Boron carbide powder synthesis

Question 1

How is BC powder synthesized?

Answer 1

1. boron oxide and graphite react endothermically to form boron carbide: 2B2O3 + 7C –> B4C + 6CO
2. brickets of B2O3-C mixtures are heat-treated in an electric arc or tube furnace at 220-2500C to facilitate the rxn
3. the product mass is then crushed to hot press or sinter grade, with chemical treatment to remove impurities from milling. Because of the high hardness of B4C, this is an expensive step

Question 2

What is an alternate synthesis route?

Answer 2

~ B4C can also be formed via self-heating synthesis (SHS) by igniting the highly exothermic rxn: 2B2O3 + 6Mg + C –> B4C + 6MgO
–> unreacted Mg and MgO product are removed by washing in H2SO4 or HCl and then hot water

Question 3

What are the characteristics of boron carbide?

Answer 3

~ covalently bonded compound with high Tm (2400C), extremely high hardness, low density, and high neutron absorption cross section

~ it is a solid soln over the range of B(10.4)C-B(4)C

Question 4

What is the structure of boron carbide?

Answer 4

~ based ona rhombohedral unit cell

~ composed of 12 atoms icosahedral clusters linked by direct covalent bonds, and through 3-atom intericosahedral chains