White Kaolin Clay
White kaolin is a versatile clay that forms naturally all over the world through the weathering of rocks that contain high amounts of feldspar, but can also be created by the hydrothermal alteration of similar rocks before they weather naturally.
Its most valuable characteristic is its pure colouration, which is used in the manufacturing of paper to improve gloss, smoothness, brightness, and opacity; in porcelain china and ceramics; in paints as an inert, functional extender with desirable flow properties; as a cost-effective filler for natural and synthetic rubber products to make them extrude more easily; in low or medium voltage PVC wires and cables to improve impact strength and electrical performance; and more. Kaolin as metakaolin also increases the strength of concrete for construction purposes and can be used in seed coverings and urea fertilizers to help retain granularity and prevent caking.
- Reduces the need for feldspar
- Pure colouration
- Improves the appearance and printability of paper
- Reduces the amount of pigment needed in paints when used as an extender
- Improves the physical durability of paint film
- Improves the strength and abrasion resistance of rubber
- Increases strength and electrical resistance of wiring and cables
- Increases seed size and plant ability as a seed coating
In its natural state, kaolin clay is a soft, white powder made primarily of kaolinite with particles of varying sizes. The particles are hexagonal and platy crystals that range from .1 micrometres to 10 micrometres or larger. They can be ordered or disordered.
Disordered kaolinite dehydroxylates between 530° C and 570° C. Ordered kaolinite dehydroxylates between 570° C and 630° C. Dehydroxylation is the removal of the O-H molecule within the clay through the formation of a water molecule. This is achieved through heat and causes a loss of the crystalline structure of the clay.
Pure kaolin clays fire to maturity at around 1800° C, so they are often mixed with other types of clay in order to increase their workability and bring the firing temperature down. This process lowers the energy needed to use kaolin clay in manufacturing and can lower other production-related costs by making the clay easier to work with.
- Particle size .1 micrometres to >10 micrometres
- Hydroxylates between 530° C and 630° C
- Fires at 1800° C
Kaolin is a naturally white clay that is mostly made up of a layered silicate mineral called kaolinite. It is commonly known as china clay because it was mined from a hill called Kao-Ling in China for centuries, where it was used to make whiteware. The fine particle size and pure colour were highly sought after for the manufacture of the fine porcelain we call “china” today.
Since then, it has been discovered that kaolin can be found around the world, and the deposits in China are not of the highest quality because they aren’t quite as pure as deposits found in some other countries. Deposits in the United States, the United Kingdom, and Brazil boast rare quality and purity, providing premium whiteness, viscosity, and other favourable characteristics that provide peak performance in any number of white kaolin clay applications.
White kaolin clay is made naturally through the weathering of aluminosilicate minerals, typically rocks rich in feldspar, and this process can be reproduced through hydrothermal alteration. Hydrothermal alteration recreates the natural weathering process to make synthetic white kaolin. Depending on the rock that is used, sodium, potassium, calcium, magnesium, iron, and other ions need to be leached from the material through the hydrothermal alteration process to form kaolinite.
White kaolin is high in alumina or aluminium oxide, an abrasive-resistant material that lends its hardness and strength to the kaolin, and is a refractory material because it fires at such a high temperature. When fired to only 800° C, it forms metakaolin, which is used to increase the strength of concrete. When fired to 1100° C, it forms calcined kaolin, which is denser, more opaque, whiter, more porous, and has sharper and harder particles. Full firing is done at temperatures near 1800° C.
White kaolin clay is known by many other names in English and languages around the world. Some of these names include argile de chine, argilla, bolus alba, caolin, china clay, heavy kaolin, hydrated aluminium silicate, kaolin leger, kaolin lourd, light kaolin, porcelain clay, silicate d’aluminium hydrate, white bole, and terre a porcelain.
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