Tetrahedral Aluminum Ions on High Purity Sub-Micron [alpha]-Alumina Powder Surfaces

The surface of six different grades of commercial sub-micron high purity α-Al2O3 powders produced by two different processes, in-situ chemical vapor deposition ("A" powders), and hydrolysis of aluminum alkoxide ("B" powders) methods, were evaluated by temperature programmed desorption mass spectrometry (TPDMS) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Desorption of CO2 molecules was detected for all the powders, but the quantity was greater for the "B" powders than the "A" powders. The maximum of the CO2 desorption peak was in the range of 230-270°C for all powders. The desorbed CO2 peak was considered to evolve from adsorbed CO2 molecules forming hydrogen carbonyl groups through interaction with the AlIV-OH groups on the α-Al2O3 surfaces. The DRIFT spectra of the powders heated at 700°C under vacuum confirmed a larger population of AlIV-OH groups on the surface of the "B" powders. The present study clearly demonstrates the presence and quality of the AlIV on the surface of α-Al2O3 powders and the effect of the type of manufacturing process on their proportion.