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{{For|microspheres made of other materials|Microsphere}}
[[Image:Glass_microsphere_in_concrete.jpg|thumb|right|[[SEM]] micrograph of a glass microsphere in [[concrete]]]]

'''Glass microspheres''' are [[microscopic]] spheres of [[glass]] manufactured for a wide variety of uses in [[research]], [[medicine]], [[consumer goods]] and various industries. Glass microspheres are usually between 1 to 1000 micrometers in diameter, although the sizes can range from 100 nanometers to 5 millimeters in diameter.<ref>[http://www.pharmaceutical-technology.com/contractors/lab_equip/whitehouse pharmaceutical-technology.com]</ref> Hollow glass microspheres, sometimes termed '''microballoons''', or '''glass bubbles''' have diameters ranging from 10 to 300 [[micrometre|micrometer]]s.

Hollow spheres are used as a lightweight [[aggregate (composite)|filler]] in [[composite material]]s such as [[syntactic foam]] and [[lightweight concrete]].<ref> [http://www.ces.clemson.edu/earnest/0699pages/16.htm "Whatever Floats Your Boat, Clemson Student Chapter of the American Society of Civil Engineers"] </ref>  Microballoons give syntactic foam its light weight, low [[thermal conductivity]], and a resistance to [[compressive stress]] that far exceeds that of other foams.<ref>Common Microballoons have a density of 0.15 to 0.20 g/cc, with an isostatic crush strength of 300 to 500 psi. Denser, high strength forms offer 0.38 g/cc with 5500 psi strength, and 0.6 g/cc (still offering considerable flotation) with 18,000 psi crush pressure. (see 3m.com data)[http://www.crgrp.net/syntactics.htm crgrp.net]</ref>  These properties are exploited in the hulls of [[submersible]]s and deep-sea oil drilling equipment, where other types of foam would [[Implosion (mechanical process)|implode]].  Hollow spheres of other materials create syntactic foams with different properties, for example ceramic balloons can make a light syntactic [[aluminium]] foam.<ref>[http://www.memagazine.org/backissues/january99/features/foams/foams.html Foams on the Cutting Edge]</ref>

Hollow spheres also have uses ranging from storage and slow release of [[pharmaceutical]]s and [[radioactive tracer]]s to research in controlled [[hydrogen storage|storage]] and release of [[hydrogen]].<ref>[http://www.osti.gov/bridge/product.biblio.jsp?query_id=0&page=0&osti_id=918691 "J.E. Shelby et al. (2007).  A radically new method for hydrogen storage in hollow glass microspheres.  DOE Technical Report FG26-04NT42170.]</ref> Microspheres are also used in composites to fill polymer resins for specific characteristics such as weight, sandability and sealing surfaces. When making surfboards for example, shapers seal the [[Polystyrene#Expanded_polystyrene|EPS]] foam blanks with epoxy and microballoons to create an impermeable and easily sanded surface upon which fiberglass laminates are applied.

Glass microspheres can be made by heating tiny droplets of dissolved [[sodium silicate|water glass]] in a process known as [[ultrasound|ultrasonic]] spray [[pyrolysis]], and properties can be improved somewhat by using an acid treatment to remove some of the [[sodium]].<ref>[http://www.mrs.org/publications/jmr/jmra/1996/nov/p02908.pdf mrs.org]</ref>  Sodium depletion has also allowed hollow glass microspheres to be used in chemically sensitive resin systems, such as long pot life epoxies or non-blown polyurethane composites

Additional functionalities, such as silane coatings, are commonly added to the surface of hollow glass microspheres to increase the matrix/microspheres interfacial strength (the common failure point when stressed in a tensile manner).<ref>[http://www.trelleborg.com/en/Advanced-Engineering-Materials/Products--Solutions/Eccospheres-Glass-Microspheres/ ]. Trelleborg.com </ref>

Glass microspheres are also produced as waste product in coal-fired power stations. Small amounts of silica in the coal are melted and as they rise up the chimneystack, which expands and forms small hollow spheres. These spheres are collected together with the ash, which is pumped in a water mixture to the resident ash dam. Some of the particles do not become hollow and sink in the ash dams, while the hollow ones float on the surface of the dams. They become a nuisance, especially when they dry, as they become airborne and blow over into surrounding areas.

==Dispensing of microspheres==
Dispensing of microspheres can be a difficult task. When utilizing microspheres as a filler for standard mixing and dispensing machines, a breakage rate of up to 80% can occur, depending upon factors such as pump choice, material viscosity, material agitation, and temperature. Customized dispensers for microsphere-filled materials may reduce the microsphere breakage rate to a minimal amount. A [[Progressive cavity pump]] is the pump of choice for dispensing materials with microspheres, which can reduce microsphere breakage as much as 80%.

==See also==
*[[Hydrogen storage]]

==References==
<references/>

==External links==
*[http://www.osti.gov/bridge/product.biblio.jsp?query_id=0&page=0&osti_id=918691 e  	 A Radically New Method for Hydrogen Storage in Hollow Glass Microspheres]
*[http://www.cospheric-microspheres.com/Polyethylene_Microspheres_vs_Glass_Microspheres_s/42.htm Polyethylene Microspheres vs. Glass Microspheres - Properties, Advantages and Applications]
*[http://www.fluidresearch.com/glass_microsphere_movie.php Microsphere Dispensing Movie]

{{Glass science}}

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{{Glass-engineering-stub}}

[[Category:Materials]]
[[Category:Glass chemistry]]
[[Category:Glass types]]
[[Category:Hydrogen storage]]
[[Category:2Fix]]