Spinel deoxidation equilibria in the Fe Mn Al O system - experiments and computation

The concentration and chemical potential of oxygen in liquid Fe--Mn alloys equilibrated with the spinel solution, (Fe, Mn)Al sub 2+2x O sub 4+3x , and alpha -Al sub 2 O sub 3 have been determined at 1873K as a function of manganese concentration. The composition of the spinel phase has been determined using electron probe microanalysis. The results are compared with data reported in the literature. The deoxidation equilibrium has been computed using data on free energy of solution of oxygen in liquid iron, free energies of formation of hercynite and galaxite, and interaction parameters reported in the literature. The activity--composition relationship in spinel solution was derived from a cation distribution model. The model is in excellent agreement with the experimental data on oxygen concentration and potential and the composition of the spinel phase. 23 ref.--AA

Reactive interdiffusion: deviation from local equilibrium in the Fe-NiTiO3 couple

Deviation from local equilibrium between Fe–Ni alloy and (Fe,Ni)TiO3 solid solution in the reaction–diffusion zone of the Fe–NiTiO3 couple at 1273 K is evaluated by comparing the measured compositions in the zone with experimentally determined equilibrium tie-lines. The deviation is quantified by computing the Gibbs energy change for the reaction, Fe + NiTiO3 → FeTiO3 + Ni, from measured compositions in the zone and activity data available in the literature. Except near the extremities of the zone, the computed Gibbs energy change is constant, 8.2 kJ mol−1 higher than the standard Gibbs energy change for the reaction.

Kinetics of carbon monoxide oxidation with Sn(0.95)M(0.05)O(2-delta) (M = Cu, Fe, Mn, Co) catalysts

Base metal substituted Sn(0.95)M(0.05)O(2-delta) (M = Cu, Fe, Mn, Co) catalysts were synthesized by the solution combustion method and characterized by XRD, XPS, TEM and BET surface area analysis. The catalytic activities of these materials were investigated by performing CO oxidation. The rates and the apparent activation energies of the reaction for CO oxidation were determined for each catalyst. All the substituted catalysts showed high rates and lower activation energies for the oxidation of CO as compared to unsubstituted SnO(2). The rate was found to be much higher over copper substituted SnO(2) as compared to other studied catalysts. 100% CO conversion was obtained below 225 degrees C over this catalyst. A bifunctional reaction mechanism was developed that accounts for CO adsorption on base metal and support ions and O(2) dissociation on the oxide ion vacancy. The kinetic parameters were determined by fitting the model to the experimental data. The high rates of the CO oxidation reactions at low temperatures were rationalized by the high dissociative chemisorption of adsorbed O(2) over these catalysts.

Structure and Photocatalytic Activity of Ti 1- x M x O 2±δ (M = W, V, Ce, Zr, Fe, and Cu) Synthesized by Solution Combustion Method

The W, V, Ce, Zr, Fe, and Cu metal ion substituted nanocrystalline anatase TiO2 was prepared by solution combustion method and characterized by XRD, Raman, BET, EPR, XPS, IR TGA, UV absorption, and photoluminescence measurements. The structural studies indicate that the solid solution formation was limited to a narrow range of concentrations of the dopant ions. The photocatalytic degradation of 4-nitrophenol under UV and solar exposure was investigated with Ti1-xMxO2±δ. The degradation rates of 4-nitrophenol with these catalysts were lesser than the degradation rates of 4-nitrophenol with undoped TiO2 both with UV exposure and solar radiation. However, the photocatalytic activities of most metal ion doped TiO2 are higher than the activity of the commercial TiO2, Degussa P25. The decrease in photocatalytic activity is correlated with decrease in photoluminescence due to electron states of metal ions within the band gap of TiO2.

