Corrosion products including passive film work as physical barrier and thus can protect the substrate metals against corrosion attack. The detail measurement may be important in corrosion protection. In this review, in-situ optical technique for the measurement of passive oxide is presented. 3-parameter ellipsometry in which the ordinary ellipsometry is combined with reflectometry can characterize the passive oxide quantitatively on the thickness and optical property. By using Raman scattering spectroscopy with combination of improved collection system of scattering light, composition of the thin passive oxide film may be determined under in-situ condition. Potential modulation reflectance（PMR）exhibits almost same response to frequency and potential as the complex capacitance. The PMR applied to the iron passive oxide film can describe the light-absorption edge from wavelength dependence of the PMR. For iron passive oxide film, the absorption edge was estimated to be about 2.5 eV. From spectrum of luminescence induced by uv light irradiation, the band-gap energy can be estimated; for example, the ban-gap energy of the anodic oxide film on titanium was determined at about 3.1 eV.
We investigated corrosion behavior of titanium heat exchangers (THEs) in strongly acidic (pH=1.6) hot-spring water. Some THEs showed high corrosion rate, the others showed no-corrosion, despite contacting the same hot-spring water. The THEs showed high corrosion rate have been used in heavy heat cycle. Therefore, a heavy heat cycle could accelerate corrosion of titanium in actual environment. On the other hand, at least two types of titanium have been distributed in Japan. One has titanium carbide in its surface and the other hasn't it. We should care about the manufacturing history of received titanium plates when we assemble titanium heat exchanger, since the existence of the titanium carbide in the surface of titanium could affect corrosion behavior of titanium.
The propagation of elastic waves in wire cables was evaluated. An elastic wave was excited and detected using the pitch-catch method and a pair of piezoelectric transducers. The group velocity dispersion was calculated using the wavelet transform of the time domain signal. The calculated wavelet contour map did not correspond to the theoretical group velocity dispersion curves for a wire and a rod with the same wire cable diameter when no tensile force was applied. The amplitude of the waveform in each wire was different, and the differences were thought to be caused by a nonuniform contact force. The time domain signals from different tensile forces were then compared. The maximum amplitude of the time domain signal increased with increasing tensile force; however, the rate of increase was different for each wave packet. The calculated wavelet coefficient corresponded to the theoretical group velocity dispersion curve for the F(1,1) mode of a rod with the same wire cable diameter when a tensile force was applied.
The authors invested efforts to develop a procedure of estimating the airborne salt level on the basis of available meteorological information. In this study, we analyzed wind direction and speed data provided by the Meteorological Observatory in Sanin to estimate the airborne salt level and compare with the monitoring data for the airborne salt level over 2 years in order to evaluate the estimation precision of the proposed method. The estimation results showed reasonable agreement with the measured airborne salt level. It is confirmed that the proposed concise evaluation procedure based on only wind direction and speed information is useful as estimation method of airborne salt level.
Corrosion of A1050-, 3003- and 4043-Al alloys has been investigated by dry-wet repeating tests with droplets of NaCl solution and pure water at 323 K, and compared with that obtained by immersion tests. Scanning electron microscopy and energy dispersive X-ray spectrometry showed that 50 - 100 μm-size pits are formed at edge areas of NaCl− droplet, while a local dissolution of Al occurs around Fe–Al–intermetallic compound phase and Si-phase at central regions of the droplets, being similar to the behavior during immersion tests in a NaCl solution. In the case of pure-water dry-wet repeating atmospheres, needle like crystalline hydroxide films are formed at edge areas of pure water-droplets, while thin amorphous hydroxide films are formed at the central regions.
Effects of stabilizing treatment of protective rust layer and alloy design on corrosion behavior of weathering steels were investigated by long-term exposure tests under the high airborne salt condition of 0.29 mdd. The stabilizing treatment was effective to suppress penetration of chloride ion by forming protective rust layer on the steel surface at the initial period of exposure. However, the effect wore off by long-term exposure, and protective rust layer was replaced to the normal rust layer corresponding to the alloy composition under the given environment. This results clearly show that it is important to select the appropriate weathering steel which forms protective rust layer under the environment of use, even if the stabilizing treatment of protective rust layer is applied on the steel surface.