Katsuhisa Sugimoto

The role of molybdenum additions to austenitic stainless steels in the inhibition of pitting in acid chloride solutions

In order to clarify the mechanism for increased resistance to pitting in acid chloride solutions by addition of Me to CrNi stainless steels, the anodic polarization curves, a.c. electrode impedances, ellipsometric parameters and X-ray photo-electron spectra have been measured on the Mo-containing steels passivated in 1N HCl. The results showed that the presence of an adequate amount of Cr is indispensable for the improvement of pitting resistance by the Mo addition. The passive films of the Mo-containing steels were found to be composed of a complex oxyhydroxide containing Cr3+ Fe2+, Ni2+, Mo6+ and Cl− and showed a rather higher d.c. resistance in HCl solution than in H2SO4 solution. The thickness of the passive film increases with increase in Mo content.

The Role of Alloyed Molybdenum in Austenitic Stainless Steels in the Inhibition of Pitting in Neutral Halide Solutions

Abstract In the passive region of austenitic stainless steels alloyed with Mo, the formation of MoO42− ions can be expected in neutral halide solutions by the transpassive dissolution of Mo. It has...

Passive and transpassive films on FeCr alloys in acid and neutral solutions

Abstract Passive and transpassive films on FeCr alloys containing 5 – 6% chromium in 1 mol l −1 Na 2 SO 4 solutions of pH 2 and pH 6 have been investigated by in situ ellipsometry coupled with electrochemical measurements. The optical constants of film-free surfaces of the alloys, which were determined by ellipsometry in dehydrated methanol immediately after stripping the surface films in a bromine-methanol solution, were used in the calculation of the thickness and optical constants of these films. It was found that the thickness and the real parts of the optical constants of the films decreased with increasing chromium content of the alloy and decreasing pH of the solution. In the case of the passive films this was most pronounced for chromium contents in the range 5–20% which indicates the occurrence of substantial variations in the nature and composition of the films. The transpassive film thickness, the rate of film growth with the potential and the real part of the optical constant were usually found to be larger than those of the passive films.

Ellipsometric Examination of Growth and Dissolution Rates of Ta2 O 5 Films Formed by Metalorganic Chemical Vapor Deposition

The formation process of Ta 2 O 5 films in MOCVD using pentamethoxy tantalum (PMT) as a metal organic source and O 2 as reactant gas has been analyzed by in situ ellipsometry at deposition temperatures of 473-773 K. According to the change in the growth rate of the films, the formation process can be divided into three stages, the initial, the transition, and the final stages. The growth rate and the optical constant of the films were found to depend on the deposition temperature and the deposition time. All the films obtained at temperatures of 473-773 K had amorphous structures

Development of a Wide Range pH Sensor based on Electrolyte-Insulator-Semiconductor Structure with Corrosion-Resistant Al2 O 3 ­ Ta2 O 5 and Al2 O 3 ­ ZrO2 Double-Oxide Thin Films

In order to develop a pH sensor having a wide pH response range from strong acid to strong alkali, electrolyte-insulator-semiconductor capacitors using corrosion-resistant Al 2 O 3 -Ta 2 O 5 and Al 2 O 3 -ZrO 2 double-oxide films as the insulator were fabricated and their response characteristics to H + and alkali metal ions were examined. The sensors with Al 2 O 3 -Ta 2 O 5 and Al 2 O 3 -ZrO 2 films having an Al 3+ cationic fraction of about 0.4 showed a wide linear pH response range of -1.5 to 13.0 and a small alkali metal ion sensitivity. The use of the Al 2 O 3 -Ta 2 O 5 film is suitable for increasing pH sensitivity and that of the Al 2 O 3 -ZrO 2 film is promising for increasing corrosion resistance against strong alkali solutions.

Stress-corrosion cracking of aged AlCuMg alloys in NaCl solution

Abstract Stress-corrosion lives and pitting potentials of Al4%Cu alloys with various aging structures have been measured in de-aerated 1M NaCl under conditions of controlled potential. It was found that the alloys aged having the higher susceptibility to stress-corrosion cracking showed two pitting potentials corresponding to pitting at grain boundaries and grain bodies, respectively. The susceptibility to stress corrosion cracking of the alloys appeared above the pitting potentials for grain boundaries. The maximum susceptibility to stress-corrosion cracking was obtained when the alloy was aged to attain the largest difference in pitting potentials between grain boundaries and grain bodies.

