Glass as Material

Owing to its chemical resistance, glass is generally excellent for water, saline solutions, acids, organic substances, and even alkalis, so that in all these cases, it is superior to most metals and plastics. The only chemicals that have a noticeably adverse effect on it are hydrofluoric acid, strongly alkaline solutions, and concentrated phosphoric acid, particularly at high temperatures. 

One exception is the special type of photostructurable glass. For the construction of microreactors, the borosilicate types of glass are the most important, but also fused silica. 

Physical properties Fused silica Borosilicate glass (B33) Photoetchable special glasses 

It is available in wafer form but also with a rectangular shape. The structuring methods most often used are described below. 

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Unlike conventional ceramic materials, glass-ceramics are fully densifted with zero porosity. They generally are at least 50% crystalline by volume and often are greater than 90% crystalline Other types of glass-based materials that possess low amounts of crystallinity, such as opals and mby glasses, are classified as glasses and are discussed elsewhere (see Glass). 

Certain glass-ceramic materials also exhibit potentially useful electro-optic effects. These include glasses with microcrystaUites of Cd-sulfoselenides, which show a strong nonlinear response to an electric field (9), as well as glass-ceramics based on ferroelectric perovskite crystals such as niobates, titanates, or zkconates (10—12). Such crystals permit electric control of scattering and other optical properties. 

Glass offers good resistance to strong acid at high temperatures. However, it is subject to thermal shock and a gradual loss in integrity as materials such as iron and siUca are leached out into the acid. Nonmetallic materials such as PTFE, PVDC, PVDF, and furan can be used for nitric acid to a limited degree, but are mainly restricted to weak acid service at ambient to moderate temperatures. 

Vitreous siUca is considered the model glass-forming material and as a result has been the subject of a large number of x-ray, neutron, and electron diffraction studies (12—16). These iavestigations provide a detailed picture of the short-range stmcture ia vitreous siUca, but questioas about the longer-range stmcture remain. 

As with the aliphatic polyamides, the heat deflection temperature (under 1.82 MPa load) of about 96°C is similar to the figure for the Tg. As a result there is little demand for unfilled polymer, and commercial polymers are normally filled. The inclusion of 30-50% glass fibre brings the heat deflection temperature under load into the range 217-231°C, which is very close to the crystalline melting point. This is in accord with the common observation that with many crystalline polymers the deflection temperature (1.82 MPa load) of unfilled material is close to the Tg and that of glass-filled material is close to the T. ... 

In order to develop measures for removal of debris from the waste matrix, the general types of debris anticipated need to be identified. A composite list, based on debris found at 29 Superfund sites, was developed. The list includes cloth, glass, ferrous materials, nonferrous materials, metal objects, construction debris, electrical devices, wood existing in a number of different forms, rubber, plastic, paper, etc., as presented in Table 11. Similar types of debris would be expected at RCRA sites. 

Fiber-reinforced plastics have been widely accepted as materials for structural and nonstructural applications in recent years. The main reasons for interest in FRPs for structural applications are their high specific modulus and strength of the reinforcing fibers. Glass, carbon, Kevlar, and boron fibers are commonly used for reinforcement. However, these are very expensive and, therefore, their use is limited to aerospace applications. 

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