Comprehensive discussion on the mechanism of induced codeposition of molybdenum with iron-group metals, especially with nickel, was made based on the results previously reported by the authors. In the process of alloy deposition, molybdenum lower oxide was estimated to be formed on the cathode by comparing the factors determining the cathode current efficiencies of the depositions from the baths of molybdenum and nickel-molybdenum alloys. The inhibiting effect of additive S- and N-compounds on molybdenum codeposition appeared to indicate that atomic hydrogen was necessary for further reduction of molybdenum lower oxide to occur. Further, the relationships between the composition of alloys and the cathode current efficiency during the electrodeposition of binary and ternary alloys of molybdenum with iron-group metals showed the two characteristic alloy compositions, the one appeared at a maximum partial current efficiency of molybdenum and the other corresponded to the limiting content of molybdenum. These characteristic compositions were in good agreement with the calculated ones based on the number of unpaired 3d electrons of iron-group metals. These led to the multi-step reduction mechanism which included the formation of the partly-reduced molybdenum oxide and the reduction of this film by atomic hydrogen held on iron-group metals by utilizing their unpaired electrons. The same mechanism may also be valid in the simultaneous electrodeposition of iron-group metals and such metals of which deposition proceed with preceding lower oxide formation as chromium or rhenium etc.

抄録全体を表示

On the assumption that low hydrogen overpotential of cobalt plating is due to the peculiar crystal structure of electro-deposited intermetallic compounds, the relationship between the crystal structure and hydrogen overpotential was exammined by X-ray diffraction method. When above 8×10^-3mol/dm³ of vanadium pentoxide was added into the citrate cobalt plating bath, an intermetallic compound, σ-CoV, was obtained reproducibly. X-ray diffraction pattern of σ-CoV, however, disappeared by annealing the electrodeposit at 500°C for 1h. Low hydrogen overpotential seems to be due to the σ phase of the electro-deposit; σ phase was stable in hydrogen evolution by electrolysis of NaOH solution. By addition of molybdenum, electrodeposited cobalt became amorphous.

抄録全体を表示

The influence of diffusion coating temperature, materials used, and the addition of Mo on the polaization behavior of austenitic stainless steels, SUS 304 and SUS 304L, diffusion-coated with Cr, was investigated by measuring anodic polarization curves of the steels in 1N-HCl and 1N-H₂SO₄ solutions. In an 1N-HCl solution, specimens diffusion-coated with Cr exhibited well defined critical current densities and passive range. Increase in the treatment temperature made the surface of the diffusion coating layer more rough and increased the amount of impurities (such as Fe, Ni, C) diffused from the base metal into the diffusion coating layer. This caused the critical current density and the passive current density to increase. SUS 304L diffusion-coated with Cr had a wider passive range and exhibited a better polarization behavior than SUS 304, although the treated SUS 304L had a higher critical current density. Mo added in the Cr diffusion coating treatment decreased the critical current density and passive current density.

抄録全体を表示

During the course of an investigation of nickel-alumina composites, it was observed for a rotating cylindrical copper cathode that the alumina content of the deposit on the cathode decreases with increasing revolution rate of the cathode. Further experiments were made to study the unusual deposit behaviours more in detail. At given revolution rates (N), the deposition rate of alumina (u_Al2O3) calculated from the observed values of volume percent deposited is directly proportional to the alumina content in the bath (C*). Irrespective of C*, the ratio of u_Al2O3 to the product of C* and current density shows an S shaped relationship to N in the range of 200 to 1000rpm. This relation-ship is well related to the observed particle distribution in the bath by a newly proposed “detaining function” under the assumption that the maximum size of alumina caught by the rotating cathode is inversely proportional to the revolution rate. This detaining function is calculated on the basis of attractive force due to London-van der Waals potential and repulsive centrifugal force.

抄録全体を表示

Hardfacing layers for steels were obtained with the paste of tungsten carbide (WC) containing a Ni-P alloy by the three heating methods; electric furnace, hot press and argon arc. It was found that the hardness of the layers was affected by the method of heating as well as the content of WC and that under present experimental conditions the hardness was highest in the method of heating by electric furnace. The characteristics of the hardfacing layers were influenced by the method of heating. A high wettability of WC with a Ni-P alloy caused the microstructures of the layers to be dense and uniform. A diffusion layer about 10-15μm in thickness lying between the hardfacing layer and the substrate showed a high bond strength for adhesion. Double carbides phase (η-phase) was found in the hardfacing layer obtained in the method of heating by argon arc.

抄録全体を表示

Susceptibility to the bipolar phenomena in electroplating has been investigated for various-plating baths. It was found that these phenomena take place more easily in the baths of lower conductivity and lower polarization. Oxide films produced by the bipolar phenomena caused a significant influence on the subsequent plating process. In the chromium plating on the passivated bright nickel plates, from a bath containing sulfuric acid, hydrated chromium oxide showing interference color or milk-white chromium metal was deposited, while bright but slightly dull chromium deposits were obtained from a bath containing sodium silicofluoride. It has been assumed that the differences in the surface states of the metal deposits from the two different baths are due to the effect of additives in the deposition process but not in the anodizing process.

抄録全体を表示