PNNL

Abstract

We report studies on the thermal and radiation stability of the hydrated salt minerals epsomite (MgSO4?7H2O), mirabilite (Na2SO4?10H2O) and natron (Na2CO3?10H2O) under the low-temperature and ultrahigh vacuum conditions characteristic of Europa. The temperature programmed dehydration (TPD) data are fit using Arrhenius-type first-order desorption kinetics. This analysis yields effective activation energies of 0.90?0.05, 0.70?0.05, and 0.45?0.05 eV for removal of approximately 90% of the hydration water for epsomite, natron and mirabilite, respectively. A simple qualitative extrapolation indicates that epsomite should remain hydrated over geologic time scales ( ~109 - 1011 years), whereas natron and mirabilite may dehydrate appreciably in approximately 105 and 101 years, respectively. A small amount of SO2 was detected during and after electron-beam (100-1000 eV) irradiation of hydrated and dehydrated epsomite and mirabilite samples, whereas products such as O2 remained below detection limits. The 100 eV electron-induced damage cross section of mirabillite and epsomite is