Name/Title
Silicon CarbideEntry/Object ID
78.63.211Description
Chemical Composition: SiC
Crystal System: Hexagonal System
Description: Common Name: Carborundum (trade name)
Group Name: Silicon carbide (SiC),
Location: Tacoma, Washington
Chemistry: Carbon and Silicate
Description: Delmar described this specimen as a large, prickly piece of man-made 'Carborundum', a trade name. Colors: Bladed and long crystals in a deep green (almost black) with rainbow sheen. Used as a abrasive.
PHYSICAL CHARACTERISTICS:
Silicon carbide exists in about 250 crystalline forms. The polymorphism of SiC is characterized by a large family of similar crystalline structures called polytypes. They are variations of the same chemical compound that are identical in two dimensions and differ in the third. Thus, they can be viewed as layers stacked in a certain sequence.
Alpha silicon carbide (a-SiC) is the most commonly encountered polymorph; it is formed at temperatures greater than 1700 °C and has a hexagonal crystal structure (similar to Wurtzite). The beta modification (ß-SiC), with a zinc blende crystal structure (similar to diamond), is formed at temperatures below 1700 °C. Until recently, the beta form has had relatively few commercial uses, although there is now increasing interest in its use as a support for heterogeneous catalysts, owing to its higher surface area compared to the alpha form.
Density (g/cm3) 3.21
Thermal conductivity (W/cm·K) 3.6 3.7 4.9
Pure SiC is colorless. The brown to black color of industrial product results from iron impurities. The rainbow-like luster of the crystals is caused by a passivation layer of silicon dioxide that forms on the surface.
The high sublimation temperature of SiC (approximately 2700 °C) makes it useful for bearings and furnace parts. Silicon carbide does not melt at any known pressure. It is also highly inert chemically. There is currently much interest in its use as a semiconductor material in electronics, where its high thermal conductivity, high electric field breakdown strength and high maximum current density make it more promising than silicon for high-powered devices. SiC also has a very low coefficient of thermal expansion (4.0 × 10-6/K) and experiences no phase transitions that would cause discontinuities in thermal expansion.
Hardness: 9 Corundum
Luster: Metallic
Occurrence: Naturally occurring moissanite is found only in minute quantities in certain types of meteorite and in corundum deposits and kimberlite. Virtually all the silicon carbide sold in the world, including moissanite jewels, is synthetic. Natural moissanite was first found in 1893 as a small component of the Canyon Diablo meteorite in Arizona by Dr. Ferdinand Henri Moissan, after whom the material was named in 1905. Moissan's discovery of naturally occurring SiC was initially disputed because his sample may have been contaminated by silicon carbide saw blades that were already on the market at that time.
While rare on Earth, silicon carbide is remarkably common in space. It is a common form of stardust found around carbon-rich stars, and examples of this stardust have been found in pristine condition in primitive (unaltered) meteorites. The silicon carbide found in space and in meteorites is almost exclusively the beta-polymorph. 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; 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.
Specific Gravity: 3.21
Variety: Because of the rarity of natural moissanite, most silicon carbide is synthetic. It is used as an abrasive, and more recently as a semiconductor and diamond simulant of gem quality. The simplest manufacturing process is to combine silica sand and carbon in an Acheson graphite electric resistance furnace at a high temperature, between 1600 and 2500 °C.Collection
Delmar Smith Mineral CollectionAcquisition
Accession
78.63Source or Donor
Delmar Smith Crystal CollectionAcquisition Method
DonationDimensions
Width
5-3/16 inDepth
3 inLength
9-3/8 inDimension Notes
Dimension taken at widest pointsLocation
Category
PermanentMoved By
Curtis GardnerDate
May 24, 2023Notes
Added current locationLocation
Container
CenterDrawer
BottomShelf
Right, RightWall
NorthBuilding
Founders RoomCategory
PermanentMoved By
Ray BlohmDate
February 20, 2012
