Dispersed Boron Nitride Research Articles

Investigations on the Nonlinear Optical Properties of 0D, 1D, and 2D Boron Nitride Nanomaterials in the Visible Spectral Region.

In recent years, boron nitride nanomaterials have attracted increasing attention due to their unique properties such as high temperature stability and high thermal conductivity. They are structurally analogous to carbon nanomaterials and can also be generated as zero-dimensional nanoparticles and fullerenes, one-dimensional nanotubes and nanoribbons, and two-dimensional nanosheets or platelets. In contrast to carbon-based nanomaterials, which have been extensively studied during recent years, the optical limiting properties of boron nitride nanomaterials have hardly been analysed so far. This work summarises a comprehensive study on the nonlinear optical response of dispersed boron nitride nanotubes, boron nitride nanoplatelets, and boron nitride nanoparticles using nanosecond laser pulses at 532 nm. Their optical limiting behaviour is characterised by means of nonlinear transmittance and scattered energy measurements and a beam profiling camera is used to analyse the beam characteristics of the transmitted laser radiation. Our results show that nonlinear scattering dominates the OL performance of all measured boron nitride nanomaterials. Boron nitride nanotubes show a large optical limiting effect, much stronger than the benchmark material, multi-walled carbon nanotubes, which makes them promising for laser protection applications.

Fatty acid eutectics embedded in guar gum/graphene oxide/boron nitride carbon aerogels for highly efficient thermal energy storage and improved photothermal conversion efficiency

Carbon aerogels with low density, high compressibility and fatigue resistance, are of great interest for the encapsulation of phase change materials (PCMs) to resolve their leakage and low thermal conductivity issues, thus providing exciting potential for thermal management and energy storage. In this work, we successfully fabricated interconnected carbon aerogels with superior mechanical performance from graphene oxide (GO), thermally conductive hexagonal boron nitride (BN), and green biomass guar gum (GG). The GG with long soft molecular chains stabilized the porous structures of the carbon aerogels through hydrogen bonding. GG also maintained the even dispersion of BN in the carbon skeleton, forming a connected thermal conductive network. Furthermore, the stearic acid (SA)-capric acid (CA) binary eutectic PCMs were successfully capsulated in the porous structures of the obtained GG/GO/BN carbon aerogels to fabricate composite PCMs with high thermal conductivity and good shape stability, which overcoming the limitations of single PCMs and expanding their thermal energy storage applications. The composite PCMs exhibited an excellent energy storage capacity of 161.63 J/g with almost no change after 100 thermal cycles. In addition, the thermal conductivity of the composite PCMs increased to 0.6061 W∙m−1∙K−1, which was nearly three times that of SA-CA, and the photothermal conversion efficiency of the composite PCMs reached 92.56 %.

Quasi-isotropic thermal conductivity of polymer films enhanced by binder-free boron nitride spheres

Heat dissipation has become increasingly crucial in miniaturized modern electronics. Thanks to the high in-plane thermal conductivity yet excellent electrical insulation, hexagonal boron nitride (h-BN) has been considered as an ideal filler material to enhance the thermal conductivity of polymers for efficient heat dissipation. However, the low out-of-plane thermal conductivity significantly limits their practical applications and a heat spreader that propagates heat along multiple directions is favorable. In this work, micro-sized, binder-free boron nitride spheres (BNSs) have been successfully synthesized using a two-step process of spray drying and high-temperature sintering. Consisting of randomly dispersed boron nitride nanosheets (BNNSs), the BNSs show an isotropic thermal conductivity of 34.8 W/mK. Using the BNSs as fillers, the out-of-plane thermal conductivity of poly(vinyl alcohol) (PVA) film is significantly enhanced to 8.1 W/mK, the second highest value compared with previously reported BN based PVA composite films. In the meantime, the in-plane thermal conductivity, up to 10.6 W/mK, is not sacrificed, indicating the quasi-isotropy in thermal conductivity. The significant thermal conductivity enhancement (∼3700%) of PVA is attributed to the formation of isotropic thermally conductive networks within the polymer matrix and strong interactions between BNNSs inside BNSs. This study provides a practical route to fabricate BN-enhanced composite films with isotropic thermal conductivity and promising materials that are valuable for heat dissipation in new-era advanced electronics and related applications.

