HYPERACOUSTIC PROPERTIES AND LOCAL-STRUCTURE IN HYDRATED MOLTEN-SALTS

Polarized Mandelstam-Brillouin scattering data in molten Ca(NO3)2 . 4.17 H2O and in its mixture with K(NO3) are presented. The measurements are performed in the deeply supercooled region. Hypersonic velocity and absorption exhibit a relaxational phenomenon to which both the structural and shear mechanisms contribute. The dynamic responses of these hydrated molten salts are interpreted in terms of existing viscoelastic models. The mean relaxation time tau-r and the relaxation modulus M(r) have non-Arrhenius behaviour, supporting that this class of glass-forming liquids can be viewed as `fragile' liquids. In addition the local order around the cations is determined by means of EXAFS measurements carried out at the PULS facility. The EXAFS data give evidence of the existence of inner shell water complexation for the cations Ca2+ and K+ that leads to a close-packed structure in which the H2O molecules are shared among the ions.