Showing papers on "Iron oxide published in 1995"

Modern and Last Glacial Maximum eolian sedimentation patterns in the Atlantic Ocean interpreted from sediment iron oxide content

Abstract: Eolian dust derived from the desert regions of North Africa is blown far into the tropical Atlantic Ocean by persistent easterly and northeasterly winds. In this paper, we demonstrate that the iron oxides, hematite and goethite, are a worthwhile addition to proxy monitors of eolian sedimentation in the tropical Atlantic. Iron oxides are identified by diffuse reflectance spectrophotometry, a technique capable of identifying these minerals in concentrations as low as 0.01% by weight. We analyze samples from both the modern and last glacial maximum (LGM) synoptic levels from 178 sample locations yielding a total of 356 samples distributed throughout the Atlantic Ocean. To determine the relative contribution of the iron oxides, we factor analyzed the modern and LGM levels as a single data set. The iron oxide factor explains about 25% of the variance in the combined core top and LGM data set. Mapped factor scores for the LGM and modern ocean indicate high iron oxide values are present in just two regions, one off eastern North America and the other off northwest Africa. In the region off eastern North America, iron oxide occurs primarily during the LGM as the previously noted “brick red lutite,” a unique sediment type derived from the erosion of Permo-Carboniferous red beds in Atlantic Canada. A larger, lobe-shaped area of iron oxide rich sediment is present off northwest Africa in both the modern and LGM levels. The modern iron oxide lobe is coincident with the distribution of eolian dust as determined by observations from ships, satellites, and analysis of air samples. During the LGM, iron oxides exhibit a similar distribution except the southern margin of the region shifts equatorward and iron oxide concentration increases.

Availability of colloidal ferric oxides to coastal marine phytoplankton

Abstract: Cell growth of a coastal marine diatom, Phaeodactylum tricornutum (stock cultures), and two red tide marine flagellates, Heterosigma akashiwo and Gymnodinium mikimotoi (stock cultures), in the presence of soluble chelated Fe(III)-EDTA (1:2) and of four different phases of ferric oxide colloids were experimentally measured in culture experiments at 20°C under 3000 lux fluorescent light. Soluble Fe(III)-EDTA induced the maximal growth rates and cell yields. The short-term uptake rate of iron by H. akashiwo in Fe(III)-EDTA medium was about eight times faster than that in solid amorphous hydrous ferric oxide (Fe2O3·xH2O) medium. In culture experiments supplied with four different ferric oxide forms, the orders of cell yields are amorphous hydrous ferric oxide>γ-FeOOH (lepidocrocite)>Fe5O7(OH)·4H2O (hydrated ferric oxyhydroxide polymer >α-FeOOH (goethite). The specific growth rates (μ) at logarithmic growth phase in Fe(III)-EDTA, amorphous hydrous ferric oxide and γ-FeOOH media were significantly greater than those in Fe5O7 (OH)·4H2O and α-FeOOH media. The thermodynamically stable forms such as Fe5O7(OH)·4H2O and α-FeOOH supported a little or no phytoplankton growth. The iron solublities and/or proton-promoted iron dissolution rates of these colloidal ferric oxides in seawater at 20°C were determined by simple filtration techniques involving γ-activity measurements of 59Fe. The orders of solubilities and estimated dissolution rate constants of these ferric oxides in seawater were consistent with that of cell yields in the culture experiments. These results suggest that the availability of colloidal iron to provide a source of iron for phytoplankton is related to the thermodynamic stability and kinetic lability of the colloidal ferric oxide phases, which probably control the uptake rate of iron by phytoplankton.

Effect of hydrothermal synthesis environment on the particle morphology, chemistry and magnetic properties of barium hexaferrite

