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Coatings Xperience: functionalzing micropheres with coating technology.

Hollow microspheres have been on the market for a number of years and find uses in the paint and coating industry as fillers and extenders, and for other functions such as reducing the density of concrete and as a buoyancy aid in shipbuilding. Adding a coating to microspheres increases their functionality and broadens their application potential. Edinburgh's Microsphere Technology Ltd. (MTL) has been exploring these opportunities.


"The idea of coating hollow microspheres is relatively new," states MTL senior scientist David Nichols. "With our coatings we can add a wide variety of properties to the beads, such as conductivity or fluorescence. With these added features, the microspheres are transformed from inactive additives to functional ingredients."


Microsphere Technology coats borosilicate glass microspheres and aluminosilicate ceramic cenospheres with coatings based on metals, metal oxides, pigments, and dyes. The glass microspheres range in size form 5 to 100 microns, with most being under 50 microns. Cenospheres, which are formed from fly ash waste, are generally larger and are available up to 300 microns, but tend to have more variation in size and irregularities on their surfaces.


With its technology, the company can closely control the thickness of the coating form a few nanometers to several microns. Microspheres of a certain size and density can be produced with a specified coating at a given thickness that is robust and continuous. "We do a lot of custom work," notes Nichols. Because the coated microspheres have only been on the market for a short time, the folks at MTL have not yet identified all of the potential applications. In addition, customers often do not reveal the end use they have in mind, either.


Microsphere Technology does have several customers in the water treatment sector that have reported that titanium dioxide-coated glass beads work well as replacements for nanopowdered products. Titanium dioxide is a known photocatalyst and is used to break down many organic and inorganic pollutants as well as destroy microorganisms in wastemater. Traditional titania nanopowders are very difficult to recover, though. Photospheres [R] from MTL, however, are buoyant, filterable, reusable, and have shown excellent photocatalytic activity against a range of water industry relevant organic and gaseous pollutants, according to Nichols.

Coated microspheres are also attracting interest from scientists involved in flow visualization. MTL has developed a range of products with the trade name Isopheres [R] that are designed for use in the experimental fluid dynamics industry. "Microspheres are available with either light scattering or fluorescent properties and come in densities designed specifically for this application," Nichols notes.

In addition to coatings of titanium dioxide, MTL can produce microspheres with other inorganic and organic pigments. Other pigments that have been used include carbon black, iron oxides, and chromium (III) oxide. Organic pigments from several difference chemical structure families can also be coated onto the hollow microspheres, extending the range of possible colors. "These coated beads provide lightweight pigments that can be used in a number of applications including aerospace and automotive paints and personal care products," Nichols comments.

Micropheres coated with metals including silver, copper, gold, nickel, and iron exhibit the properties of solid metal particles, but with a substantial weight savings. There is also a significant cost savings because much less expensive raw materials are required.

Interesting properties of metal-coated microspheres include high thermal conductivity, high electrical conductivity, mechanical strength, electromagnetic absorption, and ferromagnetism. They can be used in a variety of industries, from electronics to paints.

Ferrospheres[TM] are buoyant, superparamagnetic iron oxide-coated microspheres that possess and amine functionalized surface for the conjugation of antibodies and other ligands. "Ferrospheres are the ideal substrate for recovery of low concentration analytes from large sample volumes," says Nichols. On standing they float to the surface or, in a sample containing lots of particulate matter, they can be cleanly separated from debris by centrifugation.

Conductospheres[TM] are hollow glass microspheres with a silver coating that makes them highly electrically conductive. According to Nichols, they are considerably lighter than solid silver particles and are ideal for use in paints, adhesives, and composites, where they can provide electrical conductivity or shielding against electromagnetic interference (EMI).

Recently, Trellborg Engineered Systems signed an intellectual property license agreement with MTL that is values at over $1 million. Trelleborg will use MTL's low density pigment technology in aircraft paints, specifically with the goal of weight reduction and the subsequent advantage of savings in fuel consumption and lower [CO.sub.2] emissions. "We look forward to working closely with Trelleborg to move the technology towards the market as rapidly as possible," says MTL operations director Tom Johnston.

Microsphere Technology has also been focusing more attention on the market in the U.S. Recently, the company arranged for Sphere Services Inc. (SSI) and EPOCH Technical Services, Inc. (ETS) to provide sales and marketing services in North America for ML's line of conductive microspheres. The decision is part of the company's strategy to integrate its capability for custom design of coated microspheres with the expertise of various partners in relevant fields of application, according to MTL director John Bamforth.

Nichols aggress that both the Trelleborg deal and the establishment of a presence in North America through the agreement with SSI/ETS are critical steps for MTL. "With such a new technology, it is imperative that we develop successful partnerships with customers in various market sectors. Through these partnerships, we will be able to speed up commercialization of our intellectual property and bring products to the global market much more quickly. And the paint and coatings sector is one we review as having significant potential and will continue to receive our attention going foward."
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Publication:JCT CoatingsTech
Date:Oct 1, 2008
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