Hexagonal Boron Nitride Powder Research Articles

On the analysis of physical properties of thermal interfaces based on hexagonal boron nitride and copper

The physical properties (thermal and thermal diffusivity) of thermal interfaces based on powdered boron nitride with a hexagonal crystal lattice (h-BN) and copper with a cubic crystal lattice (Cu) for cooling the electronic component base of micro- and nanoelectronics are studied. The physical properties are determined by the flash method. The prospects of using pressed hexagonal boron nitride powder as a thermal interface without using a binder are described. A comparison with the physical properties of other thermal interfaces that are widely used at present is made.

Production of few-layer graphene and boron nitride nano onions via lamp ablation

Abstract Few-layer graphene, and separately, boron nitride nano onions have been synthesised by a novel lamp ablation method which is a one-step, high-yield process that is catalyst-free, devoid of toxic reagents, with short reaction times, and potentially scalable. The precursor for the few-layer graphene is graphite flake, while that of boron nitride nano onions is hexagonal boron nitride powder. Product nanostructures are characterised by high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS). We also report on our commercialisation trajectory to translate promising research findings in the laboratory to the market. For the few-layer graphene product, it is presently on a pre-commercial pilot plant phase.

Tribological and Structural Effects of Titanium Carbide and Hexagonal Boron Nitride Reinforcement on Aluminum Matrix Hybrid Composites

This research involves the synthesis of a hybrid composite by adding titanium carbide (TiC) and hexagonal boron nitride (hBN) powders in certain weight ratios (2.5–5%) to pure aluminum (Al) powder. When previous studies were examined, it was seen that TiC and hBN powders were added separately to Al matrix powders; however, a hybrid composite was not produced as in this study. The obtained hybrid composites were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and X-ray diffraction (XRD) analysis. Microstructure, hardness and wear tests were carried out under 3 different loads (10 N, 20 N and 30 N) and dry conditions. Weight loss and coefficient of friction measurements were obtained for each hybrid composite during the wear tests. The TiC–hBN-reinforced specimen exhibited a significantly higher hardness value of 37.08% compared to the pure Al composite. It was also found that the synthesized Al–TiC–hBN hybrid composite exhibited a 59% reduction in the wear loss value for 10 N load, 30% for 20 N load and 60% for 30 N load compared to the pure Al sample. It is believed that the hybrid composites produced in this study have the ability to compete with Al matrix materials and exhibit the potential for longer durability and cost reduction in industries that use the production of aluminum parts.

Study of the wear resistance of composite coatings modified with h-BN particles on AZ31 magnesium alloy

A low wear resistance is a significant disadvantage of magnesium-based alloys widely used in industry. The results of plasma electrolytic oxidation (PEO) carried out in an aqueous-alkaline phosphate electrolyte with the addition of hexagonal boron nitride (h-BN) powder to obtain coatings with greater wear resistance on the surface of AZ31 magnesium alloy are presented. The PEO method is one of the most promising for surface treatment of magnesium alloys, since oxidation is carried out in alkaline aluminate, silicate or phosphate electrolytes with various functional additives. The addition of nanocrystalline hexagonal h-BN powder in the form of a suspension into the electrolyte volume does not affect the electrical parameters of PEO, and h-BN particles are incorporated into the structure of the formed composite coating, increasing the wear resistance. It is shown that the resulting coatings have a relief typical of PEO with developed morphology and porosity, which change depending on the oxidation time. In this case, the incorporation of h-BN particles into the coating occurs by an inert mechanism, since they do not undergo chemical transformations with the formation of new phases. Composite coatings obtained on the surface of the AZ31 magnesium alloy by the PEO method consist of crystalline phases of MgO and Mg3(PO4)2, regardless of the addition of h-BN particles to the electrolyte. The wear resistance of coatings is 6 – 8 times higher compared to the untreated alloy. The results obtained can be used to produce PEO coatings with increased wear resistance and use them in various sectors of the economy.

Unraveling the Photoluminescence Properties of a Boron Nitride Nanosheet Dispersed in Different Solvents and Its Application to Generate White Light.

