Showing papers on "Iron oxide published in 1996"

Ceramic thin films by sol-gel processing as novel materials for integrated humidity sensors

Abstract: Thin films based on 10 at% alkali-doped TiO 2 and on iron oxide with very large humidity sensitivity were prepared using a sol-gel technique. Prototype humidity sensors were prepared by depositing metal alkoxide solutions onto Al 2 O 3 substrates with comb-type Au electrodes, by dip-coating and heating in air. Heating to 300°C produces continuous films, free of porosity, which appear as layers covering the substrates, with no detectable grains. The humidity sensing electrical properties of the films were evaluated using electrochemical impedance spectroscopy (EIS) measurements. Resistance changes, although the films are dense, even larger than those reported for porous ceramics are recorded, as high as 9 and 8 orders of magnitude in the relative humidity range tested (4-87%), for the iron oxide and 10 at% K-doped titania films heated to 300°C, respectively. These outstanding results are interpreted in terms of conduction mechanisms different from the mechanism usually accepted for porous ceramics. EIS results confirmed that, for 10 at% alkali-doped TiO 2 films, charge carriers are alkali ions and not surface protons.

Reactions of Laser-Ablated Iron Atoms with Oxygen Molecules in Condensing Argon. Infrared Spectra and Density Functional Calculations of Iron Oxide Product Molecules

Abstract: Reaction of laser-ablated Fe atoms with oxygen molecules in a condensing argon stream produced FeO, FeO2, FeO3, FeO4, Fe2O, Fe2O2, and Fe2O4 molecules, which are identified from oxygen isotopic shifts and multiplets in matrix infrared spectra. The Fe + O2 reaction gives symmetrical bent, symmetrical cyclic, and asymmetrical bent FeO2 isomeric products with triplet, triplet, and quartet isotopic absorptions, respectively, using statistically mixed 16,18O2 as the reagent. The major reaction product symmetrical bent OFeO iron dioxide molecule (150 ± 10°) is characterized by stretching fundamentals at 945.8 and 797.1 cm-1, and the asymmetric bent FeOO form exhibits a 1204.5 cm-1 absorption. The cyclic isomer Fe(O2) produced spontaneously during annealing in solid argon absorbs at 956.0 cm-1. Oxygen and iron isotopic absorptions show that FeOFe is a symmetrical bent (140 ± 10°) molecule. Rhombic Fe2O2 absorbs at 517.4 cm-1. Evidence is presented for isomers of FeO3, FeO4, and Fe2O4. Density functional theory w...

Synthesis, Structure, and Electrochemical Properties of a New Lithium Iron Oxide, LiFeO2, with a Corrugated Layer Structure

Abstract: A new lithium iron oxide, , with a corrugated layer structure was synthesized by an ion exchange reaction between γ‐FeOOH and and its structure determined by x‐ray and neutron diffraction measurements. The ion exchange reaction was carried out hydrothermally at 100 to 250°C. Higher vapor pressures produce the disordered phase, and higher reaction temperatures lead to a mixture of the disordered spinel phase, , and the new phase. Lithium cells consisting of cathodes and lithium anodes showed good charge and discharge reversibility in the voltage range, 1.5 to 3.0 V. Furthermore, the lithium intercalation and deintercalation mechanism was characterized using x‐ray diffraction results and electrochemical measurements.

Observation and Photoelectron Spectroscopic Study of Novel Mono- and Diiron Oxide Molecules: FeOy- (y = 1−4) and Fe2Oy- (y = 1−5)

Abstract: We study novel iron oxide molecules involving one and two iron atoms by anion photoelectron spectroscopy at 3.49 and 4.66 eV photon energies. Vibrationally resolved photoelectron spectra and low-lying excited states are obtained for FeOy- (y = 1−4) and Fe2Oy- (y = 1−5). In both series, the photoelectron spectra become particularly sharp and better resolved for the higher oxides, FeO3-, FeO4-, Fe2O4-, and Fe2O5-. The electron affinity of the neutral oxide molecules is observed to increase with the number of oxygen atoms, suggesting a sequential oxidation behavior. For the monoiron oxide series, an oxidation saturation is observed as evidenced by the leveling-off of the electron affinity from FeO3 to FeO4. The structures and chemical bonding of these oxide molecules are discussed based on the sequential oxidation behavior. Isomers involving possibly O2 or O3 complexes are also observed for the diiron oxides above Fe2O.

