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Andalusite, kyanite, and sillimanite are naturally occurring aluminosilicate minerals that have the composition AlSiO. The triple point of the three polymorphs is located at a temperature of 500 °C and a pressure of 0.4 GPa. These three minerals are commonly used as index minerals in metamorphic rocks.
Hydrated aluminosilicate minerals are referred to as zeolites and are porous structures that are naturally occurring materials.
The catalyst silica-alumina is an amorphous substance which is not an aluminosilicate compound.
There exist a wide variety of glass types. The characteristics of these different types depend on the chemical composition of the glass with a special focus on the oxide composition. Glasses can be categorized into many different groups, one of them including the so-called aluminosilicate glasses.
The unique properties of this glass family include:
high maximum temperature and low thermal expansion suitable for glass to metal sealing
The maximum allowable temperatures of aluminosilicate glasses of up to 800 °C are far above those of borosilicate glasses and reach the level of glass cermic materials. The relevant property to decide about maximum temperatures for glasses is the transformation temperature. The thermal expansion of this glass family can be adjusted to common electrod materials such as molybdenum. A matched thermal expansion allows for a extremely tight and gas-proof glas to metal seal which is achieved by hot forming.
This glass type can be further differentiated:
Alkaline earth aluminosilicate glasses
Characteristically, these glasses are free of alkali oxides and contain 15-25% AIO, 52-60% SiO and about 15% alkaline earths. Very high transformation temperatures and softening points are typical features. Main fields of application are glass bulbs for halogen lamps, high-temperature thermometers and thermally and electrically highly loadable film resistors.
Alkali aluminosilicate glasses
The AIO content of alkali aluminosilicate glasses is typically 10-25% and the alkali content over 10%. The high alkali content prepares the glass for ion exchange with bigger alkali ions in order to improve the surface compressive strength. Due to this particular feature, this glass type is especially suitable for the use in touch displays, solar cells cover glass and laminated safety glass. High transformation temperatures and outstanding mechanical properties, e.g. hardness and scratch behavior, are characteristic of this glass type.
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