TY - JOUR

T1 - Hydrogen desorption kinetics of hafnium hydride powders

AU - Pollard, Joseph

AU - Dumain, A

AU - Stratton, Brandon

AU - Irukuvarghula, S

AU - Astbury, Jack

AU - Middleburgh, Simon

AU - Giuliani, Finn

AU - Humphry-Baker, Samuel A.

PY - 2024/11/6

Y1 - 2024/11/6

N2 - The kinetics of hydrogen gas release from hafnium hydride are investigated by combining experiments and density functional theory. The material is a candidate neutron moderator and attenuator for compact nuclear reactors, where hydrogen release will lead to a degradation in moderating function. Experimentally, we have studied the decomposition of epsilon phase (HfH2-x) powders from 25-1000°C using thermogravimetry and X-ray diffraction. Isochronal heating reveals 3 characteristic desorption regions corresponding to the release of hydrogen from each phase (ε-HfH2-x, δ-HfH1.6-x and α-Hf), at ∼ 350, 415, and 700°C. These results are well supported by the modelling output from density functional theory. A Kissinger analysis allowed for activation energies for desorption to be calculated (∼150 kJ/mol, 170 kJ/mol and 90 kJ/mol respectively). The peak shape and desorption rate data suggests that a second order diffusion limited reaction controls the ε→ε+δ desorption, a first order interface limited reaction controls the ε+δ→δ reaction, and a surface limited zeroth order reaction limits the complete desorption of the δ+α phase. The analysis suggests that, at least for δ→α regime, engineering solutions for improved thermal stability should focus on reductions in surface reactivity.

AB - The kinetics of hydrogen gas release from hafnium hydride are investigated by combining experiments and density functional theory. The material is a candidate neutron moderator and attenuator for compact nuclear reactors, where hydrogen release will lead to a degradation in moderating function. Experimentally, we have studied the decomposition of epsilon phase (HfH2-x) powders from 25-1000°C using thermogravimetry and X-ray diffraction. Isochronal heating reveals 3 characteristic desorption regions corresponding to the release of hydrogen from each phase (ε-HfH2-x, δ-HfH1.6-x and α-Hf), at ∼ 350, 415, and 700°C. These results are well supported by the modelling output from density functional theory. A Kissinger analysis allowed for activation energies for desorption to be calculated (∼150 kJ/mol, 170 kJ/mol and 90 kJ/mol respectively). The peak shape and desorption rate data suggests that a second order diffusion limited reaction controls the ε→ε+δ desorption, a first order interface limited reaction controls the ε+δ→δ reaction, and a surface limited zeroth order reaction limits the complete desorption of the δ+α phase. The analysis suggests that, at least for δ→α regime, engineering solutions for improved thermal stability should focus on reductions in surface reactivity.

U2 - 10.1016/j.jnucmat.2024.155499

DO - 10.1016/j.jnucmat.2024.155499

M3 - Article

JO - Journal of Nuclear Materials

JF - Journal of Nuclear Materials

SN - 0022-3115

M1 - 155499

ER -