Patterning with Magnetic Materials at the Micron Scale

Abstract: This paper demonstrates the use of microcontact printing (μCP) and capillary filling (CF) to pattern the deposition of iron oxides on a surface with feature sizes of microns. Selective wetting of both self-assembled monolayers (SAMs) of alkanethiolates on gold and alkylsiloxanes on Si/SiO2 formed by microcontact printing limited the deposition of the iron oxides to the hydrophilic areas on the surfaces; thereby, the chemical functionality of the hydrophilic SAM had only a minor influence on the wetting behavior and the deposition. The iron oxides were deposited either as magnetite particles from colloidal solution, by precipitation of the oxide from previously deposited drops of water containing an iron(III) salt, or by ferrite plating. The size of the metal oxide patterns was limited to the size of the areas that could be patterned using μCP. Capillary filling using a colloidal solution of magnetite could also be used to fabricate continuous, interconnected structures of magnetite. The magnetic properties of the deposited iron oxides were characterized by magnetic force measurement (MFM) and by measurement of the magnetization. The magnetite particles deposited in these experiments showed superparamagnetic behavior; they were too small individually to support a permanent magnetization.

X-ray photoelectron spectra of the palladium : Iron bimetallic surface used for the rapid dechlorination of chlorinated organic environmental contaminants

Abstract: Palladized iron (Pd/Fe) has been successfully used for the rapid dechlorination of organic environmental contaminants in aqueous solutions. We have investigated the nature of the Pd/Fe surface by X-ray photoelectron spectroscopy. Our results indicate that the reactive Pd/Fe surface is formed by the stepwise reduction of Pd(IV) in solution to Pd(II), which replaces protons on the hydroxylated iron oxide surface and forms Pd(II)-O-Fe bonds. These bonds are unstable and collapse spontaneously to yield the reactive palladized iron in which the palladium is in the elemental state. Prolonged exposure of this Pd/Fe surface to a saturated solution of aqueous TCE results in the growth of the hydroxylated iron oxide film that deactivates the Pd/Fe surface. The thick hydroxylated iron oxide film can be removed, and the original activity of the Pd/Fe surface can be restored by washing he surface with a dilute acid solution. 5 refs., 6 figs.

Intercalation of iron oxide in layered H2Ti4O9 and H4Nb6O17: visible-light induced photocatalytic properties

Abstract: H2Ti4O9/Fe2O3·nH2O and H4Nb6O17/Fe2O3·nH2O nanocomposites containing intercalated Fe2O3·nH2O, particles of 400 nm) from a 450 W Hg lamp in the presence of Na2SO3 as a sacrificial donor. The hydrogen production activity of these nanocomposites was superior to that of unsupported Fe2O3·nH2O. The hydrogen production was enhanced to 11.3–13.6 cm3 over 5 h by doping Pt together with Fe2O3·nH2O in the interlayer. Hydrogen evolution was linear with time with the niobate system being slightly more efficient.

In situ characterization of vapor phase growth of iron oxide-silica nanocomposites : part i. 2-d planar laser-induced fluorescence and mie imaging

Abstract: Planar laser-based imaging measurements of fluorescence and particle scattering have been obtained during flame synthesis of iron-oxide/silica superparamagnetic nanocomposites. The theory and application of laser-induced fluorescence, the spectroscopy of FeO(g), and the experimental approach for measurement of gas phase precursors to particle formation are discussed. The results show that the vapor phase FeO concentration rapidly rises at the primary reaction front of the flame and is very sensitive to the amount of precursor added, suggesting nucleation-controlled particle growth. The FeO vapor concentration in the main nucleation zone was found to be insensitive to the amount of silicon precursor injected, indicating that nucleation occurred independently for the iron and silicon components. Light scattering measurements indicate that nanocomposite particles sinter faster than single component silica, in agreement with TEM measurements.

Pearlescent glass pigment

Abstract: A pearlescent pigment consists essentially of C glass flakes having a layer comprising rutile titanium dioxide or iron oxide thereon. A hydrous layer of the rutile forming titanium dioxide or iron oxide is formed on the glass flakes and the resulting coated flakes are calcined.

Electrochromic Properties of Iron Oxide Thin Films Prepared by Chemical Vapor Deposition

Abstract: Iron oxide thin films were prepared by chemical vapor deposition. The source material was iron (III) acetylacetonate. The Fe{sub 2}O{sub 3} films were produced at a substrate temperature above 200 C. The films deposited at a substrate temperature above 300 C were polycrystalline {beta}-Fe{sub 2}O{sub 3}. Reduction and oxidation of the amorphous films in a 0.3 M LiClO{sub 4} propylene carbonate solution caused desirable changes in optical absorption. Coulometry indicated that the coloration efficiency was 6.0 to 6.5 cm{sup 2}/C.

