Boron Nitride Powders Research Articles

Densification of SiO2–cBN composites by using Ni nanoparticle and SiO2 nanolayer coated cBN powder

Cubic boron nitride (cBN) powder was coated with Ni nanoparticle and SiO2 nanolayer (abbreviated as cBN/Ni and cBN/SiO2, respectively) by rotary chemical vapor deposition (RCVD), and compacted with SiO2 powder by spark plasma sintering at 1473–1973K for 0.6ks. The effects of Ni and SiO2 coatings on the densification, phase transformation of cBN and hardness of SiO2–cBN composites were compared. The phase transformation of cBN to hBN was identified at 1973K in SiO2–cBN/SiO2 composites, 300K higher than that in SiO2–cBN/Ni composites, indicating that SiO2 retarded the transformation of cBN. The relative density of SiO2–cBN/SiO2 with 50vol% cBN sintered at 1873K was 99% with a hardness of 14.5GPa.

Platinum boride nanowires: Synthesis and characterization

Platinum boride (PtB) nanowires have been successfully fabricated with direct current arc discharge method using a milled mixture of platinum (Pt) and boron nitride (BN) powders. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the compositions, morphology, and structures of the samples. The results show that PtB nanowires are 30–50nm thick and 20–30μm long. TEM and selected area electron diffraction (SAED) patterns identify that the PtB nanowires are single-crystalline in nature. A growth mechanism based on vapor–liquid–solid (VLS) process is proposed for the formation of nanowires.

Experimental and theoretical studies of Boron Nitride Nanotubes: Electric arc discharge and DFT calculations.

ABSTRACTWe present a joint experimental and theoretical study dedicated to analyze the properties of Boron-Nitride (BN) nanotubes. First, multi-walled boron-nitride (MWBN) nanotubes were prepared by means of a modified electric arc discharge technique using boron-nitride powder. In a first stage, the BN powder was subjected to a ball milling process for about 100 hours in an atmosphere of ammonia. Later on, BN nanoparticle formation took place after the preparation of a pressed pellet at 300 °C to 25 kPa which was sintered in a furnace at approximately 1000 °C in nitrogen atmosphere for 15 hrs. The pellets were subsequently incorporated to the electrical arc discharge set up to obtain the MWBN nanotubes. The as-prepared MWBN nanotubes samples were characterized by scanning electron microscope, X-ray photoelectron spectroscopy, and micro RAMAN spectroscopy. Second, and in order to understand the measured data, extensive density functional theory calculations were performed. We present low energy atomic configurations for model finite-length armchair, zigzag, and chiral single-walled BN nanotubes, as well as for two-dimensional BN sheets. We calculate the vibrational spectra and the optical gap of each one of our considered structures and reveal how precise details of the local atomic environment can be revealed. Finally, we consider BN nanotubes functionalized with NH2, glycine and S-H molecules. We present the structural characteristics of the adsorbed configurations, charge transfer effects, and the electronic behavior. We conclude by underlining the crucial role played by molecular functionalization in order to tune the properties of these kinds of systems.

Microstructure and valence bonds of Si-B-C-N-Al powders synthesized by mechanical alloying

Amorphous Si-B-C-N-Al powders have been prepared by mechanical alloying (MA) technique using crystalline silicon (c-Si), hexagonal boron nitride (h-BN), graphite (C) and aluminum (Al) powders as starting materials. Microstructural characterization was carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The results showed that Si-B-C-N-Al powders synthesized by mechanical alloying were amorphous, no nanocrystalline structure had been detected, and every element in the Si-B-C-N-Al powders was uniformly distributed. X-ray photoelectron spectroscopy (XPS) shows that the Si-B-C-N-Al powders possessed hybridization structure of several bonds, such as Si–C, B–C–N, C–C, B–N and Al–N.

A Facile Continuous Production of Hexagonal Boron Nitride Powders

Abstract An intermediate-frequency furnace was used for continuous production of hexagonal boron nitride (h-BN) by heating a mixture of C3N6H6 and H3BO3 in a flowing nitrogen gas at 1800–1950 °C. The products were examined by XRD, Raman, FTIR, and SEM. The results indicate the as-synthesized products are h-BN flakes with a purity of 98.73 wt %. A possible reaction mechanism is discussed.

