Naoyuki Shinohara

Potential oscillations during the electrocrystallization of cadmium from alkaline cyanide solutions under galvanostatic conditions

Abstract The potential oscillations during the electrocrystallization of cadmium from alkaline cyanide solutions have been studied under galvanostatic conditions. The current-potential curve under potentiostatic conditions showed a limiting current which was caused by the diffusion control of the cadmium complex ion with natural convection. Potential oscillations were observed when the electrolyses were carried out at current densities which were above the limiting current on the current-potential curve. In these cases, hydrogen bubbles were evolved periodically from the cathode surface. The potential oscillation during the electrocrystallization of cadmium results from the following processes: (i) The surface concentration of cadmium ion is decreased after the beginning of galvanostatic electrolysis. (ii) When its concentration becomes nearly zero, the potential shifts rapidly from a positive value to a negative one, which is the potential of hydrogen evolution on cadmium metal. (iii) Hydrogen bubbles are evolved from the cathode surface. (iv) The surface concentration of cadmium ion is restored close to the bulk concentration by forced convection due to the evolution of hydrogen bubbles. (v) The potential shifts from a negative value to a positive one. Thus, the potential oscillation repeats with constant amplitude and period.

Effects of aromatic carbonyl compounds on the surface morphology and crystal orientation of electrodeposited tin from acid stannous sulfate solutions

The effects of three kinds of aromatic carbonyl compounds [cinnamaldehyde(CA), benzalacetone(BA), 2-acetonaphthone(AN)] and N,N-bis(tetraoxyethylene)octadecylamine(TOOA) on the surface morphology as well as crystal orientation of electrodeposited tin from acid stannous sulfate solutions have been studied by means of electrochemical methods, scanning electron microscopic observation and measurements of X-ray diffraction patterns. The inhibitory effects of the reduction of tin(II) ion became stronger in the order BA, CA and AN in the case of oxidant, and in the order CA, AN and BA in the case of reductant. The differences in the inhibitory effects between the oxidant and reductant became greater in the order of AN, CA and BA. Block-like crystals were observed on the whole surface by adding TOOA. Plate-like, needle-like or dendritic crystals were observed but compact electrodeposits could not be obtained by adding carbonyl compounds alone. On the other hand, compact and smooth electrodesposits of tin which had a preferred orientation with the (100) plane parallel to the surface were obtained from acid stannous sulfate solutions containing TOOA and BA.

EFFECTS OF N,N-BIS(POLYOXYETHYLENE)OCTADECYLAMINES ON THE ELECTROCRYSTALLIZATION OF TIN FROM ACID STANNOUS SULFATE SOLUTIONS

Abstract The electrochemical characteristrics of three kinds of N,N -bis(polyoxyethylene)octadecylamines (POOA) and the effects of POOA on the surface morpholoy as well as crystal orientation of electrodeposited tin from acid stannous sulfate solutions have been studied by means of various electrochemical methods, scanning electron microscopic observation and measurements of X-ray diffraction patterns. The three kinds of POOA were absorbed on the electrode in the range of potential from 0 to −1.50 V, and POOA adsorbed on the electrode inhibited the electrochemical reduction of tin(II) ion. Needle-like, or columnar, electrodeposits of tin were obtained from acid stannous sulfate solution in the absence of organic additives. On the other hand, block-like or granular crystal which exhibit the (101) plane parallel to the surface were observed on the whole surface by adding POOA. It was found that the three kinds of POOA induce a uniform deposition of tin over the whole surface, and the grain size of crystals as well as the surface roughness of electrodeposited tin become smaller with increasing the chain-number of oxyethylene in POOA.

Effects of aromatic carbonyl compounds on the electrocrystallization of zinc from acid sulfate solutions

Abstract The electrochemical characteristics of N,N-bis(decaoxyethylene)octadecylamine(DOOA) and the three kinds of aromatic carbonyl compounds [cinnamaldehyde(CA), benzalacetone(BA), 2-acetonaphthone(AN)] as well as the effects of such organic additives on the electrocrystallization of zinc from acid sulfate solutions have been studied by means of various electrochemical methods and scanning electron microscope observations. DOOA and three kinds of carbonyl compounds were adsorbed on the electrode. DOOA adsorbed on the electrode as a quaternary ammonium ion strongly inhibited the electrochemical reduction of the zinc ion. BA or AN had a stronger inhibitory effect on the reduction of zinc ions than CA. Large plate-like electrodeposits of zinc (sides 3–10 μm) were obtained from acid sulfate solutions in the absence of organic additives. On the other hand, needle-like or fibrous crystals were observed on the whole surface by adding DOOA alone. Small block-like or granular crystals (sides 1–2 μm) were observed on the whole surface by adding BA or AN alone. Further, fine-grained, smooth and compact electrodeposits of zinc were obtained from acid sulfate solutions containing DOOA and BA or DOOA and AN.