Energy and Hydrogen Storage

Fundamental studies into photovoltaic materials, namely copper indium gallium diselenide, have been undertaken at Salford since the 1970’s (e.g. for solar energy applications).  A particular research focus is the development of new hydrogen storage materials (for mobile applications).  Related work includes: studies of fuel transport systems, magnetic phase transitions induced by hydrogen, and hydrogen-bonded systems (Raman spectroscopy, x-ray crystallography and nonlinear optics).

Various environmentally-friendly technologies, applications and fuels are developed, and a range of nuclear fission and fusion energy materials are investigated – a current project is part of a national effort to understand the effects of neutron irradiation on nuclear graphites.

Our contributions include the use of coherent inelastic neutron scattering to investigate the dynamics of radiation-induced defects. Thermal neutrons can be used to study the dynamics of atoms in solids, and hence the nature of the atom-atom interactions. The most powerful method involves the use of  a Triple Axis Spectrometer to measure the dispersion curves for phonons in single crystal samples.

Simulated scattering data from polycrystals associated with phonon dispersion curves (averaged over crystal orientation)

However, for many important materials, only polycrystals are available and the coherent inelastic scattering becomes very complex to analyse. For this reason, we have developed software that is capable of simulating the scattering from polycrystals – hence the acromnym polyCINS. It is still difficult  to directly extract the dispersion curves. However, we have demonstrated that it is possible to refine a force constant model to describe the results.

Within the work on graphite, small angle neutron scattering is used at the ISIS pulsed neutron source within the Rutherford Appleton Laboratory to study porosity in nuclear graphites.  The graphite moderators in advanced gas-cooled reactors are showing signs of damage from exposure to neutron  and gamma radiation during reactor lifetimes. Because of the potential shortage of electricity when these reactors are shut down, it becomes immensely important to understand the accumulated damage – with a view to extending reactor lifetimes by some years. The porosity that can be observed is produced  by anisotropic contraction as the coke particles cool.

We have, in fact, demonstrated that the porosity is fractal in nature and that it gradually disappears when the material is heated as expected. Moreover, by use of a contrast-matching technique, we have demonstrated that about 70% of the porosity is connected to the surface of the graphite. We are also  simulating the results of fast neutron damage using a molecular dynamics technique. Further to this, using total diffraction, we have been able to extract the carbon-carbon pair distribution for both virgin and highly irradiated graphite.