SiO2 films were formed on SUS 304 stainless steels by CVD using TEOS-O3 gas system. Changes in the deposition rate, composition, and refractive index of the films were investigated as a function of substrate temperature. Influences of substrate temperature and film thickness on corrosion resistance of the steels coated with SiO2 films were examined by measuring activation time and anodic polarization curve in 1kmol·m-3 HCl. The deposition rate increased with increasing substrate temperature up to 573K, whereas it decreased above 573K. The amount of Si-OH bonds in films decreased with increasing substrate temperature and the bonds hardly existed at temperatures above 573K. The refractive index of the films increased with increasing substrate temperature up to 573K, and then it stayed at a constant value of 1.45 up to 673K. The activation time increased and the critical passivation current decreased with increasing thickness of SiO2 films. The increase in the activation time and the decrease in the critical passivation current were more remarkable in the case of higher film forming temperature. Therefore, the corrosion resistance of SiO2-coated SUS 304 stainless steels increases with increasing thickness and formation temperature of the SiO2 films.
The dependence of passive current noise on passivation potential and Passivation time was investigated for SUS 304 in 0.05M H2SO4 and in ethanol solutions of different H2O concentration. The effect of Cl- addition was also examined for H2SO4. It was found that the power spectral density (PSD) resulted from FFT analysis of the current noise depended on the passivation potential and the passivation time in H2SO4 solution in the absence of Cl-, with respect to the PSD level and its changing mode. Moreover, the PSD level was confirmed to change markedly corresponding to a little change of H2O concentration in the ethanol solution even in the passivation under a constant potential. From the above facts along with the effect of Cl- addition on the PSD, the PSD level and its changing mode were interpreted in terms of the nature of two kinds of bound water incorporated in the passive film.
Fretting corrosion test of Ti-6Al-4V alloy was conducted in saline solution at 37°C in order to understand the degradation mechanism of biomedical Ti alloy in living body environment and the influence of dissimilar metal coupling with stainless steel and heat treatment of Ti alloy on the lowering of wear loss were also investigated. It was found that the corrosion potential of Ti alloy becomes electrochemically less noble than 316L stainless steel during fretting corrosion test. The weight loss by wear and the anodic current (metal ions release) of Ti alloy were remarkable comparing with those of stainless steel at controlled potential of 0mV (SCE). When Ti alloy was electrochemically coupled with stainless steel and tested at controlled potential of 0mV (SCE), none of wear reducing effect was observed during the continuous fretting corrosion test. However, it might indicate that the increase in surface hardness by heat treatment (for example 900°C WQ) of this α/β type Ti alloy was more effective to minimize the weight loss and metal ions release of biomedical Ti alloy.
The action of ultraviolet radiation on painted steel was examined using a xenon weather meter and a salt spray cabinet. The impedance, gloss, contact angle and adhesion of the paint film were decreased by ultraviolet radiation. The blistering area of the pait film, and the rusting area were increased. Paint film containing a pigment had roughened and porous surfaces. The roughened surface is easily wettable with the corrosive solution which then penetrates through the pores to the base metal, probably accelerating the corrosion of the steel. The alkyd resin clear paint film had slightly roughened surfaces and had no noticeable fine pores. A phosphate coating applied to the base metal under the paint film suppressed the corrosion accelerating effects of ultraviolet radiation of painted steels.
Secondary Ion Mass Spectrometry (SIMS) has been regarded as one of the most sensitive techniques for the three dimensional surface quantitative analysis. In this review article, general explanation is presented in concern with the principle of the measurements and data interpretations. Special emphases are laid on the quantification of the technique and the surface sensitivity when used as static SIMS. In addition, some examples are given for practical problem solving, especially for the evaluation of the various surface treatments of semiconductors, alloys and organic materials.
Applications of thermoanalytical techniques of DTA, TG and DSC were described to show inhibitory effects of the added foreign metal ions on α-FeOOH formation during aging of amorphous ferric hydroxide precipitates and α-Fe2O3 formation by heating of the hydroxides. The metals used were Cu, Co, Mg, Ni, Zn, Cr, and Al, which were added to the hydrous oxides by co-precipitation method. Gel-mixing and mortar-mixing of Cu(OH)2 and CuO were tried and showed that the former resulted in a similar inhibitory effect to the co-precipitation method and the latter was less inhibitory. Oxidation temperature for Fe3O4→γ-Fe2O3 and transition temperature for γ-Fe2O3→α-Fe2O3 were also observed to change with the foreign metals added to Fe3O4 precipitates.