Boron Nitride Matrix Research Articles

Synthesis of 2D-Material(G,GO,rGO,h-BN)-Magnetic(Fe,Fe3O4)Nanocomposites

For the purpose of synthesizing 2D-Material–Magnetic nanocomposites, several new modifications of existing 2D-materials synthesis methods by exfoliation and chemical synthesis from liquid charge are developed. Using them, graphene (G), graphene oxide (GO), reduced graphene oxide (rGO) and hexagonal boron nitride (h-BN) matrix magnetic nanocomposites for the first time are obtained by coating or intercalation their nanoparticles with ferromagnetic iron (Fe) or ferrimagnetic iron oxide – magnetite (Fe3O4). These materials are prospective for variety of high tech applications. In particular, h-BN–Fe3O4 composite nanoparticles can serve for neutron-capturing boron isotope 10B effective delivery agents in BNCT (Boron Neutron Capture Therapy) of cancer as they allow the controlling by an external magnetic field targeting to tumor tissue.

Numerical Analysis and Experimental Study on Side Dam Temperature and Stress Field of Two‐Roll Casting

The side sealing technology is crucial for ensuring the quality and process stability in twin‐roll casting (TRC). Investigating the temperature and stress distribution in side dams under operational conditions is vital, especially in understanding the causes of side dam fractures. Optimal performance of side dam materials is achieved when the boron nitride (BN) matrix is fine and homogeneous, with zirconium dioxide (ZrO2) and silicon carbide (SiC) particles evenly dispersed throughout. The fracture of the side dam after casting is mainly caused by BN interlamellar tear. The coexistence of BN lamellar tearing and BN layer fracture leads to the fracture of the side dam during the casting process. Through finite element simulation, the effects of variables such as pouring temperature, preheating temperature, and side dam thickness on temperature and stress distribution were analyzed. The findings indicate that a preheating temperature range of 1200–1300 °C minimizes thermal stress in the side dam. Building on these findings, a composite structure for the side dam is developed. Both internal and external composite structures have shown significant effectiveness in reducing thermal stress. These results are pivotal in extending the service life of side dams and enhancing the stability of the TRC process.

Obtaining Boron Carbide and Nitride Matrix Nanocomposites for Neutron-Shielding and Therapy Applications

The very high capture cross-section of (epi)thermal neutrons by the boron isotope 10B makes elemental boron and its compounds and composites prospective for serving as materials intensively interacting with neutron irradiation. In their nanostructured form, boron-rich materials reveal properties that improve their radiation-performance characteristics. In this regard, new technologies have been proposed for the synthesis of nanocomposites with matrices of boron carbide B4C and hexagonal boron nitride h-BN. For the first time, boron carbide-tungsten and hexagonal boron nitride–(iron,magnetite) composites were obtained, respectively, in the form of layered/sandwich structures of components B4C and W and h-BN nanopowders coated/intercalated with magnetic nanoclusters of iron Fe or magnetite Fe3O4. Studying of their chemical/phase composition, structure/morphology, and some other properties leads to the conclusion that the developed B4C–W and h-BN–(Fe,Fe3O4) composites would be useful for solving important problems of boron-based neutron shielding and BNCT (Boron Neutron Capture Therapy), such as attenuating the gamma-radiation accompanying the absorption of neutrons by 10B nuclei and targeted delivery of 10B nuclei, as BNCT therapeutic agents, to tumor tissues using control by an external magnetic field, respectively.

Physicochemical Fundamentals of the Synthesis of a Cu@BN Composite Consisting of Nanosized Copper Enclosed in a Boron Nitride Matrix

The thermal reduction of the copper(II) complexes [CuII(N2H4)3][B10H10]·nH2O (I·nH2O) and [CuII(NH3)4][B10H10]·nH2O (II·nH2O) has been studied in an argon atmosphere at 900 °C. It has been found that the annealing of both compounds results in a Cu@BN boron-containing copper composite. It has been shown that this process leads to the formation of a boron nitride matrix doped with cubic copper(0) nanoparticles due to the copper(II)→copper(I)→copper(0) thermal reduction. The phase composition of annealing products I900 and II900 has been determined based on powder X-ray diffraction, IR spectroscopy and thermal analysis data. The morphology, average particle size and composition of the composite have been determined by TEM and high-resolution TEM + EDS. The average particle size has been found to be about 81 nm and 52 nm for samples I900 and II900, respectively. Comparison of the results obtained using physicochemical studies has shown the identity of the composition of the products of annealing I900 and II900. The electrical properties of a coating based on an I900 sample modified with Cu0→Cu2O in situ during deposition on a chip at 300 °C in air have been studied. As a result, with increasing temperature, an increase in the electrical conductivity characteristic of semiconductors has been observed.