Study on High Thermal Conductive BN/Epoxy Resin Composites

In contemporary electronic technology era, the volume of electronic equipment and printed circuit board reduced so dramatically that the requirements of heat dissipation and insulation increase thereafter. In this research, γ-aminopropyltriethoxysilane (KH550)-treated boron nitride (BN) powder was used as a filler to modify epoxy composites. Effects of the BN particle size and concentration on the thermal conductivity of composites were investigated. SEM image showed the treated BN filler dispersed well in the composite matrix. Moreover, the thermal conductivity was enhanced as the BN concentration was increased. Similar phenomenon was also observed when the filler particle size was reduced. Results indicated that with increasing amount of BN addition, the composites’ thermal conductivity showed a nearly linear increase. When the mass fraction of BN was 30% and its particle size was 220 nm, the thermal conductivity reached 3.4 W/(m•k), which was 17 times as high as that of pure EP resin.

Pressure-induced preferential grain growth, texture development and anisotropic properties of hot pressed hexagonal boron nitride ceramics

Textured hexagonal boron nitride ceramics were prepared by hot pressing, using boron nitride powders as starting materials. The results showed that a high sintering temperature and moderate external pressure helped to form a textured microstructure when using boron nitride powder with a low degree of order and a broad particle size distribution. The flake-like boron nitride grains tended to orient along the hot pressing direction via pressure-induced preferential grain growth. The obtained textured boron nitride ceramics demonstrated strong anisotropic mechanical and thermal properties.

New grades of submicron and nanosized powders of cubic boron nitride

A technique for producing new grades of submicron and nanosized powders of cubic boron nitride (cBN) is developed. It includes preliminary treatment of powders and their surface modification to control the hydrophilic–hydrophobic balance. Processes are developed for producing submicron and nanosized powders of cubic boron nitride that change their hydrophilic–hydrophobic balance. Thermal treatment in inert environments makes the surface of cBN powders hydrophobic and electrochemical treatment makes it hydrophilic. New grades of submicron and nanosized powders of cubic boron nitride are created. Hydrophobic KSM-F and KN-F powders are recommended for the production of polycrystalline materials and tools on their basis and hydrophilic KSM-E and KN-E powders for composite coatings, suspensions, and pastes.

Effects of annealing on 320 nm cathodoluminescence from hexagonal boron nitride powders

AbstractThe effect of annealing in various atmospheres (N2, H2, NH3 O2 and vacuum) on the 320 nm emission bands of hexagonal boron nitride (h‐BN) powders has been investigated by cathodoluminescence (CL). The CL intensity was decreased by annealing in the N2, H2and NH3 atmospheres at 1200 °C, with H2and NH3 having more effect than N2. On the other hand, the annealing in the O2 atmosphere increased the CL intensity remarkably at annealing temperatures higher than 800 °C. These results suggest that the oxygen located near the particle surface is related to the enhancement of the 320 nm bands in h‐BN. The highest CL intensity, which was obtained at an annealing temperature of 900 °C, reached to about one third of that measured for ZnS:Cu,Al phosphor under the same measurement conditions. The investigation of the powder annealed at higher temperatures in a vacuum indicated that the luminescent centers responsible for these emission bands are thermally stable up to about 1300 °C (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural and microstructural characterization of SiB 0.5C 1.5N 0.8Al 0.3 powders prepared by mechanical alloying using aluminum nitride as aluminum source

SiB 0.5C 1.5N 0.8Al 0.3 powders were fabricated by mechanical alloying using crystalline silicon (c-Si), hexagonal boron nitride (h-BN), graphite (C) and aluminum nitride (AlN) powders as starting materials. The microstructure of the synthesized SiB 0.5C 1.5N 0.8Al 0.3 powders is predominantly amorphous with a very small volume fraction of AlN nano-crystalline phase. The SiB 0.5C 1.5N 0.8Al 0.3 powders appeared to possess a structure containing hybridization of several bonds such as Si–C, B–C–N, C–C, B–N and Al–N because of the solid reactions among c-Si, h-BN, graphite and AlN. 29Si and 27Al solid-state nuclear magnetic resonance spectra showed the formation of amorphous SiC structure based on SiC 4 sites and the coexistence of AlN 4 and AlN 5 units in SiB 0.5C 1.5N 0.8Al 0.3 powders, respectively.

