Investigation of the outgassing process of silicone rubber

• Published in: Vacuum 1963, Vol.13 (12), p.549-553
• Main Authors: von Münchhausen, H., Schittko, F.J.
• Format: Article
• Language: English
• ISSN: 0042-207X; 1879-2715
• DOI: 10.1016/0042-207X(63)90542-6

The results obtained in this study on silicon rubber as gasketing material can be summarized as follows: The outgassing rate of silicon rubber—as measured in vacuum—can be reduced by two orders of magnitude through heat treatment. To get best results, the pretreatment—drying in hot air—should be carried out at a temperature of 200°C for 5–8 h. If the vacuum is released, the material absorbs atmospheric air again, and after about five days, half of the original gas contents is absorbed. Further exposure to air does not increase this amount. An exception is the R30 material, which after five months showed its original gas content. Repetitive drying in hot air has the effect that the time of pre-treatment required for low outgassing rate is only 1 h, whilst 5–8 h are necessary at the first drying cycle. The outgassing rate per unit of volume from samples without pre-treatment is constant. These samples show within the accuracy of the method of measurement the same gas concentration at the surface and in the body of the sample. When the degassing rate as a function of time is plotted on a double logarithmic graph, no conclusive evidence can be obtained from the slope of the curve, whether physical desorption or diffusion is the predominant process. This applies to both untreated and treated samples. Further experiments did, however, show that in spite of marked deviations from the 1 t law the outgassing process of silicon rubber is quite definitely based on a diffusion mechanism.