Noncovalent functionalization of boron nitride via chelation of tannic acid with Fe ions for constructing high thermally conductive polymeric composites

AbstractWith the advancement of integration and miniaturization of precise instruments, the heat accumulating in electronic components is urgently needed to dissipate for ensuring their service life. In this work, boron nitride (BN) was functionalized with tannic acid/ferric ions (TA/Fe) chelate complexes to synthesize high thermally conductive natural rubber (NR) composites (NR@TA/Fe‐BN). The stable TA/Fe chelate complexes improved the interfacial compatibility between BN and NR and enhanced the BN dispersion in the NR matrix, which led to the reduction of interfacial thermal resistance and the construction of heat transfer channels in NR composites. As a result, a relative high thermal conductivity (0.327 W/(mK)) by 30 vol% NR@TA/Fe‐BN composite was achieved, being 2.44 times that of pure NR (about 0.134 W/(mK)). In addition, the insulating NR@TA/Fe‐BN composites showed outstanding elongation at break (686%) and tensile strength (15.2 MPa). This highly efficient and green TA inspired modification is expected to find application in industrial manufacturing of thermally conductive polymeric composites.

Effect of Boron Nitride on the Heat Transfer and Heat Storage of Poly(ethylene glycol)/Expanded Vermiculite Composite Phase-Change Materials.

In this work, the expanded vermiculite/poly(ethylene glycol)–boron nitride (E/PB-X) shape-stabilized composite phase-change materials with the encapsulation capacity of ∼66.16 wt % were prepared by a typical vacuum impregnation method to overcome liquid leakage during phase transition and poor thermal conductivity during heat transfer of poly(ethylene glycol). It was found that the boron nitride showed a great influence on the heat transfer and heat storage of E/PB-X. The thermal conductivity of E/PB-X was 0.45–0.49 W/(m·K), indicating that the heat transfer of E/PB-X was significantly enhanced by the dispersed boron nitride fillers, which was mainly attributed to the reduction of interfacial thermal resistance and the formation of rapid thermally conductive channels. However, the latent heat (∼55.76 J/g) of E/PB-X decreased with the increase in the boron nitride content, revealing that the heat storage behavior of E/PB-X was strongly affected by the confinement of surface interactions of boron nitride and expanded vermiculite, which was consistent with the crystallization behavior determined by X-ray diffractometer (XRD) results. Moreover, the spectroscopy (FT-IR) and thermogravimetric analyzer (TGA) results confirmed that E/PB-X exhibited excellent chemical compatibility and thermal stability, respectively, which were conducive to practical heat storage applications.

Investigation on fusion of Boron Nitride reinforced aluminium composite by cryogenic milling

Cryogenic milling was used to make boron nitride (BN)-reinforced aluminium composite powders. This composite powder was characterised for its structural characteristics and mechanical qualities by varying the amount of BN added during milling. When making metal-based nanocomposites via cold spraying, precise information on the powder shape, spreading and structural integrity of Boron Nitrates is required. The mean particle size reduced and the size distribution constricted as Boron Nitrates concentration increased in the composite powders, although all possessed sprayable particle sizes. Cryogenic milling of Al was made possible thanks to an increase in BN dispersion with increasing milling time. In spite of the fact that thorough milling significantly reduced particle size, the operation caused considerable BN degradation, resulting in a deterioration in the mechanical properties of the composites.

