Title: Boron Carbide
CAS Registry Number: 12069-32-8
Additional Names: Norbide
Molecular Formula: CB4
Molecular Weight: 55.25
Percent Composition: C 21.74%, B 78.27%
Line Formula: B4C
Literature 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.
Melting point: mp 2350° (no decompn)
Boiling point: bp >3500°
Density: d425 2.508-2.512
Use: Abrasive. In the manuf of hard and chemicals-resistant ceramics or wear-resistant tools. Finely pulverized B4C can be molded under (considerable) pressure and heat.