Papers by Keyword: Boron Nitride

Abstract: A method to synthesize boron nitride (BN) coating on the surface of graphene has been developed. BN coating was synthesized by the direct reaction of sodium borohydride and ammonium chloride at a relatively low temperature of 600 °C. Synthesized sample was characterized by RAM, XRD, FESEM, TEM and XPS. It is revealed that the BN coating combines with graphene through van der Waals interactions, and the elements B and N distribute homogeneously on the surface of graphene. Thermogravimetric analysis showed that the oxidation resistance of the graphene was improved after being coated with BN.

Abstract: The paper describes the study of mechanical activation of multi-component ceramic powder materials based on boron nitride. The mechanical activation of the powders was carried out according to the best optimal parameters in a ball mill AGO-2U. Increasing the time of mechanical activation leads to more fine-grained powders. We described the technique of mechanical activation of ceramic powder materials. We introduced the results of X-ray diffraction analysis of the ceramic powder cBN, cBN-Co, hBN-Co before and after mechanical activation. We generated mathematical equations of dependence of an average powder particle size on the average mechanical activation time. We described how the crystal lattice "a" parameters and unit cell volume "V" of cBN and hBN powders depend on mechanical activation time. We studied the chemical composition of powder materials. We also studied the structural parameters of ceramic powders.

Abstract: In this research, the effects of boron nitride (BN) and polybutadiene (BR) on thermal and mechanical properties of polylactic acid (PLA) composite films were studied. PLA thin film in the thickness of less than 0.2 mm was fabricated using the solvent casting method. The loadings of BN and BR of 0-7 wt% were applied to the PLA matrix. The morphologies of composite films were characterized by scanning electron microscopy (SEM). The thermal and mechanical properties were also investigated. It was found that the addition of BN and BR can improve the thermal properties of PLA composite films. PLA/BN3%/BR5% ternary composite films provided the higher thermal properties, tensile strength and Young’s modulus, compared to PLA/BN1%/BR5% ternary composite films.

Abstract: BN-Si₃N₄ composite ceramic wave-transparent materials with excellent mechanical properties were prepared by spark plasma sintering (SPS) using h-BN and α-Si₃N₄ powders as raw materials, Al₂O₃ and Y₂O₃ as sintering aids. The influence of sintering pressure on density and mechanical properties of BN-Si₃N₄ composite ceramics were studied. The phases were observed by X-ray diffraction (XRD), and the microstructures were identified by scanning electron microscopy (SEM). The results showed that with the sintering pressure increases, the relative density, bending strength and fracture toughness of the composite ceramics were significantly increased, and the porosity decreased rapidly. The effects of pressure on the properties of the composite ceramics was not significant at >40MPa, so 40MPa is optimal for the composite ceramics to gain good overall performance, i.e. the relative density was 89.1%, the porosity was 2.3%, the bending strength reached 215.4 MPa, and the fracture toughness was 3.1/MPa·m^1/2.

Abstract: In the last few decades, when travel makes one modest, people prefer air travel instead of car. As such, aircrews and flight passengers are prone to electromagnetic (EM) radiation exposure overtime during flight. Various researches were conducted by the Federal Aviation Agency (FAA) and European Union (EU) in order to understand its details. This paper offers reviews of EM radiation effect to human body in altitude of commercial jet and materials that may provide a convince protection for fuselage structure of aircraft. It was found that Polyethylene (PE) is a convincing material that may absorb EM radiation. NASA has found that lower effective dose toward galactic cosmic rays (GCR) was obtained in PE at 0.1 cSv/day compared to aluminum at 0.125 cSv/day at the same thickness which was 20 g/cm².

Abstract: In the present paper, the tensile mechanical behavior of different sized, almost squared shaped, boron nitride nanoribbons is numerically investigated and predicted by using a structural mechanics approach based on the use of appropriate nonlinear potential functions concerning both two-body and three-body interatomic interactions appearing within their nanostructure. According to the proposed method, appropriate spring elements are combined in nanoscale in order to simulate the interatomic interactions appearing within boron-nitride nanostructure. The dimensions of boron-nitride nanoribbons as well as the shape of their edges, which may be armchair or zigzag, have influence on the overall behavior of the nanoribbons. Therefore, the study focuses on the prediction of tensile stress-strain behavior of boron-nitride nanoribbons of different sizes and edge shapes as well as on the estimation of significant corresponding material properties such as Young’s modulus, tensile strength, tensile failure strain and tensile toughness. The numerical results, which are compared with corresponding data given in the open literature where possible, demonstrate thoroughly the important influence of size and chirality of a narrow boron nitride monolayer on its mechanical behavior.

Abstract: Boron nitride films were deposited on silicon substrate by a hot filament assisted chemical vapor deposition (HFCVD) system. The tris (dimethylamino) borane (B[N(CH₃)₂]₃) was used as the single source precursor which has both the boron and nitrogen source, ammonia gas was used as the assisted gas to increase the nitrogen concentration in the films. The films deposited by different ratios of precursor to ammonia gas flow rate and filament temperatures were investigated. The boron-carbon-nitrogen (BCN) compound films were deposited under lower filament temperature. With increasing the ammonia gas flow rate, the carbon concentration in the films decreased. Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) image reveal that hexagonal boron nitride (hBN) films were deposited at the higher filament temperature of 2000°C. Moreover, the crystallization degree of the films became better with the filament temperature increased.

Abstract: We give here an overview of our recent work on growth of rhombohedral boron nitride (r-BN) thin films on SiC substrates by chemical vapor deposition (CVD). We demonstrate the growth of twinned r-BN on various SiC polytypes at 1500 °C, using H₂ as carrier gas and triethyl boron and ammonia as precursors with an N/B ratio of ~ 640. The epitaxial relation with various substrates is determined from XRD and TEM. Adding Si to the gas phase stabilizes the r-BN phase but does not alter the electric properties of the material which remains electrically insulating.

Abstract: The epoxy composites with high thermal conductivity for metal-core printed circuit board (MCPCB) can be prepared by varnish coating and a hot press method. Alumina filler of plate-like shape was used as primary micro-filler, while plate-like alumina filler, h-BN, a-BN and s-BN filler were used for blending into the plate-like alumina filler as the secondary filler. Results showed that the secondary fillers a-BN and s-BN loaded epoxy composites have higher thermal conductivity than alumina filler single-loaded composites. Also, BN filler has high thermal conductivity, but h-BN filled epoxy composite has lower thermal conductivity than alumina filled epoxy composite. The decrease of voids in epoxy composite are very important, and the filler shape and surface modification is also necessary to achieve high thermal conductivity in epoxy composite for MCPCB

Abstract: Boron nitride (BN) coating on KD-II silicon carbide fiber was prepared from boric acid and urea by a 4-circle dip-coating process. SiCf/SiC composites were prepared from the precursor LPVCS by a HP(heat pressure) assisted PIP(precursor infiltration and pyrolysis) process. The microstructure and crystal structure of the coatings were characterized by SEM and XRD. XPS was adapted to analysis the composition and contents of different elements on the surface of BN coating. The influence of dip-coating process to the fibers was studied by the monofilament strength test. As the results, the monofilament strengths of the dip-coated fibers decreased firstly and increased subsequently. The strengths were slightly higher (3.4%) than the original fiber after 4 circles. The average flexural strength and fracture toughness of the composites with BN coating are respectively 290.8 MPa and 12.09 MPa⋅m^1/2, while those of composites without coating are 144.1 MPa and 6.72 MPa⋅m^1/2, respectively.