Showing papers on "Iron oxide published in 1991"
TL;DR: In this article, an iron oxide pillared montmorillonite with base-hydrolyzed solutions of Fe3+ salts and subsequent thermal conversion of the intercalated polycations was obtained.
142 citations
TL;DR: The distribution of particle-bound phosphorus in the suspended sediment of the Delaware Estuary was examined with a sequential chemical leaching technique as mentioned in this paper, which revealed that particulate phosphorus was associated with organic matter, aluminum oxides, iron oxides and apatite.
142 citations
TL;DR: The solubility of Fe in soils is largely controlled by Fe oxides; ferrihydrite, amorphous ferric hydroxide, and soil-Fe are generally believed to exert the major control.
Abstract: The solubility of Fe in soils is largely controlled by Fe oxides; ferrihydrite, amorphous ferric hydroxide, and soil-Fe are generally believed to exert the major control. Fe(III) hydrolysis species constitute the major Fe species in solution. Other inorganic Fe complexes are present, but their concentrations are much less than the hydrolysis species. Organic complexes of Fe including those of organic acids like citrate, oxalate, and malate contribute slightly to increased Fe solubility in acid soils, but not in alkaline soils.
135 citations
Patent•
25 Jun 1991TL;DR: In this article, a clear glass, with a substantial absence of color in transmittance, and with an attractive, bright, pure azure edge coloration is achieved in a glass having greater than 87 percent, preferably greater than 90 percent, luminous transmittances by using very small amounts of iron oxide as the sole essential colorant, with the ratio of iron in the ferrous state to total iron being at least 0.4.
Abstract: A clear glass, with the substantial absence of color in transmittance, and with an attractive, bright, pure azure edge coloration is achieved in a glass having greater than 87 percent, preferably greater than 90 percent, luminous transmittance by using very small amounts of iron oxide as the sole essential colorant, with the ratio of iron in the ferrous state to total iron being at least 0.4.
110 citations
TL;DR: In this article, the adsorption of 10 chlorophenols on synthetic, naturally occurring iron and aluminum oxides was studied to elucidate the mechanism of binding and relative bond strength of the chlorine-substituted phenols.
Abstract: The adsorption of 10 chlorophenols on synthetic, naturally occurring iron and aluminum oxides was studied to elucidate the mechanism of binding and relative bond strength of the chlorine-substituted phenols was identified by spectroscopic methods. Chlorophenolates were found to be chemisorbed on oxide surfaces via an inner-sphere coordination. Chlorophenols also bonded on oxides by weak physical forces (H bonding and condensation), but these types of weak bonding were identified only when adsorption occurred from the vapor phase onto dry surfaces. Physisorbed chlorophenols, unlike chemisorbed molecules, were readily removed from oxide surfaces by washing with water. Poorly crystallized iron and aluminum oxides showed similar mechanisms of chlorophenol binding, although the bond for chlorophenolate chemisorbed on iron oxide was stronger than that on aluminum oxide. Only physically adsorbed chlorophenols were detected on crystalline gibbsite, suggesting that the dominant (001) crystal face, with surface hydroxyl groups doubly coordinated to Al, was not specifically reactive with the chlorophenols. Chemisorption, however, was identified on the crystalline iron, geothite. From the extent of perturbation of aromatic ring electrons, the surface bond strength for chlorophenolates on aluminum oxide was found to correlate with the Lewis basicity of the phenolate anions (the higher the pK{sub {alpha}} of the chlorophenols,more » the stronger the surface bond). Nevertheless, the amount of chlorophenol adsorbed on noncrystalline iron oxide at controlled pH of 5.4 was limited by the extent of deprotonation (the lower the pK{sub a}, the more adsorption).« less
89 citations
TL;DR: In this paper, a modified version of the K~mpf and Schwertmann (1982) procedure for concentrating iron oxides in soil clays by dissolution of kaolin and gibbsite by boiling for 1 h in 5 M NaOH may not dissolve all kaolin, and also results in the precipitation of sodalite.
