Oxidation Kinetics of AlN Under CO 2 Atmosphere
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DUCTION
IN view of the increasing recycling of aluminum, the remelting of the aluminum scrap and the consequent handling of the increasing amounts of dross/salt cake is receiving significant attention. Dross has been reported to contain such compounds as chlorides, Al2O3, AlN, Al4C3, SiO2, MgO, and even organic materials like ink and varnish.[1,2] It is important to recover the potentially valuable compounds from this by-product and modify those that can cause environmental damage. For instance, value-added MgAl2O4, AlON, SiAlON, and MgAlON may be prepared by using aluminum dross as raw material. However, the oxidation behavior of AlN in the aluminum dross needs to be understood in view of the importance of this phenomenon during the synthesis. Furthermore, AlN, when dumped in nature, can get hydrolyzed by rainwater to produce NH3 gas, which is highly undesirable. The oxidation behavior of AlN under O2 and air have already been investigated by Hou et al.,[3] and various kinetics models (linear or parabolic) have been proposed. Kim and Moorhead[4] reported that the oxidation kinetics of sintered aluminum nitride followed linear rate law, but became parabolic at higher temperatures. Recently, Chou[5,6] developed a series of models that can explicitly describe the oxidation reaction under oxygen atmosphere. However, the oxidation behavior of AlN has not been studied when greenhouse gas CO2 is employed as an oxidation agent. In the present work, the oxidation behavior of AlN in CO2 gas was investigated. Experiments were carried out at different temperatures under different CO2 flow rates. The oxidation process involving gas absorption, dissociation, and gas–solid reaction is complicated and PENG LI, Ph.D. Student, is with the Royal Institute of Technology, SE-100 44 Stockholm, Sweden, and with the University of Science and Technology, Beijing 10083, People’s Republic of China. Contact e-mail: [email protected] LIDONG TENG, Graduate Student, and SESHADRI SEETHARAMAN, Professor, are with the Royal Institute of Technology. MIN GUO and MEI ZHANG, Professors, are with the University of Science and Technology. Manuscript submitted July 23, 2010. Article published online December 21, 2011. 406—VOLUME 43B, APRIL 2012
requires a critical consideration of several factors. A simple model was developed in the present work to simulate the oxidation process.
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EXPERIMENTAL PROCEDURE
A. Preparation of Samples The AlN powder used in this study was supplied by Sigma-Aldrich Company (Seelze, Germany) and maximum impurity content was less than 2 wt pct. The particle size of the powder was around 10 lm. Before the oxidation experiments, the AlN powder was dried at 573 K (300 °C) for 4 hours under vacuum (
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