Silicon boride

Silicon borides (also known as boron silicides) are lightweight ceramic compounds formed between silicon and boron. Several stoichiometric silicon boride compounds, SiB_n, have been reported: silicon triboride, SiB₃, silicon tetraboride, SiB₄, silicon hexaboride, SiB₆, as well as SiB_n (n = 14, 15, 40, etc.). The n = 3 and n = 6 phases were reported as being co-produced together as a mixture for the first time by Henri Moissan and Alfred Stock in 1900 by briefly heating silicon and boron in a clay vessel. The tetraboride was first reported as being synthesized directly from the elements in 1960 by three independent groups: Carl Cline and Donald Sands; Ervin Colton; and Cyrill Brosset and Bengt Magnusson. It has been proposed that the triboride is a silicon-rich version of the tetraboride. Hence, the stoichiometry of either compound could be expressed as SiB_{4 - x} where x = 0 or 1. All the silicon borides are black, crystalline materials of similar density: 2.52 and 2.47 g cm, respectively, for the n = 3(4) and 6 compounds. On the Mohs scale of mineral hardness, SiB_{4 - x} and SiB₆ are intermediate between diamond (10) and ruby (9). The silicon borides may be grown from boron-saturated silicon in either the solid or liquid state.