Hexagonal Boron Nitride Nanoplatelets Research Articles

Microstructure and mechanical properties of hybrid hexagonal BN nanotube and nanoplatelet reinforced AZ91 Mg matrix composites

In this research, we report fabrication of AZ91 (Mg–Al–Mn–Zn) matrix composites reinforced with a hybrid of hexagonal boron nitride nanoplatelets (BNNP) and nanotubes (BNNT) using spark plasma sintering (SPS) and hot isostatic pressing (HIP). The resultant composites present dense microstructure featured by the refined α-Mg grains decorated with eutectic along the α-Mg grain boundaries, and trace amounts of in-situ interfacial-reaction products such as Mg3N2 and MgB2 are observed to serve as chemical anchors for stronger interface. More importantly, the AZ91 composites reinforced with a hybrid of 0.4 wt% BNNPs-0.1 wt% BNNTs displays ∼209 MPa of compressive yield strength, ∼329 MPa of ultimate compressive strength and ∼19.4% of elongation, achieving satisfactory balance of strength and ductility when compared to the AZ91 composite reinforced with sole BNNPs. This improvement can be attributed to the unique three-dimensional hybrid structure, where BNNPs maintain their high specific surface area, and the de-bundled BNNTs extend like tentacles, further contributing to their interfacial adhesion with the matrix. This research is expected to pave the way for the development of Mg-based composites with an optimal balance of strength and ductility.

Facile preparation of polymer-based heat dissipation composite coating with enhanced thermal conductivity via optimizing synergistic effect of multi-scale fillers

Aluminum radiator plays a significant role in thermal managing system of passive heat dissipation for high power consuming microelectronic devices. Although inspiring strategies have been proposed to design and prepare polymer-based composites with high thermal conductivity in previous reports, it remains urgent to develop practical techniques for economically fabricating thermally conductive composite coatings in large-scale. To construct efficient heat dissipation film, two-dimensional (2D) graphene nanoplatelets (GNPs)/hexagonal boron nitride nanoplatelets (BNNPs) hybrid fillers are dispersed in polydimethylsiloxane (PDMS) solution with branch-like porous magnéli-phase Ti4O7 microparticles as heat conducting paths, and fabricated via convenient spray-coating. Thermal conductivity of the cured coating presents two-fold increase to 5.339 W m−1 K−1 as compared to the coating without Ti4O7, and a heat dissipation ratio of 13.96 %. Furthermore, the composite coating demonstrates excellent corrosion resistance under neutral salt solution spray. The as-prepared composite coating is of great potential to be applied as protective coating for aluminum radiators.

Functionalized hexagonal boron nitride nanoplatelets for advanced cementitious nanocomposites

Portland cement-based nanocomposites were successfully fabricated with low volume fractions of hexagonal boron nitride (hBN) nanoplatelets, exfoliated and functionalized using a combination of ball milling and sonicated-assisted dispersion. Surface topography, thickness, lateral dimension, and number of layers of the hBN nanoplatelets were evaluated by AFM and Raman analysis. The identification of functional groups attached onto the functionalized hBN was performed through FTIR. The results show that the functionalization successfully exfoliates the hBN nanoplatelets to few-layer thicknesses, resulting in suspensions with high colloidal stability. The grafted hydroxyl and carboxyl groups on the hBN surface interact with the Ca2+ ions of calcium silicate hydrates (CSH), improving the load-transfer efficiency from the cement matrix to the hBN nanoplatelets. Overall, the hBN reinforced cementitious composites demonstrated significant enhancement in flexural strength by ∼50%, compressive strength by ∼17%, Young's modulus by ∼56%, and fracture energy by ∼76%.

