An electroless nickel plating bath with a hydrazine reducing agent has been investigated. An electroless nickel plating bath with a deposition rate of about 3μm/hr and superior bath stability as compared to previously reported bath has been developed. The new bath is a simple system consisting of glycine and boric acid in addition to nickel and hydrazine. The optimum plating conditions for the bath are in the range of 85-90°C at a pH of 12. The deposits obtained from the developed bath are black with a surface morphology that has a dendrite structure. Characteristics of deposits such as specific resistance and solderability were superior to those of conventional nickel-phosphorus deposits. Results confirmed that nickel was directly deposited on a copper substrate from an electroless nickel plating bath with a hydrazine reducing agent without an activation step in pretreatment.
With electrodeposition of Zn-Ni alloy from a sulfate bath, less noble Zn preferentially deposits compared to noble Ni. This behavior is classified as “anomalous codeposition.” The anomalous codeposition of Zn-Ni may be due to the preferential precipitation of zinc hydroxide on the cathode and the inhibition of nickel deposition according to the hydrogen production at the cathode and the pH increase. However, when both Zn2+ and Ni2+ coexist in the solution, the zinc hydroxide does not precipitate while the double hydroxide of both metals does. In this paper, the role of the double hydroxide obtained from a plating bath containing Zn2+ and Ni2+ has been clarified. The double hydroxide production process and the electroreduction of the hydroxide have been investigated.
The effect of rhenium, boron, and carbon on Ni-Re-B-C alloy films deposited from electroless Ni-B plating bath containing ammonium perrhenate was studied. Results were assessed with differential scanning calorimetry, X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy. The rhenium content of deposited films increased steeply to about 55wt% and then slowly increased to about 60wt% as ammonium perrhenate concentration in the bath increased. In contrasts, the boron and carbon content steeply decreased. Rhenium was deposited in greater amounts than boron and carbon. The structure of Ni-Re-B-C alloy films was analyzed in terns of rhenium and boron content due to the low C content, which was less than 0.3wt%. Films with a low rhenium and high boron content (over 2.0wt%) films had a rich phase that was amorphous. Films crystallized into nickel and Ni3B after heat-treatment at over 400°C. However, films with a high rhenium content had a marked by extremely fine crystals during deposition. The electron diffraction pattern of finely crystallized films did not change even after heat-treatment at 500°C for 1hr. Under these conditions, grain growth occurred at over 500°C, and a crystallized Ni3B spot appeared at 700°C.
Two kinds of alminum specimens were prepared: 1) chemically polished specimen (CP-specimen) and 2) surface-roughened specimen (PD-specimen) obtained by removing a porous anodic oxide film through dissolution in an H3PO4/CrO3 solution. The change in the surface roughness of CP- and PD-specimens during anodizing in a neutral solution was monitored with in situ atomic force microscopy (AFM) and transmission electron microscopy (TEM) as a function of anode potential. The change in surface roughness was also simulated mathematically, by assuming the Pilling-Bedworth ratio is constant during film growth. The CP- and PD-specimens had a network structure of ridges with respective heights of 30 and 70nm. The ridge height decreased sharply during the early stage of anodizing and gradually during the late stage. The PD-specimen showed a rough surface even at anode potential, where Ea=150V. A theoretical simulation of the decrease in the ridge height with the anode potential corresponded well to the experimental results obtained by AFM and TEM.
Chemical polishing solutions for aluminum based on mixtures of phosphoric and nitric acid cause air pollution with hazardous gaseous emissions, such as NOx, during the chemical polishing process, and cause water pollution due to the effluent of wastewater that contains phosphates and nitrates. Hence, the authors attempted to polish aluminum in an alkaline solution containing sodium hydroxide as an alkaline agent and sodium persulfate as an oxidizing agent. In this process, exceptionally bright surfaces of aluminum were obtained; that is, the brightness of the surface polished in the alkaline solution was comparable with that of the surface polished in an acid chemical polishing solution. The composition of the alkaline solution that had the least polishing effect had a concentration of sodium hydroxide in a range of 0.5 to 1.5% by weight for pure aluminum and a range of 1.0 to 2.0% by weight for commercially pure aluminum, while the concentration of sodium persulfate was 35% by weight. At with a high magnification on a scanning electron microscope (SEM), network patterns were observed over the entire polished surface of the aluminum polished in the alkaline solution and that in the acid chemical polishing solution. On the surface of the commercially pure aluminum polished in the alkaline solution, very small projections were observed by SEM, that were identified by electron probe microanalysis (EPMA) as insoluble phases that included foreign elements such as Fe and Si in the aluminum. On the other hand, on the surface of the aluminum polished in the acid chemical polishing solution, very small pits were observed, formed by dissolution of the phases in the acid solution. Also, use of x-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectroscopy (FT-IR) indicated that the oxide films formed on the surface of the aluminum polished in the alkaline solution were thicker and contained a larger amount of hydroxyl radicals than those on the surface polished in the acid chemical solution.
TiB2 and TiN films were coated by chemical vapor deposition on SKD 61 steel to improve the corrosion resistivity of a diecasting machine in a melted aluminum alloy. The protectivity of the film in the melted aluminum alloy was examined by an immersion test at 900°C and a thermal cycle test between room temperature and 900°C. TiN film, which serves as a binder, greatly improves the adhesion of TiB2 film on the steel substrate. The thermal cycle test indicated that the optimum thickness of TiB2 and TiN layers is at 4 and 6μm, respectively. Compared to ion-nitrized steel, steel coated by TiB2/TiN exhibits significantly higher degree of corrosion resistivity.
SiO2-GeO2 glass films were deposited on a fused silica substrate by rf magnetron sputtering method. The rf power to the target and to the substrate along with the O2 partial pressure were changed. The refractive index of the films was measured by a prism coupler method. The GeO2 concentration in the films was determined by Inductively Coupled Plasma (ICP) optical emission spectroscopy. The internal stress of the films was derived from Stoney's equation. As the rf power to the target and to the substrate increased and the O2 partial pressure decreased, the refractive index of as-deposited films increased regardless of the GeO2 concentrations in films. These changes were considered to be caused by the difference in the oxidation state of the films due to deposition conditions. Therefore, oxygen annealing of the films has been investigated to supplement oxygen-deficient defects in SiO2-GeO2. The fluctuation of the refractive index of the films fell below the order of 4×10-4 by annealing in an O2 atmosphere for 3h at temperatures of 1100°C or higher. The optical attenuation of the waveguide was less than 7dB/m at 1300nm and 1550nm, which is sufficiently low for an optical waveguide.
Reduction of Pb has become an urgent topic in discussions of ways to reduce the burden on the environment. The authors have been developing substitutive materials made of Pb-8wt% Sn coated steel sheets (which are known as Terne sheets) for automotive fuel tanks and chassis for home electrical appliances. Results have confirmed that Sn-Zn hot-dip coated steel sheets produced by a flux method can substitute for Terne sheets. The Sn-Zn hot-dip coated layer has a lower potential than Fe due to the content of a small amount of Zn. The layer also displays sacrificial corrosion protection. Zn crystal in the coated layer becomes coarse and Zn dissolves excessively when the Sn-Zn coated layer is over 11wt% Zn. Accordingly, Sn-8wt% Zn is the most balanced composition for sheets used for inner and outer corrosion resistance in fuel tanks. Results confirmed that Sn-Zn hot-dip coated steel sheets treated with special chemically treated film can confirm to various characteristics for fuel tanks. Subsequent use of lead for automotive parts may be reduced sharply.