KINETICS AND MECHANISMS FOR NITRIDATION OF FLOATING ALUMINUM POWDER

Aluminum powder entrained by ammonia-containing nitrogen gas was react ed at various temperatures and time to form aluminum nitride powder. T he kinetics of nitride formation were determined by a quantitative X-r ay 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 fu ll conversion decreased as the temperature increased in the range 1050 degrees-1300 degrees C. The reaction rate constant at a given tempera ture was evaluated using the Avrami equation. The activation energy fo r 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 120 0 degrees C suggested strongly that the rate-controlling step changed from chemical reaction to mass transport above 1200 degrees C.