Enhanced Energy Storage Characteristics in Pmp-Based Nanodielectrics with Highly Dispersed Boron Nitride Sheets

Enhanced Energy Storage Characteristics in Pmp-Based Nanodielectrics with Highly Dispersed Boron Nitride Sheets

Improved thermal conductivity and breakdown strength of PVDF‐based composites by improving the dispersion of BN

In order to adapt to the development of electronic devices, it is necessary to improve the thermal conductivity and breakdown strength of composites. Boron nitride (BN) is an ideal candidate material with high breakdown strength and thermal conductivity. Therefore, the introduction of BN nanosheets into the polyvinylidene fluoride (PVDF) matrix can improve the thermal conductivity and breakdown strength of the composites at the same time. However, BN nanosheets can easily agglomerate in the matrix, which limits the improvement of the properties of the composites. To overcome this difficulty, appropriate water-bath heating was used to improve the fluidity of PVDF. Therefore, the dispersion of the filler is improved. When the volume fraction of BN nanosheets is 3% and the preparation temperature is 45°C, the energy storage density of the composites reached 18.5 J/cm3 at 540 kV/mm. At this point, the thermal conductivity was 0.49 W/(m⋅K), 3.5 times that of the pure PVDF film.

Exceptionally thermally conductive and electrical insulating multilaminar aligned silicone rubber flexible composites with highly oriented and dispersed filler network by mechanical shearing

The design of multilayered structure network is an effective strategy to enhance the thermal conductivity and maintain the electrical insulating performance of thermal management materials. Multilaminar aligned silicone rubber (SR) flexible hybrids (SABE) with highly oriented and dispersed boron nitride (BN) and expanded graphite (EG) filler network were constructed successfully through layer by layer assembly of SR/ABN and SR/AEG prefabricated by a facile and scalable strategy of mechanical shearing. The SABE-6 composite with 4 assembly circles exhibited excellent in-plane thermal conductivity (TC) of 23.4 W m−1 K−1 and outstanding electrical insulation (volume resistance > 1014 Ω∙cm), which displayed the highest value among reported thermal conductive SR-based composites. The TC of SABE composite showed 14379% and 178% higher than that of pure SR and simple blending SR/BN/EG (SBE) composites, respectively, which ascribed to the highly oriented and dispersed filler network. The study provides a high property of SR-based composite thermal management materials.

Mechanical and dielectric properties of functionalized boron nitride nanosheets/silicon nitride composites

Uniformly dispersed boron nitride nanosheets (BNNSs) reinforced silicon nitride (Si3N4) composites were prepared by surface modification assisted flocculation combined with SPS sintering. In order to improve the dispersibility of the BNNSs in the composites, the liquid phase stripped BNNSs are surface functionalized by a two-step covalently modification. The amino-modified BNNSs (NH2-BNNSs) and Si3N4 powders have opposite surface potential, mixed evenly by electrostatic interaction during flocculation. The results showed that mechanical properties of Si3N4 composites were obviously enhanced by adding NH2-BNNSs. The fracture toughness and bending strength of Si3N4 composites added 0.75 wt% NH2-BNNSs were increased by 34% and 28%, respectively, compared with monolithic Si3N4. Toughening mechanisms are synergistic action of the torn, pull-out or bridging of BNNSs and crack deflection mechanisms with microstructural analyzes. The dielectric properties of the Si3N4 ceramics are also improved after the addition of NH2-BNNSs.

Toxicity evaluation following pulmonary exposure to an as-manufactured dispersed boron nitride nanotube (BNNT) material in vivo

Boron nitride nanotubes (BNNT) are multi-walled nanotubes composed of hexagonal BN bonds and possess many unique physical and chemical properties, creating a rapidly expanding market for this newly emerging nanomaterial which is still primarily in the research and development stage. The shape and high aspect ratio give rise to concern for the potential toxicity that may be associated with pulmonary exposure, especially in an occupational setting. The goal of this study was to assess lung toxicity using an in vivo time course model. The sample was manufactured to be 5 nm wide and up to 200 μm long, with ~50% purity covalently bound with hexagonal boron nitride (hBN) in the sample. Following preparation for in vivo studies, sonication of the material disrupted the longer tubes in the complex and the size distribution in dispersion medium (DM) of the structures was 13–23 nm in diameter and 0.6–1.6 μm in length. Male C57BL/6 J mice were exposed to 4 or 40 μg of BNNT or DM (vehicle control) by a single oropharyngeal aspiration. Pulmonary and systemic toxicity were investigated at 4 h, 1 d, 7 d, 1 mo and 2 mo post-exposure. Bronchoalveolar lavage (BAL) studies determined pulmonary inflammation (neutrophil influx) and cytotoxicity (lactate dehydrogenase activity) occurred at early time points and peaked at 7 d post-exposure in the high dose group. Histopathological analysis showed a minimal level of inflammatory cell infiltration in the high dose group with resolution over time and no fibrosis, and lung clearance analysis showed ~50% of the material cleared over the time course. The expression of inflammatory- and acute phase response-associated genes in the lung and liver were significantly increased by the high dose at 4 h and 1 d post-exposure. The increases in lung gene expression of Cxcl2, Ccl2, Il6, Ccl22, Ccl11, and Spp1 were significant up to 2 mo but decreased with time. The low dose exposure did not result in significant changes in any toxicological parameters measured. In summary, the BNNT-hBN sample used in this study caused acute pulmonary inflammation and injury at the higher dose, which peaked by 7 d post-exposure and showed resolution over time. Further studies are needed to determine if physicochemical properties and purity will impact the toxicity profile of BNNT and to investigate the underlying mechanisms of BNNT toxicity.