Abstract: A B S T R A C T: The K~mpf & Schwertmann (1982) procedure for concentrating iron oxides in soil clays by dissolution of kaolin and gibbsite by boiling for 1 h in 5 M NaOH may not dissolve all kaolin, and also results in the precipitation of sodalite. For the complete dissolution of kaolin in kaolin-rich soil clays a boiling time of 2 h in 5 M NaOH was required. The large amounts of sodalite produced were not removed by the prescribed single wash in 0-5 M HC1. Oxalate soluble AI contents of iron oxide concentrates were sometimes very high and dithionite Fe contents were very low both in concentrates containing sodalite, and in those for which sodalite was not detected by XRD, but where a previously unsuspected amorphous sodalite-like phase may have been present. Complete removal of precipitated sodalite was achieved by two extractions with 0.5 M HCI at 25~ for 20 rain. This modified procedure does not alter the Al-substitution and crystal size of goethite, hematite and maghemite as determined by XRD measurements.
82 citations
77 citations
TL;DR: A mixture of a di- or polyphosphonic acid and a reductant wherein each is present in a sufficient amount to provide a synergistic effect with respect to the dissolution of metal oxides and optionally containing corrosion inhibitors and pH adjusting agents as discussed by the authors.
74 citations
TL;DR: In this paper, the selective catalytic reduction of nitric oxide by ammonia over iron oxide-chromia-alumina aerogels was studied over the temperature range of 423 to 750 K.
63 citations
Patent•
22 Nov 1991
TL;DR: A mineral fibre composition which is soluble in biological fluids contains substantially 45-65 % by weight of SiO2, 15-40 % of CaO, 0-20 % of MgO and 0-6 % of Na2O + K2O, and in addition aluminium and/or iron oxides as well as phosphorus oxide in such amounts that the weight ratio of P2O5 to the sum of Al2O3 and iron oxide is circa 0.4 to 6.
Abstract: A mineral fibre composition which is soluble in biological fluids contains substantially 45-65 % by weight of SiO2, 15-40 % by weight of CaO, 0-20 % by weight of MgO, 0-6 % by weight of Na2O + K2O, and in addition aluminium and/or iron oxides as well as phosphorus oxide in such amounts that the weight ratio of P2O5 to the sum of Al2O3 and iron oxide is circa 0.4 to 6.
51 citations
TL;DR: A ternary complex of Ti(III), citrate, and ethylenediaminetetraacetate (EDTA) as reductant and bicarbonate as a proton acceptor has been used to measure the abundance of free Fe oxide phases and associated elements in soils and sediments.
Abstract: A new iron oxide dissolution method designed to measure the abundance of “free” Fe oxide phases and associated elements in soils and sediments has been tested. The method employs a ternary complex of Ti(III), citrate, and ethylenediaminetetraacetate (EDTA) as a reductant and bicarbonate as a proton acceptor. The Ti(III)-citrate-EDTA-HCO3 method dissolved more synthetic amorphous ferric oxide and goethite, but less synthetic hematite, than the dithionite-citrate-HCO3 method of Mehra and Jackson. The production of acidity by the dissolution indicated that Ti(IV) is hydrolyzed to TiO2 during the extractions. The heated dithionite method dissolved 3–6 times more Al from kaolinite and nontronite standard clays than room temperature dithionite, and 4–6 times more Al than the Ti(III)-citrate-EDTA-HCO3 method. Furthermore, the release of Fe from the clay mineral samples consistently and rapidly reached a plateau during multiple extractions by the Ti(III)-citrate-EDTA-HCO3 method, indicating that a well-defined Fe oxide fraction was removed. Fe released by the dithionite method continued to increase with each extraction, suggesting that some release of structural Fe occurred. Tests on two natural sediments and one heavy mineral fraction from the Miocene Cohansey Sand in the New Jersey Coastal Plain suggested that the Ti(III)-citrate-EDTA-HCO3 method removed Fe oxides more effectively and more selectively than the dithionite method. The selectivity of the Ti(III)-citrate-EDTA-HCO3 method is enhanced by rapid extractions at room temperature and low free ligand concentrations.
