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The boron nitride nanosheets (BNNSs)/aluminum nitride (AlN) composites were prepared by hot press sintering at 1600°C. The microstructure, mechanical properties, and thermal conductivity of the samples were measured, and the effect of adding BNNSs to AlN ceramics on the properties was studied. It is found that the addition of BNNSs can effectively improve the mechanical properties of AlN. When the additional amount is 1 wt%, the bending strength of the sample reaches the maximum value of 456.6 MPa, which is 23.1% higher than that of the AlN sample without BNNSs. The fracture toughness of the sample is 4.47 MPa m1/2, a 68.7% improvement over the sample without BNNSs. The composites obtained in the experiment have brilliant mechanical properties. [ABSTRACT FROM AUTHOR]

Due to their intriguing properties, boron nitride nanosheets (BNNSs) with large lateral size and high crystallinity have great promise for many applications. However, the quantitative exfoliation of hexagonal boron nitride (h-BN) into good quality BNNSs still remains a key challenge. Herein, we report a scalable method to exfoliate BNNSs in ionic liquids (ILs) via shear-assisted thermal treatment. Few-layer BNNSs with well-preserved structural integrity are successfully prepared by this method. The synergistic effects of strong physical adsorption and intercalation of IL molecules, chemical interactions between hydrogen fluoride (HF) and h-BN, activation energy provided by heat treatment, and shear forces generated by repetitive stirring effect contribute to the exfoliation of BNNSs. [ABSTRACT FROM AUTHOR]

Boron nitride nanosheets (BNNSs)/magnesium oxide (MgO) composites were prepared via hot pressing. Mechanical properties of MgO ceramics were improved obviously in virtue of adding BNNSs. The bending strength of the 1 wt% BNNSs/MgO composite increased by about 85% than that of the monolithic MgO. The fracture toughness increased by 34% with the addition of 1.5 wt% BNNSs. Microstructural analyzes have shown that the toughening mechanisms are combinations of the pull-out and bridging of BNNSs, crack deflection, and crack bypassing mechanisms. The addition of a small amount of BNNSs don't destroy the excellent dielectric properties of composites. The dielectric constant of the sample doped with 1 wt% BNNSs was about 9.5 in the whole X-band and the vast majority of P-band, and the loss tangent was less than 5 × 10−3 in 10–15.8 GHz. [ABSTRACT FROM AUTHOR]

Well-dispersed boron nitride nanosheets (BNNSs) reinforced fused silica composites were successfully fabricated by surface modification assisted flocculation method. Surface modification can enhance the performance of flocculation process. BNNSs were homogeneously mixed with fused silica through the electrostatic interaction between hydroxylated BNNSs with negative charge and amino-modified fused silica with positive charge. The BNNSs can act as excellent nanofillers for enhancing the mechanical properties of fused silica composites. Approximately 74% and 48% increases in flexure strength and fracture toughness can be achieved for the 1.5 wt% BNNSs/fused silica composite, respectively. The toughening mechanisms were analyzed by microstructural characterization, especially for pull-out mechanism. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide@boron nitride nanosheet (RGO@BNNS) hybrids were prepared for the first time using template-assisted autoclave pyrolysis technique at the temperature as low as 600 °C. The developed method can be scaled into gram-scale synthesis of the material. The BNNSs combine with RGO through van der Waals interplanar interaction without damaging the structures of RGO. Such ultrathin BNNSs on the surface of RGO can serve as high-performance oxidation-resistant coatings in oxidizing atmospheres at high temperatures. The RGO@BNNS hybrids can sustain up to 800 °C over a relatively long period of time. [ABSTRACT FROM AUTHOR]

In order to overcome intrinsic brittleness and poor mechanical properties of fused silica (FS), boron nitride nanosheets (BNNSs) as a novel reinforcement were employed for fabrication of BNNSs/fused silica composites. BNNSs with micron lateral size were homogeneously dispersed with FS powder using a surfactant-free flocculation method and then consolidated by hot pressing. The flexural strength and fracture toughness of the composite with the addition of only 0.5 wt.% BNNSs increased by 53% and 32%, respectively, compared with those of pure FS. However, for higher BNNSs contents the improvement in mechanical properties was limited. Microstructural analyzes have shown that the toughening mechanisms are combinations of the pull-out, crack bridging, and crack deflection mechanisms. [ABSTRACT FROM AUTHOR]

BNNSs were prepared efficiently by magnesium borate nitridation. BNNSs/eutectic-composition Al 2 O 3 /YAG/YSZ ceramics were prepared by hot pressing sintering. The addition of BNNSs did not change the phase composition of BNNSs/eutectic-composition Al 2 O 3 /YAG/YSZ ceramics. The bending strength and fracture toughness of 1.5wt%BNNSs/ eutectic-composition Al 2 O 3 /YAG/YSZ ceramic were increased by 19.0% and 18.9% respectively. Doped BNNSs exist at the grain boundary between two or more different grains. The toughening mechanism of BNNSs contains mainly crack deflection, BNNSs pullout and BNNSs bridging. • BNNSs/eutectic-composition Al 2 O 3 /YAG/YSZ ceramics were originally prepared with excellent mechanical properties. • The toughening mechanism of BNNSs was discussed. • The effects of temperature and BNNSs doping amount on the mechanical properties of ceramics were explored. [ABSTRACT FROM AUTHOR]