Interfacial reaction induced synergetic strengthening effects on the plasma sprayed Ni3Al composite coating reinforced with hexagonal boron nitride nanoplatelets

Ni3Al has shown great potential in high-performance wear-resistant coating material for lots of tribological machinery components working in extremely aggressive environments owing to its anomalous strength-temperature dependence and coexistent atomic bonds (covalent and metallic bonds) in nature. In this research, hexagonal boron nitride nanoplatelet (BNNP) reinforced Ni3Al composite coatings are fabricated on Ti6Al4V substrate using plasma spray. The added BNNP can survive the harsh high-temperature conditions and are homogeneously distributed in the composite coatings. Trace amounts of in-situ synthesized AlN and AlB2 and local diffusion layer are found to form a stronger BNNP-Ni3Al interface in such a way that BNNPs act as anchors bonding Ni3Al matrix during rapid solidification. These BNNPs either locating within a splat or being sandwiched by the adjacent splats exert synergetic strengthening effects on individual splats and splat boundaries, imparting the lamellar structural composite coatings with noticeably improved mechanical and tribological properties. As compared with Ni3Al coating, BNNP/Ni3Al composite coatings showed an improvement in tensile strength, elongation, toughness, and wear resistance by 24.6 %, 21.4 %, 52.5 %, and 77 %, respectively. This research is expected to shed some light on BNNP potentials for designing and producing high-performance composite coatings using plasma spray.

Hydroxylated hexagonal boron nitride nanoplatelets enhance the mechanical and tribological properties of epoxy-based composite coatings

The relationship between microstructure and properties of hydroxylated hexagonal boron nitride nanoplatelets (denoted as OH-h-BN) reinforced epoxy composite coatings was still not clear. In this work, hexagonal boron nitride nanoplatelets (h-BN) were successfully hydroxylated to increase their dispersion and compatibility with the EP matrix, which was confirmed by the results obtained from FTIR, XPS, XRD and TEM. Subsequently, OH-h-BN reinforced epoxy resin (EP) composite coatings were prepared by means of a spraying process, and their curing characteristics, cross-linking density and mechanical and tribological properties were discussed. As a result, the EP/OH-h-BN composite coating took an excellent curing label in terms of the ‘Cure Index’ (CI) and had a cure enthalpy 1.5 times higher than that of the pure EP coating. Moreover, with the presence of OH-h-BN, the storage modulus (at 40 °C) and cross-linking density of the epoxy composite coating were enhanced by 56% and 43%, respectively. The tensile test outcomes presented approximately 16% and 138% improvements in the maximum tensile strength and elongation at break of the EP/OH-h-BN composite coating compared with pure EP coating. In addition, the friction coefficient and the wear rate were reduced by 27% and 58% because of the enhancement of mechanical strength of the EP/OH-h-BN composite coating and the formation of a continuous, dense and high load-carrying lubricating tribofilm on the dual steel ball.

Lithium‐Ion Batteries: Layered Heterostructure Ionogel Electrolytes for High‐Performance Solid‐State Lithium‐Ion Batteries (Adv. Mater. 13/2021)

Ionogel electrolytes with a layered heterostructure are developed by Mark C. Hersam and co-workers in article number 2007864, using hexagonal boron nitride nanoplatelets and two imidazolium ionic liquids with different electrochemical stability windows. Compared with ionogels using the individual ionic liquids, the layered heterostructure ionogels provide broadened electrochemical stability windows while maintaining desirable ionic conductivity, suggesting a promising electrolyte strategy for high operating voltages and rate performance in solid-state lithium-ion batteries.

Mechanical and thermal properties of 3D-printed epoxy composites reinforced with boron nitride nanobarbs

In this work, new boron nitride-reinforced epoxy-based composite inks for direct-ink write (DIW) additive manufacturing are presented. Printed composites are characterized for thermal conductivity, flexure, and impact energy, along with optical and electron microscopy. The new inks utilize boron nitride nanobarbs (BNNBs), a novel form of boron nitride nanotube, where the surface is decorated with hexagonal boron nitride nanoplatelets. BNNBs are shown to improve the thermal conductivity of the printed composites up to 32%, the strength up to 34%, and stiffness up to 44%. Anisotropy was observed in all measurements, suggesting that the BNNBs become aligned during printing.

