Cenosphere
A cenosphere is a lightweight, inert , hollow sphere of microscopic dimensions, composed primarily of silicon dioxide and aluminum oxide . This is filled with air or inert gas. More general terms are hollow microsphere , microsphere or in English Microsphere , Cenosphere .
They are typically created as a by-product of the combustion of coal in thermal power plants . The color of cenospheres varies from gray to largely white. Their densities are roughly in the range 0.4-0.8 g / cm³ so that they have a significant buoyancy in water .
Cenospheres are hard and stiff, light, water-resistant, non-toxic, and insulating. This makes them most useful in a wide variety of productions, especially as a filler . For example, cement is turned into lightweight concrete by adding cenospheres . More recently, they have also been used as fillers for metals and polymers in order to obtain lightweight mixtures from them, which, however, have a significantly higher strength than e.g. B. have foams . The term syntactic foam was coined as a name . When paired with aluminum , the vehicle construction sector has already established areas of application.
Silver- coated cenospheres are used for electrically conductive coatings, tiles and fibers. Another area of application is conductive paint for antistatic coatings and for electromagnetic shielding.
Origin of the term
The word cenosphere is derived from the two Greek words kenos (hollow, empty) and sphaera (sphere) and thus means "hollow sphere".
Manufacturing
When coal is burned in a thermal power station, fly ash is produced , which contains ceramic particles, most of which consist of aluminum and silicon oxide. These arise at temperatures between 1500 and 1750 ° C in a physico-chemical process. Their chemical composition and structure varies greatly and is determined by the composition of the coal used for combustion.
These ceramic particles of the fly ash are divided into three structural categories. The first part of the particles is massive and is called precipitator in English . The second type, which is hollow, is called the cenosphere. The third category are plerospheres , which are also hollow particles, but so large in diameter that they in turn can be filled with smaller precipitators and cenospheres.
Fuel and oil cenospheres
The definition of cenospheres has changed over the past 30 years. Up to and including the 1990s, this only meant a carbon sphere, such as is produced when combustion under oxygen deficiency (fat combustion) of droplet-like gasified liquid fuels that had been cooled to a temperature of less than 200 ° C before they were used. These cenospheres of fuel each indicated that an injection unit was used for the combustion process, which produces drops, or for the open combustion of heavy liquid fuels such as asphalt or thermoplastics activated under heat and bubble formation. The bursting of the bubbles resulted in flammable drops. This definition is still used today in environmental analysis with the microscope. In this way, a distinction can be made between imperfect combustion of liquid fuels and high-temperature fly ash, as is the case with complete combustion of fuels with inorganic admixtures. Cenospheres made from fuel are always black.
The refractory cenosphere according to the above definition is synonymous with the English microballon or the glass microsphere, while at the same time it is different from the old definition of the fuel cenosphere. The use of the term cenosphere instead of microballon is widespread.
Individual evidence
- ↑ About our Products: Silver Coated Cenospheres . Archived from the original on July 28, 2013.
- ^ Walter C. McCrone, Ronald G. Draftz, John Gustav Delly: The Particle Atlas . Ann Arbor Science Publishers, 1967, p. 349.
- ↑ Philip K. Hopke: Receptor Modeling in Environmental Chemistry . Wiley-Interscience, 1985, pp. 43-44.
- ↑ cenospheres from Diesel Fuel . Microlabgallery.com. Retrieved May 29, 2013.
- ↑ George S. Brady, Henry R. Clauser: Materials Handbook , Eleventh. Edition, McGraw-Hill, 1979, p. 490.