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X-ray stereo microscopy for investigation of dynamics in soils

Description: The presented combination of stereo imaging and elemental mapping with soft X-ray microscopy reveals the spatial arrangement of naturally aqueous colloidal systems, e.g. iron oxides in soil colloid clusters. Changes in the spatial arrangement can be induced by manipulating the sample mounted to the X-ray microscope and thus be investigated directly.
Date: September 16, 2008
Creator: Gleber, S.-C.; Sedlmair, J.; Bertilson, M.; von Hofsten, O.; Heim, S.; Guttmann, P. et al.
Partner: UNT Libraries Government Documents Department

CORROSION OF Fe-10Al-Cr ALLOYS BY COAL CHAR

Description: Corrosion of iron-base alloys at 982 C (1800 F) by coal char is observed and the phase morphologies discussed. No sulfidation was observed at 50 hours exposure. After 100 hours, internal aluminum-rich sulfides were observed along with thick outer scales of iron oxide. The species causing the high-temperature induced corrosion are probably sulfides and sulfates, present in most coal chars. Possible mechanisms for the corrosion are also discussed.
Date: October 1, 1977
Creator: Gordon, B.A. & Nagarajan, V.
Partner: UNT Libraries Government Documents Department

Flow Accelerated Corrosion Experience at Comanche Peak Steam Electric Station

Description: Flow accelerated corrosion (FAC) is a major concern in the power industry as it causes thinning of the pipes by the dissolution of the passive oxide layer formed on the pipe surface. Present research deals with comparing the protection offered by the magnetite (Fe3O4) versus maghemite (γ-Fe2O3) phases thickness loss measurements. Fourier transform infrared spectroscopy (FTIR) is used in distinguishing these two elusive phases of iron oxides. Representative pipes are collected from high pressure steam extraction line of the secondary cycle of unit 2 of Comanche Peak Steam Electric Station (CPSES). Environmental scanning electron microscopy (ESEM) is used for morphological analysis. FTIR and X-ray diffraction (XRD) are used for phase analysis. Morphological analysis showed the presence of porous oxide surfaces with octahedral crystals, scallops and "chimney" like vents. FTIR revealed the predominance of maghemite at the most of the pipe sections. Results of thickness measurements indicate severe thickness loss at the bend areas (extrados) of the pipes.
Date: May 2008
Creator: Nakka, Ravi Kumar
Partner: UNT Libraries

Influence of Iron Oxide Particles on the Strength of Ball-Milled Iron

Description: Detailed microstructural and mechanical property studies of ball-milled iron, in the powder and consolidated states, are reviewed and assessed. The analyses cover three and one-half orders of magnitude of grain size (from 6 nm to 20 mm) and focus on the influence of oxide particles on the strength. The study includes the early work of Koch and Yang, Kimura and Takaki and continues with the more recent work of Umemoto et al and Belyakov, Sakai et al. It is shown that the major contributors to strength are the nanooxide particles. These particles are created by adiabatic shear banding during ball-milling leading to a bimodal distribution of particles. The predicted strength from particles, {sigma}{sub p}, is given by {sigma}{sub p} = B {center_dot} (D*{sub S}){sup -1/2} where D*{sub S} is the surface-to-surface interparticle spacing, and B = 395 MPa {center_dot} {micro}m{sup -1/2}. A model is proposed that accounts for the influence of the bimodal particle size distribution on strength.
Date: December 7, 2005
Creator: Lesuer, D R; Syn, C K & Sherby, O D
Partner: UNT Libraries Government Documents Department

Zn-Site Determination in Protein Encapsulated ZnxFe3-xO4 Nanoparticles

Description: The X-ray absorption spectra of the Fe and Zn L-edges for 6.7 nm Fe{sub 3}O{sub 4} nanoparticles grown inside 12 nm ferritin protein cages with 10%, 15%, 20% and 33% zinc doping, shows that the Zn is substitutional as Zn{sup 2+} within the iron oxide host structure. A Neel-Arrhenius plot of the blocking temperature in the frequency dependent ac-susceptibility measurements show that the particles are non-interacting and that the anisotropy energy barrier is reduced with Zn loading. X-ray magnetic circular dichroism (XMCD) of the Fe displays a linear decrease with Zn-doping in sharp contrast to the initial increase present in the bulk system. The most plausible explanation for the moment decrease is that Zn substitutes preferentially into the tetrahedral A-site as a Zn{sup 2+} cation, generating a mixed spinel.
Date: October 1, 2008
Creator: Pool, V. L.; Klem, M. T.; Holroyd, J.; Harris, T.; Arenholz, E.; Young, M. et al.
Partner: UNT Libraries Government Documents Department

