Aluminum Nitride Oxidation by Simultaneous TG and DTA

This work is a study, by simultaneous thermogravimetry (TG) and differential thermal analysis (DTA), of the oxidation of a water resistant aluminum nitride powder which has a special protective coating, and an uncoated AlN powder which has become partially hydrated during its use. The activation energy for oxidation is estimated by the Kissinger and isoconversional methods. In the former method, the temperatures of the oxidation peaks were obtained from DTA and DTG curves. The activation energies for oxidation of the water resistant AlN, obtained by the Kissinger method, are 357±10 kJ mol^–1, 392±12 kJ mol^–1 using respectively DTG and DTA data. For the uncoated AlN, the values are 243±7 and 257±8 kJ mol^–1, respectively. By the isoconversional method, the average values obtained for coated and uncoated samples are, respectively, 323±10 and 224±7 kJ mol^–1. Therefore, the special coating, which protects the aluminum nitride from humidity action, also provides a higher resistance to oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermogravimetric study of yttrium isopropoxide and dispersant burnout in aluminum nitride ceramic processing

Yttrium isopropoxide, an yttrium oxide precursor, is sometimes used as a sintering aid for producing aluminum nitride ceramics. In the present work, this sintering aid was used with isopropanol as the solvent and polyethyleneimine as the dispersing agent. After initial ball milling and drying steps, the burnout behaviour of samples taken from isostatically pressed pellets was studied by thermal analysis in nitrogen and air. In addition to the milled and pressed pellets, each component was also analyzed separately. Complete conversion to yttrium oxide, with no residual carbon, would be a desirable property of this system. However, during the preparation of the aluminum nitride pellet, there was only partial yttrium isopropoxide decomposition. The nitrogen burnout residue contained carbon formed from the yttrium isopropoxide and dispersant overlapping thermal decomposition, mostly from an intermediary decomposition stage of the former that occurs between 300 and 550°C. The residual carbon content and the previous yttrium isopropoxide decomposition were estimated by thermogravimetry.