Effect of Polymeric In Situ Stabilizers on Dispersion Homogeneity of Nanofillers and Thermal Conductivity Enhancement of Composites

Boron nitride (BN) nanofiller-based polymer composites have been considered promising candidates for efficient heat-dissipating packaging materials because of their superior thermal conductivity, mechanical strength, and chemical resistance. However, strong aggregation of the BN nanofillers in the composite matrix as well as the difficulty in the modification of the chemically inert surface prevents their effective use in polymer composites. Herein, we report an effective method by using in situ stabilizers to achieve homogeneous dispersion of boron nitride (BN) nanofillers in an epoxy-based polymeric matrix and demonstrate their use as efficient heat-dissipating materials. Poly(4-vinylpyridine) (P4VP) is designed and added into the epoxy resin to produce in situ stabilizers during preparation of hexagonal BNs (h-BNs) and BN nanotubes (BNNTs) dispersion. In-depth experimental and theoretical studies indicated that the homogeneous distribution of BN nanofillers in epoxy composites achieved by using the in situ stabilizer enhanced the thermal conductivity of the composite by ∼27% at the same concentration of the BN nanofillers. In addition, the thermal conductivity of the h-BN/epoxy composite (∼3.3 W/mK) was dramatically improved by ∼48% (4.9 W/mK) when the homogeneously dispersed BNNTs (∼1.8 vol %) were added. The concept of the proposed in situ stabilizer can be further utilized to prepare the epoxy composites with the homogeneous distribution of BN nanofillers, which is critical for reproducible and position-independent composite properties.

Enhancing the mechanical, wear and corrosion behaviour of stir casted aluminium 6061 hybrid composites through the incorporation of boron nitride and aluminium oxide particles

This research paper portrays the enrichment of mechanical, wear and corrosion properties of the Aluminium 6061 matrix composite by incorporating hybrid reinforcements. Aluminium 6061 alloy is stir casted with different proportions of boron nitride (BN), Aluminium oxide (Al2O3) and graphite particles. Tensile test reveals that the tensile strength and ductility for the Al 6061-30 BN -10Al2O3- 5C is improved due to the presence of higher BN content along with 10% Al2O3. Significant improvement in microhardness (63HV), compressive strength (187 Pa) and impact strength (12 J) for the Al 6061-30 BN -10Al2O3- 5C when compared with the bare Al 6061 alloy. The dispersion of BN with Al2O3 improved the wear resistance for the Al 6061-30 BN -10 Al2O3- 5 C composite, where as the unreinforced bare Al alloy has caused the major surface degradation resulting in poor wear property and the worn out surfaces are examined through the scanning electron microscope. The main wear mechanism is identified as adhesive wear. The corrosion test results clearly reveals that the corrosion resistance is higher for the Al 6061-30 BN -10Al2O3- 5C (−0.526 ± 0.004 V) with a lower current density of −0.983 ± 0.004 μA cm−2 than the other composites and bare Al 6061.

