KINETICS AND MECHANISMS FOR NITRIDATION OF FLOATING ALUMINUM POWDER

Abstract

Aluminum powder entrained by ammonia-containing nitrogen gas was reacted at various temperatures and time to form aluminum nitride powder. The kinetics of nitride formation were determined by a quantitative X-ray analysis and compared with those determined by a nitrogen analysis of-the product. The conversion to aluminum nitride increased with the reaction time following a sigmoidal rate law. The reaction time for full conversion decreased as the temperature increased in the range 1050 degrees-1300 degrees C. The reaction rate constant at a given temperature was evaluated using the Avrami equation. The activation energy for the reaction was 1054 +/- 91 kJ/mol in the temperature range of 1050 degrees-1200 degrees C, and decreased to 322 +/- 70 kJ/mol above 1200 degrees C. Comparative analysis of powders formed below and above 1200 degrees C suggested strongly that the rate-controlling step changed from chemical reaction to mass transport above 1200 degrees C.