Hydrogenation Of The Titanium Aluminides
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Hydrogenation Of The Titanium Aluminides Nataiya Kazantseva, Nikolai V Mushnikov, Alexandr G Popov, Valentina A Sasonova, and Pavel B Teren'ev Institute of Metal Physics, 18, S.Kovalevskaya, Ekaterinburg, Russian Federation ABSTRACT Titanium aluminides are very important materials for elevated temperature applications, especially by its low density. The low density of these materials is also very attractive for other purpose, for example for using of these intermetallics as hydrogen accumulators or storages. It is well known that a number of metals can absorb large quantities of hydrogen. In many cases a major difficulty is getting the hydrogen into the metal. Oxide layer of titanium aluminides, which is so useful for its elevated temperature applications, prevents its hydrogen absorption. In such cases it is customary to expose the metal to hydrogen at high temperature and elevated temperature for an extended period of time, for titanium aluminides the adsorption temperature is about 800C. But such high temperature is not possible for the hydrogen accumulator. It has been discovered that ball milling of many metals under a hydrogen atmosphere promote rapid hydrogen absorption. We studied the hydrogen absorption properties of the Ti-Al-Nb system intermetallics during ball milling. We defined that the hydrogenation of the titanium aluminides under ball milling in the hydrogen atmosphere could occur at the room temperature without any requirements on quality of hydrogen. The crystal structure of the hydrides and phase transformations were also studied. INTRODUCTION It is well known that a number of metals and a lot of metallic compounds can absorb large quantities of hydrogen. The titanium aluminides are very important materials for elevated temperature applications, especially due to its low density. The low density of these materials is also very attractive for other purposes, for example for using these intermetallics as hydrogen accumulators. The reasons for choosing the intermetallics of the Ti-Al-Nb system as alloys for hydrogen storage are summarized to be the following: 1) all components of this system (Ti, Al, and Nb) are the hydride forming elements; 2) the titanium aluminides are well-known corrosion resisted materials with the high strength and high work temperature (up to 6000C); 3) they have a low density (4,5∼5 g/sm3); 4) the titanium aluminides are low cost and safe materials, the hydrogenation of which is strongly affected by the deformation and phase transformations [1]. However, the high-purity hydrogen gas at low pressure is needed for the low-temperature absorption/desorption processes. In the Ti(Al,Nb) alloys, with the initial cubic phase β0 (superstructure B2, CsCl), the β hydride (H/M=0.5, bcc, a=0.334 nm) and γ hydride (H/M>1.08, bct, a=0.331, c=0.419) were found. The β hydride is believed to be transformed to γ hydride at a pressure about 3 MPa at 500C, however, the reverse transformation does not occur unless the temperature is raised to 4000C [2]. In many cases a major difficu
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