BN Content Research Articles

Study on Glass Fiber Reinforced EP/PSF Insulating and Thermally Conductive Composite Filled with BN Particles

Polysulfone modified epoxy resin was chosen as the matrix of composite materials. The epoxy/glass fiber/boron nitride composite materials were prepared by heat press molding. The effect of different size and content of BN on the thermal, mechanical, electrical properties and thermal stability of the composite was investigated. The results showed that thermal conductivity and thermal stability of the composite increased with the content of the BN particles, the thermal conductivity of the composite reached 0.672W/m·K when filled with 1μm BN at 20 wt.%. Impact strength and flexure strength of the composite increased initially and then decreased with the increasing content of BN. The electrical insulating property of the composite remained with the content of 20 wt.% BN.

Machinable ZrB2–SiC–BN composites fabricated by reactive spark plasma sintering

A solid state reaction of ZrH2, Si3N4 and B4C has been proposed to synthesize machinable ZrB2–SiC–BN composites. Dense ZrB2–SiC–BN composites with fine grain size and homogeneous microstructure were fabricated via spark plasma sintering at 1900°C in vacuum. The kinetics of the reaction process was studied with XRD results. SEM and TEM results showed that the in-situ formed BN phase was composed of micro-sized intergranular and nano-sized intragranular h-BN particles. The influences of the BN content on the mechanical properties as well as the thermal conductivities of the composites were studied. The composites that contained >20vol% BN exhibited excellent machinability and high strength.

Effects of BaNb2O6 addition on microstructure and dielectric properties of BaTiO3 ceramics

(1 − x)BaTiO3–xBaNb2O6 [(1 − x)BT–xBN] ceramics with x = 0, 0.005, 0.008, 0.01, 0.02, 0.03 were prepared by a conventional solid-state reaction route. The effect of BN addition on phase composition, microstructure and dielectric properties of BT-based ceramics were investigated by X-ray diffraction, scanning electron microscope and impedance spectroscopy. The results showed that a systematic structure change from the ferroelectric tetragonal phase to pseudo-cubic phase was observed near x = 0.01 at room temperature. It resulted in a considerable change of density, grain size and dielectric properties of the samples when BN was introduced. Meanwhile, it also lowered the sintering temperature of the ceramics. The dielectric constant peak and the variation rate of capacitance at Curie temperature are markedly depressed and broaden with increasing BN content. Especially, the ceramics with x = 0.008 and x = 0.01 showed good dielectric properties over the measured temperature range. Optimal dielectric properties of e = 3,851, tanδ = 0.7 % at room temperature and Δe/e25 ≤ ±6.8 % (−55 to 125 °C) were obtained for the BT-based ceramics doped with 0.8 mol% BN, which was obviously superior to BaTiO3 and BaNb2O6 ceramic, and it met the requirements of EIA X7R specifications.

Study on the tribological properties of plasma nitrided bearing steel under lubrication with borate ester additive

The nitrided layer on 52100 steel was prepared by plasma nitriding treatment. The tribological behaviors were examined under lubrication with borate ester containing nitrogen (B-N). The nitrided steel exhibited a lower friction coefficient and smaller wear scar diameter compared with the untreated steel. When 1.25wt% B-N was used, the friction coefficient and wear scar diameter of nitrided steel were reduced by 34% and 45%, respectively. The main mechanism of this effect was attributed to the fact that the B-N additive can produce a tribofilm containing higher content of BN on the nitrided surface.

Effects of BN content on the structural and mechanical properties of a-SiBN ceramics

Abstract SiBN has the advantages of Si3N4 at high temperature and also presents good mechanical properties. Understanding the structural and mechanical properties of SiBN is essential in order to control the properties under fabrication. In this paper, the effects of BN content on structural and mechanical properties of SiBN ceramics were investigated using atomistic simulation. Phase separation of the SiN-rich region and the BN-rich region was observed for all the three compositions. With BN content increases, the BN-rich regions tend to be larger and the SiN-rich regions become smaller. Interestingly, Si3B3N7 shows different structural and mechanical properties compared with Si3BN5 and Si3B5N9: 1) sharper and narrower peaks for pair distribution functions and angular distribution. 2) larger values but less stability for Young's moduli at high temperatures. The larger Young's modulus of Si3B3N7 is attributed to the network structure of BN and SiN phase.

