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Halloysite


Halloysite

During the weathering of intrusive rocks a process known as “kaolinization” occurs wherein the sodium feldspar breaks down into kaolin group minerals – kaolinite and halloysite. Both are hydrated aluminosilicate minerals. Halloysite (Al2Si2O5(OH)4 2H2O) is identical to kaolinite (Al2Si2O5(OH)4 ) except halloysite has non-structural water intercalated between the aluminosilicate layers. Both halloysite and kaolinite initially occur as platelets, but imperfections in the crystal lattice of the halloysite due to interference of the interlayer of water causes a misfit between different aluminosilicate layers which in turn causes the halloysite platelet to roll up into a tubular form referred to as halloysite nanotubes or HNTs.

The value of HNTs is determined by the aspect ratio (the ratio of the length of the HNT to the diameter) and a lack of impurities. I-Minerals will produce two halloysite products HalloPure (70% halloysite 30% kaolinite) and Ultra HalloPure (+90% halloysite <10% kaolinite). Our HalloPure products have an aspect ratio few other deposits can rival. The largest producer in the world also has a halloysite with an excellent aspect ratio, but the halloysite is reported to contain cristobalite, a carcinogen which precludes its use in the high value life science applications, while other producers have some combination of a low aspect ratio or excessive heavy metals such as iron. HNTs can be as long as 10 microns with the diameter generally in the order of 10’s of nanometers. HNTs with a high aspect ratio and low levels of deleterious minerals are more highly sought after and are more valuable as they can be used in a wider range of applications.

Uses

Halloysite has historically been used in the manufacture of porcelain, bone china, and fine china. In these applications the combination of the tubular shape in clay with low iron and titanium content produces ceramic ware with exceptional whiteness and translucency. Its fine particle size enables halloysite to also be used as a suspension agent in glaze preparations as well as in filters and inkjets.

HNTs can be coated with metallic and other substances to achieve a wide variety of electrical, chemical, and physical properties. The hollow tube of HNTs can be filled with a variety of active ingredients including those used for cosmetics, household and personal care products, pesticides, pest repellents, pharmaceuticals and other agents that could benefit from extended release. I-Minerals’ HalloPure products low initial levels of trace elements provides a strong starting point for further purification to meet the stringent requirements of the pharmaceutical and cosmetic industries while the high aspect ratio adds strength in plastics and polymers applications.

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