Emil Chifu (1925-1997)
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Biomedical subjects
DA Cadenhead
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Surface Reactivity of Iron Oxide Pigmentary Powders toward Atmospheric Components: XPS, FESEM, and Gravimetry of CO and CO2 Adsorption
The adsorption of carbon monoxide and carbon dioxide (CO and CO2) on a number of specially prepared alpha-Fe2O3 samples was measured gravimetrically at 25°C. The samples were prepared from a steel-pickling waste (97 wt% FeSO4·7H2O) by roasting the original material at 700°C for 5 h in air, oxygen, and nitrogen. Estimated surface coverages by the adsorbed CO and CO2 were made on the basis of nitrogen-adsorption-based surface areas, while the nature of the sample surfaces was investigated by both X-ray photoelectron spectroscopy (XPS) and field emission SEM (FESEM) techniques. In addition a depth profiling study utilizing a sputtering argon beam and XPS was undertaken. Morphological studies using FESEM showed that neither CO nor CO2 caused any significant structural changes. The nature of the resultant alpha-Fe2O3 sample surfaces differed, with the degree of oxygenation decreasing in the order of preparatory gases: oxygen, (wet) air, nitrogen [IP(O), IP(A), and IP(N)]. The amounts of both CO and CO2 adsorbed decreased in the sample order IP(A) > IP(O) > IP(N), though in the case of CO adsorption, the amounts adsorbed on IP(A) and IP(O) were not greatly different. In all cases the amounts adsorbed represented only fractional coverage. Adsorption of the more acidic CO2 is thought to be favored more by basic Ox-2 than by O2- sites on both IP(O) and IP(A), but with surface hydroxyl groups also playing a role (particularly on IP(A)). The CO2 adsorption should result in the formation of mono-, di-, and polydentate carbonate and bicarbonate species, with increasing degassing temperatures favoring the polydentate species and the decomposition of the bicarbonate and carbonate to form undissociated CO2. The adsorption of CO (a weak base) is postulated to take place on strong Lewis acid, highly coordinated, metal sites to form metal carbonyl species, on strong base sites (O2-) to form carbonite, oxalate, and ketenic species, and, to a lesser degree, on surface hydroxyl groups to form formyl and formate species. Copyright 1997 Academic Press. Copyright 1997Academic Press
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Surface Reactivity of Iron Oxide Pigmentary Powders toward Atmospheric Components: XPS and Gravimetry of Oxygen and Water Vapor Adsorption
The adsorption of oxygen and water vapor on a number of specially prepared alpha-Fe2O3 samples was measured gravimetrically at 25°C. The samples themselves were prepared from a steel-pickling chemical waste (97 wt% FeSO4·7H2O) by roasting the original material at 700°C for 5 h in air, oxygen, and nitrogen. Estimated surface coverages by the adsorbed oxygen and water vapor were made on the basis of nitrogen-adsorption-based surface areas, while the nature of the sample surfaces was investigated by both X-ray photoelectron spectroscopy (XPS) and field emission SEM (FESEM) techniques. In addition a depth profiling study utilizing a sputtering argon beam and XPS was undertaken. Morphological studies using FESEM showed that, while the surface areas were essentially the same (27-29 m2/g) for all three samples, the sample prepared in nitrogen had a significantly larger particle size than the other two. These studies also indicated that neither oxygen nor water vapor adsorption caused any significant structural changes. The differing sample preparations resulted in differing oxygenated surfaces for the alpha-Fe2O3 samples, with the degree of oxygenation decreasing in the order of preparatory gases: oxygen, (wet) air, nitrogen. The amounts of both oxygen and water vapor adsorbed were in inverse proportion to the original degree of surface oxygenation, though the amounts of both represented fractional coverage at best. While the water vapor adsorption was always greater than that of oxygen, the former was more weakly adsorbed, as was indicated by the ease of desorption. Depth profiling failed to indicate any bulk diffusion of oxygen but could not be considered reliable since even the attenuated argon beam used here still brought about reduction of surface iron. Both oxygen and dissociative water adsorption are thought to involve surface sites of high coordination unsaturation. Oxygen is postulated to adsorb on such poorly oxygenated sites primarily as O-2; however, O2- and possibly O- or Fe = O are also thought to play a role.
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