EFFECTS OF MANUFACTURING PROCESS ON THE STATES OF COORDINATIVELY UNSATURATED SITE (SUS) OF ALUMINA POWDER SURFACES

摘要

Coordinatively unsaturated aluminum ions on the surface of commercially available high purity a-Al_2O_3 powders produced by three different processes were evaluated by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Powders were heated in situ under vacuum up to 250 °C, Difference spectra between dry air conditions and 250 °C in vaccum presented bands centered around 1640, 1580, 1530, 1460 and 1380 cm"1. The bands were interpreted to be related to water molecules, physically adsorbed and coordinated to unsaturated Al~(Ⅵ), Al~(Ⅴ), Al~(Ⅳ)-Al~(Ⅵ)and/or A1~(Ⅵ)-A1~(Ⅵ), and Al~(Ⅳ), respectively, The difference spectra of powders produced by in-situ chemical vapor deposition,"A", presented mainly physically adsorbed water, meanwhile powders produced by hydrolysis of aluminum alkoxide,"B", and thermal decomposition of ammonium alum,"C", showed mainly coordinated water bands. Thermal activation and dehydration processes appear to enhance coordinately unsaturated Al~™ and Alv surface ions. Grinding a powder produced by the in-situ chemical vapor deposition increased the surface proportion of uncoordinated Al~(Ⅴ)ions.The main conclusion of the present work is that the nature and proportion of coordinately unsaturated aluminum ions present on the surface of high purity 01-Al_2O_3 powders, intimately related to the manufacturing process, is responsible for the different hydration ability associated with each particular powder.rnThe surface proportion of coordinately unsaturated aluminum atoms presented on the surface of powders "B" and "C" was larger than for powders "A". Furthermore, the surface proportion of uncoordinated Al atoms with coordination V was increased by grinding. From the results, the surface proportion of coordinately unsaturated aluminum ions such as Al~(Ⅳ) and A(Ⅴ) might be affected by thermal activation and dehydration processes. Additionally, the grinding process appears to increase the proportion of coordinately unsaturated Al~(Ⅴ). It was possible that the different hydration ability of the powders might be linked to differences in the surface proportion of coordinately unsaturated Al(Ⅴ) atoms by different manufacturing processes.