Synthesis, structure and photocatalytic activity of nano TiO2 and nano Ti1-xMxO2-delta (M = Cu, Fe, Pt, Pd, V, W, Ce, Zr)

We have synthesized 5-7 nm size, highly crystalline TiO2 which absorbs radiation in the visible region of solar spectrum. The material shows higher photocatalytic activity both in UV and visible region of the solar radiation compared to commercial Degussa P25 TiO2. Transition metal ion substitution for Ti4+ creates mid-gap, states which act as recombination centers for electron-hole induced by photons thus reducing photocatalytic activity. However, Pt, Pd and Cu ion substituted TiO2 are excellent CO oxidation and NO reduction catalysts at temperatures less than 100 degrees C.

Antimicrobial Properties of Nanostructured TiO2 Plus Fe Additive Thin Films Synthesized by a Cost-Effective Sol-Gel Process

We prepared thin films composed of pure TiO2 or TiO2 with an Fe additive (at concentrations of 0.2-0.8 wt%) via a simple and cost effective sol gel process, and tested their antifungal properties (against Candida albicans (MTCC-1637), Candida tropicalis (MTCC-184), Candida parapsilosis (MTCC-2509), and Candida glabrata (MTCC-3019) and antibacterial properties (against Staphylococcus faecalis (NCIM-2604) Staphylococcus epidermidis (NCIM-2493), Staphylococcus aureus (NCIL-2122), and Bacillus subtilis (NCIM-2549)). The films were deposited on glass and Si substrates and subjected to annealing at 400 degrees C for 3 h in ambient air. The film structural and morphological properties were investigated by X-ray photoelectron spectroscopy profilometry and scanning electron microscopy, respectively. Antifungal and antibacterial tests were conducted using the drop test method. Among the species examined, Candida albicans (MTCC-1637), and Staphylococcus aureus (NCIL-2122) showed complete colony formation inhibition after exposure for 4 h for the TiO2 loaded with 0.8 wt% Fe thin films. These results indicate that increasing the Fe concentration increased the antimicrobial activity, with complete inhibition of colony formation after 4 h exposure.

Interdiffusion in the Fe-Pt System

Diffusion-couple experiments are conducted in the Fe-Pt system. The phase boundary compositions of the phases measured in this study are found to be different than the compositions published previously. In the gamma-FePt solid solution, the interdiffusion coefficient increases with the Pt content up to 25 at. pct Pt. Fe is the faster diffusing species in this phase. The trend in the interdiffusion coefficient is explained with the help of calculated driving force for diffusion. To reduce errors, the average interdiffusion coefficients are calculated in the FePt and FePt3 compounds.

Structural, EPR, photo and thermoluminescence properties of ZnO:Fe nanoparticles

Zn(1-x)Fe(x)O(1+0.5x) (x = 0.5-5 mol%) nanoparticles were synthesized by a low temperature solution combustion route. The structural characterization of these nanoparticles by PXRD, SEM and TEM confirmed the phase purity of the samples and indicated a reduction in the particle size with increase in Fe content. A small increase in micro strain in the Fe doped nanocrystals is observed from W-H plots. EPR spectrum exhibits an intense resonance signal with effective g values at g approximate to 2.0 with a sextet hyperfine structure (hfs) besides a weak signal at g approximate to 4.13. The signal at g approximate to 2.0 with a sextet hyperfine structure might be due to manganese impurity where as the resonance signal at g approximate to 4.13 is due to iron. The optical band gap E-g was found to decrease with increase of Fe content. Raman spectra exhibit two non-polar optical phonon (E-2) modes at low and high frequencies at 100 and 435 cm(-1) in Fe doped samples. These modes broaden and disappear with increase of Fe do pant concentration. TL measurements of gamma-irradiated (1-5 kGy) samples show a main glow peak at 368 degrees C at a warming rate of 6.7 degrees Cs-1. The thermal activation parameters were estimated from Glow peak shape method. The average activation energy was found to be in the range 0.34-2.81 eV. (C) 2012 Elsevier B.V. All rights reserved.

