Soda-lime Glass Revisited: Applying an Energy-Dependent Grüneisen Model to Shock Velocity, Temperature, and Sound Speed Data

Shock experiments constrain the thermal equation of state (EOS) of planetary materials, giving pressure (P), volume (V), internal energy (E), temperature (T), and sound velocity in Hugoniot and off-Hugoniot states. The functional form of the EOS must be adequate to cover the P-V-T range of planetary interiors with sparse data and avoid erroneous predictions. When an EOS is needed at lower (or higher) energies than the Hugoniot, the thermal pressure term is critical. Most often γ≡V(∂P/∂E)_V is taken to obey γ=γ(V) (the Mie-Grüneisen approximation), e.g. using (γ/γ_o)=(V/V_o)^q (3 parameters). This is justified for solids, where q~1. Thermal pressure in liquids behaves differently; γ increases with decreasing V (q<0). But few studies have questioned the Mie-Grüneisen approximation for liquids. Our simulations and experiments on a basaltic analogue melt showed that γ=γ(V, E); we proposed a new four-parameter γ function. We extend this form to melts of soda-lime glass, an analogue for felsic natural melts. Our shock velocity, release, sound speed, and T data up to ~120 GPa are fit by a 3rd-order Birch-Murnaghan isentrope with γ(V, E). T is lower than previous results, indicating that heat capacity C_V increases on compression in this melt.