Copper and subsequent nickel electrodeposition on magnesium alloys long used to protect magnesium alloys against corrosion has become untenable because attempts to recycle such alloys by melting results in Cu and Ni contamination that degrades corrosion resistance. The alternative electrodeposition we propose involves Zn immersion plating, Zn electroplating from a pyrophosphate bath (1A/dm2, 20 minutes at 50°C), and Sn electroplating from a stannate bath (1.5A/dm2, 20 minutes at 60°C).
Friction and wear tests were conducted to determine the tribological properties of hard materials, such as coating films and sintered ceramics, versus several types of industrial metals. TiN and CrN films deposited on flat tungsten-carbide substrates by ionplating were selected as coating film specimens. Si3N4 and SiC as sintered ceramic specimens. Each specimen was slid reciprocally against metal balls (SUJ2, SUS304, Ti-6Al-4V, Ti, and Al). After sliding experiments, specimen wear and metal transfer were studied. SiC showed the lowest friction coefficient in this study. Sintered ceramic specimens wore normally. In contrast, peeling wear occurred on the TiN film against SUJ2, SUS304, and Ti-6Al-4V. Coating films, especially CrN, have better wear resistance than sintered ceramics. Mating materials (metal balls) wore heavily in sliding against coating films, presumably the sub-micro-scale surface roughness of coating films affected the wear.
Electrodeposition of Cr-P-C alloy film from a trivalent chromium bath containing CrCl3, glycine, hypophosphite, and (NH4)2SO4 as main components was studied using a double compartment cell separated by a cation exchange membrane. Bright Cr-P-C films with a maximum deposition current efficiency of 10% were obtained from a pH 1.0 bath at a current density of 16A/dm2. P content in the film increased to 20at% with increasing hypophosphite concentration in the bath, while C content was about 2at% throughout our plating conditions. X-ray diffraction showed that the as-deposited film was amorphous and crystallized in heat treatment exceeding 600°C, raising film hardness from 500HV to 1500HV.
Effect of baking treatment on the pitting resistance of dehydrogenated and hydrogenated chromium electrodeposits was studied by potentiodynamic polarization measurements and X-ray photoelectron spectra. Pitting resistance of chromium electrodeposits can be improved by baking treatment. Dehydrogenated chromium electrodeposits can be produced having very high resistance to pitting corrosion over a wide range of baking temperatures and times than their hydrogenated counterparts. Results suggest that hydrogen in chromium electrodeposits should reduce their passive film, and then, deteriorate pitting resistance of electrodeposits during a baking treatment.
V2Ox/PPTA composite film consisting of vanadium oxide (V2Ox) and poly (p-phenylene terephthalamide) (PPTA) was prepared on ITO glass-coated with PPTA as described in the previous paper for WO3/PPTA film. Electrochemical, elctrochromic, and mechanical studies showed that V2Ox/PPTA film had essentially the same electrochemical and electrochromic properties as V2Ox film, but much greater mechanical strength (tensile strength: 86.3MPa, tensile modulus: 4.35GPa) and flexibility. We also found that V2Ox film prepared this way was amorphous; on cathodic polarization, the color reversibly changed to green and on anodic polarization to yellow. If it acquires other intermediate colors as different potentials are applied, it may be used as a multicolor indicator.
Transparent conductive Al-doped ZnO thin films were prepared on glass substrates by using radio frequency (RF) diode sputtering equipment with pure Ar gas and an Al2O3-mixed ZnO ceramic target. The samples, with constant thickness of 0.5μm, were produced by changing Ar pressure, annealing temperature, and substrate temperature in sputtering. Their electrical and optical properties and adhesion force to glass substrates were evaluated. Transparent films had low resistivity of 2.7×10-3Ω·cm and infrared ray cutoff, obtained by optimum case of Ar pressure of 1.3Pa and the substrate temperature of 723K. The adhesion force of the films were 1.7GPa in shear stress, tested by the scratch method. Films sputtered at higher Ar pressure of 13Pa also showed low resistivity of 3.4×10-3Ω·cm and sufficient infrared ray cutoff without substrate heating, although they tinged yellow and had a low adhesion force of 0.6GPa. The low adhesion force of these films was improved by postannealing above 673K.
The tribochemical reaction of ethanol on oxidized nickel surfaces was studied using gas chromatography, XPS, and exoelectron emission (EEE) and surface potential (SP) measurements. Ametal surface intentionally oxidized by heating in air at 25-800°C was rubbed with the same metal sample in ethanol vapor. EEE was measured using a Geiger counter with Ar-C2H5OH counter gas. SP was measured by a vibrating reed electrometer. Two gaseous products formed with and without friction--acetaldehyde (A) and an unidentified species (B) containing a carbonyl group. Friction increased products and EEE. Products tended to increase with EEE regardless of friction. Product formation was accompanied by carbon deposition. SP for surfaces oxidized at higher temperatures was negative, but after the reaction increased positively due to carbon deposition. The change in SP correlates with the activated tribochemical reaction, EEE appears to originate when negative charge on the oxidized surface is released due to the reduction by ethanol.
Palladium (Pd) line patterns were formed on glass and polyimide substrates by thermal decomposition of coated palladium acetate (PdAc) film using an argon ion laser. We studied the effects of substrate material and PdAc film thickness on light absorption, Pd pattern features, and size. PdAc film less than 250nm thick had low light absorption less than 5%, making direct decomposition by laser irradiation difficult. With such thin palladium acetate film, no Pd pattern was formed on glass substrates, because the Ar laser beam was almost transparent through the glass. The polyimide substrate, 50μm thick, showed high light absorption of about 95%, indicating easy heating by laser irradiation. The Pd patterns were formed, independent of PdAc film thickness, because the film was heated by thermal conduction from the substrate. Smooth, flat Pd features were formed at laser power densities of 1.5-3.5kW/cm2 that narrowed with decreasing PdAc thickness. Pattern widths were 1-2 times the laser beam diameter.
We studied the microstructure, chemical, and optical properties of dual films formed on Al anodized in a sulfuric acid bath, first by DC, then by AC in the same bath, and then deposited Sn electrolytically intomicropores. AC films grew beneath DC films forming twig-like micropores of 3-5nm diameter, 5-7nm cell·size, and 30-35nm barrier layer thickness. Metallic Sn precipitated densely into pores of AC films, and showed optical interference colors of blue, green, and gold with increasing Sn layer thickness. Corrosion and light fastness tests disclosed fairly good results, and alkali dropping tests showed eminent properties due to thick barrier layers.