[en] Differences between the data of the author (Trans. TMS-AIME 245: 287(1969)) and that of Whitton et al. (Scripta Met. 9: 851 (1975)), which was obtained using the channeling of 1-MeV He ions, are discussed

[en] Published in summary form only

[en] Samples hydrided in two different ways were investigated. The materials used were thin foils (50 μm, MARZ grade) of niobium, 10 x 25 mm in size. The two methods of hydriding produced different surface conditions which were the subject of the present investigation. One method consisted of the following procedures. The samples were outgassed and cleaned in UHV to remove virtually all the interstitial impurities from the bulk and surface. A small spot of Pd was then deposited onto the clean surface of the niobium in situ in the UHV-system by evaporation from a hot Pd filament. The second method of hydriding was similar to that used by most investigators of metal-hydrogen systems. A sample is placed in the hydriding unit and allowed to absorb a premeasured amount of hydrogen while cooling from approx. 800 C where the surface oxide is dissolved into the bulk. In order to study the effect of a poor vacuum in the hydriding unit, samples were heated to 800 C in different base pressures prior to the admission of hydrogen. One sample was heated in 1 x 10^-5 Torr oxygen

No abstract available

[en] The hidrogen embrittlement of exothermic ocluders, had been considered as due to applied stress induced hydride precipitates leading to brittle fracture. The results of simultaneous measurements of macroscopic deformation and elastic change due to hydride precipitation, using the ultrasonic pulse-echo technique are showed. THen it was tested the possibility of kinectis precipitation parameters evoluation. (Author)

[en] The free energy loss has been theoretically evaluated in the model Nb-H system at 313 K for the solid solution → monohydride and monohydride → dihydride transformations. The origin for this hysteresis loss has been explained by considering the elasto-plastic accommodation processes that occur in the Nb-H system during these hydrogen transformations. The calculated free energy loss for the solid solution → monohydride transformation shows excellent agreement with experimental results. Possible sources of error in the calculations have been elucidated. The present elasto-plastic approach is compared with previous theories of hysteresis. It is found that the elasto-plastic accommodation theory offers the best explanation for the hysteresis phenomenon observed in metal-hydrogen systems

[en] The Compton profiles of Nb and NbHsub(0.76) single crystals have been measured along [100] and [110] using 412 keV gamma-radiation from a ¹⁹⁸Au source. The changes in the band electron profile of the metal following the introduction of hydrogen are interpreted in terms of the protonic model of the hydride. Qualitative changes in the directional profiles can be understood within the rigid band approximation. (orig.)

[en] A special hydriding system was designed and constructed to satisfy conditions for hydriding niobium. This system controlled the temperature and hydrogen atmosphere surrounding the niobium while ultrasonic measurements were recorded. Ultrasonic wave velocities were determined by measurement of the times for ultrasonic pulses to transit and then echo through known dimensions of test specimens. The method which was employed is commonly known as the pulse-echo-overlap method. This study confirmed the general trends of earlier investigations. In this study C' continued to decrease and C₄₄ continued to increase up to 4.69 atomic percent hydrogen which is the maximum concentration which has yet been examined. In the case of the niobium-hydrogen system the Snoek effect may well be a contributory factor to the decrease of C' with increasing hydrogen concentration. However, crystallographic considerations preclude this effect from contributing a concentration dependence to C₄₄ or B. The observation of the present work implies that other factors must also be contributing to the overall behavior

[en] The application of ion microprobe mass spectrometry to various aspects of hydrogen behavior in niobium is discussed and the ability of the method to determine both hydrogen concentration gradients and the presence of hydrides is demonstrated. Hydrogen embrittlement of niobium is due to the cleavage of stress induced hydrides. Portions of a typical crack which propagates in a 2.1 at% H specimen are shown. In addition to hydride formation, the ion probe technique has detected segregation of hydrogen at grain boundaries

[en] Results of X-ray diffraction investigation of hydrogen permeability through niobium with different grain size are presented. It is established that hydrogenation results in hydrogen localization in tetrahedron positions and leads to anisotropic distortion of niobium lattice - a strong expansion in [110] direction and weak one - in [321]. At cyclic hydrogenation the coefficients of hydrogen diffusion (Dsub(H)) in niobium are calculated; Dsub(H) increases with a decrease of niobium grain size