Meta kaolin is the waterless calcined version of a mineral called kaolin clay or Kaolinite. Also known as china clay, Kaolinite is generally used in porcelain manufacturing. Metakaolin’s particle size is tinier than the particle size of cement. However, it is not as good as silica fumes in quality. Below is more information regarding Kaolinite, metakaolin and the thermal treatment in which it is converted from Kaolinite.
What is Kaolinite/Kaolin Clay?
First thing first, we have to discuss Kaolinite as the basic material of metakaolin. It is a clay mineral, and its composition is Al2Si2O5(OH)4. The silicate mineral coming in layers is particularly important in the mineral industry.
Historically, “kaolin” got its name from the word “Gaoling” (meaning “high ridge“), a village situated near Jingdezhen in Jiangxi Province, southeastern China. Some French missionaries brought it to England in 1727, and there it was known as “kaolin” for the first time.
Coming in a soft, earthy, white color, Kaolinite does not easily shrink and swell. It is chemically produced based on weathers by aluminosilicate minerals such as feldspar. In most parts of the world, Kaolinite comes in red with a touch of orange and pink, leaving a unique rustic hue. The mineral’s alternating layers can also be discovered at Providence Canyon State Park in Georgia, the US. Kaolin in commercial use comes in partly dry noodles, dry powder, or liquid suspension.
What is Meta Kaolin?
Also known as “calcined kaolin“, meta kaolin is a powdery white mineral with no plastic content. Basically, raw Kaolinite is heated on a thermal treatment to remove its crystal water element, making up 12% of the mineral. With the bisque firing method, you can heat raw powdered Kaolinite to convert it into calcined kaolin. The powder is put in a tiny bisque vessel and slow ramp to let the heat penetrate it evenly. It is a good example of mineralogy alteration while still maintaining its chemical components.
The process of calcination results in whiter powder and more chemical elements. It is what makes it more useful in plenty of industries, though. However, it remains underrated in the traditional tiling industry as many people are still unaware of its true values. Kaolinite is a pure clay mineral with its Al2O3 and SiO2 being chemically fired, but its raw crystals are 12% hydrated. Therefore, they still contain plasticity.
The composition of Al2O3 is significant to the large variety of kaolin glazes. Due to its requirement of SiO2, it should supply and decompose in the melting process. An alternative to the Al2O3 composition with high melting capability and affordability is feldspar mineral even though it also supplies much KNaO composition.
Raw Kaolinite also gives off the properties of suspension to the glaze liquid mixture. It also hardens the dry layers of glaze. Nonetheless, there is a little problem with raw kaolin, i.e. when the percentages have reached 20% on one recipe, the shrinkage level becomes too high, making the layers easily curl and crack. In that case, partly substituting raw kaolin to produce calcined kaolin may solve the problem.
In addition to reducing cracking, shrinking and curling, the solution can also maintain the glaze chemistry. It makes the properties controlling the glaze liquid mixture possible without changing the fired melt chemistry. Certainly, mixing the calcined and raw kaolin materials must be involved in this case (12% less calcined material is required here).
The Thermal Treatment Process
As mentioned previously, meta kaolin is a result of a calcination process, or in other words, it is converted from kaolinite/kaolin clay by a thermal treatment. The optimal parameters of which dehydroxylation is accomplished are the temperature of 650 °C as well as 90 minutes of heating duration.
This conversion is confirmed by thermally treated samples of Kaolinite and Chapelle tests. A obtained value of 0.65 g Ca (OH)2/g of the calcination result indicates that the metakaolin produced can be used as an extender to cement materials.
Metakaolin’s reactivity and quality strongly rely on the raw materials used. This mineral can be produced from various sources that contain Kaolinite, including:
- Highly pure deposits of Kaolinite
- Pure tropical soils in lower levels
- Waste of paper sludge that contains Kaolinite
- Oil sand that also contains Kaolinite
The Advantages & The Uses
There are several advantages and uses to the calcination process (a.k.a. thermal treatment), such as:
- Improving flexible and compressive strengths
- Reducing the potential for the state of efflorescence
- Reducing permeability
- Increasing resistance against chemical attacks
- Declining effects of the reactivity of alkali-silica minerals (ASR)
- Improving durability
- Reducing shrinkage, because of the “particle bulking,” leaving the concrete appears denser.
- Enhanced capability to work and finishing result of the tiles.
- Improvement of the colors by lightening the colors of concrete.
Meanwhile, speaking of uses, below are the points that should be highlighted from metakaolinite common uses:
- Lightweight concrete with high quality and durability
- Poured-mold and formed concrete
- High quality cement products (including fiber and Ferro cement)
- Reinforced tile or concrete with glass fiber material
- Countertops, kitchen islands, artistic sculptures, and many more
- Plaster and mortar for the walls, decks, etc.
Pozzolanic additive and metakaolinite are minerals that may occur because of the calcination process of kaolin clay. If it is expected to achieve optimal results, the thermal treatment should be set up to 650 °C of temperature within approximately 90 minutes. The degree of dehydroxylation suggested being also reached 0.97.
Apart from the uses mentioned above, calcined kaolin is also useful in refractory furniture, the composition of permeable ceramic, thermal insulant bodies and slip plasticity shrinkage or what is known as engobes. For additional information, engobes consist of higher grades of clay minerals. Hence, they can substitute raw kaolin parts that are being cooled or dried while getting the fired properties maintained.
Therefore, you can contact a trusted company that runs in the ceramics industry to get the best result of converting kaolin clay into meta kaolin as an extender of cement. The products have usually been thermally treated optimally and with the best prices as well.