Sintered high-density hexagonal boron nitride ceramics with exceptional properties

Abhijit Biswas
Rice University – Houston, Texas, USA
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Two-dimensional (2D) materials have limitations in scalable production and application potentials in extreme conditions due to their inherently low packing density (because of layered structures) and resultant properties. However, its atomic-scale structural engineering using unconventional synthesis processes may result in improved and unforeseeable properties beyond theoretical limits, suitable for applications.

Here, by using the high-temperature spark plasma sintering (SPS) process, we obtained near-theoretical dense, highly crystalline pure phase hexagonal BN (h-BN) ceramics, with an achieved density of ~98% of the theoretical value. SPS h-BN shows outstanding mechanical stability with a high ductility before fracture. It exhibits increased thermal conductivity, compared to the conventionally lab-sintered low-density h-BN. Furthermore, it displays an unusually high dielectric constant, which is far beyond the theoretical limit of bulk h-BN. Significantly, the SPS h-BN shows ultra-high ~98.25% thermal neutron radiation shielding efficiency with a ~42.75% attenuation coefficient, one of the highest attenuation coefficients ever reported. Our structural, chemical, spectroscopic, and microscopic characterizations and analysis reveals that SPS produces unique twisted Moiré patterns even in layered h-BN, facilitates non-basal plane crystallinity, and promotes inter-grain fusions that synergistically produces high density while preserving the 2D crystalline nature of layered h-BN, and contributes to its exceptional and anomalous properties, beyond their intrinsic limits.

Our findings provide fundamental insights into atomic-scale layer twisting and interlayer interconnections and demonstrate a scalable method for producing large-area high-density h-BN ceramics. The achievement of near-theoretical density in pure phase bulk h-BN into scalable and stable large-scale structures with extraordinary properties could unlock its significant potential in numerous applications, e.g. high-strength, energy storage, thermal management/insulations, and harmful neutron radiation shielding for nuclear energy applications.

Reference: A. Biswas et al., arXiv:2405.06007v2(2024).

Email: 01abhijit@gmail.com