The oxidation of an aluminum nitride powder studied by bremsstrahlung-excited Auger electron spectroscopy and x-ray phot
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Thomas N. Wittberg University of Dayton Research Institute, Dayton, Ohio 45469 (Received 11 July 1994; accepted 19 October 1994)
Bremsstrahlung-excited Auger electron spectroscopy (AES) was used to study the oxidation kinetics of an aluminum nitride powder oxidized in air at 750, 800, 850, and 900 °C. An equation was derived to calculate the average surface oxide film thickness from the aluminum AES spectra. The oxidation of this powder was found to follow a parabolic rate law within this temperature range. The measured activation energy was 230 ± 17 kJ/mol (55 ± 4 kcal/mol). Analysis with x-ray photoelectron spectroscopy (XPS) showed that in addition to the nitride N Is peak, there was a second N Is peak. This peak has been observed in previous studies and can be attributed to N - 0 bonding either within the growing oxide film or at the A12O3/A1N interface.
I. INTRODUCTION Aluminum nitride is one of the candidate materials for use in electronic packaging and engineering ceramics. It offers both higher thermal conductivity and superior electrical insulating properties when compared with aluminum oxide. One problem with aluminum nitride, however, is that low level oxygen impurities can have a significant effect on its thermal conductivity. Thermogravimetric analysis (TGA) has been used to study the oxidation of aluminum nitride powder1 and aluminum nitride ceramics sintered with Y 2 O 3 or YF 3 . 2 In the latter study, parabolic oxidation was observed for temperatures from 1100 °C to 1400 °C. In the study of aluminum nitride powder oxidation, Katnani and Papathomas observed an initial period of linear oxidation below 900 "C.1 At longer times and at temperatures above 900 °C, parabolic oxidation was observed with an activation energy of 235 kJ/mol (56 kcal/mol). In addition to the TGA analysis, XPS (x-ray photoelectron spectroscopy) was used to analyze the oxidized powders. On powders oxidized at 700 °C to 1000 °C, the N Is spectra showed the presence of two peaks. These peaks were identified as arising from aluminum nitride and aluminum oxynitride. Katnani and Papathomas found that the Al 2p binding energies for A1N and A12O3 are almost identical.1 They did not attempt to extract information about oxidation kinetics from the XPS data. In other more recent studies, a difference of ~2 eV was measured between the Al KLL kinetic energies for A12O3 and A1N.34 In the present study, we have found that the Al KLL peaks of A12O3 and A1N are sufficiently resolved to allow 302 http://journals.cambridge.org
J. Mater. Res., Vol. 10, No. 2, Feb 1995 Downloaded: 22 Mar 2015
them to be used to determine oxidation kinetics for A1N powders. Bremsstrahlung-excited AES was then used to determine the oxide thickness on A1N powders heated in air at 750, 800, 850, and 900 °C. This method has been used previously to study the oxidation of Si3N4 powders,5"7 SiC whiskers,8 and SiC platelets. 910 II. EXPERIMENTAL The aluminum nitride powder was obtained from Dow Chemical Company." The average particle size is 1.48 ± 0.11 /x.m. The major i
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