Mechanisms and Dynamics of Abiotic and Biotic Interactions at Environmental Interfaces

Description: The Stanford EMSI (SEMSI) was established in 2004 through joint funding by the National Science Foundation and the OBER-ERSD. It encompasses a number of universities and national laboratories. The PNNL component of the SEMSI is funded by ERSD and is the focus of this report. This component has the objective of providing theory support to the SEMSI by bringing computational capabilities and expertise to bear on important electron transfer problems at mineral/water and mineral/microbe interfaces. PNNL staff member Dr. Kevin Rosso, who is also ''matrixed'' into the Environmental Molecular Sciences Laboratory (EMSL) at PNNL, is a co-PI on the SEMSI project and the PNNL lead. The EMSL computational facilities being applied to the SEMSI project include the 11.8 teraflop massively-parallel supercomputer. Science goals of this EMSL/SEMSI partnership include advancing our understanding of: (1) The kinetics of U(VI) and Cr(VI) reduction by aqueous and solid-phase Fe(II), (2) The structure of mineral surfaces in equilibrium with solution, and (3) Mechanisms of bacterial electron transfer to iron oxide surfaces via outer-membrane cytochromes.
Date: June 1, 2006
Creator: Roso, Kevin M.
Partner: UNT Libraries Government Documents Department

Growth and Dissolution of Iron and Manganese Oxide Films

Description: Growth and dissolution of Fe and Mn oxide films are key regulators of the fate and transport of heavy metals in the environment, especially during changing seasonal conditions of pH and dissolved oxygen. The Fe and Mn are present at much higher concentrations than the heavy metals, and, when Fe and Mn precipitate as oxide films, heavy metals surface adsorb or co-precipitate and are thus essentially immobilized. Conversely, when the Fe and Mn oxide films dissolve, the heavy metals are released to aqueous solution and are thus mobilized for transport. Therefore, understanding the dynamics and properties of Fe and Mn oxide films and thus on the uptake and release of heavy metals is critically important to any attempt to develop mechanistic, quantitative models of the fate, transport, and bioavailablity of heavy metals. A primary capability developed in our earlier work was the ability to grow manganese oxide (MnO{sub x}) films on rhodochrosite (MnCO{sub 3}) substrate in presence of dissolved oxygen under mild alkaline conditions. The morphology of the films was characterized using contact-mode atomic force microscopy. The initial growth began by heteroepitaxial nucleation. The resulting films had maximum heights of 1.5 to 2 nm as a result of thermodynamic constraints. Over the three past years, we have investigated the effects of MnO{sub x} growth on the interactions of MnCO{sub 3} with charged ions and microorganisms, as regulated by the surface electrical properties of the mineral. In 2006, we demonstrated that MnO{sub x} growth could induce interfacial repulsion and surface adhesion on the otherwise neutral MnCO{sub 3} substrate under environmental conditions. Using force-volume microscopy (FVM), we measured the interfacial and adhesive forces on a MnO{sub x}/MnCO{sub 3} surface with a negatively charged silicon nitride tip in a 10-mM NaNO3 solution at pH 7.4. The interfacial force and surface adhesion of MnOx ...
Date: December 22, 2008
Creator: Martin, Scot T.
Partner: UNT Libraries Government Documents Department

The concept of delayed nucleation in nanocrystal growthdemonstrated for the case of iron oxide nanodisks

Description: A comprehensive study of iron oxide nanocrystal growth through non-hydrolitic, surfactant-mediated thermal reaction of iron pentacarbonyl and an oxidizer has been conducted, which includes size control, anisotropic shape evolution, and crystallographic phase transition of monodisperse iron oxide colloidal nanocrystals. The reaction was monitored by in situ UV-Vis spectroscopy taking advantage of the color change accompanying the iron oxide colloid formation allowing measurement of the induction time for nucleation. Features of the synthesis such as the size control and reproducibility are related to the occurrence of the observed delayed nucleation process. As a separate source of iron and oxygen is adopted, phase control could also be achieved by sequential injections of oxidizer.
Date: September 9, 2005
Creator: Casula, Maria F.; Jun, Young-wook; Zaziski, David J.; Chan, EmoryM.; Corrias, Anna & Alivisatos, Paul A.
Partner: UNT Libraries Government Documents Department

