In situ kinetic investigations during aluminium nitride purification and crystal growth processes by capillary coupled mass spectrometry

Reaction models in the system Al–N–O–C–H are essential for intelligent purification of aluminium nitride source material and to predict time- and temperature-dependent reduction of oxygen-containing impurities. For several purposes, high purity AlN is needed; consequently it is an important goal to minimize the impurity values to a minimum possible prior to the single crystal growth. For these reasons in situ kinetic investigations with capillary coupled mass spectrometry were performed in the temperature range between 1160 °C and 2030 °C under streaming nitrogen at a pressure of 600 mbar. Conventional thermoanalytical methods like TG or DTA are not sensitive enough, signals overlay with AlN sublimation and the most commercially available systems strongly suffer from long measurement times (t > 12 h) at high temperatures. Our custom built setup was optimized for a fast detection of evolved gases, for direct temperature measurement and for high temperature homogeneity of the powder sample up to 2050 °C. Kinetic parameters were calculated with model-free and model-based kinetic methods based on mass spectrometric data achieved by on-line process monitoring of gaseous species during the processes. This study highlights the usefulness of capillary coupled mass spectrometry in kinetic studies of carbothermal reduction processes. Predictions on basis of non-linear regression analyses of experimental MS data were performed.