Clay can be used to make a huge variety of ceramic articles, from tiny electronic components to bricks and baths. It is a good insulator and, when covered with a glaze, is completely waterproof. Unlike many metals, glazed clay is unreactive, so that acidic foods will not stain it, and exposure to water and the air will not tarnish or corrode it.
Clay is made from the slow chemical weathering of silicate bearing rocks like granite and feldspar and other igneous rock. Usually the weathering is from it is slightly acidic solution other times it is geothermal. It becomes a hydrolyzed aluminum phyllosillicate. Al2Si2O5 (OH)4) They form flat hexagonal sheets that are less than 2 micrometers. The sheets are made of tetrahedral silicate sheets and octahedral hydroxide sheets. There are about 30 types of clay. Natural clays are always a mixture of these many types. There are primary and secondary clays. Primary ones are found where they were formed. Secondary ones have moved by water and deposited somewhere else.
Clays sintered in fire were the first form of ceramic. Bricks, cooking pots, art objects, dishware, smoking pipes, and even musical instruments such as the ocarina can all be shaped from clay before being fired. Clay is also used in many industrial processes, such as paper making, cement production, and chemical filtering. Until the late 20th century, bentonite clay was widely used as a mold binder in the manufacture of sand castings.
Clay, being relatively impermeable to water, is also used where natural seals are needed, such as in the cores of dams, or as a barrier in landfills against toxic seepage (lining the landfill, preferably in combination with geotextiles). Studies in the early 21st century have investigated clay’s absorption capacities in various applications, such as the removal of heavy metals from waste water and air purification.
Medical use: A traditional use of clay as medicine goes back to prehistoric times. An example is Armenian bole, which is used to soothe an upset stomach. Some animals such as parrots and pigs ingest clay for similar reasons. Kaolin clay and attapulgite have been used as anti-diarrheal medicines.
As a building material: Clay building in South-Estonia Clay as the defining ingredient of loam is one of the oldest building materials on Earth, among other ancient, naturally-occurring geologic materials such as stone and organic materials like wood. Between one-half and two-thirds of the world’s population, in both traditional societies as well as developed countries, still live or work in buildings made with clay, often baked into brick, as an essential part of its load-bearing structure.
Also a primary ingredient in many natural building techniques, clay is used to create adobe, cob, cordwood, and rammed earth structures and building elements such as wattle and daub, clay plaster, clay render case, clay floors and clay paints and ceramic building material. Clay was used as a mortar in brick chimneys and stone walls where protected from water.
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