Showing papers on "Iron oxide published in 1993"

The nanophase iron mineral(s) in Mars soil

Abstract: A series of surface-modified clays containing nanophase (np) iron oxide/oxyhydroxides of extremely small particle sizes, with total iron contents as high as found in Mars soil, were prepared by iron deposition on the clay surface from ferrous chloride solution. Comprehensive studies of the iron mineralogy in these "Mars-soil analogs" were conducted using chemical extractions, solubility analyses, pH and redox, x ray and electron diffractometry, electron microscopic imaging, specific surface area and particle size determinations, differential thermal analyses, magnetic properties characterization, spectral reflectance, and Viking biology simulation experiments. The clay matrix and the procedure used for synthesis produced nanophase iron oxides containing a certain proportion of divalent iron, which slowly converts to more stable, fully oxidized iron minerals. The clay acted as an effective matrix, both chemically and sterically, preventing the major part of the synthesized iron oxides from ripening, i.e., growing and developing larger crystals. The precipitated iron oxides appear as isodiametric or slightly elongated particles in the size range 1-10 nm, having large specific surface area. The noncrystalline nature of the iron compounds precipitated on the surface of the clay was verified by their complete extractability in oxalate. Lepidocrocite (gamma-FeOOH) was detected by selected area electron diffraction. It is formed from a double iron Fe(II)/Fe(III) hydroxy mineral such as "green rust," or ferrosic hydroxide. Magnetic measurements suggested that lepidocrocite converted to the more stable maghemite (gamma-Fe2O3) by mild heat treatment and then to nanophase hematite (alpha-Fe2O3) by extensive heat treatment. After mild heating, the iron-enriched clay became slightly magnetic, to the extent that it adheres to a hand-held magnet, as was observed with Mars soil. The chemical reactivity of the iron-enriched clays strongly resembles, and offers a plausible mechanism for, the somewhat puzzling observations of the Viking biology experiments. Their unique chemical reactivities are attributed to the combined catalytic effects of the iron oxide/oxyhydroxides and silicate phase surfaces. The reflectance spectrum of the clay-iron preparations in the visible range is generally similar to the reflectance curves of bright regions on Mars. This strengthens the evidence for the predominance of nanophase iron oxides/oxyhydroxides in Mars soil. The mode of formation of these nanophase iron oxides on Mars is still unknown. It is puzzling that despite the long period of time since aqueous weathering took place on Mars, they have not developed from their transitory stage to well-crystallized end-members. The possibility is suggested that these phases represent a continuously on-going, extremely slow weathering process.

Thermally stimulated polarization and dc conduction in iron phosphate glasses

Abstract: Thermally stimulated polarization (TSPC) and depolarization current (TSDC) techniques were used to study electrical polarization and conduction mechanisms in iron phosphate and sodium-iron phosphate glasses. TSDC measurements from 120 to 350 K show two current peaks, P1, attributed to the polarization caused by intrinsic dipolar defects, and P2, due to space-charge relaxation. The electrical conductivity was examined on the basis that the activation energy for electronic conduction is lower than that for ionic conduction. The dc conductivity depends upon iron oxide content and distance between iron ions, which suggests electronic conduction. The difference in activation energy between TSDC peaks and dc conductivity is discussed. Infrared absorption spectra indicate that iron ions can act as a network former and/or modifier depending upon the Fe(II)/Fe(III) ratio in the glass.

