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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]

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]

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]