Abstract: Barium nitrate and iron nitrate have been used as precursors in the hydrothermal synthesis of barium hydroxide, iron oxide and barium hexaferrite sols under specified standard synthesis conditions (temperature, time, stirring, alkali concentration, amount of water and heating rate) as a function of the base species used during synthesis. The hydrothermal synthesis of barium hydroxide and iron oxide has been used to develop an understanding of the hydrothermal synthesis of barium hexaferrite from a mixture of their precursors. The investigation has shown that the nucleation and growth behaviour as well as the phase composition, thermal behaviour, particle size, particle-size distribution and magnetic properties are strong functions of the base species used. The electrostatic potential difference between the barium hydroxide and the iron oxide decreases with increasing cation size in the order NaOH, KOH, (C2H5)4NOH and NH4OH. Note the potential difference between the two sol species determines their tendency to coagulate into clusters; hence, the heterocoagulation will be greater when using NaOH or KOH than (C2H5)4NOH or NH4OH. Under the standard synthesis conditions, only NaOH and KOH are able to facilitate the formation of plate-like particles of barium hexaferrite. In contrast, ultrafine particles of iron oxide (10–20 nm) together with only a small amount of barium hexaferrite are produced when either NH4OH or (C2H5)4NOH base is used. The samples synthesized in the presence of the NaOH and KOH exhibit relatively higher saturation magnetization (i.e. 258 mT (39 e.m.u.g−1) and 215 mT (32 e.m.u.g−1), respectively) than those samples synthesized in the presence of NH4OH or (C2H5)4NOH which exhibit negligible saturation magnetization owing to the small amount of magnetic phase (BaFe12O19) present.

Iron Oxide-Mediated Degradation, Photodegradation, and Biodegradation of Aminophenols

Abstract: Reference LBE-ARTICLE-1995-005doi:10.1021/la00002a026View record in Web of Science Record created on 2005-03-02, modified on 2016-08-08

Selective synthesis of α-olefins on Fe-Zn Fischer-Tropsch catalysts

Abstract: Fe/Zn oxides promoted with K and Cu selectively produce α-olefins at typical Fischer-Tropsch synthesis conditions (2/1 H2/CO, 1 MPa, and 270°C). The simultaneous presence of K and Cu introduces a synergistic activity enhancement while maintaining the high olefin selectivity obtained by alkali promotion. Structural and morphological differences in Fe-Zn oxides prepared from ammonium glycolate complexes or precipitated from nitrate solutions have only a small influence on catalytic properties. Catalyst behavior is strongly influenced by synergistic promoter effects (Cu, K) and by the controlled in situ conversion of iron oxide precursors to carbides.

Attrition of precipitated iron Fischer-Tropsch catalysts

Abstract: A precipitated, doubly promoted, iron oxide catalyst was studied to elucidate phenomena that may lead to catalyst attrition during slurry phase Fischer-Tropsch synthesis. The catalyst was examined by electron microscopy (SEM and TEM), electron and X-ray diffraction, sedigraph particle size analysis and BET surface area measurements. The catalyst undergoes attrition both at the micro- as well as the nano-length scales. On the micro-scale, this involves a breakup of ca. 30 μm spherical agglomerates into ca. 1 μm particles, a process that can be initiated even by the mixing that occurs in the sedigraph analyzer. On the nano-scale, we find that exposure of the catalyst to CO at increasing temperatures transforms single crystals of α-Fe 2 O 3 into Fe 3 O 4 and ultimately to Fe-carbide, with rounded particles as small as ca. 20 nm. The details of phase transformations and the resulting crystallite morphology and size distribution could play a major role in influencing the overall attrition resistance of precipitated iron oxide catalysts. In this paper, we describe the effects of the CO activation temperature on catalyst structure at the micro- and nano-scales.

Phosphate dynamics in an acidic mountain stream: Interactions involving algal uptake, sorption by iron oxide, and photoreduction

Abstract: Acid mine drainage streams in the Rocky Mountains typically have few algal species and abundant iron oxide deposits which can sorb phosphate. An instream injection of radiolabeled phosphate (32P0,) into St. Kevin Gulch, an acid mine drainage stream, was used to test the ability of a dominant algal species, Ulothrix sp., to rapidly assimilate phosphate. Approximately 90% of the injected phosphate was removed from the water column in the 175-m stream reach. When shaded stream reaches were exposed to full sunlight after the injection ended, photoreductive dissolution of iron oxide released sorbed 32P, which was then also removed downstream. The removal from the stream was modeled as a first-order process by using a reactive solute transport transient storage model. Concentrations of 32P mass-’ of algae were typically lo-fold greater than concentrations in hydrous iron oxides. During the injection, concentrations of 32P increased in the cellular P pool containing soluble, low-molecular-weight compounds and confirmed direct algal uptake of 32P0, from water. Mass balance calculations indicated that algal uptake and sorption on iron oxides were significant in removing phosphate. We conclude that in stream ecosystems, PO, sorbed by iron oxides can act as a dynamic nutrient reservoir regulated by photoreduction.

