Hideyuki Saitoh

Hydrogen Diffusion in Ti-Cr Hydrogen Absorption Alloys by Tritium Radioluminography

Tritium radioluminography has been applied to Ti50Cr50 and Ti40Cr60 alloys with two-phase structure of BCC phase and Laves phase by examining hydrogen distributions and by measuring a hydrogen penetration profiles. Hydrogen diffusion coefficients in these alloys have been successfully determined by analyzing the tritium depth profile to be 3.3×10-12 m2/s and 1.3× 10-12 m2/s, respectively. This value has been suggested that the hydrogen diffusion in the Laves phase is slower than that in the BCC phase.

Observation of Tritium Distribution in Pure Vanadium and V-5 mol%Fe Alloy by Tritium Radioluminography

ABSTRACT Tritium radioluminography was applied to pure vanadium and V-5 mol%Fe alloy to observe the tritium distribution and to evaluate the local tritium concentration in them. It was demonstrated that the tritium distribution at a microscopic area in the specimens was quantitatively and graphically displayed. In the pure vanadium specimen, the local tritium concentration was about three times different depending on the crystal orientation of the grains. The tritium radioactivity of the grains with (001) and (111) orientation are 1 Bq/mm2 and 0.4 Bq/mm2, respectively. These values correspond to the tritium concentration of 15 mol ppb and 6 mol ppb. The difference of the local tritium concentration was attributed to the variety of the morphology of precipitated hydride depending on the crystal orientation of the grains. For the radioactivity recorded in the imaging plate, the component of the X-rays generated from tritium in the specimen was only 2%, i.e., most of the intensity was attributed to the β-rays. In the V-Fe alloy specimen, it was shown that the tritium distribution correlates with iron segregation formed during solidification after the arc melting. The cross sectional observation showed that the local tritium concentration in equilibrium distribution depends on the local iron concentration in the specimen. The local tritium concentration gradually decreases from 115 mol ppb to 70 mol ppb as the iron concentration at the iron segregated region increases from 3 mol% to 4.5 mol%.

Observation of Hydrogen Distribution in a Eutectic Mg-Ni Alloy by the Silver Decoration Method

The silver decoration method was applied to the Mg-11.3mol%Ni eutectic alloy to investigate hydrogen distribution in it. The plate specimens of the alloy were electrochemically hydrogen charged using NaOH aqueous solution at ambient temperature. The specimens were silver decoration treated using K[Ag(CN)2] solved KOH aqueous solution to visualize the hydrogen location as the location of the silver grain. An effect of Pt coating on the decoration process was also examined. The Pt coating has drastically decreased the undesirable precipitation of the silver grain that caused by the direct galvanic reaction between the specimen and the decoration solution. The observed hydrogen location on the hydrogen input side has not been the Mg phase but the Mg2Ni phase in the eutectic structure. The hydrogen location on the hydrogen output side has been also the Mg2Ni phase. It has been thought that hydrogen is preferentially absorbed in the Mg2Ni phase and penetrates into the specimen through the Mg2Ni phase.