Diffusion mechanism in the mu phase in Nb-X (X = Ni, Co, Fe) systems

Nb is one of the common refractory elements added in Ni, Co and Fe based superalloys. This lead to the formation of brittle topological close packed (tcp) mu phase, which is deleterious to the structure. It mainly grows by interdiffusion and in the present article, the interdiffusion process in different Nb-X (X=Ni, Co, Fe) systems is discussed. The activation energy for interdiffusion is lower in the Co-Nb system (173 kJ/mol) than Fe-Nb system (233 kJ/mol), which is again lower than the value found in the Ni-Nb system (319.7 kJ/mol). The mole fraction of Nb in this phase is less than Fe or Co at stoichiometric compositions in the Nb-Fe (that is Fe7Nb6) and Nb-Co (that is Co7Nb6) systems. On the other hand, the mole fraction of Nb is higher than Ni in the same phase (Ni6Nb2) in Ni-Nb system. However, in all the phases, Nb has lower diffusion rate. Possible diffusion mechanism in this phase is discussed with respect to the crystal structure.

Magnetic Properties of Fe/Cu Codoped ZnO Nanocrystals

Free-standing ZnO nanocrystals simultaneously doped with Fe and Cu with varying Fe/Cu compositions have been synthesized using colloidal methods with a mean size of similar to 7.7 nm. Interestingly, while the Cu-doped ZnO nanocrystal remains diamagnetic and Fe-doped samples show antiferromagnetic interactions between Fe sites without any magnetic ordering down to the lowest temperature investigated, samples doped simultaneously with Fe and Cu show a qualitative departure in exhibiting ferromagnetic interactions, with suggestions of ferromagnetic order at low temperature. XAS measurements establish the presence of Fe2+ and Fe3+ ions, with the concentration of the trivalent species increasing in the presence of Cu doping, providing direct evidence of the Fe2+ + Cu2+ sic Fe3+ + Cu+ redox couple being correlated with the ferromagnetic property. Using DFT, the unexpected ferromagnetic nature of these systems is explained in terms of a double exchange between Fe atoms, mediated by the Cu atom, in agreement with experimental observations.

Texture and microstructure evolution during cold rolling of Cu-Fe laminates prepared by accumulative roll bonding

Multi-layered materials have been made from Cu-Fe with approximately equal volume fractions using the Accumulated Roll Bonding (ARB) technique with less than 1 μm thickness of the individual layers. The so-obtained multi-layers have been subjected to deformation by cold rolling to 25, 50, 75, 87 and 93% reduction in thickness. A detailed characterization has been carried out using X-ray diffraction (line profile analysis and texture measurement) and electron (scanning and transmission) microscopy. It has been found that Fe layers are disintegrated whereas Cu retains its continuity within a layer. Microstructural Characterization from X-Ray Line profile Analysis (XRDLPA) through Variance Method reveals that large amount of strain is initially carried by Cu layers during deformation. In the Cu-Fe layer, the texture is comparatively weaker in Cu layer and strong in Fe layers. Brass Component increases up to 75% reduction and then decreases, while the ratio of Cu/S and Bs/S remains almost constant through out the deformation. After 50% reduction, dynamic recovery is predominant as indicated by the increase in the amount of low angle grain boundaries and decrease in dislocation density. The presence of R component indicates continuous dynamic recovery and recrystallization (CDRR) at the advanced stage of deformation.