Reduction of supported iron oxide studied by temperature-programmed reduction combined with mössbauer spectroscopy and X-ray diffraction

Abstract: The reduction of iron oxide supported on alumina, anatase and rutile and the interactions between iron oxides and these supports have been studied using temperature-programmed reduction, Mossbauer spectroscopy and X-ray diffraction. The intermediates formed during reduction depend strongly on the nature of the support, the iron loading and the reduction conditions used. Several iron species such as bulk α-Fe2O3, superparamagnetic α-Fe2O3 and surface iron–aluminium oxides are found in the alumina-supported iron oxide samples. The iron–aluminium species can be formed either by incorporation of Al3+ into the structure of iron oxide in acidic solution during the preparation of the samples or by incorporation of Fe2+ into the structure of the alumina support under high-temperature reduction. For the as-prepared Fe/TiO2 samples, the anatase and rutile have only weak interactions with the iron oxide as only bulk α-Fe2O3 species have been detected. However, some intermediates such as (1 –x)FeTiO3–xFe2O3 solid solution, surface iron–titanium oxide and bulk FeTiO3 phase can be formed during reduction because of the reducibility and mobility of titanium ions on the surface. Surface titanium ions can act as an electron-transfer medium for the reduction of Fe3+ to Fe2+ and can even be substituted for Fe3+ ions in the octahedral sites of magnetite formed during the reduction. In all cases, when the loading of iron oxide is low, Fe3+ and Fe2+ ions are stable during reduction due to the formation of iron oxide–support intermediates by strong interactions between iron oxides and the supports.

Chemical analysis of thin black layers on building stone

Abstract: Thin black layers often occur on building stone in polluted areas. Various techniques including scanning electron microscopy/energy dispersive X-radiography, electron spectroscopy for chemical analysis, Mossbauer spectroscopy and gas chromatography-mass spectrometry have been used to analyze these layers in samples from Sweden and some other European countries. The layers mainly consist of various iron oxides and iron oxide hydroxides, sulphates, soot and silicate minerals, with smaller amounts of metal, rubber and asphalt particles, and numerous organic constituents in low concentration. Air pollutants, and to some degree minerals from the interior of the stone, are the main source of the components which form the black layers.

Kinetics of Phosphorus Transfer between Iron Oxide Containing Slag and Molten Iron of High Carbon Concentration under Ar-O2 Atmosphere

Abstract: In the present report, the results are described of kinetic experiments of phosphorus reaction in a molten CaO-Li2O-SiO2-FeO-Fe2O3 slag/Fe-4.4%C molten metal/Ar-O2 gas (PO2=0-0.2 atm) system. The experimental temperature is 1300°C and the slag-metal bath is stirred by an eccentric alumina stirrer (rotation speed, R=30-300 rpm). From the experimental results, it is found that dephosphorization rate increases with increasing the oxygen partial pressure of the Ar-O2 gas atmosphere. The change in the stirrer's rotating speed does not affect the dephosphorization rate obviously, while rephosphorization rate increases with increasing the stirring speed. It is also shown that maximum phosphorus concentration ratio, ((%P)/[%P])max, obtained at the time point when the phosphorus reaction changes from dephosphorization to rephosphorization, increases with the increase in the ratio of ferric iron to total iron of the slag. The ((%P)/[%P])max ratio decreases with increasing the stirring speed in the range of R>50 rpm. The relation between the experimental conditions and the rate of the phosphorus reaction accompanied by simultaneous slag-metal-gas reactions are interpreted qualitatively in terms of the change in a hypothetical slag-metal interfacial oxygen potential. The experimental results are explained quantitatively by means of a mathematical kinetic model calculations. The model calculation fits the experimental results resonably well.

Spherical iron oxide particles synthesized by an aerosol technique

Abstract: Spherical particles of several iron oxides have been obtained by pyrolysis of an aerosol generated by ultrahigh frequency spraying of a solution. Two different precursor solutions were used to produce the aerosol: Fe(NO3)3 · 9H2O and FeC6H5O7 · 4H2O. The iron nitrate decomposition leads to the formation of α-Fe2O3, while the organic precursor pyrolysis leads to magnetic particles of either γ–Fe2O3 or Fe3O4. Structural phase, particle size, texture, and homogeneity of the products so obtained can be controlled as a function of some synthesis conditions such as precursor solution, temperature, solution concentration, and surrounding atmosphere.

