Improved oxidation resistance of boron nitride nanotubes with protective alumina nano-coatings

• Published in: Ceramics international Vol. 50; no. 22; pp. 48620 - 48627
• Main Authors: Davis, Cole R., Nuwayhid, R. Blake, Campbell, Caroline A., Mills, Sara C., Backman, Lavina, Estevez, Joseph E., Schaeffer, Manda R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15-11-2024
• Subjects: Aluminum oxide; Atomic layer deposition (ALD); Boron nitride nanotubes (BNNTs); Oxidation kinetics; Oxidation kinetics; Boron nitride nanotubes (BNNTs); Atomic layer deposition (ALD); Aluminum oxide
• ISSN: 0272-8842
• DOI: 10.1016/j.ceramint.2024.09.211

Boron nitride nanotubes (BNNTs) are gaining interest for high temperature applications due to their thermal stability at elevated temperatures. Although BNNT temperature limits are well studied, there remains a gap in quantifying the high temperature failure mechanisms and oxidation kinetics. This study characterizes the oxidation mechanisms and kinetics of BNNTs and Al2O3-coated BNNTs, via atomic layer deposition (ALD), at temperatures between 850 and 1000 °C. ALD Al2O3 surface coatings improved BNNT oxidation resistance by over an order of magnitude for coating thicknesses between 7 and 56 nm. However, the improved oxidation resistance of Al2O3-coated BNNTs decayed after prolonged exposure to oxygen at elevated temperatures, gradually reaching the same extent of oxidation as uncoated BNNTs after approximately 200 min at 900 °C. This behavior is attributed to the crystallization of as-deposited amorphous Al2O3 coatings at elevated temperatures leading to densification, cracking, and exposure of BNNTs to the oxidizing environment. While Al2O3 coatings did not completely prevent oxidation, a significant improvement in oxidation resistance was observed, extending the thermal stability of BNNTs.