Density properties of glasses of CaO(Na2O)–Al2O3(MgO)–SiO2 system, studied at pressures to 6.0 GPa, in comparison with the properties of similar melts

Abstract

The density properties (relative change in the density, (d − d0)/d, initial bulk modulus, K0, and the derivative of bulk modulus with respect to pressure, К′) of silicate glasses of the CaO(Na2O)–Al2O3(MgO)–SiO2 system are compared with those of silicate melts. It is shown that К0 values obtained for the glasses using Birch–Murnaghan equation in the pressure range with the normal behavior of bulk modulus significantly lower К0 values, which were obtained for glasses using the ultrasonic or Brillouin scattering methods. This phenomenon is explained by the different state of the glasses, which were obtained by different methods. Brillouin scattering method allows obtaining the K0 value, which characterizes the initial unstable state of glass, while with the use of other method (using Birch–Murnaghan equation in the pressure range with the normal behavior of bulk modulus) we determine K0 for glass, which is in the hypothetical metastable state, close to the supercooled liquid. K0 values for glasses, which are in the hypothetical metastable state are close to К0 values for silicate melts. When (K0)glass and (K0)melt have similar values, higher compressibility of melts is determined by smaller values of the derivative of the bulk modulus, K′, compared with glasses of similar compositions. The relation between the parameters (d − d0)/d, K0, K′ and the degree of depolymerization, NBO/T, of silicate glasses and melts was found. The greater the degree of depolymerization, the less is the compressibility of glasses and melts. Simple models for the semiempirical determination of the melts density properties in the first approximation using the density properties of the corresponding glasses are proposed. The possibility of using silicate glasses as the models of deep melts was shown by example of tholeiite basalt glass and melt.