Andalusite is an island-like anhydrous silicate mineral, one of the minerals of the andalusite group. This group of minerals has the same chemical composition Al2SiO5, but has a different crystal structure, so the physical properties are slightly different. Theoretically speaking, this group of minerals contains 362.9% Al2O. Therefore, this group of minerals is between kaolin refractories containing 337% Al2O and bauxite refractories containing 380~90% Al2O. It belongs to aluminosilicic acid with medium aluminum content. Range of salt refractories. Al in andalusite can be replaced by Fe3+ (≤9.6%) and Mn (≤7.7%).
Andalusite is mainly a mineral of metamorphic origin. In regional metamorphism, it is produced under the conditions of low metamorphic temperature and pressure, generally found in aluminum-rich argillaceous schist; often with cordierite, quartz, muscovite, garnet, staurolite, biotite and some other rich The mineral symbiosis of aluminum. It is also found in the contact zone between argillaceous rock and intrusive rock mass, and is a typical contact thermal metamorphic mineral.
Process characteristics of andalusite
Industrial use of it is mainly based on its high temperature resistance characteristics. After it is heated to 1350 ℃ under normal pressure, it begins to transform into acicular mullite parallel to the original crystal. Mullite body is the only stable form of aluminosilicate under the action of high temperature, and its theoretical conversion rate is 87.64%.
In the process of heating and converting to mullite, andalusite can form a good mullite network with a volume expansion of about 4%. This is an irreversible crystal transformation. Once transformed, it has higher fire resistance. The refractoriness can reach above 1800℃, and it is resistant to sudden cooling and heat, strong mechanical strength, strong thermal shock resistance, and strong slag resistance. The load conversion point is high, and it has extremely high chemical stability (even insoluble in hydrofluoric acid) and strong chemical resistance.
Uses of andalusite
It can be used to manufacture advanced refractory materials. It is one of the currently known high-quality refractory materials. It can also be used as a raw material for radomes. It can be used in the ceramic industry to increase the mechanical strength and rapid heat resistance of the products. It can be smelted with high strength and lightness. High-quality silicon-aluminum alloy, used for the production of metal fibers and the guiding type of supersonic aircraft and spacecraft. The rock that produces chrysanthemum stone can be used as decorative stone. Good color and transparency, coarse crystal grains can be used as gemstone raw materials. Hollow spar can be used as a good ornamental stone. Its application areas are still expanding.
