Coated hematite

The surfactants associate at the oxide surface to form hemi-micelles with their hydrophobic groups exposed to the aqueous phase at low concentrations, but at higher concentrations, with the hydrophilic groups turned outwards. Hematite coated with various proteins (ovalbumin, y-globulin, lysozyme) adopted either the iep of the proteins or a value between that of the oxide and the protein and displayed modified coagulation behaviour (Johnson and Matijevic, 1992). 

Rapid oxidation of polished samples of iron in an air/acetylene flame produces a hematite coating of 50-100 um in thickness for use as a hematite electrode (Curran... 

Middleton, A.P. (1987) Technological investigation of the coatings on some hematite-coated pottery from Southern England. Archaeometry 29 250-261 Middleton, A.P. (1992) Ceramics Materials for all reasons. In Bowman, S. (ed.) Science and the past. British Museum Press, 16-36 Mijirtskii, A.V. Langelaar, M.H. Boerma,... 

Amirbahman and Olson (1995) analysed the deposition kinetics of hematite coated with humic matter in a quartz bed filter as a function of calcium concentration. At high ionic strength and low pH, tightly... 

For the standard systems, dyed PCE was added to the water-saturated media, untreated quartz sand and Rhodorsil-treated sand. In the other systems, DDA was added to die dyed PCE phase and then the organic mixture was added to the water-saturated hematite-coated and untreated quartz sands. All botdes were capped and then vigorously shaken by hand. 

Additional contact angles were measured at 0.001 M SDS concentration. The hematite disk was conditioned in the SDS solution before adding polymer to the solution. The contact angle was measured after adding sufficient quantities of polymer for concentrations of 1, 3, and 5 ppm. For both PAA and PAM, the contact angle remained constant and identical to the value obtained in the absence of polymer. No polymer was able to adsorb on the surfactant-coated disk. It can be concluded that whichever species, surfactant or polymer, adsorbed first was not... 

Where stream waters contain Fe, boulders on the bottom are often coated with Fe oxides with no relationship to the petrography of the boulders. The amount of Fe oxide deposited is around a few mg cm (Schwertmann and Friedl, 1998) and the annual accretion rate is in the range of 100 xg cm (Carpenter Hayes, 1980). Suspended particles in brownish, drainage waters from tropical soils in the Cameroons, in which goethite with some hematite were identified, are transported from the soil profile to a spring and then to the water course (Olovie-Lauquet et al. 2000). 

The physical and chemical parameters which influence iron oxide formation vary with time and space, e. g. through changing water/air content. Microenvironments exist in pores of different sizes and with different degrees of filling. For example, hematite was identified in coatings at the (dry) surface of a basalt boulder, whereas goethite occurred in a nearby (moister) crack (Bender-Koch et al., 1995 a). In another case, goethite was the dominant oxide next to the root surface, whereas lepidocrocite predominated a few mm away from it (Schwertmann Fitzpatrick, 1977). Often, however, the exact conditions under which Fe oxides form are difficult to determine. 

Hematite is used to coat the red emiting phosphor, Y2O2EU, which is used in cathode ray tubes (Franz et al., 1993 Merckhi and Feldmann, 2000). Hematite is also used in sensors for the detection of hydrocarbon gases and carbon monoxide. The sensitivity of the sensor can be improved by sintering the oxide with 0.09 mol ° mol Al at 850 °C (Han et al., 2001 and references therein). 

Thermal decomposition of iron pentacarbonyl. Very finely divided red iron oxide is obtained by atomizing iron pentacarbonyl, Fe(CO)5, and burning it in excess of air. The size of the particles depends on the temperature (580-800 °C) and the residence time in the reactor. The smallest particles are transparent and consist of 2-line ferri-hydrite, whereas the larger, semi-transparent particles consist of hematite (see Chap. 19). The only byproduct of the reaction is carbon dioxide, hence, the process has no undesirable environmental side effects. Magnetite can be produced by the same process if it is carried out at 100-400 °C. Thermal decomposition of iron pentacarbonyl is also used to coat aluminium powder (in a fluidized bed) and also mica platelets with iron oxides to produce interference or nacreous pigments. 

Hematite ellipsoids coated with an Sn(OH)2 shell were prepared by heating an aqueous dispersion of hematite (0.3 g L ) with 4.10 M Sn(S04)2, 1.85 M urea and 0.31 M HCl at 80 °C for up to one hr both continuous stirring during precipitation and careful control of the ratio of reactants/solid were essential to ensure that coated particles rather than a mixture of coated hematite and precipitated (Sn(OH)2, were obtained (ul Haq and Matijevic, 1998). 

Gardner, W.K. Parbery, D.G. Barber, D.A. (1982) The acquisition of phosphorus by Lu-pinus albus L. I. Some characteristics of the soil/root interface. Plant Soil 68 19-32 Garg, A. Matijevic, E. (1988) Preparation and properties of uniform coated colloidal particles. II. Chromium hydrous oxide on hematite. Langmuir 4 38-44 Garg, A. Matijevic, E. (1988) Preparation and properties of uniform coated colloidal parti-... 

Kraemer, S.M. Hering, J.G. (1997) Influence of solution saturation state on the kinetics of ligand-controlled dissolution of oxide phases. Geochim. Cosmochim. Acta 61 2855-2866 Kraemer, S.M., Xu, J., Raymond, K.N. Spo-sito, G. (2002) Adsorption of Pb(II) and Eu(III) by oxide minerals in the presence of natural and synthetic hydroxamate sidero-phores. Environ. Sd. Technol. 36 1287-1291 Kraemer, S.M. Cheah, S.-F. Zapf, R. Xu, J. Raymond, KN. Sposito, G. (1999) Effect of hydroxamate siderophores on Fe release and Pb(II) adsorption by goefhite. Geochim. Cosmochim. Acta 63 3003—3008 Kratohvil, S. Matijevic, E. (1987) Preparation and properties of coated uniform colloidal partides. I. Aluminum (hydrous) oxide on hematite, diromia, and titania. Adv Ceram. Mater. 2 798-803... 

Oh, S.J. Cook, D.C. Townsend, H.E. (1998) Characterization of iron oxides commonly formed as corrosion products on steel. Hyper-fine Interactions 112 59-65 Ohmori, M. Matijevic, E. (1992) Preparation and properties of uniform coated inorganic colloidal particles. VII. Silica on hematite. J. Colloid Interface Sci. 150 594-598 Ohta, S. Effendi, S. Tanaka, N. Miura S. (1993) Ultisols of lowland Dipterocarp forest in East Kalimantan, Indonesia. Soil Sci. Plant Nutr. 39 1-12... 

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