An application of noble metal-TiO2 Schottky barrier diodes to dissolved hydrogen (DH) sensors was examined in aqueous solutions containing 2.9×10-2-24.5 mass ppb DH at 300K. It was found that Pd-TiO2 diodes showed quantitative relationship between their response voltages and DH concentrations in the range of 2.9×10-2 to 1.5 mass ppb and they could work as DH sensors. Their 90% response times to DH concentrations were less than 3ks. They also had sensitivities to H+ ions, but the sensitivities were less than 10% of their sensitivities to DH. Pd-TiO2 diodes suffered from serious hydrogen embrittlement in solutions having higher DH concentrations. To improve this fault, Pd-Au and Pd-Ag alloy-TiO2 diodes were examined. As a result, a Pd-33 at% Ag alloy-TiO2 diode was found to have a good resistance to hydrogen embrittlement. Its sensitivity to DH concentration, however, slightly deteriorated with alloying Ag.
The corrosion resistance of austenitic stainless steels was affected by Cr content and the impurity segregation at grain boundary in highly oxidizing nitric acid solution. In this study, effects of Cr (9-32%) and P (0.0002-0.034%) on the corrosion resistance of austenitic stainless steels were investigated in hot 8N nitric acid solution containing Cr6+ (0-1.0g/l). The main results are as follows: (1) The corrosion resistance in pure HNO3 was improved with the increase of Cr content. Cr oxide film was effective in pure HNO3. (2) The corrosion rate for (8-20) Cr-11Ni steels in 8N HNO3 containing Cr6+ more than 0.05g/l was increased with the increase of Cr content. This tendency on corrosion rate with Cr content was caused by the suppression of the cathodic reaction with the decrease of Cr content. (3) The corrosion rate of the austenitic stainless steels with more than 20% Ni was improved with Cr even in HNO3 containing Cr6+. (4) P less than 0.034% did not affect the corrosion resistance of the solution heat treated stainless steels. When stainless steels were sensitized at 650°C for short time, P less than 0.015% did not affect the intergranular corrosion depth. (5) The intergranular corrosion due to P segregation indicated the maximum value, when the stainless steel was sensitized at 650°C.
It has been known well that ion exchange membranes have good resistivity on electrolyte permeation. In this study, the effectiveness of additional ion exchange ability on coating films was examined by pitting potential measurement of coated aluminum specimen. Addition of polyphosphoric acid in acrylic/epoxy resin formed the cation exchange film with the effective fixed charge density value of 2.7×101mol/m3. And, it was appeared that the pitting potential of the specimen shifted to noble potential in an aqueous chloride solution at lower concentration than the effective fixed charge density value.
The effect of oxide film structure obtained by thermal treated in air on minimal corrosion release of Type 304 stainless steel in a high temperature pure water was investigated in order to clarify a cause for existing of an optimum temperature range to inhibit metal dissolution. The oxidation treatments up to ca. 600K were effective to increase the polarization resistance, and the oxide film primarily consisted of a uniform duplex oxide layer of α-Fe2O3 in outer and iron-chromium spinel type oxide in inner layer. A lot of nodular oxides, however, were formed by the oxidation treatments more than ca. 800K, the polarization resistance decreased with the increase and the growth of the nodules, and which consisted of only α-Fe2O3 from the surface to the oxide-metal interface.
The effect of grain boundary inclination on hydrogen embrittlement was investigated on Alloy 600 with coarse columnar crystals. As the deviation of the growing direction from ‹100› orientation was within 10°, the grain boundaries were treated approximately as simple tilt boundaries with ‹100› rotation axis. Brittle cracking occured at grain boundaries in tensile test after hydrogen charge. The mean crack depth (h) increased with the increases in charging time (t) and temperature. There was a relation, h∝t1/2, between h and t. The activation energy for the diffusion of hydrogen atoms obtained from the temperature dependence of h·t-1/2 was estimated to be 13.6kcal·mol-1. On the other hand, that for grain boundaries with relative tilt angle (ω) of less than 10° was estimated to be 16.9kcal·mol-1. The crack depth (h) varied considerably even at the same ω and no clear relation was found between h and ω. It suggests that h depends on other factors such as grain boundary inclination as well as ω. At the symmetrical tilt boundaries, h decreased at coincidence boundaries such as ∑5 and ∑13 against the normal relation of h with ω. It was found that the grain boundaries which have the planes close to (110) of both component crystals have lower susceptibility to cracking.
Review of the investigations on “Carbon-Coated Optical Fiber (CCF)” is given. Outstanding features of CCF is presented and its utility is discussed from a point of view of reliability of optical fiber cable in field condition. A brief history of developments of high-strength CCF is described.