Sealing materials silicon elastomers

Sealants (sealing materials) and compounds (filling materials) are thickflowing pastes which solidify in the cold. They are prepared by mixing low-molecular silicone elastomers with mineral ingredients. Sealants and compounds are supplemented with special catalysts which help them to solidify in the cold. Before using sealants or compounds, the surface of the product is sometimes covered with a sub-layer to improve adhesion. 

Perfluoropyridine (3.0 g, 17.8 mmol), anhyd KF (3.0 g, 55.9 mmol), and sulfolane (15 mL) were introduced into a Carius tube (ca. 100 mL) and hexafluoropropene (5.0 g, 33.3 mmol) was introduced from a vacuum system. The tube was sealed under vacuum and heated for 12 h at 130 C. It was then cooled in liquid air and opened to a vacuum system. The volatile components were fractionated in the vacuum system to give hexafluoropropene (0.5 g) and higher boiling material (8.0 g). The latter was separated by GC (silicone elastomer on Celite) to give derivatives of hexafluoropropene (2.7 g), perfluoropyridine (0.3 g), and per-fluoro(4-isopropylpyridine) yield 4.8 g (94%). 

Silicone elastomers are noted for high temperature and oxidative stabihty, low temperature flexibility, good electrical properties, and high resistance to weathering and oil. They are used in wire and cable insulation and surgical implants and as material for gaskets and seals. 

Specimens of Class PS (gasket type materials, preformed seals) elastomers were obtained as vulcanized, post-cured sheets, approximately 0.18 cm in thickness, from their manufacturers with the exception of silicone rubbers I and J which were supplied as calendered rolls requiring a 4 h bake at 200 C before using (Table I). 

The above criteria were employed to select several commercially supplied Class PS elastomers for laboratory screening by employing selected tests taken from National Bureau of Standards NBSIR 77-1437(j4) and ANSI/ASTM D-3667-78 specifications for "Rubber Seals Used in Flat-Plate Solar Collectors". Four silicone, three EPDM, two fluorocarbon, three epichlorohydrin, one ethylene-acrylic, one polyacrylic, one chlorosulfonated polyethylene, one bromobutyl and two butyl rubbers were studied in these screening tests. These materials are identified in Table I and those compositions which were revealed by their manufacturers are shown in Table II. Undoubtedly some materials which should have been included were omitted however, we hope that this sampling will provide an indication of the applicability of a wide range of materials for use as sealants in thermal solar collectors. 

In general, elastomer materials are used to seal PEFC, the most prominent being silicones, EPDM rubbers (Ethylene Propylene Diene Monomer class mbber) and fluorinated elastomers [74, 77, 78]. 

Elastomers used for connector insulators include polychloroprenes, silicones, fluoro-silicones and heat-setting compounds which enable the special characteristics to be incorporated for example, flame resistance, low toxicity and low smoke. Neoprene is used as spacer material and also for washers where its sealing qualities, good resistance to cracking, rotting, oils and petrol and its good low temperamre flexibility may be beneficial in specific applications. 

These materials promise to extend the range of elastomer performance available to liquid injection moulders. A related development is seal-in-place technology for fuel cells. Developed by Dow Corning in conjunction with the fuel-cell manufacturer Fiydrogenics Corporation, it is a cost-effective, automated sealing process that injects silicone materials into an assembled (but unsealed) fuel cell... 

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