Synthesis of hexagonal boron nitride coatings using concentrated solutions of alkali metal borates

Continuous nanocrystalline coatings of hexagonal boron nitride ($h$-BN) with a thickness of $\sim$1000–350 nm are prepared from highly concentrated aqueous solutions of lithium and sodium borates, which display good film-forming properties. The borate solutions were applied on silicon substrates by spin coating followed by drying in air and treatment in ammonia at a temperature of 1300$^\circ$C. This method is deemed promising for creating protective coatings (e.g., for protecting carbon products from oxidation at elevated temperatures).