Hexagonal boron nitride (h-BN) is an influential 2D nanomaterial; however, its practical optoelectronic applications rely primarily on controlling the structural defects. The photoluminescence depends explicitly on the developed vacancies and substitutional defects. The present work utilizes the concept of facile liquid-phase exfoliation of hexagonal (h) boron nitride (BN) powder in common organic solvents and cosolvent mixtures to obtain a layered boron nitride nanosheet (BNNS). Although the literature concerning the layered structure of BNNS obtained by different methods is substantial, what is lacking is a detailed photoluminescence study of the layered structure obtained by changing the solvent and cosolvent mixtures, and here lies the novelty of our work. The obtained layered structure was subjected to a detailed photoluminescence study by varying the temperature. We tried to correlate how the defects originating upon changing the solvent and cosolvent affected the photoluminescence of the layered BNNS. The obtained layered structure is suitably supported by optical and electron microscopy images. High-resolution transmission electron microscopy confirm the presence of a few layers, and X-ray photoelectron spectroscopy studies give an idea of the atomic composition of the obtained BNNS. The photoluminescence properties of the obtained BNNS in water were modulated by the addition of two different classes of block copolymers, e.g., Pluronic (F-68, P-407, and P-123) and Tetronic (T-904, T-908, and T-90R4) copolymers. As an application, we were successful in constructing a nanocomposite material made up of a BNNS-copolymer-organic fluorophore to check the possibilities of generating white light.

Alkylated modified boron nitride nanosheets/polyimide composite films with advanced thermal conductivity and low dielectric constant

Owing to the rapid development of the latest micro-electronic devices, polymer composite materials that combine high thermal conductivity and low permittivity have aroused the interest of researchers. However, it is a huge challenge to balance the above parameters. In this work, hexagonal boron nitride (h-BN) powder was ultrasonically exfoliated to obtain alkylated boron nitride nanosheets (Alkyl-BNNS). Then, a series of polyimide (PI) composites were synthesized with different amounts of Alkyl-BNNS. Attributed to more robust interfacial non-covalent interactions between Alkyl-BNNS and polymer chains to inhibit interfacial polarization, Alkyl-BNNS can be scattered well in PI substrate. Thus, the obtained PI composite behaved a high thermal conductivity of 6.21 W/(mK) and a low dielectric constant (3.23) under the load of 20 wt%. Besides, Alkyl-BNNS/PI composites have efficient thermal management capability, low water absorption, favorable electrical resistance, and prominent tensile strength. Importantly, these composite films are expected to be excellent candidates in the field of microelectronics.

Selective oxidation of methane to CO on Ni@BOx via reaction-induced vapor migration of boron-containing species onto Ni

Dynamic migration of support-derived species and subsequent encapsulation of supported metal nanoparticles (NPs) are the well-known features of the Strong Metal-Support Interaction (SMSI) effect. Here, we report occurrence of the classical SMSI state in physical mixture of Ni NPs and porous hexagonal boron nitride powder (Ni|pBN) during methane oxidation reaction at 600 ℃, in which Ni NPs are encapsulated by BOx overlayers derived from the pBN component. The SMSI state can switch the methane oxidation selectivity from CO2 on the fresh Ni|pBN catalyst to CO on the used catalyst. The encapsulation of Ni NPs by BOx overlayers has also been observed in Ni/Al2O3 catalyst which is physically mixed with pBN. Comprehensive characterizations confirm that the SMSI state is induced by vapor migration of boron-containing species e.g. BOxHy from pBN to metal surfaces, in which both high reaction temperature and water product play an important role.

Preparation of boron carbon oxynitride phosphor films with compositional and spectral tunability by chemical vapor deposition

Boron carbon oxynitride (BCNO) phosphor films exhibiting tunable chemical compositions and photoluminescence (PL) spectra were grown by chemical vapor deposition utilizing a laser using an alkylamido precursor with an oxidation gas. BCNO films exhibiting a dense, uniform microstructure and a turbostratic boron nitride (BN) structure was grown on a silicon substrate at 1323 K. Chemical bonding states investigated by X-ray photoelectron spectroscopy and X-ray absorption near edge structure of the BCNO films were like the hexagonal BN powder counterparts. The typical chemical compositions of BCNO phosphor films were B0.46−0.47C0.12−0.14N0.30−0.34O0.07−0.11, which was varied by regulating flow rates of the oxidation gas. The PL spectra generated under excitation at 360 nm exhibited multiple emission bands at 386, 405, 430, 473, 534, and 570 nm. BCNO films grown using higher C and O concentrations exhibited intensified PL peaks at 534 and 570 nm.