Effects of Cu, Mo and C on the corrosion of deformed 18Cr8Ni stainless steels in H2SO4/NaCl solutions

Abstract The effects of Mo, Cu and C on the rate and type of corrosion of 18Cr8Ni stainless steels after deformation into U-shaped specimens have been investigated in 5N H 2 SO 4 solutions containing up to 0·4M NaCl at 40°C. General corrosion, intergranular corrosion, and/or transgranular stress-corrosion cracking were found to occur, the type of attack depending on the contents of Mo, Cu and C in the steel, the concentration of NaCl in the solution, and the degree of deformation. In particular, it was observed that carbon has an effect on intergranular corrosion in these solutions, which is quite different from that observed in Strauss and Huey tests.

Ellipsometric analysis of growth process and corrosion resistance of Nb[sub 2]O[sub 5] films formed by MOCVD

The formation process of Nb[sub 2]O[sub 5] films by metallorganic chemical vapor deposition using pentaethoxy niobium (PEN: Nb(OC[sub 2]H[sub 5])[sub 5]) as a vapor source and O[sub 2] as reactant gas has been analyzed by in situ ellipsometry at substrate temperatures of 200 to 500 C, and at O[sub 2] flow rates of 0 to 2,000 cm[sup 3]/min. According to the changes in the refractive index and the growth rate of the films, the formation process can be divided into three stages, that is, the nucleation and coalescence, the homogeneous growth, and the surface roughness evolution stages. The refractive index and the growth rate of the films were found to depend on the substrate temperature and the O[sub 2] flow rate. The films deposited at 200 to 400 C had amorphous structures, and those deposited at 450 to 500 C contained a [delta]-Nb[sub 2]O[sub 5] phase in an amorphous matrix. The corrosion resistance of the films in a buffered HF solution depended on both the deposition temperature and the O[sub 2] flow rate. The film deposited at 450 C in the absence of O[sub 2] showed the highest corrosion resistance against the solution.

Ellipsometric Examination of Structure and Growth Rate of Metallorganic Chemical Vapor Deposited Ta2 O 5 Films on Si(100)

Ta 2 O 5 films, formed on Si(100) by metallorganic chemical vapor deposition using pentamethoxy tantalum as a metallorganic source and O 2 as reactant gas at deposition temperatures of 473-773 K, were analyzed by ellipsometry, x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The ellipsometric data may be explained by a double-layer optical model which presumes a thin interface layer between the Ta 2 O 5 film and the Si substrate. Ta 2 O 5 , SiO 2 , Si, and a lower oxide TaO x were detected at the interface region between the Ta 2 O 5 film and the Si substrate by XPS. Cross-sectional TEM of the interface layer formed at 773 K showed that it was 6.1 nm in thickness and was amorphous

R&D of a MW-class solid-target for a spallation neutron source

Abstract R&D for a MW-class solid target composed of tungsten was undertaken to produce a pulsed intense neutron source for a future neutron scattering-facility. In order to solve the corrosion of tungsten, tungsten target blocks were clad with tantalum by means of HIP’ing, brazing and electrolytic coating in a molten salt bath. The applicability of the HIP’ing method was tested through fabricating target blocks for KENS (spallation neutron source at KEK). A further investigation to certify the optimum HIP conditions was made with the small punch test method. The results showed that the optimum temperature was 1500 °C at which the W/Ta interface gave the strongest fracture strength. In the case of the block with a hole for thermocouple, it was found that the fabrication preciseness of a straight hole and a tantalum sheath influenced the results. The development of a tungsten stainless-steel alloy was tried to produce a bare tungsten target, using techniques in powder metallurgy. Corrosion tests for various tungsten alloys were made while varying the water temperature and velocity. The mass loss of tungsten in very slow water at 180 °C was as low as 0.022 mg/y, but increased remarkably with water velocity. Simulation experiments for radiation damage to supplement the STIP-III experiments were made to investigate material hardening by hydrogen and helium, and microstructures irradiated by electrons. Both experiments showed consistent results on the order of the dislocation numbers and irradiation hardness among the different tungsten materials. Thermal-hydraulic designs were made for two types of solid target system of tungsten: slab and rod geometry as a function of the proton beam power. The neutronic performance of a solid target system was compared with that of mercury target based on Monte Carlo calculations by using the MCNP code.