Evaluation of Nitrogen Conversion Ratio on Reaction between BN and Aluminum

The fundamental reaction behavior between aluminum powder and boron nitride (BN) powder was investigated, and a quantitative evaluation of aluminum nitride (AlN) formation was carried out. As a result of differential scanning calorimeter (DSC) analysis, an exothermic reaction between BN and aluminum was detected at temperatures between 1073 and 1173K. The conversion ratio of BN to AlN increased with increasing heating temperature. However, the nitrogen conversion ratio appeared to saturate with a holding time of 3.6 ks at temperatures above 1273K. The nitrogen conversion ratio increased by using 1mm BN powder instead of 10mm BN powder. The effect of using the fine BN powder was significant especially when the heating time was short (<300 s). [doi:10.2320/matertrans.M2011184]

Preparation of Nanocrystalline TiN Coated Cubic Boron Nitride Powders by a Sol–Gel Process

Cubic boron nitride (cBN) particles coated with 20 wt% nanocrystalline TiN were prepared by coating the surface of cBN particles with TiO2, followed by nitridation with NH3 gas at 900 degrees C. Coating of TiO2 on cBN powders was accomplished by a sol-gel process from a solution of titanium (IV) isopropoxide and anhydrous ethanol. An amorphous TiO(x) layer of 50 nm thickness was homogenously formed on the surface of the cBN particles by the sol-gel process. The amorphous layer was then crystallized to an anatase TiO2 phase through calcination in air at 400 degrees C. The crystallized TiO2 layer was 50 nm in thickness, and the size of TiO2 particles comprising the layer was nearly 10 nm. The TiO2 on cBN surfaces was completely converted into nanocrystalline TiN of uniform particles 20 nm in size on cBN particles by nitridation under flowing NH3 gas.

BN-アルミニウム間反応を利用したAlN基複合材料の合成におけるプロセス条件の影響

The reactive infiltration of molten aluminum into a powder preform was investigated as a processing route for aluminum nitride (AlN) matrix composites. As the powder preform, titanium and boron nitride (BN) powders were blended and compacted, the infiltration occurred spontaneously at temperatures ranging from 1073 K to 1673 K. The conversion ratio of BN to TiB2 and AlN turned out to be insufficient (<0.8) at temperatures below 1273 K. The conversion ratio increased by increasing the processing temperatures, and it exceeded 0.95 at 1673 K. The conversion ratio at 1473 K was almost saturated with a 3.6 ks holding and the effect of extending the holding time was not confirmed. Decreasing the BN powder size was effective to promote the reaction between aluminum, titanium and BN. The effectiveness was particularly prominent at 1473 K in comparison with the specimen fabricated at 1673 K. The titanium powder size did not show a significant effect on the formation of AlN and TiB2. The volume fraction of AlN increased by changing the atmospheric gas from argon to nitrogen.

Effect of Si/C ratio and their content on the microstructure and properties of Si–B–C–N Ceramics prepared by spark plasma sintering techniques

Nano-sized Si–B–C–N powders nearly amorphous with different mole ratio of Si/C were prepared by mechanical alloying (MA) technique using cubic silicon (c-Si), hexagonal boron nitride (h-BN) and graphite powder (C p) as starting materials, then consolidated at 1800 °C under a pressure of 40 MPa for 3 min by spark plasma sintering (SPS). Sub-micrometer sized β-SiC and nano-sized BCN phase were formed as the final components in the ceramics. The grain size of the β-SiC tend to be a little coarser with the increase of the Si/C ratio as well as their total content, but no changes are observed for the fine sub-micrometer structure characteristics of β-SiC and BCN grains. Mechanical properties of the Si–B–C–N ceramics were found remarkably increased with the increase of the mole ratio of Si/C and their total relative content. Thermal physical properties, including thermal diffusivity, heat capacity, thermal conductivity, as well as thermal expansion coefficient were also studied.

New synthetic route for nanocrystalline boron nitride powder

Nanocrystalline hexagonal boron nitride powder (h-BN) was synthesized by sol–gel polycondensation of resorcinol and formaldehyde in the presence of boric acid followed by freeze drying. Pyrolysis and subsequent heat treatment of these cryogels resulted in formation of boron nitride powder. Characterization by nitrogen adsorption showed that precomposite cryogels and the BN powders were micro and mesoporous materials with high surface areas. Materials have been analyzed by means of X-ray diffraction, Raman scattering and electron microscopy methods.

Preparation of carbon nanotube by rotary CVD on Ni nano-particle precipitated cBN using nickelocene as a precursor

Ni nano-particles were deposited on hexagonal boron nitride (hBN) and cubic boron nitride (cBN) powders by rotary chemical vapor deposition (RCVD) using nickelocene as a precursor. Ni nano-particles precipitated on hBN and cBN powders were about 20 nm and 10 to 50 nm in diameter, respectively. Carbon nanotubes (CNTs) were grown from relatively large Ni particles about 50 nm in diameter on cBN powder, whereas carbon layers surrounded Ni nano-particles on the surface of hBN powders.

