Boron Carbide Carbon Quasi-Hexaboride

Although the chemical formula for this compound is often written B4C, crystallographic studies have shown that it is actually B(CB6)2, or alternatively, B12(CBC).That is, the structure contains 13 B atoms for every 2C, so it is nearly a hexaboride (Lee et al., 1991). 

The hardness of boron carbide (carbon hexaboride) is not well defined because it is made as sintered compacts which have variable densities, compositions, and defect densities. It is very hard (up to 4400kg/mm2), and of relatively low density, so it has been used extensively as body-armor (McColm, 

Its hardness is associated with its B-C bonds (1.64A) and the C-B-C group (stronger than pure B-B bonds 1 = 1.75 A). 

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