The H-Pd (hydrogen-palladium) System

The solubility and the diffusion coefficient of hydrogen were determined in the austenitic (cubic) high-temperature phase of the shape-memory alloy NiTi The measurements were made between 500 and 950 degrees C, with hydrogen gas pressures of up to 13 bar, and with hydrogen-to-NiTi ratios of up to 0027 The hydrogen was in interstitial solid solution The absorption process is exothermic The enthalpy of solution per hydrogen atom is -183+or-40 meV The diffusion coefficient can be described by an Arrhenius relation with an activation energy E=480+or-50 meV and a pre-exponential factor D0=(47-25+39)*10-3 cm2s-1 NiTi hydride was synthesised in experiments with a higher hydrogen gas pressure (p=150 bar, T=500 K) Because of its brittleness, the hydride is readily pulverised by mechanical methods This yields, after extraction of the hydrogen, NiTi powder which is difficult to prepare by other experimental techniques

https://iopscience.iop.org/article/10.1088/0953-8984/1/14/003/pdf

Hydrogen solubility and diffusion in the shape-memory alloy NiTi

Interstitial positions and vibrational amplitudes of hydrogen in metals investigated by fast ion channeling

Thin films of vanadium produced by vapour deposition on vibrating quartz crystals were used to determine thermodynamic parameters of hydrogen occlusion from the gas phase in the pressure range 10-10<or=p<or=40 bar and temperature range -20<or=T<or=100 degrees C. The partial molar enthalpies and entropies of solution in the dilute Sieverts' law regime were found to be Delta HHx=-26 kJ (mol H)-1, Delta HDx=-28 kJ (mol H)-1 and Delta SH,Dx nc/R=-6. The pressure-composition isotherms indicated various phase transitions in agreement with the known phase diagram. Values of the enthalpies of transition Delta H (in kJ (mol H)-) and the entropies of transition Delta S/R were -35 and -5 for VHx<<1( alpha )-VH0.5( beta ); -36 and -6 for VDx<<1( alpha )-VD0.5( beta ); -37 and -7 for VD0.5( beta )-VD0.7( alpha '); -21 and -8.5 for VH( beta ')-VH2( epsilon ); and -23 and -8 for VD( alpha ')-VD2( epsilon ). The hydriding-dehydriding kinetics were dominated by surface effects.

https://iopscience.iop.org/article/10.1088/0305-4608/12/7/009/pdf

A. Magerl

Papers

Interstitial position of hydrogen in metals from entropy of solution