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Moissanite originally referred to a rare mineral discovered by Henri Moissan having a chemical formula SiC and various crystalline polymorphs. Earlier this material had been synthesized in the laboratory and named silicon carbide. Background Mineral moissanite was discovered by Henri Moissan while examining rock samples from a meteor crater located in Canyon Diablo, Arizona, in 1893. At first, he mistakenly identified the crystals as diamonds, but in 1904 he identified the crystals as silicon carbide (SiC).[2][3] The mineral form of silicon carbide was named moissanite in honor of Moissan later on in his life. The discovery in the Canyon Diablo meteorite and other places was challenged for a long time as carborundum contamination from human abrasive tools.[4] Geological occurrence Until the 1950s no other source, apart from meteorites, had been encountered. Later moissanite was found as inclusion in kimberlite from a diamond mine in Yakutia in 1959, and in the Green River Formation in Wyoming in 1958.[5] The existence of moissanite in nature was questioned even in 1986 by Charles Milton, an American geologist.[6] Moissanite, in its natural form, is very rare. It has only been discovered in a small variety of places from upper mantle rock to meteorites. Discoveries have shown that moissanite occurs naturally as inclusions in diamonds, xenoliths, and ultramafic rocks such as kimberlite and lamproite.[4] They have also been identified in carbonaceous chondrite meteorites as presolar grains.[7] In meteorites Analysis of SiC grains found in the Murchison carbonaceous chondrite meteorite has revealed anomalous isotopic ratios of carbon and silicon, indicating an origin from outside the solar system.[8] 99% of these SiC grains originate around carbon-rich Asymptotic giant branch stars. SiC is commonly found around these stars as deduced from their infrared spectra. Composition All applications of silicon carbide today use synthetic material, as the natural material is very scarce. Silicon carbide was first synthesized by Jons Jacob Berzelius, who is best known for his discovery of silicon.[9] Years later, Acheson produced viable minerals that could substitute diamond as an abrasive and cutting material. This was possible as moissanite is one of the hardest substances known, with a hardness below that of diamond and comparable with those of cubic boron nitride and boron. Since naturally occurring moissanite is so rare, lab-grown moissanite is the only commercially viable version of the mineral. More recently, pure synthetic Moissanite has been made from thermal decomposition of the preceramic polymer poly(methylsilyne), requiring no binding matrix (e.g. cobalt metal powder). Physical properties The crystalline structure is held together with strong covalent bonding similar to diamonds,[2] that allows moissanite to withstand high pressures up to 52.1 gigapascals.[2][10] Colours vary widely and are graded in the I-J-K range on the diamond color grading scale.[11] Applications Moissanite has many applications, aside from its traditional use in jewelry as a gem of its own and as a diamond simulant. Because of its hardness, it is useful for high-pressure experiments (e.g., using diamond anvil cell) competing there with diamond.[2] Large diamonds, used for anvils, are prohibitively expensive. Therefore for large-volume experiments, much cheaper synthetic moissanite is a more realistic choice. Synthetic moissanite is also interesting for electronic and thermal applications because its thermal conductivity is similar to that of diamonds.[10] High power SiC electronic devices are expected to play an enabling and vital role in the design of protection circuits used for motors, actuators, and energy storage or pulse power systems.[12] References 1. ^ http://www.webmineral.com/data/Moissanite.shtml Webmineral
* http://www.webmineral.com/data/Moissanite.shtml Retrieved from "http://en.wikipedia.org/" |
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