Uhp Synthesis And Research Of B-C-N Superhard Material

In this thesis, structures and properties of the B-C-N composite were theoreticallyand experimentally investigated. Three possible crystal structures of BC₄N were studiedby first principles calculaition. A new kind B-C-N composite, which containes B-C-Nphase, diamond phase, c-BN phase and w-BN phase, was synthesized with hightemperature and high pressure technique. The hardness of B-C-N composite is higher thanthe c-BN.The three possible crystal structures of BC₄N were found: Diamond-like BC₄N-1,Diamond-like BC₄N-2and R-BC₄N. All the structures can steadily exist because they allhave lower energy and satisfy the criteria for mechanical stability and dynamical stability.The three crystals’ hardness are respectively calculated to be64.2GPa,50.1GPa and46.8GPa by microscopic theoretical model of hardness, which shows that the B-C-Ncompounds with three crystal structures are superhard material. XRD spectra ofDiamond-like BC₄N-1and Diamond-like BC₄N-2simulated by the Reflex are agree withthat obtained BC₄N XRD results from experiment.Molar ratio of4:1of nano-carbon black and hexagonal boron nitride （h-BN） mixtureas raw materials, B-C-N ternary compound precursor was prepared using the method ofnano-treatment and vacuum sintering method. Then B-C-N ternary compound wassynthesized with high temperature and high pressure technique （HTHP）.The samples were produced at pressure of18GPa, temperature of1400℃¹800℃and maintaining time for30minutes. The XRD results show that the samples containdiamond phase, c-BN phase, w-BN phase and B-C-N ternary compound phase. Hardnessof the samples obtained from1400℃,1500℃,1600℃and1660℃are84GPa,92GPa,95GPa and100GPa, respectively. Hardness of the sample obtained at1800℃is124GPa,which exceeds the hardness of the diamond. The samples produced at1660℃maintainedfor30minutes and different pressure of18GPa and25GPa have a hardness of120GPa. Itcan be see from the XRD that the samples contain diamond phase, c-BN phase, w-BNphase and B-C-N ternary compound phase. The samples produced under the condition of 18GPa,1800℃and maintained temperature for15minutes and30minutes haveahardness of120¹24GPa.