Anisotropic corrosion of iron in pH 1 sulphuric acid

Anisotropic corrosion behaviour of a single grain of pure iron in 0.05 mol dm⁻³ sulphuric acid (pH 1) was investigated by a simple polarization technique. Both corrosion potential and corrosion current were found to be dependent on crystallographic orientation of the iron grain. A high corrosion current flowed on a grain showing a relatively noble corrosion potential, although both cathodic and anodic Tafel slopes were independent of the orientation. It was shown that cathodic hydrogen evolution reaction (HER) governed the corrosion reaction on the iron grain. Covalent bonding of Fe and H and coverage of H on Fe seem to play important roles in the HER and anisotropic corrosion behaviour of pure iron.     

Depassivation-repassivation behavior of a pure iron surface investigated by micro-indentation

Depassivation-repassivation behavior on a pure iron surface in borate buffer solution was examined under potentiostatic control by a micro-indentation test. Current peaks emerge during both downward and upward drives of the indenter due to depassivation which is caused by plastic deformation of the substrate but not elastic deformation and repassivation. The total electric charge of the current peaks is proportional to the maximum load. The total electric charge also increases with increase in intermission time of the indentation, indicating that the passive film is ruptured even during stress relaxation. It is estimated from the electric charge balance that 82% and 18% of the film rupture occurs during the downward drive and intermission, respectively, and that no rupture occurs during the upward drive. Furthermore, the film-ruptured area is estimated to be 80% of the plastic deformed surface area. The partial retainment of the passive film on iron suggests that the ductility of the passive film is higher than that of the substrate.     

EPR study of the electronic states of β′-(BEDT-TTF)(TCNQ)

β′-(BEDT-TTF)(TCNQ) is a compound of BEDT-TTF (=ET) and TCNQ molecules aligned orthogonally with each other, forming two-dimensional sheets and one-dimensional columns of 1/4-filled π band, respectively. It is known that the metal-insulator transition occurs at 330 K at ambient pressure. We have measured the electronic spin susceptibility by means of the EPR-NMR method at 50 MHz, and the angular dependence of g-factor and line width of EPR both at Q (34 GHz) and W (94 GHz) band. We successfully confirmed that the antiferromagnetic transition occurs in ET sheets and TCNQ columns, independently.     

Effects of Al and Zn additions on mechanical properties and precipitation behaviors of Mg-Sn alloy system

For the Mg-Sn-Al alloys, the ultimate strength (UTS) of an extruded Mg-9wt.%Al-2wt.%Sn alloy reached 390 MPa. TEM observation indicated that plate-like Mg₁₇Al₁₂ precipitates having Burgers orientation relationship with the matrix are responsible for the strength. This alloy also exhibits an age hardening behavior: the peak hardness appears after 15-20 h of heat treatment at 473 K. On the other hand, the UTS of the Mg-Mg-Sn-Zn alloys are on the order of 300 MPa. The precipitates in these alloys are composed of the Mg₂Sn and MgZn₂ particles. It was found that these phases often precipitate together, suggesting that the MgZn₂ phase can act as a nucleation sites for Mg₂Sn.     

Syntheses of full-density nanocrystalline titanium nitride compacts by plasma-activated sintering of mechanically reacted powder

Nearly equiatomic nanocrystalline titanium nitride (Ti₅₆N₄₄) powder with an average grain size of 5 nm has been synthesized by ball milling elemental Ti powder under nitrogen gas flow at room temperature. During the first stage of reactive ball milling (RBM) (time <3.6 ks), the metallic Ti powder tends to agglomerate to form powder particles with a larger diameter. At the second stage (3.6 to 22.0 ks), the agglomerated particles of Ti fragment to form smaller particles. These smaller particles that have new or fresh surfaces begin to react with the milling atmosphere (nitrogen) during the third stage of milling (22 to 86 ks) to form TiN powder coexisting with unreacted Ti powder. Toward the end of milling (86 to 173 ks), a single phase of nanocrystalline TiN (NaCl structure) is obtained. The powder of this end-product has a spherical-like morphology with an average particle size of about 0.4 μm diameter. A sintering procedure using plasma activation has been employed to consolidate the powder particles at several stages of the RBM. The as-milled and as-consolidated powders have been characterized as a function of the RBM time by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), optical metallography, and chemical analyses. Density measurements of the consolidated samples show that after 86 to 173 ks of the RBM time, the compacted samples are essentially fully dense (above 96 pct of the theoretical density for TiN). The results also show that the consolidated TiN compacts still maintain their unique nanocrystalline properties with an average grain size of about 65 nm. The hardness and some mechanical properties of the consolidated TiN compacts have been determined as a function of the RBM time.     

Free D-serine, D-aspartate and D-alanine in central nervous system and serum in mutant mice lacking D-amino acid oxidase

We have examined whether D-amino acid oxidase (DAO) regulates free D-serine content using mutant ddY/DAO- mice lacking DAO activity. We find that the content of D-serine in the serum and cerebellum of mutant mice is much higher than that of normal mice, whereas a slight but significant difference in the cerebral D-serine level is observed between the two strains. These results suggest that, although DAO may participate in the catabolism of D-serine in the cerebellum and periphery, there appears to be other mechanisms for catabolism of endogenous D-serine in the brain.     

Mechanism of production of midsystolic click in a prolapsed mitral valve

In order to examine the production mechanism of the midsystolic click in cases of a midsystolic click and a late systolic murmur, the relationship between the click and the motion of the mitral apparatus was studied by means of ultrasono-cardiotomography and the simultaneous recording of phonocardiograms and ultrasono-cardiograms (UCGs). It was found that the systolic click occurred in exact coincidence with the time at which the hump of the echo of the unusual early systolic anterior motion (early SAM) took its backmost position. This coincidence was found when the click was shifted either by postural changes or inhalation of amyl nitrite. The present ultrasono-cardiotomographic study demonstrated that the echo source of the early SAM could be attributed to the protrusion into the left ventricular outflow tract of the slackened elongated chordae tendineae in systole. The anterior leaflet moved suddenly to the position of maximal prolapse when the slackened chordae tendineae were stretched taut in midsystole. In other words, the midsystolic click occurred when the anterior leaflet prolapsed and the tension exerted on the chordae tendineae was at its maximum.