Fire‐Resistant Structural Material Enabled by an Anisotropic Thermally Conductive Hexagonal Boron Nitride Coating

Abstract

Fire retardant coatings have been proven effective at reducing the heat release rate (HRR) of structural materials during burning; yet effective methods for increasing the ignition temperature and delay time prior to burning are rarely reported. Herein, a strong, fire‐resistant wood structural material is developed by combining a densification treatment with an anisotropic thermally conductive flame‐retardant coating of hexagonal boron nitride (h‐BN) nanosheets to produce BN‐densified wood. The thermal management properties created by the BN coating provide fast, in‐plane thermal diffusion, slowing the conduction of heat through the densified wood, which improves the material's ignition properties. Compared with densified wood without the BN coating, a 41 °C enhancement in ignition temperature (Tig), a twofold increase in ignition delay time (tig), and a 25% decrease in the maximum HRR of BN‐densified wood can be achieved. As a proof of concept for scalability, the pieces of the BN‐densified wood are fabricated with a length larger than 25 cm, width greater than 15 cm, and thickness more than 7 mm. The improved thermal management, fire resistance, mechanical strength, and scalable production of BN‐densified wood position it as a promising structural material for safe and energy‐efficient buildings.

Atomically Thin Hexagonal Boron Nitride and Its Heterostructures

“…2D heterostructures can extend the potential applications compared with the individual constituents, since they can bring unprecedented novel properties and functions. [ 99–110 ] To date, most of devices are based on the exfoliated 2D materials and h‐BN flakes, which are highly depended on the quality of exfoliation, transfer process and interface statuses. [ 111 ] Therefore, this technique has a very low yield and significantly different performances from different researchers, [ 112 ] thereby showing only a state‐of‐art of device.…”

Nanoscale Ion Regulation in Wood‐Based Structures and Their Device Applications

“…Thermal stability or even fire resistance should also be considered for wood‐based devices. Fire‐retardant surface coatings [ 251 ] and hybridization [ 252 ] are promising methods for enhancing the fire resistance of wood‐based materials.…”

Transforming wood as next‐generation structural and functional materials for a sustainable future

“…(G) Comparison of the calculated ignition delay times of reported work with BN‐densified wood at an external heat flux of 50 kW m −2 along with a graph showing improvement in ignition temperature after the introduction of BN. Reproduced with permission 159 . Copyright 2020, Wiley‐VCH…”

“…Idealistically, a fire‐resistant wood should have anisotropic thermal conductivity, that is, low in‐plane and high across plane conduction, to suppress peak wood temperature. Gan et al prepared anisotropic wood by coating thermally anisotropic hexagonal boron nitride (h‐BN) nanosheets over the surface of densification 159 . When BN densified wood was subjected to a constant heat source, it showed heat diffusion across the surface and insulation perpendicular to the plane (Figure 30D–G).…”

“…Li-air batteries are considered one of the most promising Li batteries due to their high-estimated specific energy density (≈1700 Wh Kg À1 ), which is much higher than currently available Li-ion batteries. 159,160 However, Li-air electrodes need a novel structural design to solve competing mass transport (i.e., ion/electron/gas) issues before being considered for practical applications. A Liair battery requires a tri-pathway electrode with open porous channels for gas transport and a dual net for electron/ion transport.…”