The behavior of magnesium in anodic films formed on the surfaces of annealed aluminum foil with MgAl2O4 spinel particles at sizes of 0.1 to 0.2μm was studied on the basis of TEM observation and EDX analysis. Anodic films were formed at a current density of 50mA/cm2 in a boric acid solution at 90°C for 2min. Anodic films were stripped from the aluminum foil, and the films extractive carbon replicas and cross sections of the anodic films were used for TEM observation. Crystalline oxide γ′-Al2O3 with a round shape was formed around MgAl2O4 particles and grew over the surface with an increase in the forming voltage up to 60V. Magnesium disappeared in γ′-Al2O3 above 100V, and voids and cracks were observed around crystalline oxide particles in the anodic films formed at 150V. At 300V, crystalline oxide was directly separated by a crack. It appears that the formation of the voids and cracks is associated with the greater migration rate for Mg2+ than that for Al3+ in a high electric field.
Electroluminescence originating in rare-earth metals was observed during reanodization of barrier type anodic alumina films doped rare-earth metals by ion-implantation. In this case, EL intensity was influenced by Al surface morphology as a result of electropolishing. The influence of Al surface treatments of etching or indenting on EL intensities has been investigated. Vivid EL occurred around the pitting points of corrosion in the specimen with a surface treatment by Etching. Many projections were formed around the pitting points of corrosion, and these areas became the starting points of an electron stream. EL intensities increased with an increase in the projections deu to surface area expansion. The electron stream in the film grew larger with surface treatment by indenting, where EL intensities increased with an increase in current densities.
The role of individual components of Watts bath has been investigated using a Hull cell test and electrochemical measurement in order to research the possibility of substitution agents in place of boric acid. Boric acid inhibits hydrogen evolution as a side reaction for nickel deposition. Hydrogen evolution causes a rise in the pH of the plating bath, resulting in the appearance of burns or the precipitation of nickel hydroxide on the plated surface. Therefore, the difference in pH before and after a Hull cell test is one of the key factors in judging the performance of a nickel plating bath containing substitution agents such as pH buffers. Buffers like citric acid and nickel citrate are effective in that a difference in pH is not observed during the Hull cell test and a satisfactory appearance, as given by boric acid, is obtained. These agents or a complex with nickel ions and the agents is readily adsorbed on the surface of the cathode, resulting in the inhibition of the hydrogen evolution reaction. Citric acid and nickel citrate are possible substition agents in place of boric acid.
A zinc chloride plating bath containing acetic acid as an alternative buffer in place of boric acid has a wide range of current densities and gives off a bright appearance. The dissolution of a steel substrate in this bath is promoted because of the bath's relatively low pH value of 4. In this paper, the influence of iron ions on zinc plating and their inhibition have been investigated. Iron ions refined the grain size of deposits from a basic bath without brighteners. In a bath containing brighteners, when iron ions accumulated to more than 0.2g/L, the current range for brightness narrowerd. This result is due to iron ions that were reduced and codeposited in the zinc film; when the iron contents of the film exceeded about 0.6wt%, the grain size became coarser. The pH value in which iron hydroxide is precipitated in the bath with acetic acid is higher than 6 because of the complexing effect of acetate: thus, the elimination of iron ions is not readily accomlished. However, the codeposition of iron was inhibited by adding quadrol or gluconate to the bath and the current range for brightness was restored to a certain extent.
In a zinc cyanide system, internal stress, lattice distortion, and carbon content of plating are related to one another. The value of these physical and metallurgical properties of plating decreased with an increase in the M ratio (NaCN/Zn) of the baths, and whiskers did not grow below a particular value (i.e. internal stress: 55 MPa; lattice distortion: 0.25%; carbon content: 0.06%). High concentrations of cyanide in baths contribute to the role of the brightener and accelerate grain refinement and brightening of plating; these concentrations did not increase the internal stress and lattice distortion, which significantly affects the inhibition of whisker growth. The results of this work suggest a framework for zinc whisker growth.
The effects of the surrounding humidity on the friction and wear properties of electroless Ni-P alloy coating on iron substrate against various steel balls were evaluated by using a horizontal reciprocating friction and wear test apparatus. The friction and wear properties greatly changed due to the surrounding humidity in spite of being under equal friction and wear testing conditions. The friction coefficient and wear amount decreased with the increase in the surrounding humidity. Therefore, it was proven that the water which adsorbs to the specimen's surface showed the lubricating effect.
Adhesion of thin SiNx to a stainless steel SUS 310 substrate was done through use of an arc ion plating process. Film properties were investigated with structural analysis and adhesion to determine conditions for film deposition. For this process, the voltage of the substrate bias was -200V to -600V, the gas pressure in the plating chamber was 1.3×10-2∼6.7×10-2Pa, and gas formation was examined comparatively for 100% N2 and 50% N2/50% He. The substrate temperature remained constant at 580°C and electrode voltage was 50V. These films were evaluated in terms of critical load value (Lc) measured by a micro-scratch machine, X-ray diffraction patterns, and results of state analysis using an electron probe microanalizer (EPMA) and electron spectroscopy for chemical analysis (ESCA). The following conclusions were obtained. 1) A lower bias voltage is satisfactory, though an increase in the critical load leads to favorable adhesion. 2) A mixture of N2 and He in the chamber results in superior Lc for the deposited film. 3) The films have an amorphous mixture of Si3N4 and Si.
In this investigation, the influence of surfactant in chromating in zinc-nickel alloy electroplating through use of sulfate solutions has been examined. Results indicate that the eutectic amount of nickel in the surface layer of the deposit decreased with the addition of dodecyltrimethyl-ammonium chloride (DTAC). Therefore, the formation of chromate films became possible for this deposit and corrosion resistance with respect to white rust improved remarkably.