Manufacturing of glass ceramics

Both hydrated and anhydrous metal borates have numerous industrial uses. Some of the major uses of hydrated metal borates are the manufacture of glasses, ceramics, and industrial fluids, and as micronutrient fertilizers, fire retardants, and biostats. Anhydrous borates find use as heterogeneous catalysts, scintillation hosts, and in the fabrication of optoelectronic devices. Anhydrous aluminum borates are used as additives in oxide ceramics to promote the formation of desirable phases. Also, aluminum borate whiskers are used as reinforcing additives in composite materials. Specific nses of sodium, calcium, zinc, and barium borates are discussed in sections below. 

A number of silicon compounds have important uses. Silicon dioxide (sand) is used in the manufacture of glass, ceramics, abrasives, as a food... 

The intentionally induced crystallization used in the manufacture of glass-ceramics will be dealt with in a separate chapter. 

These mechanisms are presented by using the examples of cordierite and leucite glass-ceramics. To clearly demonstrate the mechanisms, experiments were conducted with monolithic test specimens rather than the fine-powdered glasses required in the industrial manufacturing of glass-ceramics. The following descriptions, therefore, refer only to the mechanism as demonstrated in monolithic specimens. 

Pure arsenic is presently used as a component of alloys (e.g., with lead to produce hunting ammunition). Arsenic compounds are also used in the chemical, pharmaceutical, and tanning industries, in the manufacture of glass and ceramics, and as pesticides in agriculture and fruit-farming (Nriagu and Azcue, 1990). 

Other minor uses of antimony include the manufacture of glass and ceramics and the production of plastics. In glass and ceramics, a small amount of antimony insures that the final product will be clear and colorless. In the production of plastics, antimony is used as a catalyst. A catalyst is a substance that increases the rate of a chemical reaction. The catalyst does not undergo any change itself during the reaction. 

In principle, some types of materials of similar phase compositions can be made by sintering powdered mixtures, i.e. by ceramic manufacturing techniques. However, it is impossible to achieve the fine-grained and uniform structures which are the main feature and advantage of glass-ceramics. 

The several types of glass-ceramics considered below are already being manufactured and/or have possibilities of further development (Table 23). 

Use Dyeing mordant, water purification, waterproofing fabrics, manufacture of lakes, filtering medium, chemicals (aluminum salts), lubricating compositions, manufacture of glass, sizing paper, ceramic glaze, antacid. 

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