Glass chemical compositions

Containment capacity is a function of alterability and leachability that are linked to the glass chemical composition which should comply with the specifications previously defined. Glass chemical composition will be controlled as an essential process function. 

Another key factor is the viscosity of the melt at the hquidus temperature. The liquidus temperature of a melt is defined thermodynamically as the temperature above which the melt is stable as a liquid. Whether this Hquid is very fluid or very viscous is not of thermodynamic importance. At temperatures below the liquidus temperature, the melt begins to devitrify (i.e., develop crystals) the extent of devitrification depends on the glass chemical composition, the temperature and the time allowed. 

At very short times the modulus is on the order of 10" ° N m comparable to ordinary window glass at room temperature. In fact, the mechanical behavior displayed in this region is called the glassy state, regardless of the chemical composition of the specimen. Inorganic and polymeric glasses... 

Surfaces are formed in the transition from one state of matter to another, whether the two phases are chemically distinct or not. Thus, surfaces exist at interphases or interfaces between two phases of either the same or different materials. For example, the surface of an ice cube in a glass of water represents an interface between two phases that are identical in chemical composition. The surface of a straw in the same glass of water represents an example of an interface between chemically distinct materials. 

Since successful commercialization of Kapton by Du Pont Company in the 1960s (10), numerous compositions of polyimide and various new methods of syntheses have been described in the Hterature (1—5). A successful result for each method depends on the nature of the chemical components involved in the system, including monomers, intermediates, solvents, and the polyimide products, as well as on physical conditions during the synthesis. Properties such as monomer reactivity and solubiHty, and the glass-transition temperature,T, crystallinity, T, and melt viscosity of the polyimide products ultimately determine the effectiveness of each process. Accordingly, proper selection of synthetic method is often critical for preparation of polyimides of a given chemical composition. 

A polymer blend is a physical or mechanical blend (alloy) of two or more homopolymers or copolymers. Although a polymer blend is not a copolymer according to the above definition, it is mentioned here because of its commercial importance and the frequency with which blends are compared with chemically bonded copolymers. Another technologically significant material relative to the copolymer is the composite, a physical or mechanical combination of a polymer with some unlike material, eg, reinforcing materials such as carbon black, graphite fiber, and glass (see Composite materials). 

This chapter is concerned with aspects of the structure of polymeric materials outside those of simple chemical composition. The main topics covered are polymer stereochemistry, crystallinity, and the character of amorphous polymers including the glass transition. These may be thought of as arising from the primary structure of the constituent molecules in ways that will become clearer as the chapter progresses. 

When X was 10, fluorite and anorthite crystallites were formed. With glasses of lower fluoride content (x < 10) gehlenite crystallites were also found. As X decreased, increasingly more gehlenite was formed at the expense of anorthite and fluorite. In coimection with this observation it should be noted that the chemical composition of the glass corresponds to gehlenite when x = 0 and to a mixture of anorthite and fluorite when x = 1. 

I) The electrical (apparently ionic) conductance of the glass as a function of (a) chemical composition alkali metal ions increase the conductance to... 

Glass has been the container of choice for pharmaceutical dosage forms because of its resistance to decomposition by atmospheric conditions or by solid or liquid contents of different chemical compositions [1]. Furthermore, by varying the chemical composition of glass, it is possible to adjust the chemical behavior and radiation protective properties of glass. 

Chemical Analysis. The chemical composition of ancient objects is important for their authentication. The nature as well as the relative amounts of major, minor, and trace elements in any object are of use for determining the authenticity or otherwise of ceramics, glass, or alloys. A wide range of analytical techniques, depending on the nature of the material studied, have been used for this purpose, including X-rays fluorescence analysis, mass spectrometry, atomic absorption spectroscopy, and neutron activation analy-... 

---