Kaolin

Hydrated alumina silicate, Pure clay mineral

Chemistry

Al2O3	40.210
SiO2	47.290

Volatiles

LOI

12.500

Links to Other Materials

Calcined Kaolin
Kaolin - Parent
Cache

Hazards

Kaolin

Miscellaneous

Family: Kaolin
Region: North America
Mined At: Unspecified
Raw Mineral: No
Generic: Yes

Notes

Kaolin is pure clay mineral crystal of one part alumina and two parts silica (also called China Clay). Most other clay minerals are derivatives of kaolin. Kaolin particles are flat and comparatively the largest of all clay minerals. They have a surface chemistry that gives them an affinity for water. The attached water both 'glues' particles together and acts as a 'buffer' to lubricate particle-against-particle movement in the plastic matrix.

Kaolins are whiter and cleaner than other clays because they are mined near the site where they were weathered and altered from the parent rock. Kaolin ore is mixed with other rocks and impurities which have to be separated using various wet and dry processing methods.

A huge array of kaolin products are available. These vary in plasticity, crystal and surface chemistry, particle shape and size, flow properties, permeability, etc.

Pure kaolin is the clay of choice for bodies that need to be clean and white. Many porcelains contain only a kaolin mix as their clay complement. But kaolins have relatively low plasticity when compared to other raw clay types. Thus in non-casting plastic forming bodies it is often not possible to achieve enough plasticity employing kaolin alone. Additions of ball clays, bentonites and other plasticizers are thus common. Where translucency and whiteness are paramount, highly plastic kaolins and white burning ball clays and bentonites can be used .

Because kaolinite mineral has a much larger particle size than ball clay and bentonite materials blending it with them can produce a good cross section of ultimate particle sizes (this imparts enhanced working and drying properties). Another advantage of the larger particle size of kaolins is that they are much more permeable to the passage of water. Thus kaolins, especially the larger sized ones, speed up casting rates in slurry bodies.

Kaolins are employed in glaze recipes to keep the flint, feldspar, frit and other particles from settling out (the surface chemistry of the particles gives it this ability). At the same time the chemistry of kaolin makes it the primary source of alumina oxide for glazes.

Kaolin is a very refractory aluminum silicate. Kaolin-based bodies are used to make all kinds of refractory parts for industry. Kiln wash is often made from 50:50 mix of kaolin and silica. Cordierite is made mainly from kaolin. High heat duty grogs are made by calcining kaolin.

Kaolin is used in many industries other than ceramics, in fact the ceramics industry uses only a small amount of the total kaolin produced. Kaolin companies tend to be billion-dollar operations and kaolin is used in everything from paper to cosmetics, paint to agricultural products.

See http://www.kaolin.com for more information.

(Richard Willis)

A hydrous-layer alumina-silicate earth, of the ideal form Al₂O₃, 2SiO₂, 2H₂O with a typical empirical analysis of SiO₂ 45.11%, Al₂O₃ 38.99%, Fe₂O₃ 0.46%, TiO₂ 1.46%, CaO 0.12%, MgO 0.04%, K
₂O 0.06%, Na₂O 0.03%, traces 13.97% Principal mineral is kaolinite.
Density: 2.6 Water insoluble Melts at around 1200ºC, depending on impurities, but when mixed with a feldspar their combined alumina content will add refractoriness subsequently holding off the melting point up to 1450º.
To raise the melting point even further a magnesium mineral (talc, dolomite, etc.) can be added, as in “talc porcelain” which is usually a blend of feldspar + kaolin + talc.
Kaolin is the paradigm for a “pure clay”, comprising the minimum natural form of aluminum + silicon + water (even though in its natural, unrefined, form it often has substantial portions of other minerals such as muscovite, quartz, feldspar, and anatase). Because of its purity it fires to white and because of its high refractoriness it can serve as a pillar to hold up surrounding materials as they vitrify — two qualities which, historically, made possible the white translucent ware of China
which became known as porcelain. see clay, clay minerals, Plastic Vitrox, porcelain, stoneware, etc.

Properties

Body Plasticity - Porcelain, Whtieware Bodies
It is possible to make a plastic throwing body using 50% kaolin only, however you must choose one of the highly plastic varieties such as #6 Tile. Even then you will likely need a little bentonite to augment the kaolin. There is a huge range in kaolin plasticities, test for yourself to find out.

