Preparation And Characterization Of Three-Dimensional Network Structure Nano Boron Carbide

Boron carbide (B4C) possesses various prominent properties, such as high hardness, high melting point, low density, high elastic modulus, high chemical stability, high neutron absorption cross-section, excellent thermoelectric properties, etc. Due to its attractive combination of these properties, boron carbide can be widely applied to many fields. However, B4C has poor sinterability caused by strong covalent bond and low self-diffusion coefficient. In this situation, it is a common understanding that using nanosized boron carbide is the best solution for improving sintered densification. At the moment, zero-dimensional (OD) nanostructures of boron carbide, such as nanoparticles have been reported by several groups. One-dimensional (1D) nano boron carbide, such as nanowires,nanorods, nanofibers and two-dimensional (2D) nano boron carbide, such as nanosheets have also been reported. To date, three-dimensional (3D) nano boron carbide has been not reported. Recently, renewable porous carbon source, be used to prepare nano-structure boron carbide, has attracted wide attention. So, in this study, carbonized bacterial cellulose (CBC) is high-purity carbon fiber with three-dimensional network, acting as the template carbon and source, via selecting different boron source to prepare three-dimensional nano-network structure boron carbide. The phases, morphology, structure of as-prepared B4C were characterized. The main contents are as follows.(1) Integrated thermal analyzer was used to study the pyrolysis process. The pyrolysis of bacterial cellulose was an endothermic reaction, the pyrolysis mainly occurred in the temperature range of 300 ??400 ?. CBC obtained from pyrolysis is a high-purity carbon. The carbon content is up to 88%. Similar to activate carbon and black carbon, the CBC contained a large number of graphite crystallites. CBC obtained from pyrolysis in the carbonized temperature of 1000 ? also can maintain the three-dimensional network structure as well as the bacterial cellulose.The specific surface area of CBC is 485.88 m2/g.(2) Net-like structure boron carbide powder was synthesized by a solid state thermal reaction, using carbonated bacterial cellulose with three dimensional network as carbon source. XRD, Raman, SEM and Laser Particle analyzer were used to study the phase, the structure, the morphology and particlesize, respectively. The results show that net-like structure boron carbide powderwas prepared with B/CBC molar ratios of 4:1, reaction temperature of 1400 C, and reaction time for 4h.The crystal structureof the prepared powder is rhombohedral shape. The morphology displays net-like structure composed of the equiaxed nanoparticles, which form net-like structure along with three dimensional network of CBC.(3) Three-dimensional nano network structure boron carbide was successfully synthesized via carbothermic reduction using carbonized bacterial cellulose with three-dimensional network structure as carbon source and template. XRD, Raman, SEM, TEM and XPS were used to study the structure and properties.The results show that, the same structure nano-boron carbide can be synthesized in situ, along with the three-dimensional network structure of CBC. The boron carbide prepared exhibited a sheet-like morphology with length of 1.15-1.48 ?m, and the average wide of 250 nm. The sheet-like products mutually alternated arrangement to form the three-dimensional network structure. The as-prepared boron carbide is rhombohedral crystalline.In this study, the new carbon source was provided to the preparation of nanostructured boron carbide.