Anodizing of magnesium was studied in sodium metasilicate aqueous solutions with and without 5-sulfosalicylic acid. We investigated the experimental conditions for the formation of magnesium anodic oxide films, such as the temperature of the solution, the cell voltage during anodizing, and the concentration of the 5-sulfosalicylic acid. It was found that the anodic oxide film varied at the temperature of 338 K, and that white-colored Mg-Si-O anodic oxide films formed at lower temperatures than 338 K with high voltage in 2.0 mol·dm−3 sodium metasilicate aqueous solution. Addition of 0.25 mol·dm−3 of 5-sulfosalicylic acid to 2.0 mol·dm−3 sodium metasilicate aqueous solution yielded hard and gray-colored Mg-Si-O anodic oxide films containing carbon and sulfur elements. In 5 mass% NaCl solution at 308 K, the gray-colored film sealed in boiling distilled water showed higher corrosion resistance than that of the white-colored film prepared in sodium metasilicate solution.
The properties and mechanism of peeling on nickel electroforming were investigated changing the activation treatment, the surface roughness of substrate and varying the treatment conditions (concentration, time, and temperature) of potassium dichromate solution. The results obtained are : the peeling force increases with an increse of the arithmetrical mean roughness (Ra) when the activation treatment is carried out. That is, the peeling force is proportional to Ra. Activating the surface of the substrate with an acid such as sulfuric acid reduces the peeling force below about one-half. The content (at%) of chromium in the film increases with an increse of the concentration of potassium dichromate and the treatment time. The peeling forces decrease with an increse of the content of chromium and the treatment time. On the other hand, the treatment temperature does not affect the thickness and the content of chromium in chromate film. On the basis of the results, it may be concluded that the important parameters affecting the peeling properties are as follows : firstly the roughness of surface, secondly the activation, and thirdly the conditions of chromate treatment. From measuring the thickness and content of chromate film on a substrate by AES analysis, it was found that the peeling occurs in the layer of chromate film.
In order to control the SiC content in Ni/SiC composite plating, cationic surface-active agents with different alkyl chain length, which were of the hydrophobic group, were added to a Ni/SiC composite plating bath to change the surface charge of the SiC particles from negative to positive. The influence of the cationic surfactant on the Ni plating was also studied. The crystallite size of Ni deposits decreased with the addition of the cationic surface-active agents, and an excess addition of cationic surface-active agents in the bath caused cracks in the Ni deposits. In the Ni/SiC plating, we can easily control the SiC amount in the Ni/SiC plating between about 10 and 30 vol%, changing the alkyl chain lengths of the added cationic surfactants and their concentration to change the surface potential of SiC particles.
In microstructures such as whiskers, their surface free energy is supposed to determine the criterion on whether the whisker growth can take place ; then a critical dimension for the whisker growth should exist, depending on the degree of the excessive energy that drives the whisker growth. In this respect, the excessive energy included in matt Sn deposits plated on Cu substrates has been estimated to be approximately 1×10−22 J atom−1 in terms of chemical potential. Furthermore the contribution of grain-boundary free energy and strain energy to the excessive energy has been estimated. It has been shown that the grain-boundary free energy seems not to contribute to the excessive energy. On the other hand, it has been found that the strain energy sufficient for the whisker growth requires far more stress (ca. +400 or −400 MPa) than we usually observe (ca. −10 MPa). From these, it has been suggested that such a high stress can be attributed to the extremely large distortion of crystal lattice in an atomic level instead of macro-strains. The source of the distortion is supposed to be produced by the excessive Sn atoms generated by imbalanced diffusion between Sn and Cu.
The hydrophobicity of graphite particles for composite plating was evaluated using the potentiometric titration method. Both octyl amine solution and KOH solution were used as titrants. On the basis of a detailed analysis of the titration curves for various concentrations of the surfactant, it was clarified that the amount of the surfactant required to make the particle hydrophilic could be estimated.