most likely Al 2 O 3 -based and/or TiO 2 -based.

Morphology of Different Electrodeposited Pure Metal Powders

As mentioned in other chapters, metal powders obtained by electrolytic processes are mainly dendrites which can spontaneously fall off or can be removed from the electrode by tapping or other similar techniques [1]. Also, powder particles can have other morphological forms, such as flakes or needles, fibrous or spongy, and needle or cauliflower-like ones, and the shape of powder particles depends on the electrodeposition conditions and the nature of the metal.

Properties of ZrO2 Passive Film Formed onto Zr Electrode in 1 M NaOH at Low Voltage

In this paper, results of the potentiodynamic-potentiostatic formation of a homogeneous, passive film of ZrO 2 on a Zr electrode in a 1 M NaOH solution at potentials lower than 4.0 V vs saturated calomel electrode are presented. The properties of such a film were investigated by electrochemical impedance spectroscopy (EIS) measurements. After fitting the EIS results by an appropriate equivalent circuit, the capacitance (C pf ) and resistance (R pf ), as well as the space charge capacitance (C sc ) and space charge resistance (R sc ) of this film, were determined. The film was found to become an insulator (IN) at the potentials equal to and/or more positive than 2.0 V. In the potential range 0.8 V < E < 2.0 V, a transition from a semiconducting to insulating behavior (SC-IN) has been recorded. The donor densities (N sc ), as well as their flatband potentials (E fb ) and their space charge layer (d sc ) thickness, were determined from the corresponding Mott-Schottky plots recorded in two potential ranges (0.0 V < E < 0.7 V - SC) and (0.8 V < E < 2.0 V - SC-IN), where the film behaved as an n-type semiconductor. From the potential range of the insulating behavior of the film (IN), its thickness was determined from C pf .

Fe-Mo alloy coatings as cathodes for chlorate production

The aim of this study was to gain a better understanding of the feasibility of partial replacement of dichromate, Cr(VI), with phosphate buffer, focusing on the cathode reaction selectivity for hydrogen evolution on mild steel and Fe-Mo cathodes in undivided cell for chlorate production. To evaluate the ability of phosphate and Cr(VI) additions to hinder hypochlorite and chlorate reduction, overall current efficiency (CE) measurements in laboratory cell for chlorate production on stationary electrodes were performed. The concentration of hypochlorite was determined by a conventional potentiometric titration method using 0.01 mol dm-3 As2O3 solution as a titrant. The chlorate concentration was determined by excess of 1.0 mol dm-3 As2O3 solution and excess of arsenic oxide was titrated with 0.1 mol dm-3 KBrO3 solution in a strong acidic solution. Cathodic hypochlorite and chlorate reduction were suppressed efficiently by addition of 3 g dm-3 dichromate at both cathodes, except that Fe-Mo cathode exhibited higher catalytic activity for hydrogen evolution reaction (HER). The overvoltage for the HER was around 0.17 V lower on Fe-Mo cathode than on mild steel at the current density of 3 kA m-2. It was found that a dichromate content as low as 0.1 g dm-3 is sufficient for complete suppression of cathodic hypochlorite and chlorate reduction onto Fe-Mo catalyst in phosphate buffering system (3 g dm-3 Na2HPO4 + NaH2PO4). The overall current efficiency was practically the same as in the case of the presence of 3 g dm-3 dichromate buffer (98 %). However, for the mild steel cathode, the overall current efficiency for the chlorate production was somewhat lower in the above mentioned mixed phosphate + dichromate buffering system (95%) than in the pure dichromate buffering solution (97.5%).

Electrodeposition and Characterization of Alloys and Composite Materials

It is general experience in materials science that alloy can exhibit qualities that are unobtainable with parent metals. This is particularly true for electrodeposited alloys. Some important properties of materials, such as hardness, ductility, tensile strength, Young’s modulus, corrosion resistance, solderability, wear resistance, and antifriction service, may be enhanced. At the same time some properties that are not characteristic for parent metals, such as high magnetic permeability, other magnetic and electrical properties, amorphous structure, etc., can also be obtained. In some cases alloy coatings may be more suitable for subsequent electroplate overlayers and conversion chemical treatments [1].

Morphology, Chemical, and Phase Composition of Electrodeposited Co–Ni, Fe–Ni, and Mo–Ni–O Powders

The alloy powders of the iron-group metals are of great interest for many industrial applications [1–88].

Morphology and Phase Composition of Ni-Co Alloy Powders Electrodeposited from Ammonium Sulfate-Boric Acid Electrolyte

In this paper the morphology of Ni-Co powders electrodeposited from ammonium sulfate-boric acid containing electrolyte is investigated as a function of alloy powder composition. Composition of the electrolyte, i.e. the ratio of Ni2+/Co2+ concentration is found to influence both, the alloy phase composition and the morphology of Ni-Co alloy powders. At the highest ratio of Ni2+/Co2+ ions concentration, typical 2D fern-like dendritic particles were obtained. With decrease of Ni2+/Co2+ ions ratio among 2D fern-like dendrites, 3D dendrites and different agglomerates of a size of about 100 μm, being either compact (typical for pure Co powder) or composed of a large number of small 3D dendrites on their surface were obtained. According to the X-ray analysis, with decreasing Ni2+/Co2+ concentration ratio the amount of f.c.c. β-Ni phase was found to decrease, while the amount of h.c.p. α-Co phase was found to increase being accompanied by the appearance of the f.c.c. Co phase at Ni2+/Co2+ = 0.33.