Investigation of the Role of Calcium Borate in the Growth of Hexagonal Boron Nitride Particles

Hexagonal boron nitride (h-BN) powder is a promising thermally conductive filler in resins and controlling its particle size is important. To obtain h-BN powder with a large particle size as well as high purity and crystallinity, high-temperature heat treatment over 1800 oC in N2 gas atmosphere is effective. Carbothermal reduction nitridation (CRN) involves carbothermic reduction of boric oxide in N2 gas atmosphere. In CRN using a CaO promoter, h-BN particles with large sizes can be produced through a simple heat-treatment process. During CRN, CaO forms calcium borate (CaO-B2O3), which prevents the vaporization of B2O3 and promotes h-BN particle growth at high temperatures. Up to now, the effect of CaO-B2O3 on the growth of h-BN particles during CRN is unclear. In this study, the role of CaO-B2O3 in the growth of h-BN particles during CRN was clarified via experimentation using various approaches. The results led to the ideal reaction process of CRN using a CaO promoter to produce large-particle-size h-BN powder.

EFFECT OF HBN ON WEAR OF AlCrN-COATED SPARK PLASMA - SINTERED TiB2/Ti COMPOSITES AT TEMPERATURES UP TO 900°C

In this work, hexagonal boron nitride powder was used for the lubrication of an interface of TiB2/Ti composite protected by an AlCrN coating and a ceramic Si3N4 ball. The wear behaviour of this tribo-pair in an oscillating motion was studied with an SRV tribotester at the temperature range from room temperature to 900 °C. The action of hexagonal boron nitride as a solid lubricant was analysed with the use of a 3D microscopy and energy-dispersive spectroscopy. The test results confirmed that under high-temperature conditions, the use of hexagonal boron nitride as a solid lubricant does not increase the wear resistance of the TiB2/Ti composite. The use of the AlCrN coating significantly reduces wear at the temperature up to 600 °C only, while the combined use of the AlCrN coating and hBN lubrication provides effective protection against wear even at the temperature up to 900 °C. Therefore, the synergy of the anti-wear action of the coating and the solid lubricant was proved.

Synthesis of highly purified and crystallized h‐BN using calcium‐assisted carbothermal reduction nitridation

AbstractHighly purified and crystallized hexagonal boron nitride (h‐BN) powder is suitable as thermally conductive filler in resins. To obtain h‐BN powder with large particle size, as well as high purity and crystallinity, high‐temperature heat treatment over 1800°C in a N2 gas atmosphere is effective. The carbothermal reduction nitridation (CRN) involves the carbothermic reduction of boric oxide in a N2 gas atmosphere. In CRN using a CaO promoter, h‐BN particles with high crystallinity can be obtained by a simple heat treatment process. CaO prevents the evaporation of boron oxide and aids in h‐BN particle growth at high temperatures. However, CaB6 is formed as byproduct or impurity when CRN using the CaO promoter is performed at temperatures higher than 1800°C. In this study, the relationship between the products and the reaction temperature was clarified via thermodynamic considerations and experimentation. The results clarified the ideal reaction process of CRN using a CaO promoter to obtain highly purified and crystallized h‐BN powder.

Two-Dimensional Hexagonal Boron Nitride Nanosheets as Lateral Heat Spreader With High Thermal Conductivity

A highly thermally conductive heat spreader for applications in electronic devices is becoming increasingly demanding, and therefore the removal of excess heat requires an efficient heat dissipating device. Boron nitride nanosheets (BNNSs) were prepared as thermally conductive fillers using hexagonal boron nitride (h-BN) powder as raw material by a water exfoliation method. A composite film was prepared by vacuum filtration using cellulose nanofibers (CNFs) as the substrate with an in-plane thermal conductivity (TC) of 82.4 W m−1 K−1, thermal conductivity enhancement increasing by 9,486% compared to pure cellulose film. Thus, CNF/BNNS composite films are promising as effective thermal interface materials (TIMs) in electronic devices and electronic component applications.