Defect Functionalization of Hexagonal Boron Nitride Nanosheets

A pristine hexagonal boron nitride (h-BN) powder sample with layered crystalline sheetlike particles of ∼1−10 μm in lateral sizes and a few hundred nanometers in thicknesses was mechanically treated using a ball-mill to intentionally introduce defect sites. The h-BN was ball-milled for various times and subsequently was functionalized with a long alkyl chain amine via Lewis acid−base interactions between the amino groups and the boron atoms of h-BN to obtain soluble amine-attached nanosheet samples as the products. The functionalized h-BN nanosheet samples were characterized via various microscopic and spectroscopic techniques. The results strongly support a direct correlation between increasing defect site concentrations of the h-BN nanosheet samples and improved reaction efficiency with the amine. This suggests the enhanced reactivity of defect boron atoms in comparison to conjugated ones on an unperturbed h-BN plane. NMR investigations provided the strongest evidence supporting the hypothesis that the amino groups reacted with the h-BN at specific defect sites induced by ball-milling. The mechanistic implications are discussed.

Hydrogen permeation pathways for the hydrogenation reaction of aluminum

The hydrogenation of aluminum is inhibited by the slow diffusion of hydrogen in its hydride AlH3, which covers the surface of aluminum in the initial stages of the reaction. Thus, permeation pathways for hydrogen are introduced by either mixing aluminum powder with boron nitride powder or alloying aluminum with gallium at 10 at. % Ga. The aluminum in the composite or alloy is reacted with hydrogen at high pressure and temperature. In both cases, the hydrogenation reaction yields are significantly enhanced, confirming that boron nitride and the liquid phase produced by partial melting of the alloy work efficiently as hydrogen permeation pathways.

Synthesis of Nanocrystalline Cubic Hafnium Nitride by Reactive Mechanical Alloying

Nanocrystalline cubic hafnium nitride (HfNx) powders are prepared by the mechanical milling of Hafnium and hexagonal boron nitride (h-BN) powder mixtures. The prepared nanocrystalline HfNx is analyzed and characterized using x-ray diffraction and Raman spectroscopy. HfNx formation mechanisms in both mechanical milling and annealing processes are also studied in detail. It is found that HfNx is probably formed via the phase separation of Hf(N) solid solution alloy driven by reactive mechanical milling in which Hf(N) solid solution alloy is formed by Hf and N atoms through a diffusion reaction process. Meanwhile, a phase separation can also be induced in Hf (N) solid solution as the N content exceeding its solubility limit, leading to an additional way to produce HfNx. No HfB2 has been found during both milling and annealing processes.

Thermally conductive boron nitride/SEBS/EVA ternary composites: “Processing and characterization”

AbstractThe aim of this study is to investigate the effect of hexagonal boron nitride (BN) particle shape/size and loading level on the thermal, mechanical, electrical properties, and morphology of styrene‐ethylene‐butylene‐styrene terpolymer (SEBS)/poly(ethylene‐co‐vinyl acetate) (EVA) blends to be used as thermal interface materials (TIM). It is observed from the scanning electron microscopy (SEM) of BN powders that each type has a characteristic particle size distribution and particle shape. SEM analysis conducted on matrices (i.e. SEBS/EVA blends) does not indicate any sign of interfacial delamination or phase separation between components. The surface energy measurements and subsequent wettability coefficient calculations point out that the dispersion of BN in SEBS is thermodynamically more favorable than that of BN in EVA. In other words, SEBS tends to encapsulate BN particles in comparison to EVA. Thermal conductivity of composites increases with increasing filler loading level regardless of filler size and shape. It is found that the composites with smaller BN particles (i.e. high aspect ratio and plate‐like particles) shows higher thermal conductivity than that of the composites with larger particles at the same filler content. The tensile strength of the composites reduces with the incorporation of BN regardless of BN content and matrix composition. The increasing content of BN in the matrix gradually improves the moduli of the composites. The hardness of composites enhances with BN loading level and SEBS/EVA ratio regardless of filler type. The increasing amount of EVA in the composites results in a decrease in dielectric constant of neat matrices and composites. POLYM. COMPOS., 31:1398–1408, 2010. © 2009 Society of Plastics Engineers