TL;DR: In this article, a method is described which can be used to investigate the interaction of dissolved metals with particulate material, and the preparation of rare earth radiotracers by neutron activation is discussed in detail.
Abstract: A method is described which can be used to investigate the interaction of dissolved metals with particulate material. Low level concentrations (10−9M) of rare earth radiotracers were used to investigate their sorption onto synthetic mineral oxide surfaces. The preparation of rare earth radiotracers by neutron activation is discussed in detail. A kinetic approach was employed to investigate the interaction of dissolved metals and suspended mineral oxides. Amorphous iron oxyhyroxide, a phase commonly found in nature, was used in sorption experiments carried out in seawater at pH 7.8 and 2°C. Results of this study indicate a high affinity of the rare earth elements (REE) for the iron oxide surface (evidenced by fast uptake and high partition coefficients) and reveal a fraction between light and heavy REE.
TL;DR: In this article, the kinetics of hydrogen peroxide reduction were studied on iron in borate buffered and unbuffered solutions of pH ranging from 8.6 to 13.8, with and without the presence of chloride ions.
TL;DR: In this article, the reduction behavior of iron oxide supported on magnesium oxide has been studied using temperature-programmed reduction (TPR), X-ray diffraction (XRD), and high-field magnetic measurements.
Abstract: The reduction behaviour of iron oxide supported on magnesium oxide has been studied using temperature-programmed reduction (TPR), X-ray diffraction (XRD), and high-field magnetic measurements. The catalysts, containing 1–6 wt.% Fe, were prepared by incipient-wetness impregnation of a preshaped magnesium oxide support with organometallic complexes, such as, ammonium iron(III) citrate and ammonium iron(III) EDTA. In the fresh calcined catalyst the iron oxide is present as magnesium ferrite, MgFe2O4. With TPR two broad reduction peaks, reflecting the sequential reduction of Fe3+via Fe2+ to Fe0, were observed. High-field magnetic measurements enabled us to describe the reduction behaviour in detail. In the first reduction step, proceeding at ca. 630 K, MgFe2O4 is reduced to FeO partly via Fe3O4. A second reduction step at 750 K results in the formation of metallic iron. Part of the metallic iron has been found to be present in the form of superparamagnetic particles within the MgO support.
TL;DR: In this article, the effect of the application of ferromagnetic powder of iron oxide (magnetic powder) and a gradient magnetic field on the sedimentation process was examined, and the volumetric loading rate of Polypepton was kept to 200-1,000 mgl−1 d−1 during 7 d in the activated sludge supplemented with 2,000 mg l−1 of magnetic powder.
TL;DR: The effects of chemical weathering on the mechanical properties of sandstone and conglomerate are different from those of mudstone, because the latter contains much larger amounts of clay minerals as discussed by the authors.
TL;DR: In this article, a spin-on process was used to produce thin films consisting of γ-Fe2O3 particles by using a solution of iron (III) nitrate dissolved in ethylene glycol.
Abstract: Thin films consisting of γ-Fe2O3 particles were prepared by a spin-on process using a solution of iron (III) nitrate dissolved in ethylene glycol. Film thickness was observed to be controlled by the solution viscosity as well as the revolution of a spinner. Local structures around iron ions in the solution were studied by extended X-ray absorption fine structure spectroscopy and the formation of an (FeO x ) n cluster was deduced. A film thus prepared was confirmed to consist of finely divided γ-Fe2O3 particles by TEM observation. Magnetic and optical properties of the films are briefly discussed.
