Synthesis and Sintering of Aluminium Nitride Nano-particles
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1040-Q09-21
Synthesis and Sintering of Aluminium Nitride Nano-particles Zhao HAN, Mei YANG, and Hongmin ZHU School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing, 100083, China, People's Republic of ABSTRACT Aluminum nitride (AlN) nano-particles were synthesized from aluminum chloride by sodium reduction in liquid ammonia. A liquid solution of sodium dissolved in ammonia was employed as a reduction-nitridation agent, which enabled direct nitridation of aluminum chloride at -45°C. The synthesized particles were heat-treated at 1000°C in vacuum, and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and BET surface area measurement. The results indicated that the products were hexagonal wurtzite AlN particles, with a specific surface area of 262 m2g-1. Spark plasma sintering (SPS) process was used to consolidate the as-prepared AlN nanoparticles, and dense AlN ceramic (>98.5%) with average grain size of 200-400 nm was obtained at 1600°C without the use of sintering additives. INTRODUCTION Aluminum nitride (AlN) is considered an ideal material for semiconductor substrates and electronic packaging applications. It has many attractive properties, such as high thermal conductivity (~320W·m-1·K-1), low dielectric constant (8.8 at 1MHz), low thermal expansion coefficient (4.3×10-6K-1, similar to that of silicon), good mechanical strength as well as excellent chemical stability [1-2]. However, AlN is very difficult to densify due to its high covalent bond and low atomic diffusivity. The sinterability of ceramic compact is strongly dependent on starting particle size. It is highly expected that the sintering activity will be significantly improved when the particle size of the AlN powders is reduced to a nanoscale range. Extensive attention has been attracted to develop synthesis routes of nanoscale AlN particles with low cost and large quantity. Several researchers have described the preparation of nanoscale AlN particles via direct nitridation of Al metal in nitrogen or ammonia at high temperature elevated by plasma [3-4], microwave [5-6], pulsed wire discharge [7], and laser beams [8]. AlN nanoparticles were also prepared by chemical vapor deposition[9] and gasreduction–nitridation method[10]. These methods mostly require high temperature, and particle growth is almost unavoidable. Cao et al. [11] reported the preparation of AlN nanocrystalline powders from reactions of Al metal, NH4Cl, and NH4I in liquid ammonia at 550°C. However, this method needs high pressure and very long time. In the present work, nanosized AlN particles were synthesized in liquid ammonia at 45°C. The as-synthesized particles were then consolidated by Spark Plasma Sintering (SPS). Dense AlN ceramic (>98.5% relative density) with an average grain size of 200–400 nm was achieved at 1600°C without using any sintering additives. The characteristics of the product particles and sintered bodies were investigated.
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