Effects of heating rate on mechanical and dielectric properties of the Si3N4f/BN/Si3N4 composites by PIP

The fabrication of silicon nitride (Si3N4) fiber-reinforced boron nitride (BN) and Si3N4 matrix (Si3N4f/BN/Si3N4) composites with BN interphase through precursor infiltration and pyrolysis (PIP) process is reported. The effects of heating rate during PIP process on mechanical and dielectric properties of composites are analyzed. When the heating rate is 5 °C/min, the overall performance of Si3N4f/BN/Si3N4 composites is optimal, and the flexural strength and fracture toughness attain 138 MPa and 5.7 MPa m1/2, and the dielectric constant and dielectric loss are 3.90 and 0.008, respectively. The composites achieve a synergy combining structural with functional properties. The influence mechanism of the heating rate during PIP process on the Si3N4f/BN/Si3N4 composites disclose the following. First, the heating rate makes an effect on the carbon content in the Si3N4 matrix, and consequently the dielectric properties of the composites are changed. Second, at 8 °C/min, the modulus of Si3N4 matrix is the lowest due to the existence of nanopores. At 2 °C/min, the strong axial tensile stress results in severe cracking of the Si3N4 matrix, so the matrix modulus decrease. Third, the heating rate strongly affects the radial stress state at the interphase, which affects the interfacial shear strength of the composites. The matrix modulus and interfacial shear strength can be optimized at 5 °C/min to improve the mechanical properties of the composites.

Texture and anisotropy of hot-pressed h-BN matrix composite ceramics with in situ formed YAG

Textured hexagonal boron nitride (h-BN) matrix composite ceramics were prepared by hot-pressing using different contents of 3Y2O3−5Al2O3 (molar ratio of 3:5) as the sintering additive. During hot-pressing, the liquid Y3Al5O12 (YAG) phase showing good wettability to h-BN grains was in situ formed through the reaction between Y2O3 and Al2O3, and a coherent relationship between h-BN and YAG was observed with {left[ {010} right]_{{rm{h}} - {rm{BN}}}}{rm{//}}{left[ {111} right]_{{rm{YAG}}}} and (002)h-BN//(321)YAG. In the YAG liquid phase environment formed during hot-pressing, plate-like h-BN grains were rotated under the uniaxial sintering pressure and preferentially oriented with their basal surfaces perpendicular to the sintering pressure direction, forming textured microstructures with the c-axis of h-BN grains oriented parallel to the sintering pressure direction, which give these composite ceramics anisotropy in their mechanical and thermal properties. The highest texture degree was found in the specimen with 30 wt% YAG, which also possesses the highest anisotropy degree in thermal conductivity. The aggregation of YAG phase was observed in the specimen with 40 wt% YAG, which resulted in the buckling of h-BN plates and significantly reduced the texture degree.

Enhanced mechanical properties of cBN-Al-Si3N4 composites by introducing diamond

Cubic boron nitride (cBN) matrix composites were fabricated by introducing submicron diamond under high pressure and high temperature (5.5 GPa, 1500 °C). A systematic evaluation of the effects of diamond content on phase composition, microstructure, and mechanical properties of the composites was conducted. We found that diamond has a significant effect on improving the mechanical properties of the composite. The introduction of a small amount of submicron diamond is beneficial to obtain a dense microstructure. The hardness of the composite increased monotonously with increasing diamond content, and the maximum value reached 54.92 GPa. With diamond content of 4 wt%, flexural strength, relative density, and fracture toughness of the composite all reached the maximum value, which was 726.27 MPa, 99.21%, and 7.46 MPa·m1/2, respectively.