Thermal and Mechanical Properties of Polypropylene/Boron Nitride Composites

The purpose of this study is to improve thermal conductivity and properties of polypropylene (PP) by adding functionality fillers. Boron nitride (BN) was used for improving the thermal conductivity of polymers. Two types of BN with different particle sizes were used. In addition, two types of PP with different viscosities were used as the polymer matrix. The thermal conductivity, storage modulus and loss modulus increased with the content of BN. The thermal conductivity of PP can be effectively enhanced by adding BN with large particles. Moreover, the melting temperature and crystallization temperature of PP/BN composites were larger than those of neat PP. The degree of crystallization of PP increased with BN. The effect of BN with small particles on the crystallization of PP was slightly stronger than that of BN with large particles. From the SEM observation, the agglomeration of BN with small particles was locally observed. In contrast, BN with large particles dispersed well in the PP matrix. This study found that BN with large particles effectively enhanced the thermal and properties of PP/BN composites. In addition, the above properties were independent of the matrix viscosity.

Interfacial microstructure and strengthening mechanism of BN-doped metal brazed Ti/SiO2-BN joints

Ag–Cu–Ti + BN composite filler was developed to braze SiO 2 -BN ceramic and titanium. The effects of BN particles content on the microstructure and mechanical properties of the joints were investigated. The fine TiB whiskers and TiN particles were synthesized in the brazing seam by introducing BN particles. TiN–TiB 2 reaction layer formed adjacent to SiO 2 -BN ceramic while Ti–Cu compound layer formed at Ti substrate. With the increase of BN content, more fine-grains formed in the joint and the reaction layer nearby the base materials became thinner. The hardness and modulus of the reaction phases were characterized by nanoindentations to reveal the plastic deformability of the brazing seam. The improvement of the joint strength was 340% with 3 wt.% BN addition. The joint strength was determined by the thermal expansion mismatch between the joined materials, plastic deformation in the brazing seam, and interfacial structure of the joint.

Oxidation Resistance and High Temperature Thermal Insulation of a Polymeric Precursor Derived BN/SiC Ceramics Foam

A kind of BN/SiC open-cell ceramic foams were fabricated from complex co-polymeric precursors of polycarbosilane and tris(methylamino)borane [B(NHCH3)(3)] using a high-pressure pyrolysis foaming technique. The obtained foams exhibited cell sizes ranging from 1 mm to 5 mm with bulk densities varying from 0.44 g/cm(3) to 0.73 g/cm(3), depending on the proportion of the starting precursors. Studies on the microstructure and thermal property of the porous ceramics showed that the addition of BN into SiC could improve dramatically the oxidation resistance from 800 to 1100 degrees C. The compression strength of the composite foams was 5-10 times higher than that of pure SiC foam, which increased with increasing of BN content in the ceramic foams. Heat insulation performance of the ceramic foam fabricated from the starting precursors with a proportion of 1:1 in weight was analyzed by a device designed for insulation performance at high-temperature. When the temperature at the center point of hot surface of the foam was 1400 degrees C, the temperature at the center point of the back achieved only 280 degrees C. The heating history of the foam was simulated by finite- difference method, and the results showed that thermal conductivity of the composite foam was 4.0 W/(m.K), which was almost identical to the experimental result.

Effect of BN content on microstructures, mechanical and dielectric properties of porous BN/Si3N4 composite ceramics prepared by gel casting

Abstract Porous BN/Si 3 N 4 composite ceramics with different BN contents have been fabricated by gel casting. The rheological behaviors of the suspensions, microstructure, mechanical properties, dielectric properties and critical temperature difference of thermal shock (Δ T C ) of porous BN/Si 3 N 4 composite ceramics with different BN contents were investigated. With BN contents increasing, the mechanical properties of the porous BN/Si 3 N 4 composite ceramics were partially declined, but the dielectric properties and thermal shock resistances were enhanced at the same time. For the porous Si 3 N 4 ceramic without BN addition, the porosity, flexural strength, dielectric constant and critical temperature difference were 48.1%, 128 MPa, 4.1 and 395 °C, while for the 10 vol% BN/Si 3 N 4 porous composite ceramics, they were 49.4%, 106.6 MPa, 3.8, and 445 °C, respectively. The overall performance of the obtained porous BN/Si 3 N 4 composite ceramics indicated that it could be one of the ideal candidates for high-temperature wave-transparent applications.

The Influence of Boron on Structural Properties of Martensitic 8-10%Cr-Steels

Four alloys on the basis of 8-10% CrWVTa steel were melted to study the influence of boron on the structure and precipitation behavior. Boron contents in the alloys amounted to 0.0083 and 0.1 wt.%, respectively. One batch was nearly free of boron. The individual alloys were examined metallographically and characterized in the initial state and after aging treatments up to 800 °C. It was found that the grains of boron-containing alloys were coarsened when the alloys were subjected to tempering. At the same time, the precipitate content was reduced. The different phases of precipitates were analyzed as primary carbides with tantalum and tungsten, and due to the higher content of boron BN, B(C, N), and (Fe, Cr)2B. M23C6 was developed in all alloys after the heat treatment.