INVESTIGATION OF MECHANICAL METHODS OF SCALE REMOVAL FROM HRT HEAT EXCHANGERS

Description: Tests were conducted to determine methods of removing scale deposits from the HRT heat exchangers. A mockup of the heat exchanger header was cleared of a deposit of iron rust by reverse flushing at a flow rate below 75 gpm. A tube bundle consisting of 109 1/4 in OD X 0.049 in. wall tubes was plugged with rust. Approximately 80% of these tubes were unplugged by using a 70 psi water pressure differential in combination with vibration from a pneumatic rivet gun. No mechanical method was employed in the tests which could clear the remaining tubes. (auth)
Date: July 21, 1959
Creator: Gabbard, C.H.; Eissenberg, D.M.; Moyers, J.C. & Namba, I.K.
Partner: UNT Libraries Government Documents Department

Alpha Ferric Oxide: Low Temperature Heat Capacity and Thermodynamic Functions

Description: ABS>The heat capacity of synthetic alpha ferric oxide was determined at 5 to 350 K. The experimental technique is described, and the heat capacity and molal thermodyamic functions are tabulated. The heat capacity vs. temperature is shown graphically. (J.R.D.)
Date: January 1, 1957
Creator: Gronvold, F. & Westrum, E. F., Jr.
Partner: UNT Libraries Government Documents Department

Electronic/ionic conductivity and oxygen diffusion coefficient of Sr-Fe-Co-O system

Description: Oxides in the system Sr-Fe-Co-O exhibit both electronic and ionic conductivities. Recently, Sr-Fe-Co-O system attracted great attention because of the potential to be used for oxygen permeable membranes that can operate without the electrodes or external electrical circuitry. Electronic and ionic conductivities at various temperatures have been measured on two compositions in Sr-Fe-Co-O system named SFC-1 and SFC-2. The electronic transference number is much greater than the ionic transference number in SFC-1 sample, while the electronic and ionic transference numbers are very close in SFC-2 sample. At 800{degrees}C, the electronic conductivity and ionic conductivity are {approx}76 S{center_dot}cm-1 and =4 S-cm-1, respectively, for SFC-1. While, for SFC-2, the electronic and ionic conductivities are =10 S-cm-1 and {approx}7 S-cm-1, respectively. By a local fitting to {sigma}{center_dot}T = A exp(-E{sub {alpha}}/{kappa}{Tau}), we found that the oxide ion activation energies are 0.92 eV and 0.37 eV respectively for SFC-1 and SFC-2 samples. Oxygen diffusion coefficient of SFC-2 is {approx}{times}10{sup {minus}7} cm{sup 2}/sec at 900C.
Date: March 1, 1995
Creator: Ma, B.; Park, J.H.; Balachandran, U. & Segre, C.U.
Partner: UNT Libraries Government Documents Department

Influence of Microbial Iron and Nitrate Reduction on Subsurface Iron Biogeochemistry and Contaminant Metal Mobilization

Description: Although toxic metal and radionuclide contaminants can not be destroyed, their toxicity and mobility can be dramatically altered by microbial activity. In addition to toxic metals, many contaminated sites contain both iron-containing minerals and co-contaminants such as nitrate NO{sub 3}{sup -}. Successful implementation of metal and radionuclide bioremediation strategies in such environments requires an understanding of the complex microbial and geochemical interactions that influence the redox speciation and mobility of toxic metals. Our specific objectives have been to (1) determine the effect of iron oxide mineral reduction on the mobility of sorbed, representative toxic metals (Zn{sup 2+}), (2) study the biogeochemical interactions that may occur during microbial reduction of NO{sub 3}{sup -} and iron oxide minerals, and (3) evaluate the kinetics of NO{sub 3}{sup -}-dependent, microbial oxidation of ferrous iron (Fe{sup 2+}).
Date: April 10, 2002
Creator: Picardal, Flynn W.
Partner: UNT Libraries Government Documents Department

