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Scientific Report 2007-2009
Laboratories and Facilities of the Department of Physics
L6. Laboratory on
”Nanomaterials for alternative energies: solid-state hydrogen storage”
The Lab has been active since 1968 in applying the anelastic
spectroscopy, the acoustic emission, and the thermal analysis to
study various solid systems, from the investigation of the motion
of hydrogen in metals and of its quantum behaviour down to
the liquid helium temperatures, to the high TC superconductors
and manganites, to the lithium-ion batteries and the polymer
electrolytes fuel cells. Over the last 8 years the activity has
been focused on the novel complex hydrides for the solid-state
hydrogen storage.
A large variety of experimental techniques is available. The
Lab is equipped with four main experimental stations which can
work independently. The anelastic spectroscopy facility allows
measurements of elastic energy loss and dynamic modulus in
high vacuum in the temperature range between 1.3 and 900
K. Anelastic spectroscopy is a well established experimental
technique to quantitatively determine the dynamics and the diffusion
parameters of mobile species in solids and the occurrence
of phase transitions, including chemical reactions. An external
stress, applied to a sample through its vibration perturbs the
Figure 1: The experimental apparatus for anelastic spectroscopy
measurements.
energy levels of atoms of fractions of meV and induces redistribution of mobile species in the material (defects or lattice
atoms) among the perturbed levels. The motion parameters are measured while, by thermal activation, the new equilibrium
is being attained.
Figure 2: The system for concomitant
thermogravimetry, differential scanning
calorimetry and mass spectrometry.
The analysis of the data provides the parameters of the local or long
range diffusion processes, like the relaxation rates and their pre-exponential
factors, the activation energies for classical processes, or the splitting of
the energy levels and the power laws of the relaxation rates for quantum
tunnelling phenomena. Moreover, anelastic spectroscopy can sensitively
detect structural and magnetic phase transitions through the dynamic elastic
modulus, which is extremely sensitive to the formation of new phases or
of atom complexes in materials. It has been shown that the dynamic
Young modulus allows the monitoring of the evolution of the decomposition
reactions in complex hydrides as a function of temperature and time.
Anelastic relaxation gives essential information often not obtainable by
other techniques and is complementary to neutron scattering, NMR, and
NQR.
The group uses a flexible system for concomitant measurements of thermogravimetry
and differential scanning calorimetry. This apparatus can operate
both in inert gas atmospheres and in high vacuum, and the exploitable
temperature range is between 300 and 1300 K. The system is complemented by
a quadrupole mass spectrometer which allows the identification of the released
gaseous species.
The thermal analysis Section is equipped with a commercial Dynamic
Mechanical Analyzer, which is able to measure, also in liquid corrosive
environments, but at a lower performance level, the elastic
moduli and the elastic energy dissipation of solid samples in a wide
temperature range, between 78 and 900 K. This system is particularly
well suited for the study of polymers. By the home-made Sieverts
apparatus, it is possible to determine the thermodynamic p-c-T
curves of the various solid-hydrogen systems, through the volumetric
measurement of absorbed/desorbed hydrogen. This system is operative
in a wide range of temperatures (80-600 K) and pressures (0-200
bar).
Related research activities: C39.
Sapienza Università di Roma 180 Dipartimento di Fisica