Effect of Firing Condition and Ingredients on the Swelling Behaviour of Iron Ore Pellets

Abstract: In the present investigation an attempt has been made to determine the effect of firing temperture, firing time and ingredients/additives (CaO, MgO, SiO2, Al2O3) on the swelling behaviour of iron ore pellets. For this purpose two Indian iron ore fines from Bailadila and Noamundi deposits and chemically pure iron oxide were used.From the results obtained, it is observed that the swelling of iron ore pellet is controlled by the firing temperature, firing time and additives/ingredients present in the pellet. The growth of iron whisker is controlled by these ingredients. The presence of free lime promotes the swelling index of the pellet.

Ultrafine iron-containing rutile titanium oxide and process for producing the same

Abstract: Ultrafine iron-containing rutile type titanium dioxide particles useful for UV shielding cosmetics, pharmaceutical compositions and UV shielding paints are disclosed. They are rutile type crystalline titanium dioxide particles having an average single particle size of 0.01 to 0.1 μm and containing an iron component at a concentration of 1 to 15% by weight as expressed as Fe based on the titanium dioxide in the crystalline structure. They can be produced by using a fine titania sol comprising rutile crystallites as basic particles, precipitating iron oxide or hydrated iron oxide onto the surfaces of the titania particles to effect coating, then firing and grinding.

Reactivity and durability of iron oxide high temperature desulfurization sorbents

Abstract: As iron oxide high-temperature desulfurization sorbents, eight kinds of iron ores and sorbents prepared from iron ore powder and blast furnace dust using binder were examined. SiO 2 , TiO 2 , and Al 2 O 3 were used as binders. The potential of these sorbents to remove H 2 S was tested before and after activation with H 2 , and also their mechanical strength (compressive strength) was measured. Reactivity of iron ore was not correlated to its compressive strength, but the compressive strength of the iron ore was roughly correlated to its bulk density. SiO 2 was useful as a binder. Na present as an impurity in SiO 2 binder induced localization of SiO 2 in the pellet at the high temperature calcination step

Residual oil cracking with generation of hydrogen: deactivation of iron oxide catalyst in the steam-iron reaction

Abstract: The deactivation of iron oxide catalyst in residual oil cracking with generation of hydrogen was studied. This new process consists of two main stages: the cracking of residual oil and hydrogen generation resulting from the steam-iron reaction, and the reduction of the iron oxide catalyst. We found that the hydrogen-producing activity of the iron oxide catalyst declined during consecutive reduction and oxidation cycles. The aging rate was dependent on the reaction conditions. When the rate of oxidation was not fast enough to convert prereduced wustite (FeO) to magnetite (Fe3O4), the wustite accumulated and the activity declined. The accumulation of wustite is considered to induce the sintering of the catalyst. This hinders the free access of the reaction gases and reduces the rate of the iron oxide-gas phase reaction. We concluded that it is essential to balance the stoichiometry of the reduction and oxidation to prevent the deactivation of the catalyst.

Mechanism of Spinel Ferrite Dust Formation in Electric Arc Furnace Steelmaking.

Abstract: By investigating the behavior of spinel ferrite particles in EAF dust, an insight into the mechanism of spinel ferrite dust generation was examined. The results are summarized as follows: (1) the chemical formula of spinel ferrite particles in EAF dust is (MnxZnyFe1-x-y)Fe2O4; (2) when oxygen is transferred at the slag-metal interface, a series of oxide layers form on the molten steel (going from the surface to the interior of the liquid, one progresses through (Mn, Zn)Fe2O4, (Mn, Zn)Fe2O4-Fe3O4, Fe3O4-(Mn, Fe)O and (Mn, Fe)O, respectively); (3) some of the coarse spinel ferrite powders are often hollow contain surface blowholes suggesting that CO gas atomizes liquid iron oxides; and (4) CO gas evolution atomizes various liquid oxides. These droplets may oxidize to varying degrees as they solidify and cool producing various compositions of (Mn, Zn)Fe2O4 and/or (Mn, Zn)Fe2O4-Fe3O4 powders.

