Papers by Author: Yoshihisa Matsumoto

Abstract: A series of accelerated degradation experiments at high temperatures have been performed for Pd-coated V-10 mol% Fe alloy membranes in order to investigate the degradation behavior of hydrogen permeability. The degradation of the membrane becomes severer with increasing testing temperature. The temperature dependence of the 20% degradation rate almost obeys the Arrhenius relationship, suggesting that the degradation phenomenon occurs by a kind of thermal activation process. It is found that the addition of a small amount of W into Pd overlayer improves the durability of the membrane significantly.

Abstract: The concept for alloy design of Nbbased hydrogen permeable membrane is applied to NbWMo ternary system. The alloying effects of tungsten and molybdenum on the solubility of hydrogen, the resistance to hydrogen embrittlement, the hydrogen permeability and diffusivity are investigated in a fundamental manner. It is found that the addition of tungsten and molybdenum into niobium decreases the hydrogen solubility. As a result, the resistance to hydrogen embrittlement improves and higher hydrogen pressures can be applied to the NbWMo alloy membrane. It is shown that the designed Nb5mol%W5mol%Mo alloy membrane with single solid solution phase exhibits excellent hydrogen permeability together with strong resistance to hydrogen embrittlement. In addition, it is found that the alloying of tungsten and molybdenum with niobium enhances the hydrogen diffusivity. In fact, the activation energy for hydrogen diffusion decreases in the order, pure Nb > Nb5mol%W > Nb5mol%W5mol%Mo.

Abstract: The hydrogen solubility and the hydrogen permeability have been measured for Nb-based alloys in order to investigate the alloying effects on the hydrogen diffusivity during hydrogen permeation. It is found that the hydrogen solubility decreases by the addition of ruthenium, tungsten or molybdenum into niobium. The mobility for hydrogen diffusion during hydrogen permeation is estimated from the linear relationship between the normalized hydrogen flux, , and the product of the hydrogen concentration and the difference of hydrogen chemical potential, . It is found that the mobility for hydrogen diffusion during hydrogen permeation is larger for Nb-based alloys than pure niobium, especially at low temperature. The activation energy of the mobility for hydrogen diffusion decreases by the addition of ruthenium, tungsten or molybdenum into niobium.

Abstract: A concept for alloy design of Nb-based hydrogen permeable alloys has been proposed based on the mechanical properties of niobium in hydrogen atmosphere and also on the hydrogen chemical potential in metal membrane. Following this concept, Nb-based alloys are designed and developed that possess excellent hydrogen permeability without showing any hydrogen embrittlement.

Abstract: The hydrogen solubility and the hydrogen permeability have been measured for Nb-based alloys in order to investigate the alloying effects on the hydrogen diffusivity during hydrogen permeation. The hydrogen diffusion coefficient during hydrogen permeation is estimated from a linear relationship between the normalized hydrogen flux, , and the difference of hydrogen concentration, C, between the inlet and the outlet sides of the membrane. It is found that the hydrogen diffusion coefficient during the hydrogen permeation is increased by alloying ruthenium or tungsten into niobium. On the other hand, the activation energy for hydrogen diffusion in pure niobium under the practical permeation condition is much higher than the reported values measured for dilute hydrogen solid solutions. It is interesting that the activation energy for hydrogen diffusion decreases by the addition of ruthenium or tungsten into niobium.

Abstract: The tensile property and hydrogen embrittlement (HE) behavior in the submicrocrystalline ultra-low carbon steel produced by HPT straining were investigated. Elongated grains with 300 nm thickness and 600 nm length with high dislocation density were formed by the HPT straining at a rotation-speed of 0.2 rpm under a compression pressure of 5 GPa. The engineering tensile strength of the HPT processed ultra-low carbon steel for > 5 turns was 1.9 GPa, which is similar to the value of maraging high-alloy steels. The elongation increased with strain (at 5 to 10 turns), is caused by the reduction of the stress concentration due to the existence of continuously recrystallized grains. HE occurred in the HPT processed specimen for 5 turns with high tensile strength of 1.9 GPa under hydrogen atmosphere. However, its HE was suppressed via recovery process by annealing at low temperature while maintaining the high strength.

Abstract: The hydrogen diffusion coefficients are investigated during the hydrogen permeation through Nb-based hydrogen permeable membranes at high temperature. It is found that the hydrogen diffusion coefficient for pure niobium under practical conditions is much lower than the reported values measured for dilute hydrogen solid solutions. Surprisingly, the hydrogen diffusion is found to be faster in Pd-Ag alloy with fcc crystal structure than in pure niobium with bcc crystal structure at 773K during the hydrogen permeation. It is also found that the addition of Ru or W into niobium increases the hydrogen diffusion coefficient under the practical conditions.