Pasquale Rispoli

The decomposition reaction of lithium amide studied by anelastic spectroscopy and thermogravimetry

Abstract The high temperature decomposition transformation of lithium amide into imide has been studied by anelastic spectroscopy and thermogravimetry. At the amide-to-imide phase transformation a huge elastic modulus increase takes place, whose change increases with the evolution of the decomposition. The modulus variation has been used to monitor the time and temperature progression of the reaction, and indications have been obtained that the reaction rates are faster than those usually reported. Moreover, formation of different phases is also detected at extremely low concentrations.

Release of Tetrahydrofuran, Structural Phase Transitions and Dynamic Relaxation Processes in Ca (BH4)2

Various calcium borohydride samples were investigated by means of combined measurements of thermogravimetry and mass spectrometry, and anelastic spectroscopy. On heating, the release of 2-5% tetrahydrofuran (THF) is detected in all the samples at temperatures below ~480 K, even in those which were previously thermally treated, according to procedures known from the literature, in order to remove the solvent. Dehydrogenation takes place above 480 K. Above room temperature the temperature dependence of the Young modulus of Ca (BH4)2 clearly monitors the release of THF and two irreversible structural phase transitions: from the α to the α’ phase around 460 K and from the α’ to the β phase, nearly completely evolved around 590 K. Moreover, the coefficient of elastic energy dissipation presents two dynamic processes below room temperature; a peak around 120 K characterized by an activation energy of 0.20 eV and a pre-exponential factor typical of atom-cluster relaxations, that we attributed to the dynamics of THF molecules retained in the borohydride lattice, and a peak around 200 K, possibly due to the relaxation of H vacancies.