The State of Hydrogen in Nb-based Nb-Mo Alloys Analyzed by the Channelling Method

Abstract

In order to locate hydrogen dissolved in metals a channelling method utilizing a nuclear reaction 1 H( 11 B, a)aa with a 11 B beam has been developed. This method has been applied to study the effect of metallic solutes on the state of hydrogen in metals. The lattice location of hydrogen in Nb-based Nb-Mo alloys with different concentrations (C Mo ) of undersized Mo atoms of 3, 10, 20 and 26 at% has hitherto been investigated. These results are summarized in this paper and the interaction of hydrogen with metal solutes is discussed. At low Mo concentrations less than 10 at% hydrogen is trapped by Mo atoms at room temperature due to attractive interaction to be located at sites displaced from tetrahedral (T) sites by about 0.6 Å toward the nearest neighbour Mo atom. In the case of C Mo ϭ3 at%, hydrogen is detrapped at 373 K and enter a T site. The number of H atoms trapped by one Mo atom is limited. It is 0.7-1.0 for C Mo ϭ3 at% and decreases with increasing C Mo . The excess H atoms are located at T sites. For C Mo ϭ20 at% such trapped site occupancy is not observed, and 70-80 % of the H atoms are located at T sites and the rest are at octahedral (O) sites at low H concentrations. For C Mo ϭ26 at%, most of the H atoms are located at T sites.KEY WORDS: hydrogen; lattice location; channelling analysis; solute atoms; Nb-Mo alloy.um, whose lattice location has been investigated extensively by both neutron and channelling methods, there has been only a few studies made in metallic alloys. 12) The present study for Nb-Mo alloys with the same crystal structure as Fe will give helpful information to investigations of the state of hydrogen in iron and its alloys. Experimental MethodThe reason why the nuclear reaction 1 H( 11 B, a)aa was applied is as follows. In the detection of impurities by ion beams, usually the Rutherford backscattering spectroscopy (RBS) is used, but this method is not useful to the detection of hydrogen. Therefore, the nuclear reaction was utilized. This reaction exhibits a narrow resonance with a resonance width of about 66 keV at about 1.8 MeV of a 11 B beam. 13,14) The energy of an incident 11 B beam (ϳ2 MeV) is reduced to about 1.8 MeV at the depth of a few thousand Å in a specimen, and there the resonance reaction takes place effectively to emit a particles. Hydrogen can be detected by measuring these a particles, whose energy ranges from zero to about 5 MeV. To locate hydrogen, this hydrogen detection technique was combined with the channelling method.Specimens are Nb and Nb-Mo alloy single crystal slices whose largest face is perpendicular to the ͗110͘ axis. They were annealed and then doped with hydrogen from the gas phase up to a desired concentration lower than the solubility limit. They were mounted on the specimen holder of the three-axis-goniometer. Channelling analyses were performed at room temperature for the ͗100͘ and ͗110͘ axial channels, the {100} planar channel, and, if necessary, the {111} planar channel at different spots on the same specimen with a 11 B ion beam of about 2 Me...

Effect of substitutional Mo on diffusion and site occupation of hydrogen in the BCT monohydride phase of V–H system studied by 1H NMR

“…the V-H 2 system. Yagi et al have reported that hydrogen atoms shift to Mo atoms below x = 0.1 in the ␣ phase of Nb 1−x Mo x -H and that those occupy not only the T sites but also the O sites above x = 0.2 [33,34]. On the other hand, Tanaka and Kimura have determined the diffusion coefficient of hydrogen, D H , in the ␣ phase of V-H and V 0.99 Mo 0.01 -H by means of the electric resistivity method [18].…”

Effect of substitutional Cr on hydrogen diffusion and thermal stability for the BCT monohydride phase of the V–H system studied by 1H NMR

“…This indicates that addition of Cr reduces mobility of hydrogen on the O sites in the ␤ phase although addition of Mo and Ti enhances the mobility. [32][33][34]. They observed displacement of hydrogen atoms from the T sites toward the nearest Mo atom that has a smaller atomic radius than Nb using the channeling method.…”

“…Meanwhile, Sumin et al have reported that displacement of hydrogen atoms on the T sites in the ␣ phase of Nb 1−x Mo x -H (x = 0.05, 0.20) is not observed using the neutron spectroscopy [35]. Yagi et al considered that the strain field locally introduced by Mo atoms reduced the energy of interstitial sites around them and hydrogen was trapped there [32][33][34]. The trapping energy was roughly estimated to be an order of 5 kJ mol −1 [34].…”