Uniformly dispersed boron nitride nanosheets (BNNSs) reinforced silicon nitride (Si 3 N 4) 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 (NH 2 -BNNSs) and Si 3 N 4 powders have opposite surface potential, mixed evenly by electrostatic interaction during flocculation. The results showed that mechanical properties of Si 3 N 4 composites were obviously enhanced by adding NH 2 -BNNSs. The fracture toughness and bending strength of Si 3 N 4 composites added 0.75 wt% NH 2 -BNNSs were increased by 34% and 28%, respectively, compared with monolithic Si 3 N 4. 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 Si 3 N 4 ceramics are also improved after the addition of NH 2 -BNNSs. [ABSTRACT FROM AUTHOR]

Boron nitride nanosheets (BNNSs) with relatively low dielectric constant and excellent mechanical strength were employed for fabrication of BNNSs/fused silica (FS) composites. High-temperature mechanical behavior and microstructural evolution of the composites were investigated. The addition of BNNSs can improve the mechanical properties of FS efficiently, and the reinforcement from BNNSs can be preserved during the high temperature service. The flexural strength of BNNSs/FS composites exhibited anomalous gains at certain high temperature range, which can be explained by the softening of FS matrix, the heal of defect tips, and the reinforcement from BNNSs. [ABSTRACT FROM AUTHOR]

In this study, Zn 8 B 3 H 3 O 14 nanosheets were synthesized through a one-step coprecipitation process and employed as both a boron source and substrate templates for the fabrication of boron nitride nanosheets (BNNSs), which were synthesized efficiently at low temperatures by the borate nitration method using ammonia as the nitrogen source. The thickness of the synthesized BNNSs ranged from 3 to 10 nm with a flake dimension of about 2.56 μm. The prepared BNNSs using this method realized 98.8% boron source utilization and single batch yields up to gram level. In addition, BNNSs/SiO 2 microwave-transparent composites were prepared to investigate the potential for large-scale applications of the BNNSs produced by using this method. The composites demonstrated a remarkable increase in bending strength and fracture toughness, reaching 122.02 MPa and 2.31 MPa·m1/2, respectively, with the addition of only 0.5 wt% BNNSs. Compared with SiO 2 without BNNSs, the fracture toughness of the composites is increased by 106%. A novel crack plugging strong toughening mechanism of BNNSs is proposed. Simultaneously, the composites exhibit exceptional microwave-transparent properties, with dielectric constants below 4 in the real part and below 0.03 in the imaginary part. Therefore, this study has successfully achieved the low-temperature and efficient synthesis of micron-scale BNNSs, laying the groundwork for their large-scale application. [Display omitted] • Zn 8 B 3 H 3 O 14 nanosheets were used as substrate templates for the synthesis of BNNSs. • BNNSs were synthesized with high efficiency at low temperatures (900 °C). • The single batch yield of BNNSs reached up to the gram level. • The BNNSs/SiO 2 wave-transparent composites with ultrahigh toughness were obtained. • A novel mechanism for strengthening and toughening (BNNSs plugging) is proposed. [ABSTRACT FROM AUTHOR]

Silica is one of the most widely used ceramics due to its excellent chemical stability and dielectric property. However, its destructive brittle nature inhabits it from wider application as a functional ceramic. An improvement in toughness is a challenging topic for silica ceramic, as well as other ceramics. In the paper, silica ceramic with different types of boron nitride powders and alumina platelets was fabricated by hot-pressing. Introduction of the additives had great influence on the composites' mechanical properties and microstructure. The silica matrix composite containing micro-sized boron nitride powders possessed the best mechanical properties, including the bending strength (134.5 MPa) and the fracture toughness (1.85 Mpa·m1/2). Meanwhile, the introduction of alumina platelets combined with boron nitride nanosheets achieved an effective enhancement of fracture toughness while maintaining the bending strength. Compared with the monolithic silica, the composite with simultaneous addition of alumina platelets and boron nitride nanosheets had a fracture toughness of 2.23 Mpa·m1/2, increased by approximately 27% (1.75 Mpa·m1/2). The crack deflection and platelet pullout were contributing to enhancement of the fracture toughness. The improved mechanical properties, combined with the intrinsic excellent dielectric and chemical properties, make the silica matrix composites promising wave transparent and thermal protection materials. [ABSTRACT FROM AUTHOR]

Abstract Boron nitride nanosheets (BNNSs) have attracted increasing attention in the field of two-dimensional materials. In the paper, the BNNSs/alumina composites were fabricated by a flocculation method and hot pressing. It is found that the BNNSs were dispersed uniformly in the alumina matrix by the flocculation technique via pH adjustment. The experimental results showed that with the increasing BNNSs content, the density of the composites decreased. Compared with the monolithic alumina, bending strength of the composite with 1.0 wt% BNNSs was increased by 58.6%; while the fracture toughness was increased slightly. The addition of BNNSs changed the fracture pattern, refined the grains of composites and inhibited abnormal grain growth, which contributed to the improvement of mechanical properties of the composites. [ABSTRACT FROM AUTHOR]