Glass chemical inertness

Ethylene. Under the influence of pressure and a catalyst, ethylene yields a white, tough but flexible waxy sohd, known as Polythene. Polyethylene possesses excellent electric insulation properties and high water resistance it has a low specific gravity and a low softening point (about 110°). The chemical inertness oi Polythene has found application in the manufacture of many items of apparatus for the laboratory. It is a useful lubricant for ground glass connexions, particularly at relatively high temperatures. 

The separator must be stmcturaHy sound to withstand the rigors of battery manufacturing, and chemically inert to the lead—acid cell environment. Numerous materials have been used for separators ranging from wood, paper, and mbber to glass and plastic. The majority of separators used are either nonwoven—bound glass or microporous plastic such as PVC or polyethylene. 

Care must be taken with both sintered glass and porous base crucibles to avoid attempting the filtration of materials that may clog the filter plate. A new crucible should be washed with concentrated hydrochloric acid and then with distilled water. The crucibles are chemically inert and are resistant to all solutions which do not attack silica they are attacked by hydrofluoric acid, fluorides, and strongly alkaline solutions. 

A desirable glass melts at a reasonable temperature, is easy to work with, and yet is chemically inert. Such a glass can be prepared by adding a third component that has bonding characteristics intermediate between those of purely ionic sodium oxide and those of purely covalent silicon dioxide. Several different components are used, depending on the properties desired in the glass. 

Vitreous silica is the most chemically inert glass for most purposes. 

Two major classes of hydrophobic chemical substances can be applied to glass in ultrathin layers to inhibit surface wetting. Siloxanes or polysiloxanes or silicones are polymers with a backbone of alternating silicon and oxygen atoms. These macromolecules are quite chemically inert, show resistance to water, and exhibit stability at high and low temperatures. The most common siloxane polymer, polydimethylsiloxane, is composed of the monomeric (i.e., repeating) unit illustrated in Fig. 7.5.1. 

Multinuclear NMR spectroscopy is being used increasingly to study catalytic reactions. In order for such studies to be possible, all contact betv een the sample solutions and the metal part of the cell body has to be avoided because of possible catalytic effects. All materials in contact vith the sample solution have to be chemically inert and nonmetallic quartz, glass, PTFE, Vespel (polyimide polymer, Dupont de Nemours), PCTFE (poly-chlorotrifluoroethylene), Viton seals, etc. 

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