Mass production of high thermal conductive boron nitride/nanofibrillated cellulose composite membranes

Boron nitride nanoplates (BNNPs) are highly desirable in thermal management applications. To achieve better performance, boron nitride (BN) has to be extensively exfoliated and dispersed in liquids. However, most of current techniques suffer from being high in cost, time consuming, and environmentally unfriendly, which limits the mass production of BNNPs for a wide range of applications. Herein, we demonstrate a simple yet green manufacturing process for efficient exfoliation and dispersion of BN and bamboo cellulose via stress-induced simultaneous exfoliation/dispersion (SISED) in an aqueous medium. This method can produce well exfoliated BNNPs/ nanofibrillated cellulose (NFC) with the average BNNPs thickness of 51 nm and NFC diameter of 43 nm after only 1.98 h treatment. Thanks to the excellent dispersion, heat-conducting and electric-insulating BNNPs/NFC nanocomposite membranes with an BNNPs content of 40 wt% are fabricated through vacuum-assisted filtration. The micro-structures of the membranes as well as their mechanical and thermal properties can be tailored by changing the refining time and the pan gap to meet different needs. The resultant membranes exhibit high mechanical properties with a tensile strength of 74.6 MPa and excellent thermal conductivity of 20.64 W m−1 K−1, suggesting their great potential in fabricating next-generation portable electronics.

Competition between stimulated Brillouin scattering and two-photon absorption in dispersed boron nitride.

The design of transparent optical materials with stimulated Brillouin scattering (SBS) suppression is a topic of current interest. We measured two-photon absorption (2PA) cross-section σ2PA and Brillouin gain factor gB of a suspension of hexagonal boron nitride (hBN) in N-methyl-2-pyrrolidone at the second harmonic of a Nd:YAG laser. SBS exhibits a significant quenching with hBN concentration, like previously observed in graphene suspension. The melting of hBN flakes due to a large 2PA and the related changes in the acoustic damping coefficient explain the quenching mechanism.

UV-curable boron nitride nanosheet/ionic liquid-based crosslinked composite polymer electrolyte in lithium metal batteries

Crosslinked polymer electrolyte (CPE) and composite polymer electrolyte are two of the most promising polymer electrolyte (PE) systems for improving the resistance to Li dendrite growth, but the trade-off and agglomerated effects of these PEs hinder the development of safe Li metal battery (LMB). Herein, a new class of crosslinked composite polymer electrolyte (CCPE) with the combination of confined ionic liquid (IL) polymer network and homogeneously dispersed boron nitride nanosheet (BNNS) for LMB is reported. This UV-curable CCPE is formed on electrode via in-situ crosslinking of a precursor solution in a rapid and solvent-free step, and the assembly process of LMBs and interfacial contact/adhesion are maximum optimized. The critical point of this CCPE is that a facile channel for Li+ transfer and a robust skeleton for confining IL and strengthening interface are simultaneously achieved via the introduction of network structure and 2D BNNS in PE. Consequently, the LiFePO4ǀLi batteries involving CCPE show a great improvement in the charge-discharge cycling stability and rate performance compared with those of the cells with pure CPE. This study offers an effective and facile strategy for fabricating dendrite-resistant CCPE with potential applicability in next-generation energy storage systems.

Thermo-physical properties of pure ethylene glycol and water–ethylene glycol mixture-based boron nitride nanofluids

Nanofluids are suspensions of solid nanoparticles in conventional heat transfer fluids, and they often exhibit improved heat transfer characteristics. Different nanoparticles (metals, oxides, nitrides, etc.) have been used for the synthesis of nanofluids. The nanosized hexagonal form of boron nitride (BN) has versatile properties, such as chemical inertness, electrically insulating and high in-plane thermal conductivity (~ 600 W m−1 K−1) making it a prospective dispersoid in nanofluids for heat transfer applications. The present study reports the synthesis of pure ethylene glycol (EG)- and ethylene glycol–water mixture (EG/W, 40/60 vol. ratio)-based nanofluids containing a dispersion of BN nanoparticles. Form the study, it emerged that with the increase in particle concentration, the BN nanofluids showed an increment in the thermal conductivity manifesting a maximum of 15.5% and 12.5% for 3 vol.% of BN dispersion in EG- and EG/W-based nanofluids, respectively. Also, the thermal conductivity enhancement of BN nanofluids was found to be nearly independent of temperature in the temperature range of 30–60 °C. The viscosity of BN nanofluids increased with the increase in particle concentration showing a maximum of 41 and 33% for 2 vol.% of BN in EG-based and EG/W-based nanofluids, respectively. Further, BN nanofluids exhibited shear-thinning behaviour at lower shear rates and a Newtonian nature at higher shear rates. A new correlation has been developed to estimate the thermal conductivity and viscosity of BN nanofluids on the basis of experimental data.

