Glass-ceramics crystal structures

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Glass-Ceramics Based on Silicate Crystals. The principal commercial glass-ceramics fall into this category. These can be grouped by composition, simple silicates, fluorosilicates, and aluminosilicates, and by the crystal structures of these phases. 

Fluorosilicates. Compared to the simple silicates, these crystals have more complex chain and sheet structures. Examples from nature include hydrous micas and amphiboles, including hornblende and nephrite jade. In glass-ceramics, fluorine replaces the hydroxyl ion fluorine is much easier to incorporate in glass and also makes the crystals more refractory. Four commercial fluorosilicate glass-ceramic compositions and their properties are listed in Table 2. 

Microabrasion using compressed air is a modification based on sandblasting, the micropowder blasting. This process enables all types of glass, ceramics and semiconductor materials, irrespective of their chemical composition and crystal structure, to be inexpensively processed down to the micrometer scale. The micropowder blasting is a masked procedure and works quasi-parallel on the whole substrate. A powder jet drives systematically over the substrate. Material is removed at the mask openings (see Figure 2.17). 

The interaction of water with other inorganic solids such as ceramics, glasses and catalysts is often a key scientific and technological problem. Hydrogen species in such cases are invariably bonded to oxygen and can occur in many different forms. Protons can be present in a crystal structure as stoichiometric OH groups, water molecules, or hydro-nium ions. Hydroxyl groups can also play an important role in substitutions such as... 

Many aluminosilicate glass ceramics are based on framework structures of AIO4 tetrahedra, which, when crystallized, posseses low thermal expansions. This gives the glass ceramics based on them near zero expansions and thus excellent dimensional stability, thermal shock resistance, and mechanical strength. Aluminosilicate glass ceramics are used commercially as telescope mirrors, thermally stable structures for satellites and space probes, gyroscope components, heat-resistant windows, stove tops, and cookware. 

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