Nano-Particulate of Aluminum Nitride Prepared by Pulsed Wire Discharge
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Nano-Particulate of Aluminum Nitride Prepared by Pulsed Wire Discharge
Yoshiaki Kinemuchi, Channarong Sangurai, Tsuneo Suzuki, Hisayuki Suematsu, Weihua Jiang and Kiyoshi Yatsui Extreme Energy-Density Research Institute, Nagaoka University of Technology, Nagaoka, Niigata, 940-2188, Japan ABSTRACT Nanoparticulates of aluminum nitride (AlN) have been synthesized by novel dry process, namely pulsed wire discharge where aluminum wire is exploded by an intense pulsed current (10-20 kA at the peak, half cycle of 10 µs) in NH3/N2 gas. The average size of the nanoparticulates was found to be 28 nm. Furthermore, narrow particle distribution of the particulates was observed, where geometric standard deviation was 1.29. Increasing charging energy enhances the nitridation of aluminum. The maximum content of AlN in synthesized particulates was ~95 %. The sintered body with 80 % of density has been obtained by sintering at 1,600°C for one hour.
INTRODUCTION Recently, nano technology and nano materials have been received much attention due to their superior properties that are never seen in bulk with the size of micron or more. For instance, nanoparticulates have shown photoluminescence depending on the particle size as found in nano silicon particulates. It has been found that aluminum nitride (AlN) also shows photoluminescence of blue emission centered at 420 nm [1,2]. Furthermore, the nanoparticulates are interesting not only in new technologies but also in well-established technologies such as sintering. Due to high surface energy of nano-particulates, it is possible to reduce process temperature during sintering. Sintered aluminum nitride has been widely used as electric substrate required high thermal conductivity such as that for CPU. Here, pure particles with less oxygen are required because the oxygen in the lattice of aluminum nitride causes phonon scattering, which results in low thermal conductivity. Therefore, the synthesis of pure nanoparticulates of aluminum nitride is very important in terms of industrial applications where energy-efficient and cost-effective process is aspired to. In this paper, we will demonstrate the synthesis of nanoparticulate of aluminum nitride by novel process, namely pulsed wire discharge (PWD) [3-5]. The properties of particles will be reported.
EXPERIMENTAL PROCEDURE Figure 1 shows the experimental setup of pulsed wire discharge. It contains high voltage generator, capacitor and gap switch. The aluminum wire (diameter 0.25 mm, 25 mm long, purity 99.99%) is settled in the chamber (22 l in volume) which is filled with mixture gas of N2 and NH3. Total gas pressure was maintained at 750 Torr with the concentration of NH3 at 20 %. W5.4.1
Pump
Filter Window
10 8
Wire
6 I / kA
Holder Gas Inlet Chamber
4 2
Window
0 Electrode
-2
Insulator
-10
H.V.
10
20
30
40
50
t / µs
Capacitor Bank
Figure 1.
0
Figure 2. Typical current waveform for wire discharge.
Experimental setup.
Intense pulsed current is fed to the wire. The wire is melted, evaporated and ionized by the pulsed
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