Effect of BN filler on thermal properties of HDPE matrix composites

The effects of boron nitride (BN) content and particle size on the thermal properties of BN/high density polyethylene (HDPE) composites were investigated. The thermal conductivities and thermal diffusivities of the composites were dependent on the BN content. For composites with same amount of BN, the thermal conductivity and thermal diffusivity increased with an increase in the size of the BN particles. Composites with a mixture of different-sized BN particles exhibited higher thermal conductivities than those of composites with single-sized BN particles. The specific heat capacities of the composites were also affected by the BN content and particle size. Several theoretical models were employed to predict the effective thermal conductivities of the composites, and the predicted values were compared with those obtained experimentally.

Fabrication of High Strength α-SiAlON/BN Composition Ceramics by Hot Pressing

Dense Y3+-dopted α-SiAlON/BN composition ceramics was fabricated by hot pressing at 1900 °C for 60 min, and flextural strength at room and 1000 °C was investigated through three-point bending test. The results show that h-BN contribute to the densification of powder body, but h-BN have little affect on the key temperature region of sintering densification of α-SiAlON ceramics. When content of BN is lower, which didn’t affect on the phase transformation of α-SiAlON, but when content of BN is higher, besides of major phase α-SiAlON, a little of β-SiAlON was also formed. For the α-SiAlON/BN composite ceramics content of 20 wt.% h-BN, the higer flexural strength( room-temperature and 1000 °C) were abtained, the formation of β-SiAlON should be an important resonon for the higher strentgh, more important is , whose flexural strength at 1000 °C is higher 50 MPa than at room temperature, the differnce of thermal properties between SiAlON and BN should contribute to the improve of high-temperature flextural strength.

High Frequency Dielectric Properties and Thermal Conductivity of AlN-BN Composites by Spark Plasma Sintering

AlN-BN composite is considered to be a promising material for microwave transparent applications. In this paper, a series of AlN-BN composites with various content of BN (0 wt%, 5 wt%, 15 wt% and 30 wt%) were prepared by spark plasma sintering with multiple components sintering additives at a low temperature (1650 °C), and the effect of sintering conditions and composition on the thermal conductivity and high frequency dielectric properties within frequency range from 10 MHz to 1.5 GHz was investigated. The results show that the spark plasma sintering process and the multiple components of the sintering additives promote the densification of the samples. The thermal conductivity and dielectric constant of samples decrease with increasing BN content, while the variation of the dielectric loss depends on the content of residual carbon and other impurities which may result in the relaxation loss of electronic polarization and conductive loss.

Preparation and Properties of Porous Si<sub>3</sub>N<sub>4</sub>/SiO<sub>2</sub>/BN Composite Ceramics

Porous Si3N4/SiO2/BN composite ceramics with high strength and low dielectric constant were prepared by dry-pressing process and pressureless sintering at 1750°C for 1.5 h in flow nitrogen. The influences of BN content on microstructure, porosity, mechanical and dielectric properties of the porous Si3N4/SiO2/BN composite ceramics were discussed. The results showed that the porous Si3N4/SiO2/BN composite ceramics with porosity ranging from 29% to 48% were fabricated by adjusting the content of BN. The flexural strength of the porous Si3N4/SiO2/BN composite ceramics was 78215 MPa. The dielectric constant of the porous Si3N4/SiO2/BN composite ceramics was 3.9~5 at 1 MHz.

Dielectric and Mechanical Properties of Porous Si<sub>3</sub>N<sub>4</sub>-BN Ceramic Composites

Recently, ceramic composites with low dielectric constant, low loss tangent, high flexural strength and high thermal shock resistance have received a considerable attention as candidate materials for certain high speed radome. In this paper, Si3N4-BN ceramic composites were fabricated by dry-press processing and cold isostatic pressing, with α-Si3N4 and BN as starting powder, Al2O3 and Yb2O3 as sintering additives, PMMA as pore-forming agenSubscript textt. After sintering for 2 h at 1750°C, porous Si3N4-BN ceramic composites with a three-point bending strength of 50~120MPa and a dielectric constant of 3.2~4.4 at 7~18 GHz frequency were obtained. The sintered body was mainly β-Si3N4 grains; BN was dispersed in the grains. The formation of β-Si3N4 grains was demonstrated by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) respectively. Furthermore, the influence of the BN content on the dielectric and mechanical properties was also studied. The porous Si3N4-BN ceramic composites showed a lower dielectric constant and shrinkage. For above excellent properties, Si3N4-BN ceramic composites have been became one of the most hopeful candidate materials for high speed radome.