Iron oxide adsorption and UF to remove NOM and control fouling

Abstract: This study applied a novel single-fiber membrane module to study fouling of ultrafiltration (UF) membranes by natural organic matter (NOM) molecules, and used a combined iron oxide-UF process to reduce that fouling. Addition of iron oxide particles to a UF system can significantly increase NOM removal efficiency, because NOM molecules that would otherwise pass through the membrane sorb to the oxides and are retained. Furthermore, despite the fact that iron oxide particles cannot selectively adsorb foulant molecules, their presence in the system can reduce the membrane fouling dramatically. This effect is mediated through two processes: a decrease in the NOM concentration in the circulation loop because of sorption and the formation of iron oxide cake layer deposits on the membrane surface. In such a system, the condensed layer of NOM forms on top of the cake, protecting the underlying membrane surface.

Reactive Solute Transport in Streams: 2. Simulation of a pH Modification Experiment

Abstract: We present an application of an equilibrium-based solute transport model to a pH-modification experiment conducted on the Snake River, an acidic, metal-rich stream located in the Rocky Mountains of Colorado. During the experiment, instream pH decreased from 4.2 to 3.2, causing a marked increase in dissolved iron concentrations. Model application requires specification of several parameters that are estimated using tracer techniques, mass balance calculations, and geochemical data. Two basic questions are addressed through model application: (1) What are the processes responsible for the observed increase in dissolved iron concentrations? (2) Can the identified processes be represented within the equilibrium-based transport model? Simulation results indicate that the increase in iron was due to the dissolution of hydrous iron oxides and the photoreduction of ferric iron. Dissolution from the streambed is represented by considering a trace compartment consisting of freshly precipitated hydrous iron oxide and an abundant compartment consisting of aged precipitates that are less soluble. Spatial variability in the solubility of hydrous iron oxide is attributed to heterogeneity in the streambed sediments, temperature effects, and/or variability in the effects of photoreduction. Solubility products estimated via simulation fall within a narrow range (pKsp from 40.2 to 40.8) relative to the 6 order of magnitude variation reported for laboratory experiments (pKsp from 37.3 to 43.3). Results also support the use of an equilibrium-based transport model as the predominate features of the iron and pH profiles are reproduced. The model provides a valuable tool for quantifying the nature and extent of pH-dependent processes within the context of hydrologic transport.

Surface electrochemical transformations on spinel iron oxide electrodes in aqueous solutions

Abstract: The effect of potential and electrolyte composition on the surface stoichiometry in magnetite oxide electrodes has been investigated by a variety of electrochemical techniques: open-circuit potential, chronoamperometry, surface redox titration by galvano-static pulses, electrochemical impedance spectroscopy and electroreflectance. These studies revealed a continuous change in surface iron composition with potential that results in a low-frequency, potential-dependent pseudo-capacitance. The capacitance–potential curves for different electrolyte pH were analysed in terms of: (a) the iron spinel system Fe3–δO4(0 ⩽δ⩽ 0.33) and (b) a modified Fe3O4 electrode with octahedral surface iron complexes, to accommodate the change of surface stoichiometry. The second model is consistent with the experimental data and the resulting dependence of FeII surface sites on potential and pH predicts the kinetics of O2 electroreduction on Fe3O4. Similar electrochemical behaviour of oxidized magnetite electrodes and passive iron in alkaline solutions has been found, which parallels the analogous kinetics observed for oxygen electroreduction on these oxides.

Process for treating metal oxide fines

Abstract: The present invention provides for a process for recovering elemental iron by treating metal oxide fines including oxide therein. The process includes combining the metal oxide fines with a carbonaceous material containing more than about 20 wt% volatile matter to form a mixture. The mixture is agglomerated under conditions sufficient to mobilize the volatile matter to function as a binder that bonds the mixture to form green compacts. The green compacts are heated for a time and at a temperature sufficient to reduce the iron oxide to elemental iron. The carbononaceous material functions as a reductant for the iron oxide.

Preoxidation and hydrogen reduction of ilmenite in a fiuidized bed reactor

Abstract: Studies on preoxidation and hydrogen reduction of Quilon-grade ilmenite have been carried out in a fluidized bed reactor. During preoxidation, the effect of various parameters such as temperature, gas flow rate, and period of reaction has been studied. Hydrogen reduction studies have been carried out both for raw and preoxidized ilmenite. Results obtained on the conversion rate of iron oxide to metallic iron for the preoxidation as well as the reduction period showed three distinct stages: (1) initial slow induction stage; (2) intermediate acceleratory stage; and (3) final slowing down process. Kinetic data plot on -In (1 -x) vs time for metallization of iron oxide showed a linear trend for preoxidation and hydrogen reduction.