Molecular diffusion of CF3SF5 in pure water and artificial seawater

Abstract

We have experimentally determined the diffusion coefficient for trifluoromethyl sulfur pentafluoride (CF3SF5) in pure water and artificial seawater over a temperature range of −2.0°C to 30.0°C. A working gas standard containing known concentrations of CF3SF5 and sulfur hexafluoride (SF6) was prepared. The working standard was allowed to diffuse across a water barrier, stabilized with agar gel, and the diffused gas was swept into a gas chromatograph with an electron-capture detector to measure the resulting gas mixing ratio. The mixing ratios for both CF3SF5 and SF6 were measured to determine the diffusivity for each species. The diffusion coefficient for SF6 was determined during these experiments as a check against existing literature values and to validate our experimental setup. The experimental data were fit to the Arrhenius equation to yield the following equationsDCF3SF5=0.0015exp(-12.9/RT) and DSF6=0.037exp(-19.8/RT), where R is the gas constant in units of kilojoules per mole per kelvin and T is the temperature in kelvin. At the mean temperature of the ocean, 18°C, DCF3SF5=7.02×10-6±9.9% and DSF6=1.03×10-5±13.8%cm2/s. The diffusion coefficients for SF6 matched the literature data within 4.3% for all temperatures.