PHASE COMPOSITION AND MORPHOLOGY of Ni, Zn-ALLOY SURFACE, ELECTRODEPOSITED FROM SULPHATE-AMMONIUM SOLUTION
Electrodeposited nickel-zinc alloys are widely used in the industry as anticorrosive coatings as they are less toxic compared to cadmium coatings. However the former cannot replace the latter completely.
Fine-crystalline nickel can be obtained by modifying the nickel-zinc alloy by means of removing a less noble component. This nickel can be used as a catalyst in hydrogen hydrogenation and electrochemical reduction reactions. The activity of such catalysts depends on the composition of the original alloy, the modification conditions, and the morphological characteristics of the resulting fine-crystalline nickel.
The aim of the research was to obtain and study the morphology and the phase composition of electrolytic Ni, Zn-alloy deposited on nickel base.
The deposition was carried out in a sulphate-ammonium solution at a constant potential of 1.150 V. The thickness of the deposited alloy, as estimated by micro interferometer MEI-4, was 1.1± 0.01 μm.
To study the composition and the morphology of the deposited coating surface, the following methods were used: chronopotentiometric (IPS-compact), X-ray phase analysis (Empyrean B.V., PANalytica, the Netherlands); atomic power microscopy (SOLVER P47, NT-MDT, Russia), and scanning electron microscopy (JSM 6380LV, JEOL Ltd., Japan).
Micro-X-ray spectral analysis showed (Table 1) that the atomic ratio of nickel and zinc in the coating was 1: 4.
Phase composition detection was carried out by means of the chronopotentiometric method in 2M NaOH with a current density of 0.025 mA / cm2 by dissolving an electrolytic alloy to a potential of -0.400 V. Nickel is in an oxidized state under these conditions and does not accumulate in the solution, and zinc is oxidized to soluble complex forms. The presence of nickel ions in the solution was monitored by the photocolorimetric method in the presence of dimethylglyoxime on KF-77.
The intermetallic phases NiZn and NiZn3 were detected in the coating by the the chronopotentiometric method (Fig. 2). The potentials on chronopotentiometric curves correspond to the electrochemical dissolution of the intermetallic phases: -0.900 ± 0.020 V (NiZn3), 0.650 ±0.020 (NiZn).
X-ray phase analysis revealed the intermetallic phases NiZn3, and NiZn in the deposited coating. In the modified alloy, an undissolved zinc is recorded in NiZn (Fig. 3).
It was established by atomic force microscopy that during the modification of the alloy in 2 NaOH, the surface phase of the fine-crystalline nickel is formed, while the surface area of the electrode increases 5 times (Fig. 4). Modified electrodeposited Ni, Zn - alloy consists of particles with a size of 20 to 200 nm, and crystals 40-60 nm in size predominate (Fig. 5).
The results of the research were obtained using the equipment of the Centre for Collective Use of Scientific Equipment of Voronezh State University.
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