Preparation of Boron Nitride Nanoplatelets via Amino Acid Assisted Ball Milling: Towards Thermal Conductivity Application.

Hexagonal boron nitride nanoplatelets (BNNPs) have attracted widespread attention due to their unique physical properties and their peeling from the base material. Mechanical exfoliation is a simple, scalable approach to produce single-layer or few-layer BNNPs. In this work, two amino acid grafted boron nitride nanoplatelets, Lys@BNNP and Glu@BNNP, were successfully prepared via ball milling of h-BN with L-Lysine and L-Glutamic acid, respectively. It was found that the dispersion state of Lys@BNNP and Glu@BNNP in water had been effectively stabilized due to the introduction of amino acid moieties which contained a hydrophilic carboxyl group. PVA hydrogel composites with Lys@BNNP and Glu@BNNP as functional fillers were constructed and extensively studied. With 11.3 wt% Lys@BNNP incorporated, the thermal conductivity of Lys@BNNP/PVA hydrogel composite was up to 0.91 W m−1K−1, increased by 78%, comparing to the neat PVA hydrogel. Meanwhile, the mechanical and self-healing properties of the composites were simultaneously largely enhanced.

Enhanced Scratch Performance of Plasma Sprayed Hydroxyapatite Composite Coatings Reinforced with BN Nanoplatelets

In recent years, research on hydroxyapatite (HA) coatings has been driven by the demands of clinical applications. However, the intrinsic brittleness of HA limits its potential in the use for the load-bearing implant. To improve mechanical properties of the HA coating itself, a HA composite coating reinforced with hexagonal boron nitride nanoplatelets (BNNP) was fabricated using plasma spray, and its scratch behavior was investigated in this research. Typical brittle fractures such as microcracks both in and beyond the residual groove and material chipping were observed in the HA coating, while stronger and tougher BNNP/HA coatings exhibited a dominant role in protecting them from scratch damage through resisting plastic deformation and brittle microfracturing. Moreover, easier grain sliding within a splat and splat sliding at the splat boundaries due to the presence of BNNPs, and the nature porosity at different length scales of the as-sprayed HA composite coatings would provide significant self-lubricating effects to reduce the lateral force during scratching and alleviate the contact damage. Therefore, the addition of BNNPs renders HA coating with low scratch friction and enhanced tolerance to surface damage, which is naturally beneficial for the long-term durability and reliability of the implants.

Investigation of wetting behavior of HDPE reinforced with nanoscopic 1D/2D filler system using contact angle goniometry

Current work investigates wetting abilities of High Density Polyethylene (HDPE) based composites and hybrids. The samples were prepared by varying weight fractions of Multi Walled Carbon Nanotubes (MWCNTs) and hexagonal-Boron Nitride Nanoplatelets (h-BNNPs). The technique used for fabrication was melt mixing followed by injection moulding process. The wetting abilities of the test samples were assessed using an in situ contact angle measurement test setup. The test results confirmed the superior wetting abilities by 0.25 MWCNT/0.15 BNNP hybrid composite. A comparison between angle of contact and surface roughness of test samples was also presented. It was concluded that rough surface tends to more hydrophobic then smoother surfaces.

High-Modulus Hexagonal Boron Nitride Nanoplatelet Gel Electrolytes for Solid-State Rechargeable Lithium-Ion Batteries.

Solid-state electrolytes based on ionic liquids and a gelling matrix are promising for rechargeable lithium-ion batteries due to their safety under diverse operating conditions, favorable electrochemical and thermal properties, and wide processing compatibility. However, gel electrolytes also suffer from low mechanical moduli, which imply poor structural integrity and thus an enhanced probability of electrical shorting, particularly under conditions that are favorable for lithium dendrite growth. Here, we realize high-modulus, ion-conductive gel electrolytes based on imidazolium ionic liquids and exfoliated hexagonal boron nitride (hBN) nanoplatelets. Compared to conventional bulk hBN microparticles, exfoliated hBN nanoplatelets improve the mechanical properties of gel electrolytes by 2 orders of magnitude (shear storage modulus ∼5 MPa), while retaining high ionic conductivity at room temperature (>1 mS cm-1). Moreover, exfoliated hBN nanoplatelets are compatible with high-voltage cathodes (>5 V vs Li/Li+) and impart exceptional thermal stability that allows high-rate operation of solid-state rechargeable lithium-ion batteries at temperatures up to 175 °C.