TL;DR: In this article, the Bingham yield stress for suspensions of illite-iron oxide complexes is examined as a function of pH and iron oxide content, and it was shown that the addition of iron oxides to illite increased the yield stress over a pH range of 3 to 10.
Abstract: The Bingham yield stress for suspensions of illite-iron oxide complexes is examined as a function of pH and iron oxide content. Addition of iron oxides to illite increased the yield stress over a pH range of 3 to 10. With increasing pH the yield stress decreased for the complexes with iron oxides of 2 and 5% while the complexes with iron oxides of 7, 10, and 20% exhibited the maximum yield stresses at pH values from 6 to 8. The iron oxides which are not associated with the illite enhanced the yield stress more than the iron oxides precipitated on the illite surfaces. The yield stress for the complexes was correlated with their zeta potential, and the higher yield stress is considered due to smaller interparticle repulsion.
TL;DR: X-ray photoelectron spectroscopy (XPS) and electrochemical techniques have been applied to the investigation of the surface oxidation of pentlandite as mentioned in this paper, which indicates that the initial reaction on exposure to air is removal of iron from the Pentlandite lattice to form a hydrated iron oxide overlayer and leave a metal-deficient pentlanditic in addition to a restructured nickel-ion sulphide further oxidation resulted in some nickel being transferred to the oxide.
Abstract: X-ray photoelectron spectroscopy (XPS) and electrochemical techniques have been applied to the investigation of the surface oxidation of pentlandite. Photoelectron spectra indicate that the initial reaction on exposure to air is removal of iron from the pentlandite lattice to form a hydrated iron oxide overlayer and leave a metal-deficient pentlandite in addition to a restructured nickel-ion sulphide Further oxidation resulted in some nickel being transferred to the oxide. In dilute acetic acid, the oxide layer was largely soluble
TL;DR: In this article, a detailed investigation of the gas-sensing properties of other metal oxide single crystals, including tin oxide (SnO2), titanium oxide (TiO2) and iron oxide (Fe2O3), to CO, CH4 and water vapour is presented.
Abstract: Polycrystalline n-type semiconducting metal oxides have been utilized as gas-sensing materials for the detection of toxic and flammable gases for many years. Although these devices can be highly sensitive to reducing gases, a frequent disadvantage is their lack of selectivity. However, work on zinc oxide has shown that using single crystals markedly improves the selectivity of the material to carbon monoxide. This paper reports a detailed investigation of the gas-sensing properties of other metal oxide single crystals, including tin oxide (SnO2), titanium oxide (TiO2) and iron oxide (Fe2O3), to CO, CH4 and water vapour.
TL;DR: Borggaard et al. as discussed by the authors tested the hypothesis of different mechanisms for the dissolution of iron oxides in EDTA and oxalate due to different surface complexes, such as tetranuclear surface complexes.