Soil or ground reinforcement treatment method

Abstract: A soil or ground reinforcing material consisting of Al--Fe oxides mixture the main contents of which are iron oxide made from fine iron oxide powder byproduced in steel production and Aluminum oxide made from red mud by-produced in Aluminum smeltering and lime added therein is mixed into a soil containing crushed stones, natural soil, etc., and further Titanium oxide is mixed into the above soil or ground reinforcing material to make Al--Fe--Ti oxides mixture in which lime is added and mix this material into a soil or ground containing crushed stones, natural soil, etc. to enhance the strength and viscoelasticity thereof. The content of the Titanium oxide in the soil or ground reinforcing material is within the range of 0.5-2.0% by weight.

Nonmagnetic ferrite for composite laminated component, and composite laminated component

Abstract: PURPOSE:To contrive reduction in the difference of linear expansion coefficient between the magnetic materials used by a method wherein MgO, Bad, SiO2 B2O3 SnO2 and CaO are added to the ferrite, containing Fe2O3, CuO and/or ZnO, in such a manner that the total quantity of the adding material is in the prescribed range. CONSTITUTION:To the nonmagnetic ferrite composition, containing iron oxide, oxidized. copper and/or a zinc oxide, of fe2O3 and/or ZnO of 100mol%, four kinds of oxide component of magnesium oxide, barium oxide, silicon oxide and boron oxide, or five or six kinds of oxide component, consisting of the above-mentioned four kinds of oxide component and one or more kinds selected from tin oxide, calcium oxide, is added. As a result, the difference of the linear expansion coefficient of the magnetic ferrite and the like used can be made small and the deterioration of characteristics can be prevented.

Effect of excess of iron oxide and lead oxide on the microstructure and dielectric properties of lead-iron tungstate ceramics

Abstract: Lead-iron tungstate Pb(Fe2/3W1/3)O3; PFW) perovskite ceramics were prepared by the conventional mixed oxides method. Additional amounts of Fe2O3 and PbO were used to examine the role of excess oxides on the phase development, densification behaviour and dielectric properties. The stoichiometric mixture of the oxides results in a residual phase (Pb2WO5) besides the perovskite. Excess Fe2O3 eliminates the Pb2WO5, with a marked increase in the dielectric constant, whereas excess PbO leads to an unexpected increase of the amount of the second phase and a consequent decrease of the dielectric constant. The densification behaviour and the microstructures obtained after firing were very dependent on the starting stoichiometry. The PFW phase obtained using PbO or Fe2O3 excesses shows various degrees of ordering which seem to be correlated with the presence of either W6+ vacancies or of Pb2+ vacancies.

Reduction, sulfidation, and regeneration of mixed iron-aluminum oxide sorbents

Abstract: The reduction and sulfidation of Fe_2O_3 and Fe_2O_3-Al_2O_3 sorbents were investigated by thermogravimetric analysis (TGA). Mixed iron-aluminum oxides were reduced more slowly and by a more complex mechanism than pure iron oxide. Several phases that were responsible for this difference were identified by temperature-programmed reduction (TPR), X-ray diffraction (XRD), BET surface area (BET), and scanning electron microscopy (SEM). Sulfidation of reduced sorbents in the TGA at 600 "C produced two crystalline phases: high-temperature, hexagonal pyrrhotite (Fe_(1-x)S), and unreacted FeAl_2O_4. The reaction of the pure and mixed oxide with a mixture of H_2S-H_2-H_2O-N_2 was studied in a tubular microreactor to evaluate the performance of these materials as high-temperature H2S sorbents. At 650 °C the mixed oxide yielded considerably lower prebreakthrough outlet H_2S levels than the pure iron oxide. Regeneration in pure SO_2 and SO_2-air mixtures of sulfided samples resulted in complete conversion of iron sulfide to iron oxide and quantitative recovery of elemental sulfur.