Texture and microstructure improvement of hot-deformed magnets with platelet-like nano h-BN addition

The microstructure of ribbons interface was optimized by doping the hexagonal boron nitride nanoplatelets (h-BNNP) in hot-deformed magnets. The remanence increased markedly and reached to a maximum value of 14.06 kGs. The coercivity and the energy product exhibited similar variation trends to the remanence, showing maxima of 16.92 kOe and 49 MGOe, respectively. Microscopy observations revealed that surface grains of ribbons tended to align with the interior grains due to the uniform local compressive stress induced by h-BNNP with relatively large flat surface, resulting in hot-deformed magnets with microscopically homogeneous structure and improved texture.

Assessment of Bulk Mechanical Properties of HDPE Hybrid Composite Filled with 1D/2D Nanofiller System

Current work reports on evaluation of bulk mechanical properties of High Density Polyethylene (HDPE) reinforced with functionalized 1D (Multi Walled Carbon Nanotubes- (MWCNTs) and 2D (hexagonal-Boron Nitride Nanoplatelets-(h-BNNPs) fillers. Mechanical mixing and injection moulding technique was used to prepare the composites. Evaluation of bulk mechanical properties like hardness, yield stress, fracture stress, impact toughness and Young`s modulus was carried out. The optimum properties were exhibited by HDPE/0.25 MWCNT/0.1 BNNP. Hardness, yield stress, fracture stress, impact toughness and Young`s modulus was observed to increase by 93.84, 80.83, 59.23, 115 and 42.05% on comparison with pure HDPE. TEM images confirm the tubular and hexagonal morphology of MWCNT and h-BNNP. It is concluded from test results that addition of MWCNT and h-BNNP into HDPE has improvised mechanical properties.

Non-covalent functionalized hexagonal boron nitride nanoplatelets to improve corrosion and wear resistance of epoxy coatings

In the present study, a non-covalent method was employed to modify hexagonal boron nitride (h-BN) nanoplateletsviaπ–π interaction of amine-capped aniline trimer (AT), which resulted in a stable dispersion of h-BN nanoplatelets in organic solvents.

Alkylamine-functionalized hexagonal boron nitride nanoplatelets as a novel material for the reduction of friction and wear.

Hexagonal boron nitride nanoplatelets (h-BNNPs), which are structurally analogous to graphene, were prepared via the ultrasound-assisted exfoliation of h-BN powder using N-methyl pyrrolidone as the solvent. The alkylamines with variable alkyl chains and electron-rich nitrogen atoms were grafted onto the boron sites of the h-BNNPs based on Lewis acid-base chemistry. The grafting of the alkylamines onto the h-BNNPs was confirmed using FTIR, XPS, TGA and (13)C SSNMR analyses. The crystalline and structural features of the alkylamine-functionalized h-BNNPs were studied using XRD and HRTEM analyses. The TGA and FTIR results revealed a higher grafting of octadecylamine (ODA) on the h-BNNPs compared to trioctylamine (TOA). The cohesive interaction between the alkyl chains grafted onto the h-BNNPs and the hydrocarbon chains of mineral lube base oil facilitates the dispersion of the alkylamine-functionalized h-BNNPs. The TOA-grafted h-BNNPs (h-BNNPs-TOA) exhibited long-term dispersion stability compared to the ODA-grafted h-BNNPs and this was attributed to a higher degree of van der Waals interactions between the octyl chains of the TOA molecules grafted onto the h-BNNPs and the hydrocarbon chains of the mineral lube base oil. The tribo-performance of the h-BNNPs-TOA as an additive to mineral lube base oil was evaluated in terms of the coefficient of friction and wear using ball-on-disc contact geometry. A minute dosing (0.02 mg mL(-1)) of h-BNNPs-TOA significantly improved the lubrication characteristics of the mineral lube base oil and showed a 35 and 25% reduction of friction and wear, respectively. The presence of boron and nitrogen on the worn scar of an aluminium disc, as deduced from elemental mapping, confirmed the formation of a tribo-chemical thin film of h-BN lamellae on the contact interfaces, which not only reduced the friction but also protected the contact interfaces against undesirable wear events.