Electrodissolution of electrodeposited iron oxides

Description: Galvanostatic reduction of ferric oxide was studied in phosphate solutions over a range of pH values. The oxides were prepared on gold by anodic electrodeposition from dilute ferrous borate solution. With increased pH, the potential of the reduction arrests decreased and the charge associated with the arrest increased. A dependence of -60 mV/pH was observed except between pH 7.5 and 8.5 where the slope approximated -180 mV/pH. Above pH 7.5 the slope was consistent with the thermodynamic predicted slope of -180 mV/pH expected from reductive dissolution of ferric oxide forming soluble ferrous ions. At higher pH values, a slope of -60 mV/pH has been accounted for by oxide reduction to form a solid lower valent oxide.
Date: December 31, 1996
Creator: Isaacs, H.S.; Ryan, M.P.; Kalonousky, D.N. & Virtanen, S.
Partner: UNT Libraries Government Documents Department

Defect structure of the mixed-conducting Sr-Fe-Co-O system

Description: Electrical conductivity of the mixed-conducting Sr-Fe-Co-O system was investigated at high temperatures and various oxygen partial pressures (pO2). The system exhibits not only high combined electrical and oxygen ionic conductivities but also structural stability in both oxidizing and reducing environments. Conductivity of SrFeCo{sub 0.5}O{sub x} increases with temperature and pO2, within the experiment pO2 range (1-10{sup -18} atm). p-type conduction was observed, the activity energy of which decreases with pO2. A model of the defect chemistry in the Sr-Fe-Co-O system is proposed. The pO2- dependent conducting behavior can be understood by considering the trivalent-to-divalent transition of the transition metal ions in the system.
Date: November 1, 1996
Creator: Ma, B.; Balachandran, U.; Chao, C.-C. & Park, J.-H.
Partner: UNT Libraries Government Documents Department

Oxidation in HVOF-sprayed steel

Description: It is widely held that most of the oxidation in thermally sprayed coatings occurs on the surface of the droplet after it has flattened. The evidence in this paper suggests that, for the conditions studied here, oxidation of the top surface of flattened droplets is not the dominant oxidation mechanism. In this study, a mild steel wire (AISI 1025) was sprayed using a high-velocity oxy-fuel (HVOF) torch onto copper and aluminum substrates. Ion milling and Auger spectroscopy were used to examine the distribution of oxides within individual splats. Conventional metallographic analysis was also used to study oxide distributions within coatings that were sprayed under the same conditions. An analytical model for oxidation of the exposed surface of a splat is presented. Based on literature data, the model assumes that diffusion of iron through a solid FeO layer is the rate limiting factor in forming the oxide on the top surface of a splat. An FeO layer only a few thousandths of a micron thick is predicted to form on the splat surface as it cools. However, the experimental evidence shows that the oxide layers are typically 100x thicker than the predicted value. These thick, oxide layers are not always observed on the top surface of a splat. Indeed, in some instances the oxide layer is on the bottom, and the metal is on the top. The observed oxide distributions are more consistently explained if most of the oxide formed before the droplets impact the substrate.
Date: August 1997
Creator: Smith, M. F.; Neiser, R. A. & Dykhuizen, R. C.
Partner: UNT Libraries Government Documents Department

Microbial acquisition of iron from ferric iron bearing minerals

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Iron is a universal requirement for all life forms. Although the fourth most abundant element in the geosphere, iron is virtually insoluble at physiological pH in oxidizing environments, existing mainly as very insoluble oxides and hydroxides. Currently it is not understood how iron is solubilized and made available for biological use. This research project addressed this topic by conducting a series of experiments that utilized techniques from both soil microbiology and mineral surface geochemistry. Microbiological analysis consisted of the examination of metabolic and physiological responses to mineral iron supplements. At the same time mineral surfaces were examined for structural changes brought about by microbially mediated dissolution. The results of these experiments demonstrated that (1) bacterial siderophores were able to promote the dissolution of iron oxides, (2) that strict aerobic microorganisms may use anaerobic processes to promote iron oxide dissolution, and (3) that it is possible to image the surface of iron oxides undergoing microbial dissolution.
Date: December 31, 1998
Creator: Hersman, L.E. & Sposito, G.
Partner: UNT Libraries Government Documents Department