Mechanically Strong Polymer Sheets from Aligned Ultrahigh-Molecular-Weight Polyethylene Nanocomposites.

Ultrahigh-molecular-weight polyethylene (UHMWPE) is of great interest as a next-generation body armor material because of its superior mechanical properties. However, such unique properties depend critically on its microscopic structure characteristics, including the degree of crystallinity, chain alignment, and morphology. Here, we present a highly aligned UHMWPE and its composite sheets containing uniformly dispersed boron nitride (BN) nanosheets. The dispersion of BN nanosheets into the UHMWPE matrix increases its mechanical properties over a broad temperature range. Experiments and simulation confirm that the alignment of chain segments in the composite matrix increases with temperature, leading to an improvement in mechanical properties at high temperature. Together with the large thermal conductivity of UHMWPE and BN, our findings serve to expand the application spectrum of highly aligned polymer nanocomposite materials for ballistic panels and body armor over a broad range of temperatures.

High-performance, recyclable ultrafiltration membranes from P4VP-assisted dispersion of flame-resistive boron nitride nanotubes

Regenerable ultrafiltration membranes were fabricated via filtration of thermally-stable, highly dispersed boron nitride nanotubes (BNNTs). The highly debundled BNNTs were produced by employing judiciously-chosen poly(4-vinylpyridine) (P4VP) as an efficient steric stabilizer. Density functional theory calculations showed strong adsorption energies of P4VP monomers on top of the BNNTs, illustrating the role of P4VP stabilizers. High performance of the BNNT ultrafiltration membranes with large permeation flux was demonstrated by exclusion of polystyrene and gold nanoparticles (~ 25nm) with higher than 99% removal efficiency. The BNNT membranes were successfully regenerated and recycled continuously at 450°C due to their excellent mechanical and thermal properties, demonstrating a stark contrast to the membranes from the carbon nanotubes. Our work indicates that unlike the membranes from carbon nanotubes, BNNT membrane can be a promising candidate for the application in cost efficient industrial ultrafiltration.

The influence of the diamond wheel grinding process on the selected properties of boron nitride dispersion in cemented carbide (BNDCC) composites

The paper presents the results of research into the influence of the process of grinding boron nitride dispersed cemented carbide (BNDCC) composite using diamond wheel with vitrified bond on the selected properties of this composite. Cutting tools of BNDCC composite were manufactured using several machining operations. At first stage, they were EDM (electrical discharge machining) wire cut from tablets and later on ground with diamond wheels (which removed the “white layer” produced by EDM cutting). Rake and flank faces of prepared cutting tools were examined by microscopic, topographic, and surface analytical techniques before and after grinding. The paper presents comparative results of BNDCC tools and tools made of H10S cemented carbide. Values of the grinding efficiency parameters, Qw, average material removal rate of grinding, Q′w, average material removal rate per unit active grinding wheel for the two materials, were similar, indicating an insignificant effect of introduction of the harder BN phase into WCCo on these parameters. Ra, surface roughness of flank face, was 0.040 μm for BNDCC composite and 0.51 μm for H10S after grinding, compared to 1.14 and 1.30 μm, respectively, before grinding. WC residual stress measurements in the flank faces of BNDCC tools were inconclusive; in the flank faces, the stresses were compressive, decreasing, e.g., from − 230 to − 1670 MPa after grinding. For the H10S tools, there was no comparable effect. The results also indicate that the vitrified bonded diamond abrasive wheel used is effective in grinding WCCo and BNDCC cutting tools.