Kinetic and structural aspects of tantalum hydride formation

Abstract

Tantalum hydrides of various composition were synthesized by equilibrating tantalum with hydrogen at six different temperatures from 573 to 823 K, under a constant hydrogen pressure of 1 bar. Both the exact Ta/H mole ratios and the kinetic parameters of hydriding were determined on the basis of the dependence of the H/Ta mole ratio on time. The influence of stoichiometry on the appearance of X-ray powder diffractograms at room temperature was studied. As a consequence of hydriding, for ratios H/Ta > 0.2, the original bcc Ta-lattice undergoes distortion, manifesting itself as both a shift and a splitting of the X-ray patterns in the X-ray diffractograms. For samples with H/Ta < 0.2, the appearance of some superstructure reflections at low Bragg angles was noted, which suggests a long range ordering of hydrogen with orthorhombic symmetry.