Irreversible Sorption of Contaminants During Ferrihydrite Transformation

Description: A better understanding of the fraction of contaminants irreversibly sorbed by minerals is necessary to effectively quantify bioavailability. Ferrihydrite, a poorly crystalline iron oxide, is a natural sink for sorbed contaminants. Contaminants may be sorbed/occluded as ferrihydrite precipitates in natural waters or as it ages and transforms to more crystalline iron oxides such as goethite or hematite. Laboratory studies indicate that Cd, Co, Cr, Cu, Ni, Np, Pb, Sr, U, and Zn are irreversibly sorbed to some extent during the aging and transformation of synthetic ferrihydrite. Barium, Ra and Sr are known to sorb on ferrihydrite in the pH range of 6 to 10 and sorb more strongly at pH values above its zero point of charge (pH> 8). We will review recent literature on metal retardation, including our laboratory and modeling investigation of Ba (as an analogue for Ra) and Sr adsorption/resorption, during ferrihydrite transformation to more crystalline iron oxides. Four ferrihydrite suspensions were aged at pH 12 and 50 °C with or without Ba in 0.01 M KN03 for 68 h or in 0.17 M KN03 for 3424 h. Two ferrihydrite suspensions were aged with and without Sr at pH 8 in 0.1 M KN03 at 70°C. Barium or Sr sorption, or resorption, was measured by periodically centrifuging suspension subsamples, filtering, and analyzing the filtrate for Ba or Sr. Solid subsamples were extracted with 0.2 M ammonium oxalate (pH 3 in the dark) and with 6 M HCl to determine the Fe and Ba or Sr attributed to ferrihydrite (or adsorbed on the goethite/hematite stiace) and the total Fe and Ba or Sr content, respectively. Barium or Sr occluded in goethite/hematite was determined by the difference between the total Ba or Sr and the oxalate extractable Ba or Sr. The percent transformation of ferrihydrite to goethite/hematite was estimated ...
Date: May 19, 1999
Creator: Anderson, H. L.; Arthur, S. E.; Brady, P. V.; Cygan, R. T.; Nagy, K. L. & Westrich, H. R.
Partner: UNT Libraries Government Documents Department

SUPPORTED DENSE CERAMIC MEMBRANES FOR OXYGEN SEPARATION

Description: Mixed-conducting membranes have the ability to conduct oxygen with perfect selectivity at elevated temperatures, which makes them an extremely attractive alternative for oxygen separation and membrane reactor applications. The ability to reliably fabricate these membranes in thin or thick films would enable solid-state divisional limitations to be minimized, thus providing higher oxygen flux. Based on that motivation, the overall objective for this project is to develop and demonstrate a strategy for the fabrication of supported Wick film ceramic mixed conducting membranes, and improve the understanding of the fundamental issues associated with reliable fabrication of these membranes. The project has focused on the mixed-conducting ceramic composition SrCo{sub 0.5}FeO{sub x} because of its superior permeability and stability in reducing atmospheres. The fabrication strategy employed involves the deposition of SrCo{sub 0.5}FeO{sub x} thick films onto porous supports of the same composition. In the second year of this project, we completed characterization of the sintering and phase behavior of the porous SrCo{sub 0.5}FeO{sub x} supports, leading to a standard support fabrication methodology. Using a doctor blade method, pastes made from aerosol-derived SrCo{sub 0.5}FeO{sub x} powder dispersed with polyethylene glycol were applied to the supports, and the sintering behavior of the thick film membranes was examined in air and nitrogen atmospheres. It has been demonstrated that the desired crystalline phase content can be produced in the membranes, and that the material in the membrane layer can be highly densified without densifying the underlying support. However, considerable cracking and opening of the film occurred when films densified to a high extent. The addition of MgO into the SrCo{sub 0.5}FeO{sub x} supports was shown to inhibit support sintering so that temperatures up to 1300 C, where significant liquid formation occurs, could be used for film sintering. This successfully reduced cracking, however the films retained open porosity. The ...
Date: June 30, 2000
Creator: Ward, Timothy L.
Partner: UNT Libraries Government Documents Department

Materials to be used for radionuclide transport experiments (milestones SPL3A1M4)

Description: Experiments to determine the effect of canister corrosion products on the transport of radionuclides will be undertaken using the FE(III) oxides goethite and hematite as proxies for the expected corrosion envelope that will form as a result of alteration of the corrosion allowance overpack prior to the breaching of the waste container. Samples of ESF invert concrete that have been crushed, or left intact but fractured, and that have been subjected to hydrothermal alteration will be used to determine the effect of cementitious materials on transport of radionuclides. A mixture of CaCO{sub 3}, Si0{sub 2}, and aggregate will be used as a proxy for completely carbonated concrete.
Date: February 1, 1998
Creator: Viani, B., LLNL
Partner: UNT Libraries Government Documents Department