Abstract: The content of poorly crystalline iron oxides, mainly ferrihydrite, in soils is commonly determined by the oxalate method and less commonly by the ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA) method (Schwertmann, 1964; Schwertmann et al., 1982; Borggaard, 1981, 1988). Comparable amounts of i ron are dissolved by the two methods from many soils (Borggaard, 1988), and both ligands presumably act via surface complexat ion (Chang and Matijevic, 1983; Zinder et al., 1986). Recently, however, various differences in the d i s s o l u t i o n m e c h a n i s m s have been suggested (Borggaard, 1990). In contrast to EDTA, oxalate is rather unstable and decomposes, for example, in the presence of light (Schwertmann, 1964). Decomposi t ion ofoxala te leads to the formation ofiron(II) , which may accelerate the dissolution o f iron oxide (Cornell and Schindler, 1987). Furthermore, EDTA, having four carboxyl groups, has been postulated to be adsorbed onto iron oxide surfaces by the formation of tetranuclear surface complexes at room temperature (Borggaard, 1990). Such surface complexes may retard or inhibit iron oxide dissolution because several bonds must be broken before the i ron-EDTA complex can be released (Chang and Matijevic, 1983). Oxalate is bidentate and forms binuclear (and monodentate) surface complexes (Parf i t t e t al., 1977; Cornell and Schindler, 1987), which obviously cannot prevent the dissolution o f crystalline iron oxide (Borggaard, 1982, 1988). I f the surface complexes are different, however, the EDTA and oxalate methods should respond differently i f competing anions, such as phosphate, are present simultanously. Phosphate should increase the dissolution rate in EDTA because it eliminates or suppresses the formation of tetranuclear surface complexes, whereas the competition for adsorpt ion sites should slow down the dissolution in oxalate. The purpose of this paper is to test the hypothesis of different mechanisms for the dissolution of iron oxides in EDTA and oxlate due to different surface complexes. Therefore, adsorpt ion and dissolution properties o f the system iron oxide-EDTA/oxalate with and
TL;DR: Seven different types of iron oxide were examined for carcinogenic properties in intratracheal instillation and intraperitoneal injection tests on rats, which represent particularly sensitive methods for local carcinogenic effects.
Abstract: Seven different types of iron oxide were examined for carcinogenic properties in intratracheal instillation and intraperitoneal injection tests on rats, which represent particularly sensitive methods for local carcinogenic effects. The total doses lay in the range of maximum tolerance (390/1,530 mg/kg i.t. or 600 mg/kg i.p.). With one exception, at least 50 male and 50 female Sprague-Dawley rats were used per test group, control group and route of administration. Two iron oxides were additionally instilled intratracheally in combination with benzo[a]pyrene. No carcinogenic effect could be demonstrated for the test iron oxides RBW 07105/SV2 (fibrous, magnetic, surface doped with 1.85% cobalt), development product Bayferrox AC 5100 M (fibrous, magnetic, bulk doped with 2.1% cobalt), Bayferrox 1352 (fibrous alpha-Fe2O3), Bayferrox 920 (fibrous alpha-FeOOH), Bayferrox 130 (cubic alpha-Fe2O3), Bayferrox 306 (cubic Fe3O4), or Brazilian iron ore AC 5031 N (alpha-Fe2O3).
TL;DR: In this article, the reduction/oxidation of a high loading iron catalyst supported on γ-Al203 has been studied using dynamic X-ray diffraction (DXRD) in situ determination of changes in the lattice parameters as magnetite was reduced to iron indicated that aluminum was unevenly incorporated into the matrix of the supported iron oxide particles, leading to a form of metal-support interaction and manifested by reduction rates which are much slower than for unsupported magnetite.
TL;DR: In this article, a preshaped magnesium oxide support to incipient wetness with poorly crystallizing organometallic complexes has been used for the preparation of iron oxide catalysts supported on magnesium oxide.
Abstract: Iron oxide catalysts supported on magnesium oxide have been prepared by impregnation of a preshaped magnesium oxide support to incipient wetness with poorly crystallizing organometallic complexes. As organometallic complexes ammonium iron(III) citrate and ammonium iron(III) EDTA have been used. After impregnation the iron has appeared to be homogeneously distributed throughout the magnesium oxide support bodies. Upon calcination in air, the precursors decompose to form magnesium ferrite at temperatures as low as ca. 800 K. Calcination in air at 973 K results in the formation of small MgFe2O4 crystallites with a typical size of ca. 200 A, as determined by X-ray diffraction and electron microscopy.
Patent•
20 Feb 1991
TL;DR: In this paper, a superparamagnetic fine particles of iron oxide, suitable for use in a magnetic recording medium, have an unsaturated fatty acid adsorbed on the surface thereof, a magnetization of not less than 50 Amµ/kg (50 emu/g), and an Feµ³ content (calculated as a Fe³:Fe³µ molar ratio) of from 0.16 to 0.5:1.