Data

Melting Point (MP): 1770C M
Specific Gravity: 2.62
Specific Gravity: 2.62
Melting Point (MP): 1770C M

Suppliers

Generic

Authors

Tony Hansen (Owner)

XML

<?xml version="1.0" encoding="UTF-8"?>
<material name="Kaolin" descrip="Hydrated alumina silicate, Pure clay mineral" generic="1" rawmineral="0" searchkey="China Clay" loi="12.50">
<families>
<family name="Kaolin"/>
</families>
<regions>
<region name="North America"/>
</regions>
<oxides>
<oxide symbol="Al2O3" name="Aluminum Oxide, Alumina" status="" percent="40.210" tolerance=""/>
<oxide symbol="SiO2" name="Silicon Dioxide, Silica" status="" percent="47.290" tolerance=""/>
</oxides>
<volatiles>
<volatile symbol="" name="" percent="12.500" tolerance=""/>
</volatiles>
<references>
<reference name="seealso" reason=""/>
<reference name="seealso" reason=""/>
</references>
<hazards>
<hazard name="Kaolin"/>
</hazards>
<suppliers>
<supplier name="Generic" country="" url="" label=""/>
</suppliers>
<notes>
<note>Kaolin is pure clay mineral crystal of one part alumina and two parts silica (also called China Clay). Most other clay minerals are derivatives of kaolin. Kaolin particles are flat and comparatively the largest of all clay minerals. They have a surface chemistry that gives them an affinity for water. The attached water both \'glues\' particles together and acts as a \'buffer\' to lubricate particle-against-particle movement in the plastic matrix.

Kaolins are whiter and cleaner than other clays because they are mined near the site where they were weathered and altered from the parent rock. Kaolin ore is mixed with other rocks and impurities which have to be separated using various wet and dry processing methods.

A huge array of kaolin products are available. These vary in plasticity, crystal and surface chemistry, particle shape and size, flow properties, permeability, etc.

Pure kaolin is the clay of choice for bodies that need to be clean and white. Many porcelains contain only a kaolin mix as their clay complement. But kaolins have relatively low plasticity when compared to other raw clay types. Thus in non-casting plastic forming bodies it is often not possible to achieve enough plasticity employing kaolin alone. Additions of ball clays, bentonites and other plasticizers are thus common. Where translucency and whiteness are paramount, highly plastic kaolins and white burning ball clays and bentonites can be used .

Because kaolinite mineral has a much larger particle size than ball clay and bentonite materials blending it with them can produce a good cross section of ultimate particle sizes (this imparts enhanced working and drying properties). Another advantage of the larger particle size of kaolins is that they are much more permeable to the passage of water. Thus kaolins, especially the larger sized ones, speed up casting rates in slurry bodies.

Kaolins are employed in glaze recipes to keep the flint, feldspar, frit and other particles from settling out (the surface chemistry of the particles gives it this ability). At the same time the chemistry of kaolin makes it the primary source of alumina oxide for glazes.

Kaolin is a very refractory aluminum silicate. Kaolin-based bodies are used to make all kinds of refractory parts for industry. Kiln wash is often made from 50:50 mix of kaolin and silica. Cordierite is made mainly from kaolin. High heat duty grogs are made by calcining kaolin.

Kaolin is used in many industries other than ceramics, in fact the ceramics industry uses only a small amount of the total kaolin produced. Kaolin companies tend to be billion-dollar operations and kaolin is used in everything from paper to cosmetics, paint to agricultural products.

See http://www.kaolin.com for more information.</note>
<note>A hydrous-layer alumina-silicate earth, of the ideal form Al2O3, 2SiO2, 2H2O with a typical empirical analysis of SiO2 45.11%, Al2O3 38.99%, Fe2O3 0.46%, TiO2 1.46%, CaO 0.12%, MgO 0.04%, K
2O 0.06%, Na2O 0.03%, traces 13.97% Principal mineral is kaolinite.
Density: 2.6 Water insoluble Melts at around 1200&ordm;C, depending on impurities, but when mixed with a feldspar their combined alumina content will add refractoriness subsequently holding off the melting point up to 1450&ordm;.
To raise the melting point even further a magnesium mineral (talc, dolomite, etc.) can be added, as in &#147;talc porcelain&#148; which is usually a blend of feldspar + kaolin + talc.
Kaolin is the paradigm for a &#147;pure clay&#148;, comprising the minimum natural form of aluminum + silicon + water (even though in its natural, unrefined, form it often has substantial portions of other minerals such as muscovite, quartz, feldspar, and anatase). Because of its purity it fires to white and because of its high refractoriness it can serve as a pillar to hold up surrounding materials as they vitrify &#151; two qualities which, historically, made possible the white translucent ware of China
which became known as porcelain. see clay, clay minerals, Plastic Vitrox, porcelain, stoneware, etc.

</note>
</notes>
<testdata>
<testitem testname="2" value="1770C M"/>
<testitem testname="2" value="2.62"/>
<testitem testname="2" value="2.62"/>
<testitem testname="2" value="1770C M"/>
</testdata>
</material>

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