Thin water film is formed on metal surfaces that are exposed to the atmosphere. The conditions of this film change according to environmental factors, such as temperature, wind, and rainfall. Hence, it is difficult to investigate atmospheric corrosion on metal surfaces.

This paper aimed to develop a measurement system for the pH distribution on a metal surface in simulated atmospheric environment. The surface pH distribution was measured with agar film including pH indicators and MgCl₂. The pH indicators used were a universal indicator and an MR-BTB indicator. Agar film of 0.5 mm thickness was placed on an iron specimen. The specimen was set in a chamber with a relative humidity of 100% to prevent the agar film from drying out. The surface pH distribution was determined from the color of the agar film with an RGB color model. The surface pH distribution on the iron showed that anodic reactions produced acidic regions and cathodic reactions produced basic regions. The observed phenomena were the same as that found under a water droplet which contained the pH indicator and MgCl₂. Therefore, we conclude that the agar film could simulate thin water film in an atmospheric environment and allow measurement of the surface pH distribution on iron under atmospheric corrosion.

Global concerns over the environmental impact and health effects of the lead-based solders have led to the development of lead-free solder alloys. Further improvements in the reliability of lead-free solder alloys at high temperatures are required for downsizing of electronic components in vehicles. In this work, tensile and creep tests and microstructure analysis were carried out to determine the effect of Bi or Sb addition on high-temperature deformation behavior in Sn-Cu-Ni solder alloys. The addition of Bi or Sb increased the strength of the Sn-Cu-Ni solder alloys. The stress exponent was estimated to be ≥3, indicating that the high-temperature deformation was controlled by dislocation creep. Furthermore, in both the alloys, the stress exponent observed in the low stress region was nearly equal to 3 and discontinuously increased to ≥7 in the high stress region. For Sb addition, the solute atmosphere drag mechanism was observed in the low stress region.

Polycrystalline tungsten surfaces were irradiated at room temperature with two kinds of nitrogen ions—N⁺ and N₂⁺—at 2.5 keV by using an ion beam apparatus. Results of X-ray photoelectron spectroscopy (XPS) experiments performed using synchrotron radiation at SPring-8 showed that upon irradiation of the tungsten sample with either kind of ion, the full widths at half maximum (FWHM) of the W 4f_7/2 and W 4f_5/2 peaks broadened and the peaks at 35.8 eV and 37.8 eV—which correspond to WO₃ binding energies—increased slightly; this indicated the formation of tungsten nitride at the subsurface below the interface. The N 1s spectra of tungsten after nitrogen ion beam irradiation were decomposed into four component peaks. The positions of these component peaks were observed to be the same as those of the standard tungsten oxynitride W_0.62(N_0.62O_0.38), which exhibited W₂N peaks in X-ray diffraction analysis. The main decomposed peaks at 397.3 eV and 398.1 eV were attributed to W-N bonds and W-N-O bonds, respectively. The variation of the intensity ratio of the N 1s peak at 397.3 eV to the W 4f doublet peaks (corresponding to W-N bonds) as a function of the escape depth, which was measured by angle-resolved XPS, apparently followed a normal distribution for the irradiated samples. This indicates that the W-N bond density of the tungsten surface irradiated with N₂⁺ ions is higher than that of the surface irradiated with N⁺ ions and also that the N₂⁺ ions penetrate slightly deeper than the N⁺ ions.

Mater. Trans. 57（2016） 1609-1614に掲載

For clarification of vibrating electromagnetic force effect on concentration boundary layer thickness formed near solid-liquid interface, a metal copper working as an anodic electrode was dissolved into an electrolyte aqueous solution under the imposition of a vibrating electromagnetic force. For its excitation, a current composed of DC and AC components and a static magnetic field were simultaneously imposed on an electrolyte aqueous solution. Because the copper divalent ions concentration is related with brightness of the solution by Lambert-Beer law, brightness of the recorded data using a video camera was directly used for evaluation of the concentration boundary layer thickness formed near the anodic electrode. The concentration boundary layer thicknesses formed under the imposition of the DC current and the static magnetic field, under the imposition of the DC & AC superimposing current without a static magnetic field, and under the imposition of the DC current without a static magnetic field were almost the same, while that formed under the imposition of the DC & AC superimposing current and the static magnetic field was thinner in comparison with the other three conditions. Hydrodynamic instability induced by the vibrating electromagnetic force through a large velocity gradient when the DC & AC superimposing current and the static magnetic field were imposed on the solution might be the reason of the thinner concentration boundary layer. This might be a new tool for controlling mass transfer rate in a concentration boundary layer.

Spherical samples of Tm_1-xSc_xFeO₃ were solidified from the undercooled melt under the containerless state using an aerodynamic levitation (ADL) furnace. The change of solidification behavior from double recalescence to single recalescence and powder X-ray diffraction (XRD) analysis of as-solidified samples revealed that metastable hexagonal LnFeO₃ (h-LnFeO₃) stabilizes with increasing of mole fraction of Sc. The reason for this stabilization was ascribed to the decrease of the difference in the liquidus temperatures of stable orthorhombic LnFeO₃ (o-LnFeO₃) and metastable h-LnFeO₃ phases. Annealing the as-solidified samples at 1473 K for 1 hour resulted in the two-phase coexistent states of o-LnFeO₃ and garnet (c-A₃B₅O₁₂) at 0<x<0.3, c-A₃B₅O₁₂ and h-LnFeO₃ at 0.3<x<0.5_, and h-LnFeO₃ and c-ScFeO₃ at 0.5<x<1.0. Based on these results, we proposed the quasi binary phase diagram between TmFeO₃ and ScFeO₃.