Solubility and diffusion of noble gases in vitreous albite

Abstract

Noble gas sorption experiments were performed on albite composition melts in an internally heated pressure vessel at 0.1–5 kbar pressure, in the temperature range 750°C <T < 1200°C. Solubility of Ne, Ar and Kr in quenched samples was determined by gas chromatography and Knudsen cell mass spectroscopy (KMS). The concentration of dissolved gas increases approximately linearly with pressure. Ar solubility in albite melt shows no temperature dependence for the investigated temperature interval. Modelling of noble gas solubility using Langmuir isotherms yields the following values for the number of sites (M) available for noble gas atoms: Ne: M = 1.5·1021 sites/cm3 melt at 1000°C; Ar: M = 1.8·1020 sites/cm3 melt at 1000°C; and Kr: M = 6.4·1019 sites/cm3 melt at 750°C. Henry’s law constant (K) can be calculated from low-pressure solubility at the indicated temperature as follows: Ne (1000°C), K = 1.5·10−3 cm3 STP g−1 bar−1; Ar (1000°C), K = 3.0·10−4 cm3 STP g−1 bar−1; Kr (750°C), K = 1.8·10−4 cm3 STP g−1 bar−1.Desorption kinetics were investigated by KMS at a constant heating rate of 4 K min−1. The temperature maxima of release spectra are linearly related to noble gas atomic diameter. The temperature dependence of diffusivities was obtained from Knudsen cell rate-heating and fitted to an Arrhenius equation D = D0exp(−Ea/RT), where D0 in cm2 s−1 and Ea in J mol−1, yielding DHe = 5.0·10−4 exp(−67000/RT), DNe = 2.2·10−2 exp−95000/RT), DAr = 9.0·10−4 exp(−133000/RT) and DKr = 4.3·10−3 exp(−168000/RT). The radius of diffusing noble gas shows a linear relationship with the square root of activation energy.