Nomenclature
CAS number: 12069-32-8
Norbide.
CB
4; mol wt 55.25.
C 21.74%, B 78.27%.
B
4C.
Description and references
Usually prepd in an electric furnace at 2500°
according to the equation 2B2O3 + 7C → B4C + 6CO: Ridgway, Trans. Electrochem.
Soc. 66, 117-133 (1934); also formed by reducing
boric anhydride with magnesium in the presence of carbon: Dawihl, DE 752324 (1942 to Krupp); BIOS rept. no. 925, p 22 (1947). Lab prepn by
the reduction of boron trichloride with hydrogen in the presence of
carbon or hydrocarbons: Bell Labs. Record 28, 477 (1950). Comprehensive monograph: P. W. Gilles
in Adv. Chem. Ser. 32, entitled “Borax to Boranes,” D. L. Martin, Ed. (ACS, Washington,
DC, 1961).
Properties
Black shiny rhombohedra or octahedra. d425 2.508-2.512. mp 2350° (no decompn); bp >3500°.
Its hardness is less than that of industrial diamonds, but higher
than the hardness of silicon carbide: ca 5,000 kg/mm2,
on Mohs' hardness scale = 9.3. Less brittle than most ceramics.
Remarkably resistant to chemical action. Not attacked by hot HF,
HNO3 or HCrO4. Decomposed by molten alkalis
at red heat. Does not burn in oxygen flame.Use
Abrasive. In the manuf of hard and chemicals-resistant
ceramics or wear-resistant tools. Finely pulverized B
4C can be molded under (considerable) pressure and heat.