Synthesis of nanosize powders of aluminum nitride by pulsed wire discharge

Abstract

Summary form only given, as follows. Nanosize powders of aluminum nitride (AlN) have been successfully synthesized by pulsed wire discharge. Using Joule heating, the wire of aluminum (4N purity, 0.25 mm in diameter, 25 mm long) is evaporated to produce plasma. The plasma is rapidly cooled by the ambient gas of NH/sub 3/N/sub 2/, condensing into nanosize powders. The discharge was carried out by use of capacitor of 10 /spl mu/F at the charging voltage of 4 kV. The powders were collected by the evacuation through membrane filter. The powders synthesized were characterized by X-ray diffraction, transmission electron microscopy, electron diffraction, and energy dispersive spectroscopy. Median diameter was found to be 28 nm. The particle size obeys log-normal distribution, and geometric standard deviation was 1.29 which is close to that of mono-dispersed powders. Aluminum particles of sub micron in diameter have been also observed in the powders. Amorphous oxide layer of I nm thick has been observed on the surface of AlN powders. The content of AlN is influenced by partial pressure of NH/sub 3/ and NH/sub 3//N/sub 2/ ratio. Since the dissociation energy of NH/sub 3/ is lower than that of N/sub 2/, the enhancement of nitridation has been observed at higher concentration of NH/sub 3/. The AlN content is not only a function of the partial pressure of NH/sub 3/, and strongly depends on N/sub 2//NH/sub 3/ ratio. In fact, the content of AlN in the synthesized powders reached 80% at NH/sub 3/ concentration of 20% for the mixed gas of NH/sub 3//N/sub 2/ at 750 Torr.