Abstract: Superparamagnetic fine particles of iron oxide, suitable for use in a magnetic recording medium, have an unsaturated fatty acid adsorbed on the surface thereof, a magnetization of not less than 50 Am²/kg (50 emu/g), a rate of change of magnetization of not more than 10%, and an Fe²⁺ content (calculated as a Fe²⁺:Fe³⁺ molar ratio) of from 0.16 to 0.5:1.
TL;DR: In this paper, a mathematical model is proposed to explain the simultaneous reactions in this slag-metal system, and the C oxidation rate decreases with increasing Si concentration in the metal.
Abstract: Kinetic experiments have been made on C oxidation between FetO containing slag and molten iron of high C concentration ([%C])≅4.4) at 1300°C under mechanical stirring conditions. Effects of Si and P in the metal and P in the slag on the C oxidation reaction rate have been examined, as well as effect of mechanical stirring on the reaction rate.The C oxidation rate is considerably reduced by slight increase in P concentration in the slag. It is also found the P in the metal has no significant effect on the C oxidation rate. The C oxidation rate decreases with increasing Si concentration in the metal. A mathematical model is proposed to explain the simultaneous reactions in this slag-metal system.
TL;DR: In this article, the catalytic behavior of iron oxide catalysts supported on magnesium oxide in the non-oxidative dehydrogenation of but-1-ene to buta-1,3-diene has been studied.
Abstract: The catalytic behaviour of iron oxide catalysts supported on magnesium oxide in the non-oxidative dehydrogenation of but-1-ene to buta-1,3-diene has been studied. Under dehydrogenation conditions the magnesium ferrite phase of the fresh catalyst was found to be reduced to FeO in the bulk of the ferrite particles, where FeO is strongly stabilized by the formation of a solid solution with MgO. At the surface of the particles magnesium ferrite is reduced to Fe3O4. In the reduced state a catalyst containing ca. 3 wt.% Fe shows a but-1-ene conversion of 26% combined with a buta-1,3-diene selectivity of 65% at 873 K. The activation energy for dehydrogenation was found to be 47 kcal mol–1.The (unpromoted) catalyst gradually deactivates owing to carbon deposition. Under dehydrogenation conditions the catalyst surface is completely covered by a layer of amorphous carbon within 20 h.
TL;DR: AES and EELS are used to study the effect of oxygen on the FeS2 surface in this paper, where the main Auger Fe M2.3VV attenuates with increased oxygen exposures and shifts to lower kinetic energy while the high kinetic energy feature due to an autoionization process remains unaltered in energy.
Abstract: AES and EELS are used to study the effect of oxygen on the FeS2 surface. The main Auger Fe M2.3VV attenuates with increased oxygen exposures and shifts to lower kinetic energy while the high kinetic energy feature due to an 'autoionization process' remains unaltered in energy. The EELS spectra measured as a function of oxygen exposure clearly indicate the formulation of iron oxide similar to that of alpha -Fe2O3. For the FeS2+O2 system, the authors show that Ueff is negligibly small and is in good agreement with the estimated Ueff for Fe2O3. A slight change in the S L2.3VV Auger peak is observed on adsorption of oxygen and the formation of sulphur oxides is ruled out.
Patent•
26 Mar 1991
TL;DR: A gas generating grain has a water-based particulate booster coating that consists of an alkali metal azide, a water soluble inorganic oxidizer in approximately a stoichiometric ratio of oxidizer to azide and a nucleating amount of a small particle size metal oxide.
Abstract: A gas generating grain has a water-based particulate booster coating thereon The coating comprises an alkali metal azide, a water-soluble inorganic oxidizer in approximately a stoichiometric ratio of oxidizer to azide, and a nucleating amount of a small particle size metal oxide The inorganic oxidizer is potassium perchlorate A preferred metal oxide is selected from the group consisting of iron oxide, nickel oxide and aluminum oxide The coating is applied to the grain from a water slurry and dried