The artificial hip joints have galvanic couple between femoral head made of CoCr alloy and stem made of Ti or Ti alloy, and are subjected to high levels of mechanical stress. Therefore, tribocorrosion of artificial hip joints has been frequently reported. In this study, we performed the first electrochemical numerical simulation for CoCr alloy and Ti with friction in simulated body fluid. We constructed single metal model and galvanic coupling metals model to investigate the effect of the cathodic reaction on the tribocorrosion behavior. In single metal model, CoCr alloy with friction is referred to as CoCr(Tribo.). In galvanic coupling metals model, CoCr alloy with friction in contact with Ti is referred to as CoCr(Tribo.)-Ti. In single metal model, the current density of CoCr(Tribo.) was larger than that of Ti(Tribo.). For the CoCr alloy with friction, the current density of galvanic coupling metals model(CoCr(Tribo.)-Ti) was larger than that of single metal model(CoCr(Tribo.)). The current density of both single metal model and galvanic coupling metals model increased as the increase in area of the non-friction part increased. The current density of CoCr(Tribo.)-Ti was largest, and the rate of increase in current density with the increase in area was also largest.

To diagnose the corrosiveness of an environment in which electronic equipment is installed, a new electrical-resistance type corrosion sensor with a gas-intake channel was developed. The developed sensor measures the electrical resistance of a thin metal film corroded in the gas-intake channel. In addition to utilizing the difference in electrical resistances of corroded and non-corroded metal films, the sensor takes into account the diffusion phenomenon of corrosive gas and the corrosion reaction of metals in order to convert electrical resistance to the amount of metal corrosion. If the amount of metal corrosion is obtained, the corrosiveness of the installation environment can be diagnosed on the basis of indicators defined in ISO standards and ANSI/ISA standards. Silver is sensitively reacted with reduced sulfur, which is a major factor in the risk of sulfide corrosion in electronic equipment. In this report, a corrosion sensor composed of a silver thin film was fabricated, and the performance of the sensor was evaluated by installing it in a mixed-gas environment simulating an actual machine room housing electronic equipment. According to the results of the evaluation, the amount of corrosion obtained with the new corrosion sensor agreed reasonably well with that obtained by a conventional corrosion sensor with an error of 20%. The lifespan of the corrosion sensor is twenty-times longer than that of conventional sensors, making it suitable for long-term monitoring. Moreover, it is small and inexpensive, so it can be applied at various sites where electrical equipment is installed.

We have developed inverse analysis method that simultaneously estimates the three-dimensional position of measuring instrument and output current from sacrificial anode. Inverse analysis is a method of estimating an unknown output current from sacrificial anode from potential data measured near the sacrificial anode. In development method, relationship between potential data and state quantities (three-dimensional position and output current from sacrificial anode) to be estimated is defined as state space model. This study can be thought of as generalized state estimation problem that estimates state quantities from measured values and state space model. And, this generalized state estimation problem is solved by Particle Filter. Development method is expected to be able to evaluate output current from sacrificial anode by simple measurement without depending on the movement behavior of measurement instrument. And twin numerical experiment was used to verify the effectiveness of development method. As a result of twin numerical experiment, it was found that both three-dimensional position and output current from sacrificial anode could be estimated with sufficient accuracy. Then, as results of 100 trials of this twin numerical experiment, they were shown that the distribution of estimated values of output current from sacrificial anode was sufficiently small. The above results show effectiveness of development method.

Instantaneously noble potential caused by DC stray current has been observed in rare cases under cathodic protection of pipelines in service. Moreover, anodic current was simultaneously observed. In this study, the influence of instantaneously noble potential on corrosion protection of buried steel pipes under cathodic protection was studied in three kinds of soil by using IR-free probe. Furthermore, the relationship between corrosion weight loss of the steel and total electric quantity of anodic current caused by the noble potential was investigated. Results of this study indicate that the corrosion caused by noble potential below -0.75 V (vs. Cu/CuSO₄ (sat.)) is negligibly small. Moreover, the results also indicate that the percentage of corrosion current to the anodic current is no more than 1%; most of the anodic current is estimated to be contributed by repeated oxidation reaction of iron rust on the steel surface.

We have examined the corrosion behavior of a rusted carbon steel coated with a paint containing metallic salt under wet and dry cyclic condition. The rust layer of the carbon steel was already grown in a coastal region of Japan before the coating. It was found that the addition of metallic salt to the coating film decreased the corrosion rate of the coated steel. The X-ray diffraction analysis of the rust layer revealed that the addition of metallic salt resulted in drastic increase of α-FeOOH during the cyclic corrosion test. The rust layer under the coating film containing metallic salt suppressed penetration of Cl^- to the steel surface. Electrochemical analyses indicated that the coating with metallic salt decreased cathodic reduction rate of the rust layer due to the formation of α-FeOOH in the rust layer.

