Kaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O5(OH)4. It is a layered silicate mineral, with onetetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra.[4] Rocks that are rich in kaolinite are known as china clay, white clay, or kaolin.
The name is derived from Chinese: 高陵/高嶺; pinyinGaoling or Kao-ling (“High Hill”) in JingdezhenJiangxi provinceChina.[5] The name entered English in 1727 from the French version of the word: “kaolin”, following Francois Xavier d’Entrecolles‘s reports from Jingdezhen.[6]
Kaolinite has a low shrink-swell capacity and a low cation exchange capacity (1-15 meq/100g.) It is a soft, earthy, usually white mineral (dioctahedral phyllosilicate clay), produced by the chemical weathering of aluminium silicate minerals like feldspar. In many parts of the world, it is colored pink-orange-red by iron oxide, giving it a distinct rust hue. Lighter concentrations yield white, yellow or light orange colours. Alternating layers are sometimes found, as at Providence Canyon State Park in GeorgiaUSA.
Kaolin is used in ceramicsmedicinecoated paper, as a food additive in toothpaste, as a light diffusing material in white incandescent light bulbs, and in cosmetics. It is generally the main component in porcelain.
It is also used in paint to extend titanium dioxide (TiO2) and modify gloss levels; in rubber for semi-reinforcing properties; and in adhesives to modify rheology.[9]
Kaolin was long used in the production of common smoking pipes in Europe and Asia.
The largest use is in the production of paper, including ensuring the gloss on some grades of paper. Commercial grades of kaolin are supplied and transported as dry powder, semi-dry noodle or as liquid slurry.
Kaolinite can contain very small traces of uranium and thorium, and is therefore useful in radiological dating. While a single magazine made using kaolin does not contain enough radioactive material to be detected by a security-oriented monitor, this does result in truckloads of high end glossy paper occasionally tripping an overly-sensitive radiation monitor.[10]
Kaolinite has also seen some use in organic farming, as a spray applied to crops to deter insect damage, and in the case of apples, to prevent sun scald.
In April 2008, the US Naval Medical Research Institute announced the successful use of a Kaolinite-derived aluminosilicate nanoparticle infusion in traditional gauze, known commercially as QuikClot Combat Gauze.[11]
When heated to between 650 and 900 °C kaolinite dehydroxylates to form metakaolin. According to the American National Precast Concrete Association this is a supplementary cementitious material (SCM). When added to a concrete mix, metakaolin affects the acceleration of Portland cement hydration when replacing Portland cement by 20 percent by weight.
In ceramics applications, the formula is typically written in terms of oxides, thus the formula for kaolinite is Al2O3·2SiO2·2H2O
Using the cement chemist notation this can be even written as AS2H2, with the oxides respresented as A = Al2O3, S = SiO2, H = H2O.
Kaolinite was also used as filler in Edison Diamond Discs[12][citation needed].
Medicinal and culinary uses
folk medicine use is to soothe an upset stomach, similar to the way parrots (and later, humans) in South America originally used it.[13]
Kaolin is, or has been, used as the active substance in liquid anti-diarrhea medicines such as Kaomagma and Kaopectate. Such medicines were changed away from aluminium substances due to a scare over Alzheimer’s disease[citation needed], but have since changed back to compounds containing aluminium as they are more effective.
Kaolin is known in traditional Chinese medicine by the name chìshízhī (赤石脂),[citation needed] literally “crimson stone resin”.
In Africa, kaolin is sometimes known as kalaba (in Gabon[14] and Cameroon[15]), calaba, and calabachop (in Equatorial Guinea). It is used for facial masks or soap[16] and is eaten for pleasure or to suppress hunger,[15] a practice known as geophagy. Consumption is greater among women, especially during pregnancy.[17]
This practice is also seen among black women in the Southern United States, especially Georgia.[18] There, the kaolin is called white dirtchalk or white clay.[18]
{Information courtesy Wikipedia}