Effect of resonant core-level excitation in an atom on photoemission from the neighboring atoms

The effect of a core-to-valence resonant photoexcitation in an atom on photoemission from the neighboring atoms has been experimentally investigated. The samples investigated were simple silicon compounds composed of two kinds of atoms (SiO 2 and Si 3 N 4 ). For SiO 2 fine powder mixed with boron nitride matrix, it was found that the intensity of the O 1 s photoelectrons was reduced around the Si 1 s → 3 p * resonant photoexcitation. On the other hand, the intensity of the B 1 s or N 1 s photoelectrons from the matrix material did not change regardless of the photon energy. Similar phenomenon was also observed for Si 3 N 4 powder mixed with cellulose as a matrix material. The results demonstrated that photoemission from the nearest-neighbor atoms that are directly bound to silicon is reduced by the core-to-valence resonant photoexcitation in silicon. Using the phenomenon, it is expected that species of the nearest neighbor atom can be identified by a resonant core-level excitation in a target atom.

Dynamics of Emim+ in [Emim][TFSI]/LiTFSI Solutions as Bulk and under Confinement in a Quasi-liquid Solid Electrolyte.

Quasi-liquid solid electrolytes are a promising alternative for next-generation Li batteries. These systems combine the safety of solid electrolytes with the desired properties of liquids and are typically formed by solutions of Li salts in ionic liquids incorporated into solid matrices. Here, we present a fundamental understanding of the transport properties in solutions of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][TFSI]), either in bulk form or incorporated in a boron nitride (BN) matrix. We performed a series of quasi-elastic neutron scattering experiments that, given the high incoherent neutron scattering cross section of hydrogen, allowed us to focus on the Emim+ dynamics. First, [Emim][TFSI]/LiTFSI solutions (0.5 and 2.5 mol·kg-1) were investigated and we show how the increase in the concentration reduces the Emim+ mobility and increases the activation energy of their long-range motions. Then, the 0.5 mol·kg-1 solution was incorporated into the BN matrix and we report that the diffusivities of the Emim+ cations that remain mobile under confinement are highly accelerated in comparison with the bulk sample and the activation energy of these motions is drastically reduced. We present the experimental evidence that this effect is related to the content of the Emim+ cations immobilized near the surfaces of the BN pores.

Boron nitride self-assembly cladding structure promoting thermal property and dimensional stability of polymer composites

A common problem in thermal conductive materials is poor interface compatibility between fillers and the matrix, which has caused high interfacial thermal resistance and lower thermal conductivity than expected. In this work, highly reactive graphene oxide (GO) was introduced as a bridge to simplify the complex surface treatment between inactive boron nitride (BN) and inert polyolefin matrix. Through electrostatic self-assembly and rapid alkylation modification in aqueous solution, the BN coated by modified GO (BN@MGO) is acquired. After treatment, the surface concentration of C element has increased for an order of magnitude, which builds a strong interface interaction between fillers and polypropylene (PP). Later in-situ reduction improved phonon matching of hybrid fillers and furtherly reduced phonon interface scattering. The effects of structure and dispersion on performance were characterized. The thermal conductivity of PP/BN@RGO composites is 22.8 and 1.9 times higher than that of the raw PP and PP/BN, respectively. Modified Hashin-Shtrikman model demonstrates that PP/BN@RGO composites possess lower thermal resistance. Tortuous path effect and high thermal stability make the composites exhibit highly flame-retardant property. The thermal expansion coefficient of the material is also effectively reduced to 26.58 ppm/°C. The comprehensive features of PP/BN@RGO make it a promising material with broad potential in highly efficient heat dissipation electronic equipment, household appliances and thermal management field.

The effects of holding time on grain size, orientation degree and properties of h-BN matrix textured ceramics

Hexagonal boron nitride (h-BN) matrix textured ceramics were prepared by hot pressing sintering assisted with grain rearrangement during Digital Light Processing (DLP), using CaO-Y2O3-Al2O3 as a sintering additive. The effects of holding time on h-BN grain size, texture degree, mechanical and thermophysical properties were investigated. Under liquid phase sintering, the C-axis of the flaky h-BN grains was preferentially arranged in the direction parallel to the sintering pressure. With the increase of holding time, the texture degree of the material was gradually improved, and the mechanical and thermal physical properties of anisotropy were gradually enhanced. When the holding time was 4 h, the material had the most typical anisotropic characteristic and properties. Grain size and grain orientation degree were the main factors affecting the anisotropic properties.

Preparation of highly oriented h-BN based textured ceramics via grain rearrangement under DLP printing and low-pressure sintering

Highly textured hexagonal boron nitride (h-BN) matrix ceramics with Al2O3 and Y2O3 as sintered additives were fabricated by digital light processing (DLP) printing and hot-press (HP) sintering. The orientation degree of sintered h-BN-Y3Al5O12 (YAG) ceramic was evaluated by X-ray diffraction and pole figures. Due to the highly textured character, the BN-YAG ceramic shows obvious anisotropic thermal conductivity. By using the rearrangement of crystal grains during photocuring, a textured ceramic having high orientation degree can be prepared under a short holding time and a low sintering pressure.