Copper tubes are used in heat exchangers of refrigerators and air conditioning units. However, in some cases, the mechanically processed locations of copper tubes experience pitting corrosion. Therefore, a test scheme to rapidly evaluate the corrosion resistance of copper tubes at such sections and the effectiveness of the “initial treatment” on the corrosion have been investigated. “Initial treatment” is one of the chemical treatments that improves the corrosion resistance of copper tubes. The corrosion of the copper tube was investigated by observing the surface after immersing the copper tube in various solutions containing hydrogen peroxide, chloride, sulfate, benzotriazole and bicarbonate for one day. The test solution that contained a combination of hydrogen peroxide H₂O₂ 10 mg/L, chloride ion Cl^- 300 mg/L, sulfate ion SO₄^2- 300 mg/L and benzotriazole 10 mg/L could replicate the actual aspects of corrosion on the copper tubes for a day. In this solution the corrosion of copper tubes was concentrated at the mechanically processed sections. The results indicated the high tendency of corrosion at the mechanically processed sections. The improvement of corrosion resistance at such sections by initial treatment was also confirmed in the test solution. Additionally, it was found that the corrosion resistance of copper tubes at mechanically processed section was weaker as the residual carbon content increased.

This research aimed to investigate transients of corrosion morphology and weight loss of Cu in concentrated LiBr aqueous solution for understanding corrosion process of copper parts in an absorption heat pump. Cu plate specimens were immersed in an aqueous solution containing 65 mass% LiBr and 0.2 mass% LiOH at 353 K for various times, and then subjected to weight measurement tests and surface analysises. The specimen immersed in the solution suffered pit-like corrosion. The number of the pit increased linearly with an increase in an immersion time until 691.2 ks, and thereafter almost no pit was initiated. Each pit was semi-spheroid, and grew at a constant rate in each direction of horizontal and vertical. A corrosion weight loss showed an accelerated increase as an immersion time elapsed. The transients of the weight loss until 1728 ks was successfully simulated by assuming the corrosion process of the initiation and the growth of the pits. The simulation also revealed that a corrosion area was in good agreement with the whole specimen surface in around 1728 ks, and then that aspect of the corrosion shifted from pit-like corrosion to general corrosion. The empirical corrosion rate after 1728 ks obtained by the weight measurement test was also in good agreement with the vertical growth rate of the pit.

To establish the creep life prediction method for Ni-based alloys, the microstructure, hardness and dislocation density measurement was done for various creep damaged samples of γ’-Ni₃Al precipitation strengthened alloy, TOS1X-2. The hardness and dislocation density of creep interrupted and ruptured samples at 700℃ and 750℃ increased with creep strain and creep time. TEM analysis showed that large amount of dislocations induced by creep was present in γ matrix, and γ’ precipitates were almost free from dislocation. The hardness increase at gauge portion of specimens showed linear increase with square root of dislocation density, suggesting that hardening by creep damage obeys the Bailey-Hirsch’s strain hardening relationship. Based on this strain hardening relationship and combining the creep constitutive equation, the creep residual life of interrupted specimens was estimated with high accuracy from measured hardness.

Er,O-codoped GaAs is a promising candidate for application to light sources in fiber-optic communication, due to sharp luminescence from Er³⁺ ions at 1.54 µm and temperature insensitivity of their luminescence wavelength. In this report, we demonstrate coupling of luminescence from Er³⁺ ions in Er,O-codoped GaAs to the resonant mode of multi-step double heterostructure two-dimensional photonic crystal (PhC) nanocavities. The structure of the fabricated sample has an ultra-high designed cavity Q-factor of 1.7 × 10⁶. In micro-photoluminescence (µ-PL) measurements, ~25 and 1.7-fold enhancements of peak and integrated intensities from Er³⁺ ions are observed as the result from the coupling between Er luminescence and the cavity modes of the PhC nanocavities. Furthermore, incident pump power dependence of Er luminescence in the PhC nanocavity exhibits nonlinear behavior, whose possible models for the mechanism of the coupling are discussed. The obtained results would pave the way for understanding the interaction between cavity modes in PhC nanocavities and luminescence from rare-earth elements towards application in wavelength standards in fiber-optic communications or single photon emitters in quantum information technologies.

Herein, we perform an unsaturated seepage test on four soil types with different fine fraction contents and investigate various methods for expressing the wetting scanning curve of soil. The results confirmed that 1) the natural maximum saturation S_max for the target soil is approximately 60%–90%, and the lower the saturation before water absorption S_r0, the lower the natural maximum saturation S_max; 2) when expressing the unsaturated seepage characteristics of the soil (main drying curve and wetting scanning curve) using van Genuchten model, there exists a relation (α_sw≒2α_md ) between the wetting scanning curve constant α_sw and main drying curve constant α_md; furthermore, the relation (n_sw≒n_md) exists between the wetting scanning curve constant n_sw and main drying curve constant n_md; and 3) the natural maximum saturation S_max can be expressed with almost perfect precision using Land method; moreover, this can easily be estimated from the saturation before water absorption S_r0.