Pressure-Composition Isotherms of TiC<SUB>1−<I>x</I></SUB>–H System at Elevated Temperatures

Abstract

Pressure-composition isotherms of TiC1� x–H system were measured at 773, 873 and 973 K over a pressure range from 10 � 2 to 10 5 Pa. The obtained isotherms could be divided in three concentration regions. In the low concentration region in which ½H� =½TiC �� 1:4 � 10� 3, Sieverts’ law held, and the solubility of hydrogen clearly increased with decreasing temperature. The enthalpy of solution was � 70 � 5 kJ mol � 1 . In the region in which 1:4 � 10� 3 < ½H� =½TiC �� 8:0 � 10� 3, the dependence of hydrogen concentration, CH, on pressure and temperature weakened as pressure increased. Finally, CH was independent of temperature when it reached 8:0 � 10 � 3 . This CH was comparable with the concentration of carbon vacancies in TiC1� x. In the high concentration region in which ½H� =½TiC �� 8:0 � 10 � 3 , Sieverts’ law held again, but the solubility of hydrogen was almost independent of temperature. These observations indicated that hydrogen dissolved in carbon vacancies in the low and middle concentration regions with the above-mentioned value of enthalpy of solution, and also occupied much less stable sites in the high concentration region. [doi:10.2320/matertrans.M2010307]