Superparamagnetic particles, process for their manufacture and usage

Abstract: Superparamagnetic particles consist of superparamagnetic one-domain particles and aggregates of superparamagnetic one-domain particles to whose surfaces are bound organic substances optionally having further binding sites for coupling to tissue-specific binding substances, diagnostic or pharmacologically active substances. The superparamagnetic particles consist of a mixture of small superparamagnetic one-domain particles with a particle size from 3 to 50 nanometers and stable, degradable aggregates of small superparamagnetic one-domain particles with a particle size from 10 to 1000 nanometers. They are made of iron hydroxide, iron oxide hydrate, iron oxides, iron mixed oxides or iron to the surface of which are bound mono- and/or polyhydroxylic group-containing aromatic substances, polyglycerines, amino-acid-containing substances, silicate group-containing substances among the orthosilicic acids and their condensation products and phosphate group-containing substances among the ortho- or metaphosphoriic acids and their condensation products. These substances may have further binding sites. These new particles may be used to destroy tumors, increase immunity, in magnetic drug targeting, for cell fusion, gene transfers, as contrasting agents, for in vitro diagnosis, as magnetic ion exchangers and magnetic adsorbents, if required by exposure to magnetic fields.

Effect of Nickel Oxide Doping on the Kinetics and Mechanism of Iron Oxide Reduction

Abstract: Experiments were conducted on pure Fe2O3 fines (–250 mesh) which were mixed with 1, 2.5, 5 and 10% by weight of pure NiO of the same size. The powder mixtures were pressed into compacts and fired at 1473 K for 20 h. The fired compacts were isothermally reduced at 1173-1473 K with hydrogen. The reduction course was followed up by means of weight loss technique. Porosity measurements, reflected light microscope and X-ray diffraction analysis were used to elucidate the reduction kinetics. NiO was found to have a significant effect on the reduction of iron oxide. The rate of reduction at both the initial and final stages increased with the increases of dopant content at all reduction temperatures and this was attributed to the formation of mickel ferrite (NiFe2O4) phase and the consequent increase in the total porosity of compacts. Nix, Fey solid solution (ferronickel alloy) was produced during reduction at all tempetatures studied. The values of apparent activation energy calculated from the experimental results, the structure of partially reduced compacts and the application of gas-solid reaction model were used to elucidate the reduction mechanism.

Importance of the surface oxide layer in the reduction of outgassing from stainless steels

Abstract: Temperature dependence of outgassing was measured for differently surface treated type 316L stainless steel chambers in the temperature range of 25–330 °C Based on the temperature dependence and outgassing characteristics of major outgassing species, the mechanism of outgassing from the stainless steel surface is discussed and the technique to produce an extremely low outgassing surface is indicated The following are the important findings (1) At temperatures below 250 °C, the outgassing species is predominantly hydrogen, which is released by diffusive outgassing from the bulk of the stainless steel (2) At temperatures above 250 °C, the contribution from water and carbon monoxide outgassing becomes significant because of the enhanced surface reaction to generate these gas species (3) The surface oxide layer formed by the oxidation in air is predominantly iron oxide and appears to serve as a more effective diffusion barrier for hydrogen outgassing compared with the mixed iron and chromium oxide layer

Polarography and voltammetry of mixed titanium(IV) oxide/iron(III) oxide colloids

Abstract: The polarographic and voltammetric study of mixed titanium oxide/iron oxide colloids shows that the composition and presumably also the structure of the colloidal particles varies with their size. Iron seems to prevail in the smallest particles ; titanium dominates in the surface layers of the bigger ones. Polarographic maxima indicate the particle size. The electroreduction of the trivalent iron in the particles proceeds as a bulk irreversible reaction, while the reduction of the titanium component remains, as in pure TiO 2 particles, a partly reversible surface process. In the colloids with low iron content, the reduction of the both electroactive parts occurs independently of each other ; however, when the iron content exceeds 50%, the reduction of Fe(III) dominates the mechanism of the Faradaic process.