Hexagonal boron nitride (h-BN)-reinforced ceramic nanocomposites represent a significant advancement in materials science, particularly for applications requiring exceptional thermal management, lubricity, and stability under extreme conditions. These composites leverage the unique properties of h-BN, a material often referred to as white graphene due to its layered structure analogous to graphite but with superior thermal and chemical stability. The integration of h-BN into ceramic matrices enhances performance in demanding environments such as aerospace propulsion systems, thermal barriers, and high-power electronics.

The thermal conductivity of h-BN is a key attribute, with in-plane values reaching up to 400 W/mK, rivaling some metals. When incorporated into ceramic matrices like alumina (Al2O3) or silicon nitride (Si3N4), the resulting nanocomposites exhibit anisotropic thermal conduction, enabling efficient heat dissipation in specific directions. This property is critical for electronic substrates or insulating components in high-temperature systems. The thermal enhancement depends on the dispersion quality, interfacial bonding, and alignment of h-BN platelets within the matrix. Colloidal processing routes, including slurry casting and tape casting, are commonly employed to achieve uniform dispersion. These methods involve stabilizing h-BN particles in solvents with tailored surfactants to prevent agglomeration before mixing with ceramic precursors.

Lubricity is another defining characteristic of h-BN-reinforced ceramics. The weak van der Waals forces between h-BN layers facilitate easy shearing, reducing friction coefficients to as low as 0.15–0.25 in dry conditions. This makes such composites suitable for bearings, seals, and wear-resistant coatings in aerospace engines, where conventional lubricants fail at elevated temperatures. The lubricating performance is preserved up to 900°C in oxidizing atmospheres and even higher in inert environments, outperforming graphite, which oxidizes above 500°C. The compatibility of h-BN with non-oxide ceramics like silicon carbide (SiC) further extends its utility in extreme environments, as SiC-h-BN composites demonstrate synergistic improvements in both wear resistance and thermal shock tolerance.

High-temperature stability is a hallmark of h-BN-reinforced ceramics. Unlike polymer or metal-matrix composites, ceramic-h-BN systems retain structural integrity at temperatures exceeding 1500°C. This stability stems from the inherent oxidation resistance of h-BN, which forms a protective boric oxide layer at high temperatures, slowing further degradation. In oxide matrices like zirconia (ZrO2), h-BN additions improve fracture toughness by promoting crack deflection and bridging, while in non-oxide systems like boron carbide (B4C), they enhance sinterability without degrading mechanical properties. Spark plasma sintering (SPS) and hot pressing are preferred fabrication methods for these composites, as they enable densification at lower temperatures compared to conventional sintering, minimizing h-BN decomposition.

Processing challenges include achieving strong interfacial bonding between h-BN and the ceramic matrix. Poor adhesion can lead to delamination under thermal cycling or mechanical load. Surface functionalization of h-BN with silane or polymer coatings improves compatibility with oxide matrices, while in-situ reactions during sintering—such as the formation of boron oxynitride phases—can enhance bonding in non-oxide systems. The optimal h-BN content varies by application: typically 5–20 vol% for thermal management, where higher loadings risk compromising mechanical strength, and 10–30 vol% for lubricating coatings, where maximized h-BN exposure is desirable.

In aerospace, h-BN-reinforced ceramics are employed in turbine blade coatings, reducing friction and thermal stress in jet engines. Their electrical insulation properties also make them ideal for radome materials, which require transparency to radar waves alongside thermal resilience. In electronics, these composites serve as heat spreaders in high-power devices, where their thermal conductivity and dielectric properties prevent overheating and electrical interference. Emerging applications include crucibles for molten metal handling and substrates for high-temperature sensors, capitalizing on the chemical inertness of h-BN.

The following table summarizes key properties of h-BN-reinforced ceramic nanocomposites:

Property | Typical Range/Behavior
Thermal Conductivity | 30–150 W/mK (isotropic), up to 400 W/mK (anisotropic)
Friction Coefficient | 0.15–0.25 (dry conditions)
Oxidation Resistance | Stable up to 900°C (air), >1500°C (inert)
Fracture Toughness | 4–8 MPa·m¹/² (varies with matrix)
Optimal h-BN Loading | 5–30 vol% (application-dependent)

Future developments may focus on optimizing hierarchical architectures, such as aligning h-BN platelets in 3D-printed ceramic scaffolds for directional thermal pathways, or combining h-BN with other 2D materials like graphene to create multifunctional composites. The scalability of colloidal processing and advances in sintering techniques will further drive commercialization, particularly for large-scale aerospace components. By addressing interfacial engineering challenges and refining processing protocols, h-BN-reinforced ceramic nanocomposites are poised to expand their role in next-generation high-performance applications.