Synthesizing AlN powder by mechanochemical reaction between aluminum and melamine
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A solid state mechanochemical reaction (MCR) method for synthesizing AlN powder with aluminum and melamine powders as the reactants was proposed and put into practice. It was found that the solid state MCR between aluminum and melamine is an instantaneous and exothermic reaction. For a certain charge ratio, a critical ball milling time is needed for the MCR to occur. The higher the charge ratio, the faster the MCR. Cryogenic environments help to accelerate the MCR between Al and melamine. In addition to the direct one-step MCR synthesis approach mentioned above, AlN powder can also be synthesized by pre-ball-milling Al and melamine powders followed by heat treatment. Using this two-step approach, the heat treatment temperature is only about 638 C, which is much lower than that used in other ways for synthesizing AlN powder. The lower heat treatment temperature can be attributed to the combined effect of both the adoption of melamine and the high reactivity of powders caused by ball milling. Comparatively, the present solid state MCR method for synthesizing AlN powder may be more cost-effective and hence more promising to be used to industrially produce both AlN powder and in situ AlNP reinforced aluminum matrix composites. I. INTRODUCTION
Aluminum nitride (AlN) is an important ceramic material and widely used in refractory, abrasive wheel, and cutting tool materials, as an integrated circuit substrate and for cooling fin materials as well as semiconductor packaging materials because of its excellent properties such as high thermal and electric conductivities, low coefficient of thermal expansion, high hardness, high strength, good resistance to elevated temperature, and high chemical stability.1 Another important application of AlN is that it can be used as a reinforcement to reinforce metals. For example, high volume fraction AlNp reinforced aluminum matrix composites, which have relatively low coefficient of thermal expansion and high thermal conductivity, are suitable for use as substrate materials for electronic packaging applications.2 Therefore, synthesis of AlN has attracted much research attention in recent years. There are several options for synthesizing AlN, including gas-gas, gas-solid, liquid-liquid, gas-liquid, and solidsolid reactions.3–7 So far, the two primary methods of commercially synthesizing AlN powders are: (i) direct nitridation of Al with N2 or NH3; and (ii) carbothermal reduction of Al2O3 with carbon black in the presence of N2. In nature, the two methods belong to a gas-solid reaction. Compared with the direct nitridation method, AlN a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0076
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http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 3, Mar 2010 Downloaded: 13 Mar 2015
powder produced through the carbothermal reduction method has better properties in many aspects including purity, sinterability, and stability against humidity. However, the carbothermal reduction method also has some disadvantages, such as the relatively h
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