Silicon Carbide
524
SILICON CARBIDE
Vol. 22
SILICON CARBIDE
1. Introduction
Silicon carbide [409-21-2] (SiC) is a technologically important material that is one of the small number of unusual materials that were first created synthetically and then subsequently discovered in nature. Silicon carbide was first observed in its natural form in 1905 by the Nobel-prize-winning chemist Henri Moissan, who discovered it in the meteor that created the Diablo Canyon in Arizona. The transparent mineral, now known as moissanite [12125-94-9], is almost as brilliant and as hard as diamond and is therefore often used as a gemstone. The color of SiC depends strongly on the level of impurities ranging from colorless and transparent for the pure form through pale yellow to dark black for very impure specimens. To date, SiC has been found to occur in nature in only minute quantities, and therefore, for practical purposes, all SiC used today is synthetic. The first artificial synthesis of SiC in 1891 is usually attributed to Edward Acheson who unexpectedly discovered small black crystals of SiC in an electrically heated melt of carbon and alumina (1). The subsequent refinement of this technique (the so-called Acheson process) led to the commercial production of large volumes of small SiC crystals (ground into powder form) for use as an industrial abrasive (2). The commercial product, which is made in an electric furnace, is usually obtained as an aggregate of iridescent crystals. The iridescence is
Kirk-Othmer Encyclopedia of Chemical Technology. Copyright John Wiley & Sons, Inc. All rights reserved.
Vol. 22
SILICON CARBIDE
525
caused by a thin layer of silica produced by superficial oxidation of the carbide. The loose black or green grain of commerce is prepared from the manufactured product by crushing and grading for size. Although Acheson’s 1891 experiments are credited with being the first known synthesis of SiC, work about 10 years earlier had produced tetratomic radicals of
SILICON CARBIDE
Vol. 22
SILICON CARBIDE
1. Introduction
Silicon carbide [409-21-2] (SiC) is a technologically important material that is one of the small number of unusual materials that were first created synthetically and then subsequently discovered in nature. Silicon carbide was first observed in its natural form in 1905 by the Nobel-prize-winning chemist Henri Moissan, who discovered it in the meteor that created the Diablo Canyon in Arizona. The transparent mineral, now known as moissanite [12125-94-9], is almost as brilliant and as hard as diamond and is therefore often used as a gemstone. The color of SiC depends strongly on the level of impurities ranging from colorless and transparent for the pure form through pale yellow to dark black for very impure specimens. To date, SiC has been found to occur in nature in only minute quantities, and therefore, for practical purposes, all SiC used today is synthetic. The first artificial synthesis of SiC in 1891 is usually attributed to Edward Acheson who unexpectedly discovered small black crystals of SiC in an electrically heated melt of carbon and alumina (1). The subsequent refinement of this technique (the so-called Acheson process) led to the commercial production of large volumes of small SiC crystals (ground into powder form) for use as an industrial abrasive (2). The commercial product, which is made in an electric furnace, is usually obtained as an aggregate of iridescent crystals. The iridescence is
Kirk-Othmer Encyclopedia of Chemical Technology. Copyright John Wiley & Sons, Inc. All rights reserved.
Vol. 22
SILICON CARBIDE
525
caused by a thin layer of silica produced by superficial oxidation of the carbide. The loose black or green grain of commerce is prepared from the manufactured product by crushing and grading for size. Although Acheson’s 1891 experiments are credited with being the first known synthesis of SiC, work about 10 years earlier had produced tetratomic radicals of