230 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



cal processes. A grain of sand is, in effect, a complex molecule of 

 silica. Each silicon atom is linked to four oxygen atoms which in 

 turn link it with other silicon atoms. In making silicones, part of 

 those oxygen atoms are replaced by organic hydrocarbon groups de- 

 rived from coal or oil. 



This is a complex process which is interesting primarily to chem- 

 ists. The job of silicone chemists, and, to no little extent, their art, 

 is so to "tailor" the high-polymeric organo-silicon oxide molecules 

 that a variety of products, each designed to meet specific use require- 

 ments, can be produced. 



Already a large group of new engineering materials have been 

 derived from sand. These materials are available in a wide variety 

 of physical forms. They include oils, compounds having a grease- 

 like consistency, resins for heat-resistant enamels, laminates and mold- 

 ing plastics, and even a semi-inorganic rubber called "Silastic." In 

 this age of chemical marvels, when people expect the chemist to pull 

 new and ever more astounding marvels from under his hat, the pro- 

 duction of rubber from sand is among the more astounding accom- 

 plishments of chemistry. 



HEAT STABILITY 



All these silicone products are characterized by a higher order of 

 stability to heat and by greater resistance to moisture than conven- 

 tional organic materials in the same physical forms. This heat stability 

 and the suitability of silicone compounds for use in electrical insula- 

 tion are inherent in their chemical structure. In the silicones, only 

 two kinds of chemical bonds, the Si-O-Si and the C-Si bonds, are 

 significant. The silicon-oxygen-silicon bonds are extremely stable to 

 heat, as one would expect from the fact that these are the same bonds 

 which exist in the mineral silicates. The carbon-silicon bonds also 

 have a higher order of heat stability and greater resistance to oxida- 

 tion than the carbon-to-carbon bonds which are basic in organic 

 materials. 



As a consequence of this greater heat stability, the silicone resins are 

 natural complements to fibrous glass, mica, and asbestos insulating 

 materials. The silicone resins provide the heat-resistant resinous di- 

 electric necessary to bond these materials together. They also bond 

 the insulating materials to the copper and steel used in building elec- 

 tric equipment. This bond is highly resistant to heat. It not only 

 holds the insulation together, but also excludes moisture even after 

 long exposure to high temperatures, as rigorous laboratory tests have 

 shown. Thus, through the use of silicones together with inorganic 

 insulating materials, a new type of electrical insulation has become 

 available. This new class — silicone insulation — is almost immune to 



