Vlada D. Jović

Identification of phases in Ag + Pd alloys electrodeposited by the electrochemical ALSV technique

Abstract The well-established anodic linear sweep voltammetry (ALSV) technique has been used to identify the phases present in electrodeposited thin layers of Ag+Pd alloys. Alloys were deposited both potentiostatically and galvanostatically on glassy carbon and gold rotating-disc electrodes from a chloride-containing electrolyte at elevated temperatures. It is shown that electrodeposited Ag+Pd alloys appear in two different phases (ordered structures) depending on the chemical composition and the amount (thickness) of electrodeposited alloy. It is also found that the temperature of the electrolyte for alloy deposition and/or dissolution has a slight effect on the ALSV peak potentials but has no influence on the phase composition of the alloy. The concentration of chloride ions in the electrolyte for alloy dissolution (characterization) was found to be a limiting factor in successful and complete dissolution of Ag+Pd alloys.

Characterization of electrodeposited Co + Ni alloys by application of the ALSV technique Professor Aleksandar Despic to commemorate his 70th birthday

Abstract Anomalous codeposition of Co and Ni onto a gold RDE was investigated in a solution containing simple sulfate salts with the addition of sodium citrate. It was shown that the dependence of the percentage of Co in the deposit on the percentage of Co in the bath follows the shape found in the literature, with the percentage of Co in the deposit being slightly higher than in electrolytes containing pure simple salts. Alloy layers of different composition, electrodeposited at constant charge Q dep = 1 C cm −2 (thickness 0.34 μm) were submitted to anodic dissolution at a sweep rate of 1 mV s −1 (ALSV technique) in a solution of 1 M NaCl, pH 2. All samples were found to dissolve through a single anodic peak, indicating that both constituents of the alloy dissolve simultaneously. Alloys with higher Ni content (above 40at.%) were found to dissolve at potentials more positive than the potential of pure Ni dissolution as a consequence of the Gibbs energy change of formation of electrodeposited solid solution type Co + Ni alloys. The composition of electrodeposited alloys was determined by the atomic absorption technique. An attempt was made to obtain a correlation between the peak potentials of anodic dissolution of alloy samples and the composition of alloys, to determine the composition of the alloy from the peak potential of its dissolution. It is found that such a correlation can be used only for strictly defined conditions of alloy deposition and dissolution, caused by the contribution of the Gibbs energy change of formation of electrodeposited alloys. Also, the presence of a CoNi 3 ordered structure in the system is not detected as a separate ALSV peak, but its existence could be the cause of the shape of the Gibbs energy change with composition of the alloy for alloys electrodeposited at low current density.

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.

ALSV investigation of phase transformation kinetics in electroplated CuCd alloys

Abstract The phase transformation kinetics in electrodeposited CuCd alloys has been investigated by the application of the ALSV technique. By the analysis of the charge under the corresponding ALSV peaks it is shown that a lot of free Cd remains after phase transformation, while all Cu is found to crystallize into two intermetallic compounds, CuCd 3 and Cu 5 Cd 8 . A solid state reaction kinetic has been analyzed by the Johnson and Mehl equation for heterogeneous reactions. It is found that the nucleation process is slow and highly dependent on the alloy thickness, reflecting the catalytic effect of the substrate.

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.

The Effect of Reversing Current on the Properties of Copper and Electrolytic Copper Powder. I. The Morphology of Powder Particles

The selective dissolution of copper dendrites during electrodeposition by reversing current was discussed and the effects on the morphology of copper powder particles were elucidated.

Corrosion of Ti3SiC2 and Ti4AlN3 in Concentrated HCl Solutions

In this paper the mechanism of SiO2 layer formation onto Ti3SiC2 and the properties of the passive films formed on Ti3SiC2 and Ti4AlN3 in concentrated HCl solutions were investigated by SEM, polarization and EIS measurements. It is shown that the rate of the formation of a protective layer of SiO2 onto Ti3SiC2 surface during anodic oxidation is faster in the beginning, while after an induction period this rate is established at a value of about 130 μm cm -2 per year, giving the rate of Ti dissolution of about 9 x 10 -4 moles cm -2 per year. By analyzing the Mott-Schottky plots it was shown that the passive film onto Ti3SiC2 is an n-type semiconductor dominated by space-charge capacitance. Preliminary results for Ti4AlN3 indicate the presence of the passive film of a p-type semiconductor.