Combustion synthesis method for synthesis of aluminum nitride powder using aluminum containers
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A combustion synthesis method was developed for synthesis of AlN powder. Al powder and small amounts of NH4Cl were thoroughly mixed and placed in low-melting-point containers made of a thin, perforated aluminum sheet. The combustion reaction was ignited by heating the top surface of the powder stack, and the aluminum container was converted completely to AlN during the combustion reaction. High product yields were obtained under N2 pressures of 0.2–0.5 MPa. The product was composed of a dense outer portion and a loose inner portion. Effects of several process parameters on the product yield were investigated and discussed.
I. INTRODUCTION
Aluminum nitride possesses many unique properties such as high thermal conductivity, high electrical resistivity, low thermal expansion coefficient (close to that of silicon), moderately low dielectric constant, good thermal shock resistance, and good corrosion resistance.1,2 It has been considered for many applications such as electronic substrates, packaging materials for integrated circuits, heat sinks, high thermally conductive composite materials, and hardware for containing or processing molten metals and salts.3,4 Despite the many desirable properties, AlN has not yet been used widely in industry mainly because of its high market prices due to high production costs. Development of new processes for producing AlN powder at low cost is thus an interesting research topic. Many processes have been developed for the synthesis of AlN powder.5,6 These include carbothermal reduction,7–9 direct nitridation,10–12 floating nitridation,13,14 chemical vapor deposition,15,16 vapor phase synthesis,17 organometallic precursors,18,19 and combustion synthesis20–22 methods. Among these, carbothermal reduction and direct nitridation are the methods currently employed in industry for commercial production of AlN powder.8,11 Both methods require heating at elevated temperatures (>1500 K) and long processing times (>5 hours). In addition to high energy consumption, the production rates are slow. Our research objective was to investigate the use of combustion synthesis [self-propagating high-temperature synthesis (SHS)] method for the production of AlN a)
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http://journals.cambridge.org
J. Mater. Res., Vol. 16, No. 12, Dec 2001 Downloaded: 18 Mar 2015
powder. The SHS method, originally developed in the former Soviet Union,23 has been applied to synthesis of various materials including ceramics, intermetallics, and composites. It has many potential advantages such as low processing cost, energy efficiency, and high production rate.24 Many combustion synthesis processes have also been developed for synthesis of AlN powder.20–22,25–35 These processes can be divided into two categories according to their methods for holding the reactants. In one category, the reactant powders are pressed into reactant compacts,22,25–31 and in the other category, the reactant powders are contained in refractory containers such as grap
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