To improve the corrosion resistance to salt and acidic attack of magnesium alloy, composite films consisting of a chemical conversion film or an anodic oxide film and a coating layer deposited thereon were prepared by the sol-gel process using tetraethoxysilane as a metal alkoxide. These composite films prepared by repeating three or five dip-coatings indicated an excellent corrosion resistance to salt attack. Furthermore, the acidic corrosion resistance of composite film formed on anodic oxide film was examined using an electromotive force measurement test. In comparisons between the composite films prepared by repeating three dip-coatings and an anodic oxide film of magnesium alloy, the acidic corrosion resistances of these films to various acids increased by a factor of 12 to 33 on the anodic oxide film in the thickness of 7μm and a factor of 3.4 to 7.6 for thickness of 15μm. These improvement of corrosion resistance are considered to be caused by the production of some reaction products in the path of a salt solution or an acid that is penetrating into the composite film.
An aluminum specimen covered with porous type oxide films with 3 to 54μm thickness was irradiated by a pulsed Nd-YAG laser through a convex lens with 20 mm focal length in a solution to examine the mode of oxide film removal by laser irradiation. A prototype printed circuit board was fabricated using laser irradiation and Au electroplating. Thin oxide films were removed instantaneously after laser irradiation onset by the laser ablation mechanism. Thick oxide films were destructed initially from the upper part of the oxide films by the thermal shock mechanism, and then by the laser ablation mechanism. Further laser irradiation after the film removal caused the formation of many cracks in the oxide film surrounding the irradiated area. By scanning a laser beam over a specimen covered with oxide films with 9μm thickness, the oxide film was removed uniformly with a 30μm line width. Fine pattern coils of 30μm wide Au lines were fabricated on the insulating board by consecutive processes of aluminum anodizing, laser irradiation, Au electroplating, resin attaching, and removal of aluminum substrate and oxide film.
For the purpose of micromachining application, we have studied basic characteristics of electrochemical etching of NiTi Shape Memory Alloy (SMA) in new electrolytes of inorganic salt in alcohol for comparison with conventional H2SO4-methanol solution, especially from the viewpoint of the suppresion of the etching rate. In the case of conventional H2SO4-methanol solution, good etching with planarized etched surface and high etch rate could be carried out, however, the etch factor (etching depth/side etching width) and surface flatness became worse under low etch rate conditions. The electrochemical etching of SMA also could be carried out in new electrolyte solutions using NH4Cl, NaClO4 and LiCl solute. Especially in the case of LiCl-ethanol, good etching properties such as controllable low etch rate of 3.5μm/min, planarized etched surface and high etch factor of 1.5 were realized. Although the etching condition was not in the electrolytic polishing region, the etched surface was planarized because there were no influences of a reaction of passivation, which inhibits the surface planarization. In the case of LiCl-methanol, the etching rate was over 10μm/min, however, planarized etched surface and high etch factor were also realized.
Electroless deposition of metal onto nonconductors, such as ceramics, glass and plastics, requires a catalyzation pretreatment of substrates. Adsorbates formed on glass or mica substrates by two-step catalyzation (sensitization-activation) have been investigated by quantitative analysis of Sn and Pd on substrates, XPS and AFM. Adsorbates, formed on the substrate by the sensitization, included divalent Sn and O, and no Cl was included. There were two kinds of Sn adsorbates, weak adsorbed ones and strong adsorbed ones. The former was in an equilibrium state to Sn2+ in the sensitizer, therefore, it was desorbed from the substrate by immersion into HCl solution, and was recovered to the same amount by the sensitization after the immersion into HCl solution. Elemental Pd which included no Cl was produced on the substrate by the activation after the sensitization. The amounts of Sn and Pd adsorbates were increased by the repetition of sensitization and activation. The activity of the catalyzed substrate for the electroless deposition was lost by the sensitization. AFM inspection showed that fine particles (10–15nm in size, 0.5–1.0nm in height, 4–5×103 particles μm-2 in density) were formed on the substrate by the sensitization, and the height and density of particles were enlarged by the activation. The process of two-step catalyzation was explained by using a model based on these results.
Pt/Ti thin films were grown on SiO2/Al2O3 substrates by sputtering under argon-oxygen gas mixtures and annealed in air ambient. In comparison with Ar-sputtered films reported in the previous paper, Ar-O2-sputtered films show flat Pt surfaces and high values of temperature coefficient of resistance (TCR). In order to probe the cause of these phenomena, microstructures of these films were investigated by means of X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy and glow discharge optical emission spectroscopy. The Ar-O2-sputtered Pt/Ti films differ from the Ar-sputtered ones in the following aspects : (1) Ti deposition rate becomes slower by about a third ; (2) Pt grains with preferred (111) orientation grow about three times larger in diameter ; (3) Ti atoms form TiO2 precipitates with the rutile-type structure mostly at the Pt/SiO2 interface, but the precipitates rarely exist in Pt film. From these features, it is shown that the surface flatness and TCR of the Pt film sputtered under argon-oxygen gas mixtures are improved by controlling the formation of TiO2 precipitates in the Pt film.
CuCN was dissolved in highly concentrated alkaline solution. The color of the dissolved solution showed a transparent blue. The production of soluble cyanide copper complex was indicated by the measurement of ultraviolet and visible absorption spectra for the supernatant solution obtained by filtration. CN- ion were not detected in the solution during the reaction process. The concentration of OH- ion decreased about 5-fold in comparison with the initial concentration of CuCN. The soluble cyanide copper complex changed to insoluble fine black particles by reacting with OH- ions. From the XRD measurement, the fine black particles were identified as CuO. From the gravimetric analysis, the production yield of CuO could estimated to be 50% due to change of the oxidation number from I to II.