Enhancing the mechanical and thermal properties of boron nitride nanoplatelets/elastomer nanocomposites by latex mixing

Hexagonal boron nitride nanoplatelets (BNNPs) can serve as two-dimensional (2D) fillers for elastomer nanocomposites due to their excellent and intriguing mechanical and thermal properties.

Effect of non-ionic surfactant assisted modification of hexagonal boron nitride nanoplatelets on the mechanical and thermal properties of epoxy nanocomposites

Hexagonal boron nitride (hBN) nanoplatelets have attracted considerable interest recently. In this work, hBN nanoplatelets have been prepared using chemical exfoliation route. The exfoliation of hBN nanoplatelets takes place along the (0 0 2) plane without destroying the crystal structure. The hBN nanoplatelets are modified using polyvinylpyrrolidone (PVP), a non-ionic surfactant in order to achieve finer dispersion of hBN nanoplatelets in ethyl alcohol, and subsequently in the epoxy matrix. The enhanced dispersion of hBN nanoplatelets achieved using PVP is due to the adsorption of PVP over the hBN nanoplatelets, and PVP miscibility with epoxy resin in an uncured state. Due to the finer dispersion of hBN nanoplatelets in the epoxy matrix, the flexural properties are higher as compared to pure epoxy. PVP assisted dispersed hBN nanoplatelets reinforced with epoxy nanocomposites have higher flexural properties as compared to pure hBN nanoplatelets-reinforced epoxy nanocomposites. The enhanced dispersion of hBN nanoplatelets using PVA also limits the decrease in glass transition temperature (Tg). Further, thermal stability of the epoxy increase with an addition of PVP modified and unmodified hBN nanoplatelets in the epoxy matrix as compared to pure epoxy. Fractography studies reveal that addition of PVP modified and unmodified hBN nanoplatelets in the epoxy matrix depict rough surface with many small facets due to resistance offered by the dispersed nanoplatelets.

Alkyl-chain-grafted hexagonal boron nitride nanoplatelets as oil-dispersible additives for friction and wear reduction.

Hexagonal boron nitride (h-BN), an isoelectric analogous to graphene multilayer, can easily shear at the contact interfaces and exhibits excellent mechanical strength, higher thermal stability, and resistance toward oxidation, which makes it a promising material for potential lubricant applications. However, the poor dispersibility of h-BN in lube base oil has been a major obstacle. Herein, h-BN powder was exfoliated into h-BN nanoplatelets (h-BNNPs), and then long alkyl chains were chemically grafted, targeting the basal plane defect and edge sites of h-BNNPs. The chemical and structural features of octadecyltriethoxysilane-functionalized h-BNNPs (h-BNNPs-ODTES) were studied by FTIR, XPS, XRD, HRTEM, and TGA analyses. The h-BNNPs-ODTES exhibit long-term dispersion stability in synthetic polyol ester lube base oil because of van der Waals interaction between the octadecyl chains of h-BNNPs-ODTES and alkyl functionalities of polyol ester. Micro- and macrotribology results showed that h-BNNPs-ODTES, as an additive to synthetic polyol ester, significantly reduced both the friction and wear of steel disks. Elemental mapping of the worn area explicitly demonstrates the transfer of h-BNNPs-ODTES on the contact interfaces. Furthermore, insight into the lubrication mechanism for reduction in both friction and wear is deduced based on the experimental results.