Investigation on mechanochemical synthesis of Al2O3/BN nanocomposite by aluminothermic reaction

Alpha-alumina–boron nitride (α-Al₂O₃–BN) nanocomposite was synthesized using mixtures of aluminum nitride, boron oxide and pure aluminum as raw materials via mechanochemical process under a low pressure of nitrogen gas (0.5 MPa). The phase transformation and structural evaluation during mechanochemical process were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential thermal analysis (DTA) techniques. The results indicated that high exothermic reaction of Al–B₂O₃ systems under the nitrogen pressure produced alumina, aluminum nitride (AlN), and aluminum oxynitride (Al₅O₆N) depending on the Al value and milling time, but no trace of boron nitride (BN) phases could be identified. On the other hand, AlN addition as a solid nitrogen source was effective in fabricating in-situ BN phase after 4 h milling process. In Al–B₂O₃–AlN system, the aluminothermic reaction provided sufficient heat for activating reaction between B₂O₃ and AlN to form BN compound. DTA analysis results showed that by increasing the activation time to 3 h, the temperature of both thermite and synthesis reactions significantly decreased and occurred as a one-step reaction. SEM and TEM observations confirmed that the range of particle size was within 100 nm.