X-ray photoelectron spectroscopic study of hydrated aluminas and aluminas
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X-ray photoelectron spectra of hydrated aluminas (boehmite, diaspore, bayerite, and gibbsite), transition aluminas (y, S, 77, 6, %, and K -A1 2 O 3 ) and corundum (a?-Al 2 O 3 ) have been studied for spectral characterization of each compound. The Ols spectra are shifted 0.2-1.2 eV to higher binding energy (Eb) in the order of a - A l 2 O 3 < boehmite, diaspore < bayerite, gibbsite, and this agrees with the order of bulk 0H/A1 molar ratio in samples. The Eb and FWHM values of Ols spectra of transition aluminas depend on the ratio O H / 0 , i.e., the amount of O H " ions chemisorbed on them, and tend to decrease toward those of a - A l 2 O 3 with increasing calcination temperature. Therefore, it is considered that an attracting effect of the proton on valence electrons in the hydroxyl oxygen causes the increased binding energy between core electrons and oxygen atomic nuclei. The broad Ols spectra of boehmite and diaspore can be deconvoluted into equal contribution from the two oxygen species in O 2 and O H " ions in their structures.
I. INTRODUCTION X-ray photoelectron spectroscopy (XPS) is a useful technique to determine the chemical structure of a surface. Actually, information about the chemical composition and chemical bonding of surface species can be obtained by analyzing chemical shifts, multiplet structure, and satellites in the XPS spectra. Recently, XPS has been extensively applied to the studies of catalysts, inorganic materials, corrosion products, and so on. Particularly, in connection with the identification of surface corrosion products on materials such as stainless steel and other alloys, oxides and hydroxides of nickel,1 copper,1'2 and iron3 have been the subject of a number of XPS studies, and have been characterized by their different chemical shifts and satellites. Hydrated aluminas and aluminas are very important inorganic materials and have different forms, properties, and applications. We are interested in the characterization of these compounds by XPS and magic angle spinning 27A1 nuclear magnetic resonance (27A1 MASNMR) spectroscopy. Although the XPS spectra of some of the individual forms have been reported, very few comparative studies of hydrated aluminas and aluminas have been undertaken.4 In this study, in order to confirm and extend the earlier work, the x-ray photoelectron spectra of the following, extensive number of different hydrated aluminas and aluminas are systematically compared: monohydrates (boehmite and diaspore), trihydrates J. Mater. Res., Vol. 9, No. 11, Nov 1994
(gibbsite and bayerite), transition aluminas (y, 8, rj, 6, x, and K - A 1 2 O 3 ) , and corundum ( a - A l 2 O 3 ) . II. EXPERIMENTAL All spectra were obtained using an ESCALAB Mk II (VG Science LTD) photoelectron spectrometer. A sample was mounted on the gold mesh and evacuated at a pressure of 1CT7 Pa for 24 h. Nonmonochromatized Mg Ka exciting radiation was used with the x-ray power normally set at 320 W. Sample charging was measured by the displacement of the surface carbon Cls line from 285.0 eV and range
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