Kaolin clay is chemically hydrated aluminium silicate and structurally unmodified. Water washed kaolin is made by slurrying the raw clay and then centrifuging or hydrocycloning it to remove impurities. Chemical bleaching is done to improve the brightness of the kaolin before it is then produced into the specific grades. Kaolin has a platy structure, hydrophilic and thus readily water dispersible.
Surface treated kaolin clay is a substrate for chemical surface treatment. The range of treatments is quite varied and application specific. Generally silicone treatments reacted on the kaolin surface to later cross-link with an intended polymer system. Due to the improved chemical bond strength achieved, improved physical & electrical properties of the final product are realized.
The surface of any of our products can be treated with silicones of various types either according to customer requirements or in the form of standard products. By selecting the proper aluminum silicate and applying the appropriate silicone for a given resin or polymer system, new products can be formed with improved dispersion, electrical, hydrophobic and physical properties. In most instances the silicone will act as a coupling agent to give these improvements. This allows the compounder or formulator the use of aluminum silicate advantages in compounds or coatings not ordinarily compatible with aluminum silicates, or additional loading in those already containing aluminum silicates. Our surface treated clays retain the physical and optical characteristics of the clays and gain the ability to improve compound properties. Information on clays treated for specific systems is available on request.
Calcined Kaolin is also called Anhydrous Aluminum Silicates. Calcined clay is made by the thermal treatment of water-washed and bleached kaolin to achieve purity, improved residues, brightness, and achieve a desired particle size distribution, and then subject to calcinations (heat treatment) to effect the anhydrous state through the removal of 14% water of hydration.
Calcined grades differ by method of exposure to heat. Conventional calcined grades are processed in vertical kilns with a substantial period of exposure. The unique calcination method is to flash calcine the material by exposing the feed clay to higher temperatures for only a few seconds duration. Both methods fully remove the water of hydration, but effect different particle shapes, specific gravity, and optical characteristics.
Low-temperature calcination, at about 650-700ºC, removes structural hydroxyls and forms amorphous metakaolin. Specific gravity is reduced from 2.58 to about 2.50 in the process, while hardness and porosity, and thus brightness, opacity and oil absorption, are increased. Fully calcined clays, with maximum brightness and opacity, are produced in the 1000-1150ºC range. This is hot enough to totally collapse the amorphous structure, with a consequent increase in specific gravity to 2.6-2.7, without causing the mineralogical transformation to mullite (specific gravity 3.2, hardness 6-7). The balance of opacity and sheen derived from calcined clays can be manipulated by the temperature, rate of heating and fluxes used in the calcination process.
The primary use of kaolin in coatings is as a TiO2 extender in waterborne architectural paints. Calcined clays generally provide the best brightness, TiO2 extension and dry hide. Water-washed and delaminated grades also contribute to extension and dry hide, as well as covering power and gloss control (finer particle size = higher gloss).
Brown clay is a mineral similar to kaolin clay, with a soft consistency and earthy texture. It is easily broken and can be molded or shaped, especially when wet. Brown clay is a lackluster and uninteresting mineral on its own. As one of the most common clay mineral, its darker brown color or sometimes orange or reddish-brown tone is due to iron oxide impurities.
Hard clay is relatively poorly crystallized, very fine grained kaolin which is about 1 micron median particle size by sedimentation and high surface area. It provides reinforcement in rubber, resulting in hard compounds.