Hydrogen evolution behaviors for pure titanium plate samples, in which hydrogen has been thermally charged with gas phase hydrogen at a pressure of 0.1 MPa, were investigated by means of thermal desorption spectroscopy (TDS). Hydrogen concentration in the samples were varied from an extremely low level to a high one, as to form the hydride, by changing the charging times (up to 20 h) and temperatures (398-773 K). After hydrogen dissolution of low concentration level at the initial stage of the dissolution, four kinds of hydrogen evolution peaks were found at 850, 900-950, 1050 and 1150 K in TDS spectra. The hydride formation occurred abruptly at charging temperatures more than 680 K and at the hydrogen concentration level of more than 15-16 at.%, leading final hydrogen concentration of more than 47 at.% hydrogen. For the sample with high hydrogen concentration level as to form the hydride, another TDS peak at 750 K was observed in addition to that at 850 K. The sample hydrogenated evolved a large amount of hydrogen accompanying with a TDS peak from 550 to 900 K. The composition of the hydride was estimated to be TiHx (x:1.1).
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