INVESTIGATION OF POLYURETHANE-BASED HALLOYSITE NANOTUBE AS SOLID-SOLID PHASE CHANGE MATERIAL FOR THERMAL ENERGY STORAGE

Halloysite nanotubes (HNTs) have become one kind of promising supporting material for composite phase change materials (PCMs) owing to their nanostructure, the hollow tubule structure, and high surface area. In the present study, a novel solid-solid phase change material (SSPCM) was prepared based on polyethylene glycol as the soft segment and HNTs as the rigid segment through the two-step polymerization method. As a result, the prepared SSPCMs possess a steady crosslinking structure, and the SSPCMs own good crystallization properties. The SSPCM (PEG, 86.5 wt %) has high phase change enthalpy (tm is 56.49 ℃, ΔHendo is 149.0 J/g) and good crystallinity of 89.1%. Moreover, the TGA results reveal that the SSPCMx has good thermal reliability. Besides, hexagonal boron nitride (h-BN) and graphite powder (GP) were added into the system to optimize the thermal transfer properties, and the thermal conductivities of synthesized SSPCMs can be enhanced 59.0% as compared with that of pure PEG which is 0.196 W/(m K). It can be concluded that the SSPCMs possesses not only excellent phase change properties but also outstanding thermal reliability and a fast thermal response rate. Herein, the synthesized SSPCM displays the promising potential for thermal energy storage application.

Increase of durability of CCM rollers by electric arc surfacing method with use of promising surfacing materials. Part 1. Structure, phase composition and properties of deposited layers

Experimental compositions of flux-cored wires for electric arc surfacing of rollers of continuous casting machine at JSC OEMK named after A.A. Ugarov. To improve the properties of the deposited layers, refractory components were introduced into the charge of the base wire ASM 4603-SA: micro- and nanodispersed powders of tungsten carbide (3–12 %), as well as hexagonal boron nitride powder (0.1–0.2 %). A complex of studies of the structure, composition and properties of the deposited layers has been carried out. An increase in the content of the refractory WC additive in the ASM 4603-SA charge from 3 % to 12 % promotes an increase in the hardness of the deposited layer from 48.9 HRC to 55.1 HRC. The maximum hardness of the deposited layer is set for the specimen deposited with the ASM VI wire – 57.1 HRC. It was found that the phase composition of the deposited layers consists of solid solutions based on α-Fe and γ-Fe iron. The maximum amount of α-Fe was found in the layer deposited with ASM VI wire (84 %). It is shown that the structure of the deposited layers consists of martensite grains surrounded by interlayers of austenite.

Structural evolution of hexagonal boron nitride powder by Bead-milling

The structural evolution of h-BN powder by bead-milling is investigated. A unique initial stage in h-BN milling is discovered in which the x-ray diffraction (XRD) out-of-plane (0 0 2) and (0 0 4) peak intensities increase distinctly up to 3 and 4.8 times respectively, corresponding to an effective c-axis ordering of the h-BN particles. The structural evolution of h-BN due to milling is correlated to the change in the dominant milling mechanism from out-of-plane cleaving to in-plane cutting. An abnormal contraction of out-of-plane (0 0 2) interplanar spacing up to 0.044 Å due to bead-milling is reported, which could be attributed to the introduction of oxygen functional groups (B-O and N-O) on the h-BN powder.

Luminescence properties of hexagonal boron nitride powders probed by deep UV photoluminescence spectroscopy.

