| Abstract: | A radioactive tracer technique has been devised to measure the permeability of thick membranes and layers of synthetic rubbers and glass-fibre laminates to liquefied hydrocarbons. The technique involves the use of the tritium-labelled hydrocarbon, prepared by treating the appropriate Grignard reagent with tritiated water. The labelled hydrocarbon is transferred to a thermostatted permeability cell. Permeate is trapped in a vial which contains liquid scintillation phosphor and is cooled in liquid air. The trapped permeate is measured by liquid scintillation counting of the sealed vial. Such measurements, made over an appropriate period, allow permeability constants to be calculated. Propane transfer rates down to 10?10 g/h have been measured, with membranes of thickness ranging from about 0·5 to 1·5 mm, giving permeability constants of the order of 10?11 g cm?1 h?1 atm?1. Abnormal rate/time curves have been found for some membranes. Factors affecting the accuracy of the measurements, and the safety precautions necessary, are discussed. Finally, extension of the technique to the study of hydrocarbons of low boiling point such as methane is considered. |
