PERMEATION THROUGH ELASTOMERIC 0-RING SEALS*

Permeation of He, Ne, Ar, Kr, Xe and 0 2 through 0-ring seals of fluorocarbon rubber (e.g. Viton), ethylene-propylene rubber (EPDM) and silicone rubber (VMQ) has been measured at temperatures from 290 K up to the destruction of the materials, at about 600 to 700 K. Test gas pressures ~p up to 2 bar were applied. The quantiry of the test gas that permeated was detected using high sensitivity quadrupole mass spectrometry. To investigate the influence of seal geometry, permeation through VMQ 0-rings was measured as a function of their compression and compared with measurements of sheet geometry for the same material . The measured time dependence of the permeation gas flow is well described by theoretical predictions, when the flow through the 0-ring is considered as the sum of flows through a number of rectangular slabs approximating the shape of the compressed 0-ring. Equilibrium gas flow, the permeation coefficient, solubiliry, the diffusion coefficient, the activation energy of diffusion and the heat of solution are derived from the measurements and are compared with values given in the literature, where available. By extrapolating the results for rare gases He to Xe, permeation parameters for Rn are estimated for the three elastomers under investigation.