The Synthesized And Characterization Of Boron Nitride And Vanadium Nitride

Boron nitride is a kind of important inorganic non-metallic material; it has become a key research direction in material sciences recently because of its superior physical characters and chemical properties. Generally, BN has four polymorphs with well-defined crystallographic structures, including sp2-bonded hexagonal BN (h-BN), rhombohedral BN (r-BN) and sp3-bonded cubic BN (c-BN), wurtzite BN (w-BN). Boron nitrides possess advantageous thermodynamics, chemical and mechanical properties, it also has broadband gap, anti-oxidation, corrosion-resistant, and so on. These advantageous properties made BN widely used in machinery, metallurgy, electronics, and aerospace and other high-tech areas, especially in the optoelectronic and resist radiation aspects. Based on the excellent properties and wide application, many researchers have engaged in the preparation,structures measurement and electrochemical performance test of boron nitride.Vanadium nitride has very high thermal and chemical stability and mechanical properties, it has been widely used in abrasive tool, cutting tool and structural materials; meanwhile vanadium nitride possess other properties such as very good catalyst property, high selectivity, high catalytic activity, high stability and resistance to poisoning performance. Fine grit vanadium nitride can effectively enhance the catalytic activity, improve the structure material toughness. In addition, vanadium nitride can also be used in microelectronics field owning to it high melting point and low resistance properties,On the basis of comprehensive and thorough investigation of literatures concerning the developments of boron nitride (BN) and vanadium nitride (VN) nanomaterials synthesis and application, in the dissertation, we dedicated to explore the facile route of synthesis of BN and VN nanomaterials in autoclaves. The phase and morphologies of the as-prepared products were characterized and the properties were investigated. The main contents are summarized as follows:1. One-step solid state method for the synthesis of rhombohedral or hexagonal boron nitride nanoplates in autoclave is developed. Firstly, triangular r-BN nanoplates have been prepared through the reaction of B2O3, NH4F and Na at 500℃for 30h, which were labeled as "Sample 1", the typical XRD pattern of Sample 1 can be indicted as rhombohedral BN. The calculated lattice constant is a=2.503 Aå'Œc= 9.992 A, which is close to the reported value (JCPDS card no.45-1171:a=2.504 A and c=10.000 A).The morphology and structure of the as-prepared samples were further analyzed by SEM and TEM. The images indicate that Sample 1 is composed of a large quantity of triangular nanoplates with widths mainly ranging from 100-200 nm and the average thickness is about 20 nm. The HRTEM image indicate the high crystallinity of Sample 1, the clear fringes with an average spacing of 0.20 nm corresponds to the (012) lattice spacing of r-BN crystal. We found the temperature has important influence on the phase and morphology of the products. When the temperature was improved to 700℃, while the other parameters remain unchanged, the typical XRD pattern of Sample 2 can be indicted as h- BN. The calculated lattice constant is a=2.501 Aå'Œc= 6.627 A, which is close to the reported value ((JCPDS card no.34-0421).The SEM and TEM images indicate the products is composed of amounts of hexagonal nanoplates with widths mainly ranging from 300-500 nm and the average thickness is about 100 nm. The HRTEM image reveals the average spacing of 0.21 nm corresponds to the (100) lattice spacing of h-BN crystal.2. A facile method for the synthesis of VN nanomaterials under mild condition is developed. Firstly, VN nanoblocks were synthesized by NH4VO3, N2H4·2HC1 and Mg at 500℃for 12h. The typical XRD pattern of the products can be indicted as VN. The calculated lattice constant is a=4.139 A, which is close to the reported value (JCPDS card no.35-0768).The morphology and structure of the as-prepared samples were further analyzed by SEM and TEM. The SEM images indicate the product is composed of nanoblocks which has the average diameters in the range of 200-500 nm. The HRTEM image shows resolves fringes separated by 0.21 nm, which corresponds to (200) d-spacing of the VN. The effects of different synthesis conditions on the final products such as reaction temperature, reactant dosage were also investigated.