Boron nitride aerogel is a kind of new nanomaterials with three-dimensional porous network structure, which takes solid as the framework and gas as the dispersion medium. It has high specific surface area, high porosity, low density and other excellent properties. In addition, compared with graphene aerogels, it exhibits better insulation, oxidation resistance, thermal stability and chemical stability. These outstanding properties make it promising application in the fields of gas adsorption, catalysis, sewage purification, thermal insulation/conduction. This article systematically reviewed the preparation methods of boron nitride aerogels including the hard template method, soft template method, low-dimensional boron nitride assembly method, and template-free method in the light of domestic and foreign research status. Moreover, the important applications of boron nitride aerogels in key fields are summarized, and the future development direction is prospected.

In all kinds of aerogels, silicon-based aerogel possesses the most comprehensive mechanism of Sol-Gel process and maturest synthesis process. In this work, different types of silicon-based aerogels were prepared via different silicon precursors including tetraethoxysilane (TEOS), methyltrimethoxysilane (MTMS), vinylmethyldimethoxysilane (VMDMS) and the mixed precursor of MTMS and dimethyldimethoxysilane (DMDMS). All samples display high specific surface area and porous microstructure. Effect of the precursor structure on the mechanical and thermal properties of final samples was deeply investigated. The results show that elastic property of silicon-based aerogels depends greatly on the crosslinking degree of their skeleton. The lower the crosslinking degree of the sample is, the better the elastic property is. Furthermore, the elastic property can be further improved by introducing hydrocarbon chains into the skeleton. Thermal conductivity of the obtained aerogels is between 0.032 and 0.041 W/(m·K) at room temperature. Their weight loss increases with the increase of the organic component in the skeleton. Superior mechanical and thermal properties enable silicon-based aerogels to be promising candidates for thermal insulation and energy storage.

As a nano-porous material with high porosity, low density, high specific surface area, excellent heat-resistance, and low thermal conductivity, the alumina aerogel shows broad application prospect in high-temperature thermal insulating areas such as the thermal protective system for space vehicles and the thermal insulation for industrial kilns. However, pristine alumina aerogels can’t be directly used because of their relatively poor thermal resistance above 1000 ℃, mechanical strengths and high-temperature thermal insulating performance. They need to be improved by introducing reinforcements and opacifiers (namely the alumina aerogel composite). This paper summarizes the latest research progress of synthesis of heat-resistant alumina aerogels, and preparation and properties of alumina aerogel composites. Researchers improved the thermal stability of alumina aerogels by modifications such as in-situ doping, deposition, organic chains or carbon coatings. The introduction of whiskers, particles, porous skeletons or fibers into alumina aerogels contributes to considerable improvement of mechanical performance. The cooperation of fibers and opacifiers help to increase the inhibition of infrared radiation and lower the high-temperature thermal conductivity of alumina aerogels. The future of alumina aerogel composites is also proposed: a) finely tailoring the bulk density, micro structures, and introducing proper foreign elements and opacifiers, are supposed to further optimize the thermal stability of alumina aerogels and thermal insulating performance of their composites; b) deeper attention should also be paid on the evolution of structure and properties of composites at elevated temperatures, and on the interaction between alumina aerogel and reinforcement. As a novel thermal insulation, alumina aerogel composites are expected to take their advantages and be widely applied in the future.

Extrusion stress due to phase change of the NiS, internal stress due to CTE mismatch between the NiS and glass, and local concentrated stress around the NiS due to synergistic effects above were quantitatively calculated based on equal strength theory and the deformation coordination relation between NiS and glass in this work. The effects of NiS particle diameter, local strength of glass and ambient temperature on spontaneous breakage of tempered glass were analyzed. The critical diameter of NiS particles was determined as well. The results show that the fundamental reason for spontaneous breakage of tempered glass is the circumferential concentrated stress (tensile stress) near the NiS particle. There exists non-linear relations between circumferential stress and NiS particle diameter of which the circumferential stress decreases rapidly with the decrease of NiS particle diameter when it is less than 0.2 mm, but circumferential stress increases moderately when it is greater than 0.5 mm. The critical diameter of NiS particle which causes the spontaneous breakage of tempered glass decreases with the increase of surface stress in the tempered glass. It is difficult to induce spontaneous breakage of tempered glass when the diameter of NiS particle is less than 0.1 mm. The circumferential stress increases linearly with the increase of ambient temperature, and the stress increases slightly faster for the NiS with larger diameter.

Architectural laminated glass exhibits significant vulnerability under hard body impacts such as windborne debris impacts. In this work, a prediction model is proposed for assessing the impact status of laminated glass under hard body impact. Multiple design variables including the glass make-ups, interlayer types, support conditions and size are considered. The impact tests with consecutive impact attempts are first conducted. A comprehensive database encompassing the failure condition of each glass layer is then established. This database has 567 groups of PVB laminated glass data and 210 groups of SGP laminated glass data. A combined WOA-KELM machining learning based model is subsequently developed to predict the impact status of laminated glass. The modelling results are compared with that from SVM and LSSVM based models. The results show that the proposed model has a prediction accuracy of 88.45% in failure status of each glass layer. Such model can well predict the impact status of laminated glass and shows better performance in both accuracy and computation cost than other models.