Chemical Synthesis And Characterization Of B-C-N And C-N Compounds

One of key areaes that have attracted more attention in current light element material is the experimental synthesis of novel B-C-N and C-N materials. In this thesis, the study development of such two compounds during the past decates has been sumerized, and some facing promblems during the experimental synthesis of B-C-N and C-N have been proposed. The probabilities for the synthesis of B-C-N compound through solvothermal reaction and chemical reduction methods have been investigated.In this paper, the solvothermal reaction for the synthesis of B-C-N compounds by using Ca₃B₂N₄ and CCl₄ as reactants at different temoeratures (350～550℃) was studied. The obtained products were characterized by using X-ray diffraction (XRD), energy dispersive spectrum (EDS), Fourier infrared spectrcopy (FTIR), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The experimental results show that the most proper temperatures for the reaction are 400℃and 450℃. In the synthesized sample at 400℃, two kinds of hexagonal B-C-N crystals of BCN₂, and BC_xN(x<1) have been formed. While for the reaction at 450℃, besides of BC_xN(x<1), the BC_2.5N crytals were also obtained. Depenting on the experimental results, the possible reaction mechanism for the reaction procedure at different temperatures have been proposed. First-principles calculations on hexagonal BCN₂ were performed. The calculation results show that the h-BCN₂-VI with AA stacking sequence is the most stable structre of h-BCN₂. The calculated results of electron energy band and density of states indicate that the layered BCN₂ show metallicity, and could be a kind of exellent conduct material.C₃N and BC₂N compounds have been simotaniously synthesized via a chemical reduction method by using BBr₃, CCl₄ and Li₃N as reactants, and Na as reductant at 400℃. The synthesized C₃N has a hollow sphere-like morphology and amorphous structure. While the synthesized BC₂N is piece-like and has hexagonal structure. The determined lattice parameters for the synthesized h-BC₂N are a = 2.43(A|°),c = 6.64(A|°). Depending on the experimental results given by whether sodioum were added or not, the reaction mechanism for the formation of C₃N and BC₂N compounds have been studied.A yellow-brown carbon nitride powder sample was synthesized at 400℃by the reaction between C₃N₃Cl₃ and NH₄Cl. The dominant phase in the sample is polycrystalline graphite-like carbon nitride. Simultaneity, polycrystalline cluster-likeα-C₃N₄ particles with the size about 2～3 nm were also formed in the synthezied carbon nitride sample. Its determined lattice parameters are a = 6.47(A|°) and c = 4.71(A|°).Boron carbide crystals have been synthesized via a chemical co-reduction mthod by using BBr₃ and CCl₄ as reactants and Na as co-reductant at 700℃. The carbon content in the synthesized boron carbide crytals are from 9% to 11%.A chemical reaction for the synthesis of B-C-N compound by using C₃N₃Cl₃ and BBr₃ ans reactants and sodium as co-reductant was carried out and studied. The experimental results show that the product obtained at 400℃includes both h-BN and h-B_0.5C_0.07N_0.43. The syntheised h-BN crystals show the rod-like and tube-like morphology, while the synthesized h-B0.5C0.07N0.43 particles are polycrystalline and have piece-like morphology.