Controlling current flow in sintering: A facile method coupling flash with spark plasma sintering.

A facile method is described to couple flash sintering (FS) and spark plasma sintering (SPS). Flash spark plasma sintering (FSPS) combines advantages of both techniques: the use of pellet-shaped samples under mechanical load with the controlled passage of electric current through the sample. FSPS is realized by partially replacing graphite pressing tools (two punches and one matrix) used in standard SPS. An insulating boron nitride matrix substitutes the conducting graphite matrix to force the electric current through the sample. Additionally, external heating of the boron nitride matrix is implemented. Microstructures of standard and flash-SPS are compared using aluminum doped zinc oxide as an example. Scanning electron microscopy reveals that different microstructures are generated for SPS and FSPS. The new setups provide novel processing routes for different current sintering methods of materials under mechanical load and assist in identifying the role of the electric current or field in the microstructure.

Microstructure and mechanical properties of Si3N4f/BN composites with BN interphase prepared by chemical vapor deposition of borazine

The boron nitride (BN) interphase of silicon nitride (Si3N4) fiber-reinforced BN matrix (Si3N4f/BN) composites was prepared by chemical vapor deposition (CVD) of liquid borazine, and the microstructure, growth kinetics and crystallinity of the BN coating were examined. The effects of coating thickness on the mechanical strength and fiber/matrix interfacial bonding strength of the composites were then investigated. The CVD BN coating plays a key role in weakening the interfacial bonding condition that improves the mechanical properties of the composites. The layering structure of the BN coating promotes crack propagation within the coating, which leads to a variety of toughening mechanisms including crack deflection, fiber bridging and fiber pull out. Single-fiber push-out experiments were performed to quantify the fiber/matrix bonding strength with different coating thicknesses. The physical bonding strength due to thermal mismatch was discussed.

Surface modification of boron nitride by bio‐inspired polydopamine and different chain length polyethylenimine co‐depositing

We established a novel, easy, and versatile method of obtaining diverse and controllable interphases between epoxy resin and fillers. The method involved the co‐deposition of polydopamine (PDA) and polyethyleneimine (PEI) with different molecular lengths on boron nitride (BN) surface. The obtained PDA/PEI‐modified BN composites showed significantly improved mechanical properties, including tensile strength, toughness, and elongation at break. For example, the tensile strength, fracture toughness, and elongation at break of EP composite increased by 51%, 132%, and 170% compared with EP when the PEI molecular weight was 10 000, respectively. These results suggested that the interphases between BN and EP matrix can be adjusted by changing the molecular lengths of grafted modifiers, thereby offering a new method for the reasonable designing and exploitation of the BN‐based composite materials.

Preparation of h-BN-Based Textured Ceramics by Grain Rearrangement During Ultraviolet Curing Assisted Hot-Press Sintering

Highly textured hexagonal boron nitride (h-BN) matrix ceramics with Al2O3 and Y2O3 as sintered additives were fabricated by digital light processing (DLP), stereolithography (SLA) 3D pringting and hotpress (HP) sintering. The orientation degree of sintered h-BN-YAG ceramic was evaluated by X-ray diffraction and pole figures. Due to the highly textured character, the BN-YAG ceramic shows obvious anisotropic thermal properties. By using the rearrangement of crystal grains during photocuring, a textured ceramic having high orientation degree can be prepared under a short holding time and a low sintering pressure.

Comparative study on the joining performance of TiH2 and ZrH2 modified AgCu28 brazing alloys with pulsed laser welding-brazing

