Toughness window glass

Figure 8. Temperature dependence of the apparent fracture toughness of a standard window glass. ...

Saran (Dow polyvinylidene dichloride) is a tough, chemically resistant plastic available in a variety of forms that are useful in the laboratory. Saran pipe or tubing can easily be welded to itself or sealed to glass and is useful for handling corrosive solutions. Thin Saran film, available commercially as a packaging material, is useful for windows, support films, etc. Mylar (du Pont polyethylene terephthalate) film and other polyester films are also useful for these purposes. Mylar is chemically inert and has excellent electrical properties for electrical insulation and for use as a dielectric medium in capacitors. Much thinner than these are films that can be made in the laboratory by allowing a dilute ethylene dichloride solution of Formvar (polyvinyl acetal) to spread on a water surface and dry. 

Polycarbonates are condensation copolymers formed by the reaction of carbonic acid with compounds such as bisphenoi A (Figure 15-31). This reaction forms the polycarbonate termed Lexan. Polycarbonates form clear, tough plastic materials that, if thick enough, can even stop bullets. Consequently, polycarbonate is often used in eye protection, as a scratch-resistant coating for eye glasses, and in bulletproof windows. 

A patent has been issned for a glass composition in which 1.4 parts of beryUinm carbonate are fused with 4.3 parts of lithium carbonate and 18.5 parts of boric acid to produce a borate glass suitable for X-ray tube windows. This glass has a high coefficient of expansion, very high permeability to ultraviolet rays, is quite tough and easily worked. Note Inhalation of particles of any BeO-containing material should be avoided because of their toxicity. 

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