Preparation Of Boron
Boron is a relatively rare element, accounting for only 0.0010% of the Earth’s crust by
mass. Nevertheless, boron is readily available because it occurs in concentrated
deposits of borate minerals such as borax, Na2B4O7 · 10 H2O.
Elemental boron can be prepared by the high-temperature reduction of B2O3 with
magnesium, but the product is impure and amorphous:
B2O3(l) + 3Mg(s) 2B(s) + 3MgO(s)
High-purity, crystalline boron is best obtained by the reaction of boron tribromide
and hydrogen on a heated tantalum filament at high temperatures:
2BBr3(g) + 3H2(g) 2B(s) + 6HBr(g)
Crystalline boron is a strong, hard, high-melting substance (mp 2075 °C) that is
chemically inert at room temperature except for reaction with fluorine. These properties
make boron fibers a desirable component in high-strength composite materials
used in making sports equipment and military aircraft.