Abstract: Siloxane compositions comprising 100 parts by weight of polydiorganosiloxane, 10 to 100 parts by weight of reinforcing silica filler, and 0.1 to 5 parts by weight of manganous oxide are elastomeric bases. When further compounded with organic peroxide and optional additives and cured, the finished products exhibit improved heat stability. If flame-retardant additives are used, the finished products exhibit improved flame-retardancy. The manganous oxide is a purified material having a maximum particle size of 15 micrometers.

Abstract: A silicone rubber composition prepared from a mixture of 100 parts by weight polydiorganosiloxane gum, 25 to 75 parts by weight of a reinforcing silica filler, 5 to 20 parts by weight of a hydroxylated diorganosilicon compound having about two hydroxyl radicals per molecule and the organic radicals are 10 to 50 percent phenyl, 2 to 20 percent vinyl and the remainder methyl, fiberized blast furnace slag fibers in amounts of 20 to 80 parts by weight and 0 to 10 parts by weight of alkoxy silicon compound having at least 25 weight percent alkoxy radical provides a silicone rubber when cured which has a high modulus, improved tear strength and can be made oil resistant by adding magnesium oxide to the composition. This silicone rubber can be used for seals, gaskets and particularly where magnesium oxide is present the use can be in contact with oils.