Electroless Ni-alloy films were prepared as an electric resistor material, and the effect of heating on their resistance properties is reported, along with an overview of electric resistor materials and their essential properties. Ni-alloy films having stable resistance to elevated temperature were obtained by codeposition of a high melting point metal-W, Mo etc.-into the electroless Ni-P alloy films. The mechanism of thermal stabilization is explained as follows. In the case of W codeposition, W atom inhibits the crystallization of the Ni-P amorphous structure. In the case of Mo codeposition, a mechanism is quite different from W codeposition. Mo atom makes two phases (crystalline and amorphous) in the as-deposited state and this condition could be kept by proceeding the Mo segregation process between two phases. A pulse heating method, which can provide practical and quick evaluation of the thermal stability of resistor materials, was also described.
Electroless Ag plating was investigated as a method of coating of Al2O3 ceramics with YBCO superconducting oxides. The adhesion strength of the Ag plating increased greatly when the ceramics were pretreated by both mechanical and chemical etchings. From a study on the electrophoretic deposition of superconducting oxides particles from acetone baths, it was found that the amount of deposit increases with the I2 and H2O content of the bath, but excessive addition of I2 or H2O caused an increase in bath conductivity and electrolytic current, resulting in significant hydrogen evolution and a decrease in deposition. After electrophoretic deposition of the superconducting oxides on the ceramics, the ceramics were heat-treated at 940°C for 6h and at 450°C for 4h. The oxide coating was found to be smooth, uniform, and adhesive, and the superconducting properties of the coating were fully verified by X-ray diffraction, diamagentic measurement, and measurement of resistivity. Moreover, coil of Ag wire (φ0.7mm) was completely coated with superconducting oxides just like as above. These facts confirmed that electrophoretic deposition is an effective method for the preparation of superconducting oxides on various substrates of various shapes.
A method to form LaCrO3 oxide films on metals was developed. It was found that cathodic polarization of metals in La (III)-Cr (VI) solutions forms La (III)-Cr (VI) oxyhydroxide films on the metals. By controlling solution composition and pH, cathode potential, and electrolysis time, LaOH (CrO4)xH2O films were obtained with good reproducibility. The compound was found to decompose to LaCrO3 at lower temperarures and with shorter pyrolysis times than La (III) and Cr (III) compound precursors. The LaCrO3 film on stainless steels displayed good oxidation resistance. The LaCrO3 powder can also be synthesized from La (III)-Cr (VI) systems with lower enegy consumption.
Ni-B-SiC composite coatings were deposited from two different types of electroless nickel bath. Bath 1 which had NaBH4 as a reducing agent, gave produced coatings with a higher boron content than coatings deposited from Bath 2 which contained DMAB. In both cases, the SiC content of the coatings increased with increases in the concentration of SiC particles and the rotation rate of the agitator. The hardness of the coatings was increased from 600Hv to 950Hv by the incorporation of 5-6wt. % SiC. The hardness of coatings deposited from Bath 1 was further increased to 1080-1420Hv by heating in a vacuum for 1h, but the hardness of coatings deposited from Bath 2, on the other hand, was greatly reduced by the heating. X-ray analysis of the coatings deposited from Bath 1 indicated that the large increment in hardness induced by heating is attributable to precipitation hardening owing to the formation of Ni3B. The softening of the Bath 2 coatings is explained by the recrystallization of nickel assisted by the codeposited thallium derived from a stabilizer.
The mechanism of adhesion between electroless-plated films and polished alumina ceramic substrates was investigated. The adhesion strength of the electroless Cu and Ni-P films for etched alumina substrate, Ra 0.04μm, was 1.4kgmm-2 and 2.7kgmm-2, respectively. It was found that the difference in the morphology between these films at the initial deposition state causes the difference in their adhesion strength. The Cu deposit was rough and granular at the initial state, but the very thin (0.05μm) Ni-P film underlayer film changed the morphology of the Cu deposit into fine-grainy condition, and improved the adhesion strength of the Cu film drastically up to 2.7kgmm-2. It is concluded that the initial deposition condition is one of the most important factors in controlling the adhesion strength between Cu films and alumina substrates.
Electrochromic manganese dioxide thin films have been electrodeposited on optically transparent electrodes (OTE) from an aqueous solution of manganse (II) sulfate. Brown MnO2 thin film on the OTE glass is electrochemically reduced to a lower valence state, which is almost colorless, by the reaction. MnO2+H++e_??_MnOOH This reaction is reversible and its scheme is nearly the same as that of a dry cell. The conditions of electrolysis that yields the electrochromic brown MnO2 vary greatly depending on the temperature. The deposits was stable in alkaline solution, and at ±500mV in a NaOH solution, showing reversible coloration and bleaching for up to 104 repetition.
Aluminum (Al) is violently dissolved in 1, 1, 1-trichloroethane (CCl3CH3) once the induction period has passed. In the present paper, the dissolution rate of Al in CCl3CH3 was investigated. It was found that: 1) The dissolution reaction of Al in CCl3CH3 was zero-order, as in such liquid organic halides as carbon tetrachloride (CCl4), trichloroethylene and tetrachloroethane. 2) At temperatures ranging from room temperature to boiling point (347K) of CCl3CH3, the activation energy for the dissolution of Al in CCl3 CH3 was smaller than that in CCl4 reported previously, indicating that the reactivity of CCl3CH3 to Al is higher than that of CCl4. 3) When such organic reagents as methyl alcohol, n-buthyl alcohol, sec-buthyl amine, etc., were added as inhibitors in CCl3CH3, an increase occurred in the induction period of the reaction but there was no effect on the dissolution rate of Al. 4) CCl3CH3 solution to which AlCl3 was added exhibited electrical conductivity, and based of this observation, the dissolution mechanism could be well explained by the ionic reaction. 5) Dissolution of Al was accompanied by the generation of a large quantity of hydrogen chloride, so it is thought that the dissolution rate of Al was greatly increased by a number of chain reactions.