Converting Graphene Oxide Monolayers into Boron Carbonitride Nanosheets by Substitutional Doping

To realize graphene-based electronics, bandgap opening of graphene has become one of the most important issues that urgently need to be addressed. Recent theoretical and experimental studies show that intentional doping of graphene with boron and nitrogen atoms is a promising route to open the bandgap, and the doped graphene might exhibit properties complementary to those of graphene and hexagonal boron nitride (h-BN), largely extending the applications of these materials in the areas of electronics and optics. This work demonstrates the conversion of graphene oxide nanosheets into boron carbonitride (BCN) nanosheets by reacting them with B(2) O(3) and ammonia at 900 to 1100 °C, by which the boron and nitrogen atoms are incorporated into the graphene lattice in randomly distributed BN nanodomains. The content of BN in BN-doped graphene nanosheets can be tuned by changing the reaction temperature, which in turn affects the optical bandgap of these nanosheets. Electrical measurements show that the BN-doped graphene nanosheet exhibits an ambipolar semiconductor behavior and the electrical bandgap is estimated to be ≈25.8 meV. This study provides a novel and simple route to synthesize BN-doped graphene nanosheets that may be useful for various optoelectronic applications.

High Hardness BaCb-(BxOy/BN) Composites with 3D Mesh-Like Fine Grain-Boundary Structure by Reactive Spark Plasma Sintering

Boron carbide B4C powders were subject to reactive spark plasma sintering (also known as field assisted sintering, pulsed current sintering or plasma assisted sintering) under nitrogen atmosphere. For an optimum hexagonal BN (h-BN) content estimated from X-ray diffraction measurements at approximately 0.4 wt%, the as-prepared BaCb-(BxOy/BN) ceramic shows values of Berkovich and Vickers hardness of 56.7 +/- 3.1 GPa and 39.3 +/- 7.6 GPa, respectively. These values are higher than for the vacuum SPS processed B4C pristine sample and the h-BN -mechanically-added samples. XRD and electronic microscopy data suggest that in the samples produced by reactive SPS in N2 atmosphere, and containing an estimated amount of 0.3-1.5% h-BN, the crystallite size of the boron carbide grains is decreasing with the increasing amount of N2, while for the newly formed lamellar h-BN the crystallite size is almost constant (approximately 30-50 nm). BN is located at the grain boundaries between the boron carbide grains and it is wrapped and intercalated by a thin layer of boron oxide. BxOy/BN forms a fine and continuous 3D mesh-like structure that is a possible reason for good mechanical properties.

Laser processing of in situ synthesized TiB–TiN-reinforced Ti6Al4V alloy coatings

In situ synthesized TiB–TiN-reinforced Ti6Al4V alloy composite coatings were laser deposited on commercially pure Ti using premixed Ti6Al4V and BN powder. The amount of TiB/TiN was found to increase with increasing BN concentration and laser energy input. Due to the increase in the BN content from 5 to 15 wt.%, the top surface hardness and Young’s modulus increased from 543 to 877 HV and from 170 to 204 GPa, respectively, while the thickness of the coating varied from 467 to 1236 μm.

Tribological Properties of Plasma Nitriding GCr15 Steel under Lubrication with Borate Containing Nitrogen Additive

An approach combining the plasma nitriding with lubrication additive is proposed to improve the durability of the antifriction bearing.The nitrided layer on GCr15 steel is prepared in a plasma nitriding furnace.Its surface morphologies,phase structure,and hardness are analyzed by means of scanning electron microscope(SEM),X-ray diffractometer(XRD) and microhardness tester.Its friction and wear behaviors are examined on a four-ball friction and wear tester under lubrication with borate containing nitrogen additive,compared with that of plain GCr15 steel.The composition and chemical binding state of tribofilm formed on the wear steel surface is analyzed by X-ray photoelectron spectroscope(XPS).The results show that an unexpected excellent synergistic effect occur between the nitrided surface and additive,the nitrided steel exhibits lower friction coefficient and better anti-wear properties compared with untreated steel,especially when 1.25% additive is used,the friction coefficient and wear scar diameter reduce by 34% and 45% separately.The main mechanism of this effect is attributed to that the borate containing nitrogen additive can produce a tribofilm containing higher content of BN on the nitrided surface,which is not found on the plain steel surface.

Preparation and properties of Si3N4/BN ceramic composites

Using Si and BN powders as raw materials, silicon nitride/hexagonal boron nitride (Si3N4/BN) ceramic composites were fabricated at a relatively low temperature by using the reaction bonding technology. The density and the nitridation rate, as well as the dimensional changes of the specimens before and after nitridation were discussed based on weight and dimension measurements. Phase analysis by X-ray diffraction (XRD) indicated that BN could promote the nitridation process of silicon powder. Morphologies of the fracture surfaces revealed the fracture mode for Si3N4/BN ceramic composites to be intergranular. The flexural strength and Young's modulus decreased with the increasing BN content. The ceramic composites showed good machinability with BN addition.