Morphology and Composition Controlled Synthesis of BN-Coated Aluminum Borate Nanowhiskers
Large quantities of BN-coated aluminum borate (Al18B4O33) nanowhiskers with typical 20 - 50 nm in diameter and 0.5 - 2 m in length have been successfully synthesized by sol-gel and post-thermal-treatment methods. The dependence of morphology and structures on the synthetic process of the coated nanowhiskers has been investigated systematically. Al4B2O9 nanowhiskers were first prepared at a relative low temperature, and then converted into Al18B4O33 nanowhiskers at higher temperatures in the air due to their high-temperature instability. Besides Al18B4O33phase, Al5BO9 and B2O3 could also be generated in the process of transition. However, if a flow of NH3 gas was introduced during the post-thermal-treatment of Al4B2O9 nanowhiskers, the Al5BO9 and B2O3 phases disappeared and BN-coated Al18B4O33 nanowhiskers were finally obtained. Uniform BN layers were coated on the surface of the nanowhiskers by the interfacial reaction between NH3 and B2O3 vapor which was in-situ generated from the nanowhiskers. The NH3-introducing temperature has a significant effect on the morphology and composition of the nanowhiskers. The BN-coated Al18B4O33nanowhiskers are envisaged to become prime candidates as reinforcement in light metal matrix composites.
S.T. Tu, G.Z. Wang and J.M. Gong
Z. J. Mo et al., "Morphology and Composition Controlled Synthesis of BN-Coated Aluminum Borate Nanowhiskers", Advanced Materials Research, Vol. 509, pp. 125-131, 2012