An electrosynthesis method for lead used as a negative electrode active material for lead-acid batteries with high electrochemical activity and a conductive network was investigated. The lead was deposited on a conductive carbon felt substrate with a large surface area from various electrolytes by direct and pulse current. The lead deposits were uniform when they were obtained by pulse plating from an electrolyte with a high cathodic overvoltage. The optimun conditions were: 0.1mol·L-1 Pb (NO3)2+5.0mol·L-1 NaOH electrolyte, 0.01s pluse period, 0.5 duty ratio, 50C·cm-2 cathodic charge density, and 150mA·cm-2 current density. In this case, utilization of the lead deposits was 37%.
Electrodeposition of CdTe was studied in an ammonia-alkaline ammonium sulfate solution in which Cd (II) and Te (IV) ions respectively existed as Cd (II)-ammine complex and TeO32-. It was possible to prepare ammonia-ammonium sulfate solutions containing 50mol·m-3 Te (IV) and 50mol·m-3 Cd (II) at ambient temperature. Cathodic polarization curves were measured at various concentrations of Cd (II) and Te (IV) at room temperate. Electrodeposition of Te was found to be inhibited by the presence of Cd (II) ions, suggesting that there is strong interaction between Cd (II) and Te (IV) ions. Polycrystalline CdTe was obtained by electrodeposition at constant cathode potentials ranging from -0.6 to -1.0V vs SHE at 348K. The deposition currents of CdTe was about 50A·m-2 at -0.8V vs SHE, which is one order of magnitude greater than that of conventional acidic solutions. Polycrystalline CdTe could also be obtained by heat treatment of amorphous deposits obtained by electrodeposition at room temperature.
In this study, we investigated a mechanism for improving paint adhesion by using Ni surface conditioning prior to dry-in-place chromate treatment, which is usually applied to hot dip Zn-coated steel sheets as a paint base. The results showed that the scattered deposits of Ni on the Zn surface formed micro cells with the Zn as the anode and the Ni as the cathode. Through these micro cells, insoluble chromate film (Cr(III)) deposited on the Ni through an electrochemical reaction of reducing the Cr(VI) in the dry-in place chromate solution. This mechanism of generating chromate film should contribute greatly to improved paint adhesion.
Various corrosion characteristics of bright Ni-Cr electroplated steel panels subjected to the CASS test are discussed phenomenally and statistically. The panels exhibited a large degree of variation in the various corrosion characteristics. Changes in the smoothed corrosion characteristics at each thickness of Ni as a function of the CASS test cycle are related to the fact that the barrier effect of the Ni coating increases with increasing Ni thickness. The spatial distribution of the pits followed a Poisson process regardless of the course of the CASS test cycle. The distribution of the Ni thicknesses at the bottom of pores in the Ni coating can follow a logarithmic normal distribution. From these results, it was concluded that the large variation in the corrosion characteristics of bright Ni-Cr electroplating is a natural phenomenon for the pits.
In order to examine the corrosion process of Zn-Ni alloy electroplated steel in a solution containing chlorine ions (3%NaCl aqueous solution), the time dependence of the corrosion potential was measured during an immersion test and the corrosion products were analyzed by XPS. The corrosion potential shifted to a noble potential in a complex manner as corrosion proceeded. The shift of the corrosion potential was characterized by the following corrosion process. At the beginning of corrosion, selective dissolution of Zn occured, and Zn oxide or hydroxide formed as a corrosion product on the surface of the Zn-Ni alloy plating. In the early stages of corrosion, the thickness of the corrosion product layer increased. As corrosion progressed, ZnCl2·4Zn(OH)2 formed outside the Zn oxide (hydroxide) layer. Therefore, the surface of the Zn-Ni alloy electroplated steel took on a layered structure of ZnCl2·4Zn(OH)2/Zn oxide or hydroxide/Zn oxide or hydroxide+metallic Ni/steel substrate. Dissolution of iron from the underlying steel occurs by passing through these corrosion products layers.
Hard diamond-like-carbon (DLC) films were deposited on aluminum alloy (JIS A6063) substrate by RF plasma CVD using CH4 and H2 as reactant gas. CH4 concentration, deposition time, and RF power were varied to determine preferable deposition conditions that would not cause undesirable softening of the substrate during the deposition process. The thickness of DLC film was about 4μm under conditions of gas pressure: 27Pa, CH4: 30%, RF power: 300W, and deposition time: 3h. Friction and wear experiments were conducted using a reciprocating friction and wear test apparatus. DLC film deposited under the above conditions was slid against bearing steel (JIS SUJ 2) balls to investigate fundamental friction and wear properties from room temperature to 200°C. The results were compared with those for substrate without the deposited DLC film. With the DLC film, friction and wear in the aluminum alloy were greatly reduced up to 100°C. The above results suggest that DLC film should improve the tribological performance of aluminum alloys used for sliding parts.
Reciprocating friction experiments were conducted to determine the effect of temperature (20°C-300°C) on the friction characteristics of silicon-based ceramics slid against pure metals. After the sliding experiments were performed, metal transfer to the ceramic surfaces was also investigated. Up to 100°C, the friction coefficient of SiC was lower than that of Si3N4. The friction coefficients of both ceramics rose at over 200°C, however the difference between SiC and Si3N4 became negligible. At 20°C, chemically more active metals showed higher friction coefficients against Si3N4. The friction coefficients of all metals became higher as the temperature rose, especially against SiC. The friction coefficients for Ag against both ceramics were extremely high, for example, at temperatures over 200°C they exceeded 2.0. Except for Ag and Mo, the pure metals used in this study transferred to the ceramic surfaces. Transfer occurred when the shear strength of the pure metal substrates was weaker than that of the metal oxides.
The aim of this study was to determine whether or not a spray technique would be useful in improving the surface of press metallic molds. A punch was coated with a hard WC-12%Co layer by low pressure plasma spraying, thermally treated, and applied in deep drawing work. The results were as follows. (1) Cr and Ni diffusion layers formed at the interface between the top and under layers under vacuum heat treatment at 900∼1100°C. A Fe layer also formed at the interface between the under layer and the substrate. (2) Although the hardness of the sprayed layer was lowered somewhat under vacuum heat treatment, wear resistance was improved. (3) The results of field test of deep drawing work showed that the combination of the spray technique and heat treatment should be very useful in improving the surfaces of press metallic molds.
The hardness of the anodic oxide film that forms on aluminum is several times harder than the aluminum base metal. Sometimes this phenomenon causes problems when the limit PV value is too low in friction and wear of the anodized coating. In this study we attempted to clarify the relationship between the hardness of the anodic oxide film and that of the aluminum base metal using a compression test that simulated the state of a large P value in friction and wear. The following results were obtained: (1) Anodic oxide film in which cracks occured in the first step of the compression test was buried into the aluminum base metal in accordance with the magnitude of the compressive weight. (2) Both the anodic oxide film and the aluminum base metal were hardened in the compression test. (3) When the aluminum base metal was hard, there was little burying of the anodic oxide film. This means that a large limit PV value, and in particular a large P value, may be obtained in friction and wear.