M.G. Pavlović

Electrodeposition of Metal Powders with Controlled Particle Grain Size and Morphology

The processes of metal deposition can be categorized into three main groups each of which has different requirements with respect to the physical state of the cathodic product. In electroplating the crystal layer is required to be fine grained, smooth, strongly adhesive, and glassy, i.e., to be easily polished. In refining and electrodeposition relatively coarse grained, rough, but adhesive deposits are required. They have to be of high purity and firm enough to endure handling before melting and casting into shapes suitable for further processing. In metal powder production by electrodeposition, a controlled product particle size is necessary and the product is favored not to or weakly to adhere to the cathode. Generally, powder production requires other conditions than those in electroplating.

Deposition of zinc of foreign substrates

Abstract Initial stage of deposition of zinc from buffered zinc sulphate solution (pH = 3.55) was studied using platinum, gold and graphite as substrates. The phenomenon of underpotential deposition, noted by recording potential sweep voltammograms (PSV), was taken as a criterion of the existence and strength of interaction between a substrate and the depositing metal. Strong adhesive interactions (including alloy formation) were found in the case of platinum and gold with indication of the existence of multiple states of zinc atoms at the surface. Graphite exhibited no notable interaction and at cathodic overpotentials a characteristic surface growth loop was recorded in the PSV. The later was submitted to a semiquantitative interpretation assuming instantaneous 3-D nucleation and growth with overlap of growing centres. Kinetics of deposition was investigated under the same conditions using a specially design potential pulse sequence enabling separate estimate of zinc deposition and hydrogen evolution partial currents. Recorded current responses were in line with the hypothesis that the deposition at substrates exhibiting strong interactions proceeds without notable nucleation effects. In the absence of such interactions phenomena typical of three-dimensional nucleation and growth are observed.

Morphology of lead dendrites electrodeposited by square-wave pulsating overpotential

The effect of square-wave pulsating overpotential on the morphology of lead dendrites is discussed. It is shown that the morphology of lead dendrites strongly depends on the parameters determining the shape of the pulsating overpotential wave.

Electrodeposition of Ag from nitrate solutions : Part I. Effect of phosphate ions on morphology

The initial steps of silver deposition from nitrate solutions on silver and platinum substrate were studied. The formation of boulders was observed on both substrates, their growth onto platinum being the more regular. A compact Ag-surface film was not produced under the applied conditions, even after prolonged deposition. Instead, growth of (i) independent large Ag grains occurred at lower overpotentials and (ii) dendrites formed at higher overpotential values. In the presence of phosphate in unstirred solutions 2D and/or 3D dendrites were formed at lower and higher overpotentials, respectively. Increase in electrolyte temperature above 25∘C was found to cause dendrite coarsening, even at lower overpotentials. In stirred solutions compact Ag-surface films were deposited over a wide range of overpotentials, showing different structural features depending on the applied overpotential.

The visualization of the electrochemical behaviour of metal particles in spouted, fluidized and packed beds

Abstract The electrochemical behaviour of metal particles in spouted, packed and fluidized bed electrodes can be visualized in the same way as in the electrochemical corrosion demonstration. The cathodic reaction, indicated by bright red colour (grey in black-white photographs), occurs on the particles in contact with the cathode current feeder. The profile of red colour corresponds to the current density distribution. This is relevant for all particles in the fixed packed bed and in the annulus of the spouted bed, and for those particles in the fluidized bed which are in contact with the cathode current feeder. All the particles in the spout and fountain of the spouted bed and the majority of the particles in the fluidized bed are not in contact with the cathode current feeder. They are characterized by bipolar behaviour because the resistance of the electrical transfer through the particle is less than that through the surrounding electrolyte. The anodic reaction, indicated by dark blue colour (black in black-white photographs), occurs on the part of the particles in the direction of the cathode current feeder, while the opposite side of the particles is under the cathodic reaction, visualized by bright red colour. The method described could be used for the optimization of three-dimensional electrodes.

Electrode surface coarsening in pulsating overpotential copper electrodeposition

Abstract It is shown that copper deposits obtained in pulsating overpotential electrodeposition are different in structure and less coarse than deposits obtained in the constant overpotential regimes.

The initiation of dendritic growth of electrodeposited copper on a rotating disc electrode with changing copper concentration and diffusion layer thickness

It is shown that the critical overpotential of dendritic growth initiation increases with increasing copper concentration under identical hydrodynamic conditions, as well as with increasing rotation speed to the rde (rotating disc electrode).

Morphology of tin powder particles obtained in electrodeposition on copper cathode by constant and square-wave pulsating overpotential from Sn(II) alkaline solution

Abstract It is shown that the morphology of tin powder particles strongly depends on deposition overpotential and parameters determining the wave of pulsating overpotential. The possible effect of pulsating overpotential on the morphology of tin powder particles is discussed.

Electrode surface coarsening in potentiostatic copper electrodeposition

Abstract The increase of electrode surface coarseness during copper electrodeposition is discussed. It is shown that electrode surface coarsening is caused by the differences in deposition current densities at different points, which arises from mass-transport limitations and different deposition rates on different crystallographic planes in mixed-controlled and activation- controlled deposition respectively.

The current density distribution on stationary wire electrodes during copper and lead electrodeposition

Abstract The current density distribution during lead and copper electrodeposition on to stationary copper wire electrodes was investigated by inspection of the morphology of the deposit. It was shown that the tip current density was much larger than that on the rest of the electrode during deposition from low conductive solutions. In contrast, the current densities are practically the same for the deposition from solutions characterized by large conductivity. A mechanism of transformation of Ohmic potential drop in the homogeneous current field in electrochemical overpotential at the edge of a plane and the tip of a wire electrode is proposed by considering the current line dissipation between the cathode edge, tip, anode and cell walls. There are a large number of current lines between two symmetrically-positioned points on the edges (assumed as lines) of the anode and cathode making the Ohmic drop along each of them negligible. Because of this the electrochemical overpotentials and current densities at these points must increase in order to compensate the Ohmic drop between two symmetrical points in a homogeneous field on the anode and cathode. The above reasoning is obviously valid for the tip of a wire electrode (assumed as a point) because the dissipation of current lines in this case takes place through space while in the parallel plane electrode arrangements it takes place in one plane normal to the electrodes to which two symmetrically-positioned points belong.