The properties of Viton “A” elastomers

Abstract The solubility of atmospheric constituents in Viton “A” has been evaluated from long-term sorption data. The solubility of air in Viton “A” elastomer at 18°C and at a relative humidity of 50 per cent was found to be 4.25 atm. cc per cc of elastomer with a deviation of ±3.5 per cent. From previously published data it is deduced that the sorbed gases are mainly water vapour and carbon dioxide. The overall sorption mechanism is discussed in terms of surface adsorption and diffusion into the bulk of the material. The time taken to reach any particular gas content depends on the diffusion coefficient, the temperature and the initial conditions (previous history) of the material. The influence of these factors on the gas emission process in high vacuum applications is discussed, using the model established for the sorption process. This suggests a reason for the apparent discrepancies in reported outgassing values. The advantages of pre-outgassing and storing under vacuum an elastomer intended for high vacuum use are demonstrated. A formula is quoted which appears to relate, for the samples tested, the cord diameter to the time required for decline in sorption rates.