Deep ultraviolet (UV) photoluminescence (PL) spectroscopy was employed to study the luminescence properties of hexagonal boron nitride (h-BN) crystal powders after annealing the samples at different temperatures in the range of 100–900 °C for 1 h in ambient air. The PL spectrum from the h-BN powder samples annealed around 700 °C showed strong luminescence intensity at 5.49 eV along with enhanced phonon-assisted band-edge emission at 5.90 eV. Additionally, it revealed sharp atomic-like emission lines in UV region at 4.10, 4.12, 4.14, and 4.16 eV with line widths less than 1 nm from the annealed samples which were not present in the unannealed samples. Power- and temperature-dependent PL measurements of the sharp atomic-like emission lines exhibited robust nature of the energy peak positions. Based on the theoretical reports, the sharp emission lines could be carbon-related defects.

Synthesis of size-controlled and in-situ OH functionalized hexagonal boron nitride powder by hetero-phase reaction

Hexagonal boron nitride (h-BN) is one of the most attracting insulating ceramics for the application as thermal interface materials (TIM) because it possesses high thermal conductivity coupled with electrical insulation property. Although the uniform size control of h-BN is a crucial factor in quality control of the TIM, the synthetic technology of h-BN with uniform and narrow size distribution has been limited, and the typical scale-up process necessitates high-temperature reaction involving the use of toxic vapor reactants of boron and nitrogen sources. In this research, we present a simple fabrication process for single-step massive production of size controlled in-situ hydroxyl group functionalized h-BN powder. The main idea behind the synthesis of h-BN powder lies in the application of liquid-vapor phased reactants coupled with calcination at reduced temperature, rather than other typical synthetic processes of h-BN in a semi-closed system. Analysis showed that the lateral size of h-BN is controlled between 20 and 225 nm with a narrow distribution. The h-BN powder forms hydroxyl groups via in-situ synthesis.

Effect of Boron Nitride Addition on Densification, Microstructure, Mechanical, Thermal, and Dielectric Properties of β-SiAlON Ceramic

In this present communication, an investigation was carried out to examine the influence of hexagonal boron nitride (h-BN) powder addition and its particle size on the density, microstructure, mechanical, thermal, and dielectric properties of h-BN containing β-SiAlON ceramic. It was observed that with the increase in BN content up to 5 wt.% in starting composition, the bulk density of β-SiAlON decreases drastically from 3.22 (for pristine SiAlON) to 3.05 g/cm3 and 2.90 g/cm3 for small and large particle size containing β-SiAlON, respectively. The bulk density and mechanical properties such as Young’s modulus, Vickers hardness, flexural strength, and fracture toughness of pristine β-SiAlON are superior in comparison with both types of β-SiAlON-BN ceramic. On the other side, the density and mechanical properties of β-SiAlON prepared with fine BN powder show superior value compared to that of larger BN particle-added β-SiAlON. The thermal properties such as thermal conductivity for both BN powder-added β-SiAlONs are higher compared to that of pristine β-SiAlON. However, larger BN particle-added β-SiAlON exhibits superior thermal conductivity than that of fine BN powder-added β-SiAlON. The dielectric constant of h-BN-added SiAlON is relatively lower than that of pristine β-SiAlON.

A porous hexagonal boron nitride powder compact for the production and release of radioactive 11C

A porous pre-sintered hexagonal boron nitride powder compact was recently developed as target for the production of intense 11C beams for Positron Emission Tomography-aided hadron therapy. In a previous study, this target has been characterized regarding its operational limitations. In this work, microstructural characterization with respect to the target's grain size, porosity and pore structure, and a dedicated fractional release study from activated targets, i.e. how much 11C is extracted by a short heat treatment, is presented. Corresponding results include an average grain size of approximately 1.7(1) μm, total and open porosity of 40(5) and 21(7)%, respectively, which is mostly composed of pores with sizes ranging from 120 to 470 nm. From the measured release fraction the order of magnitude of carbon's diffusion coefficient D(1500 °C) = 10−15 − 10−14 cm2 s−1 in porous boron nitride, and a 11C extraction efficiency of about 10% at 1500 °C target temperature were estimated.

Covalently Linked Hexagonal Boron Nitride-Graphene Oxide Nanocomposites as High-Performance Oil-Dispersible Lubricant Additives

The present study demonstrates an improved and facile method for the exfoliation and chemical oxidation of bulk hexagonal boron nitride (h-BN) powder. Further, chemical functionalization of oxidize...