Brazed alloys between cubic boron nitride (cBN) grits and matrix extremely affect the service life of the grinding wheel. The aim of this study was to investigate the addition of elemental Zr to improve the connection effect of alloys. The plates of pure titanium (Ti) Gr. 1 and AISI 1045 steel had been applied to conduct the welding-brazing experiments with active brazing alloys of AgCu28-4.5Ti and AgCu28-4.5Ti-4Zr. Brazing alloys was heated with an Nd:YAG pulsed laser welding-brazing system under inert argon gas atmosphere. Transition zones between the brazed alloys and matrices were investigated with scanning electron microscope (SEM), energy dispersion spectrometer (EDS), and X-ray diffraction (XRD) analyses. In addition, hardness of the brazed layer was analyzed as well as tribology. The results showed that the active element, zirconium (Zr), significantly accelerated the bidirectional diffusion and improved the gradient evolution of the main elements in the transition zones. Compared to Zr-free brazing alloys, the active element, Zr, inhibited the overproduction of the hard-brittle phase of Cu3Ti and formed other intermetallic compounds, such as AgZr2 and Cu10Zr7, which were beneficial to the metallurgical joint. A brazed layer with a lower friction coefficient, a more uniform hardness distribution, and better ductility was obtained, though the wear resistance slightly decreased. A solid solution product of Zr-Cu was formed during laser welding-brazing process, which strengthens the brazed layer and improves its overall performance.

Anisotropic properties of textured h-BN matrix ceramics prepared using 3Y2O3-5Al2O3(-4MgO) as sintering additives

Textured hexagonal boron nitride (h-BN) matrix composite ceramics were prepared by hot pressing using 3Y2O3-5Al2O3 (mole ratio of 3:5) and 3Y2O3-5Al2O3-4MgO (mole ratio of 3:5:4) as liquid phase sintering additives, respectively. During the sintering process with liquid phase environments, platelike h-BN grains were rotated to be perpendicular to the sintering pressure, forming the preferred orientation with the c-axis parallel to the sintering pressure. Both h-BN matrix ceramic specimens show significant texture microstructures and anisotropic mechanical and thermal properties. The h-BN matrix ceramics prepared with 3Y2O3-5Al2O3-4MgO possess higher texture degree and better mechanical properties. While the anisotropy of thermal conductivities of that prepared with 3Y2O3-5Al2O3 is more significant. The phase compositions and degree of grain orientation are the key factors that affect their anisotropic properties.

A comparative study of characterization and water absorption behaviour of polyester composites with inorganic and organic fibers

Abstract The research deals with fabrication and characterization of h-BN composites with polyester as the matrix material as well as hybrid composites incorporating inorganic as well as organic filler. The inorganic ceramic filler like h-BN tends to enhance the thermal properties and imparting moisture resistant properties whereas organic fillers like Peanut husk increases the strength and stability of the composites. The implications of embedment of h-BN on the thermal conductivity (keff), mechanical characteristics, and morphological parameters are apprehended. It is observed that increase in filler content increases the effective thermal conductivity. With 35 wt% of h-BN the improvement of keff is appreciably elevated to 23.69%.In case of hybrid composites, the keff value decreases to some extent due to insulative property of peanut husk fibers but shows an improvement in mechanical properties with addition of peanut husk fibers. Therefore, thermal conductivity is compromised a little for achieving a balance between physical, mechanical and thermal properties. Though theoretical Rule of Mixture model aids to be well co-correlation to estimate keff for spherical Boron Nitride particles in composites, a better model is proposed for the same. At about filler volume fractions more than 20%, there is a conductivity jump in the composites because of the interaction between Boron Nitride particles and matrix forming conductive networks and this phenomenon occurs at a volume fraction called the percolation threshold. Hence, with higher thermal conductivity and good mechanical properties with very low water absorption, composites with appropriate amount of particulates can be utilized in various fields like heat engine laminates, engine casings, military equipments, fins and heat sinks, printed circuit board substrates etc. where faster heat transfer is a necessity.

Silane surface modification of boron nitride for high thermal conductivity with polyphenylene sulfide via melt mixing method

Polyphenylene sulfide (PPS) is a promising engineering polymer, which is used for various industrial applications. In this study, we developed a highly thermally conductive PPS composite containing boron nitride (BN) as a thermally conductive ceramic filler. (3‐Aminopropyl) triethoxysilane was doped onto the surface of hydroxyl‐functionalized BN using a simple sol–gel process. The modified BN particles were embedded in a PPS matrix via a melt mixing process using a twin extruder to form BN‐Si composites. The maximum thermal conductivity 3.09 W/m·K was exhibited by the surface‐modified BN‐Si containing 60 wt%. This value was 116% higher than the thermal conductivities of the pristine BN and PPS matrix, respectively. The surface‐treated composites also showed an improved storage modulus because of an improvement in the interfacial adhesion and interaction between the BN filler and the PPS matrix. Copyright © 2017 John Wiley & Sons, Ltd.