A) Boron nitride is very hard material
B) It has planar structure
C) It is less harder than boron carbide
D) Boron nitride is isomorphous with diamond
Correct Answer: A
Solution :
Boron nitride has not been found in nature and therefore is produced synthetically. Hexagonal boron nitride is obtained by the reactivity boron tiroxide \[{{B}_{2}}{{O}_{3}}\] or boric acid \[\left[ B\left( O{{H}_{3}} \right) \right]\] with ammonia \[\left( N{{H}_{3}} \right)\] or urea \[\left[ Co{{\left( N{{H}_{2}} \right)}_{2}} \right]\] in a nitrogen atmosphere. \[{{\operatorname{B}}_{2}}{{O}_{3}}+2N{{H}_{3}}\,\xrightarrow{{}}\,\,2BN+3{{H}_{2}}O\,\,(T=900{}^\circ C)\] \[\operatorname{B}{{\left( OH \right)}_{3}} + 2N{{H}_{3}} \xrightarrow{{}}\,\,BN + 3{{H}_{2}}O \,\left( T= 900{}^\circ C \right)\]\[{{\operatorname{B}}_{2}}{{O}_{3}} + CO{{\left( N{{H}_{2}} \right)}_{2}} \xrightarrow{{}} 2BN + C{{O}_{2}} + 2{{H}_{2}}O\] \[\left( T>1000{}^\circ C \right)\] \[{{\operatorname{B}}_{2}}{{O}_{3}} + 3Ca{{B}_{6}} + 10{{N}_{2}}\,\to \,\,20BN + 3CaO\]\[\left( T>1000{}^\circ C \right)\]
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