Wet-chemical coating of silicon carbide fibers with hexagonal boron nitride layers

Hexagonal BN fiber coatings and BN powders were prepared by pyrolysis of the raw materials boric acid and urea in an atmosphere consisting of hydrogen and nitrogen. The powders were used to determine the appropriate mixing ratio of the raw materials to produce BN with the desired composition and crystal structure. The pyrolysis of boric acid and urea in a molar mixing ratio of 1:2 resulted in a BN that was hexagonal and had a nearstoichiometric composition. To prepare a solution for the coating of fibers, boric acid and urea were dissolved in an ethanol-water mixture. The coating was then applied to SiC filaments using a continuous roll-to-roll dip-coating process. It could be shown by SEM/EDS that BN layers were applied to the fibers. No significant bridging in the fiber bundle was found. Furthermore, it could be demonstrated by grazing incidence x-ray diffraction that the layers were crystalline.

Automated summary

Hexagonal BN fiber coatings and powders were prepared by pyrolysis of boric acid and urea in a hydrogen and nitrogen atmosphere. The appropriate mixing ratio of raw materials for desired BN composition and crystal structure was investigated, resulting in hexagonal BN with near-stoichiometric composition. Coatings applied on SiC filaments showed crystalline BN layers without significant bridging in fiber bundles, as confirmed by SEM/EDS and grazing incidence x-ray diffraction analysis.