(484c) Thermally Driven Stable Expansion of Hexagonal Boron Nitride through Intercalated Acid Treatment

Hexagonal boron nitride (h-BN) is a 3D ceramic material composed of layered 2D boron nitride nanosheets (BNNS) interconnected by van der Waals forces. While isolated BNNS offer unique mechanical properties and applications, h-BN demonstrates exceptional thermal conductivity and stability in its 3D form. This study aims to extend previous methods of h-BN intercalation to isolate a stable expanded h-BN structure. Expanded graphite structures, currently utilized for various applications due to their excellent thermal properties, serve as a reference. However, graphite's electrical conductivity poses limitations. This study explores expanded h-BN as an alternative with superior thermal properties and electrical insulation, rendering it suitable for diverse applications, including electronics.

By employing sulfuric and phosphoric acid, we successfully intercalated bulk h-BN of varying lateral sizes, confirmed through X-ray diffraction (XRD) spectra. While smaller particles exhibit better intercalation, larger flakes offer potential for greater expansion due to a larger interface. Subsequently, the material undergoes exposure to temperatures ranging from 500-900 ℃ to investigate the extent of thermal shock. A preheated tube furnace with rapid transfer capabilities facilitates this process, trapping acid vapors and promoting layer expansion. Scanning electron microscopy (SEM) reveals rough and separated edges of the h-BN flakes compared to the parent material. XRD spectra analysis confirms distinct changes in lattice spacing, indicative of layer expansion. X-ray photoelectron spectroscopy (XPS) characterizes the composition, particularly identifying potential decomposition products from the acids. Exploiting this expanded h-BN form, applications such as binder-less h-BN thin films become feasible.