Synthesis and characterization of Fe- and Co-based ferrite nanoparticles and study of the T-1 and T-2 relaxivity of chitosan-coated particles

In pursuit of newer and more effective contrast agents for magnetic resonance imaging, we report in this article the use of biocompatible chitosan-coated ferrite nanoparticles of different kinds with a view to determine their potential applications as the contrast agents in the field of nuclear magnetic resonance. The single-phase ferrite particles were synthesized by chemical co-precipitation (CoFe2O4 and Fe3O4) and by applying ultrasonic vibration (CoFe2O4 and Co0.8Zn0.2Fe2O4). Although magnetic anisotropy of CoFe2O4 nanoparticle leads to finite coercivity even for nanoensembles, it has been reduced significantly to a minimum level by applying ultrasonic vibration. Fe3O4 synthesized by chemical co-precipitation yielded particles which already possess negligible coercivity and remanence. Substitution of Co by Zn in CoFe2O4 increases the magnetization significantly with a small increase in coercivity and remanence. Particles synthesized by the application of ultrasonic vibration leads to the higher values of T-2 relaxivities than by chemical coprecipitation. We report that the T-2 relaxivities of these particles are of two orders of magnitude higher than corresponding T-1 relaxivities. Thus, these particles are evidently suitable as contrast agent for T-2 weighted MR images.

Low temperature CO oxidation and water gas shift reaction over Pt/Pd substituted in Fe/TiO2 catalysts

We demonstrate the activity of Ti0.84Pt0.01Fe0.15O2-delta and Ti0.73Pd0.02Fe0.25O2-delta catalysts towards the CO oxidation and water gas shift (VMS) reaction. Both the catalysts were synthesized in the nano crystalline form by a low temperature sonochemical method and characterized by different techniques such as XRD, FT-Raman, TEM, FT-IR, XPS and BET surface analyzer. H-2-TPR results corroborate the intimate contact between noble metal and Fe ions in the both catalysts that facilitates the reducibility of the support. In the absence of feed CO2 and H-2, nearly 100% conversion of CO to CO2 with 100% H-2 selectivity was observed at 300 degrees C and 260 degrees C respectively, for Ti0.84Pt0.01Fe0.15O2-delta and Ti0.73Pd0.02Fe0.25O2-delta catalyst. However, the catalytic performance of Ti0.73Pd0.02Fe0.25O2-delta deteriorates in the presence of feed CO2 and H-2. The change in the support reducibility is the primary reason for the significant increase in the activity for CO oxidation and WGS reaction. The effect of Fe addition was more significant in Ti0.73Pd0.02Fe0.25O2-delta than Ti0.84Pt0.01Fe0.15O2-delta. Based on the spectroscopic evidences and surface phenomena, a hybrid reaction scheme utilizing both surface hydroxyl groups and the lattice oxygen was hypothesized over these catalysts for WGS reaction. The mechanisms based on the formate and redox pathway were used to fit the ldnetic data. The analysis of experimental data shows the redox mechanism is the dominant pathway over these catalysts. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Compositionally Graded Microstructure for Ag-Fe Nanoparticles

Ag-Fe nanoparticles with a highly Ag rich average composition were synthesized by the sonochemical route. Silver-iron system exhibits a wide miscibility gap in the bulk materials. Interestingly, a graded compositional profile along the nanoparticle radius was observed. Regions at and near the surface of the nanoparticle contained both Ag and Fe atoms. The composition got relatively deficient Fe towards the center of the particle with particle core made up of pure Ag. Alloying of Ag and Fe is confirmed by the absence of diffraction signal corresponding to pure Fe phase and presence of a paramagnetic phase in nanoparticles containing a diamagnetic (Ag) and ferromagnetic (Fe) elements.

Synthesis of nanosized Ce0.85M0.1Ru0.05O2-delta (M = Si, Fe) solid solution exhibiting high CO oxidation and water gas shift activity

Nanosized Ce0.85M0.1Ru0.05O2-delta (M = Si, Fe) has been synthesized using a low temperature sonication method and characterized using XRD, TEM, XPS and H-2-TPR. The potential application of both the solid solutions has been explored as exhaust catalysts by performing CO oxidation. The addition of Si- and Fe-in Ce0.95Ru0.05O2-delta greatly enhanced the reducibility of Ce0.85M0.1Ru0.05O2-delta (M = Si, Fe), as indicated by the H-2-TPR study. The oxygen storage capacity has been used to correlate surface oxygen reactivity to the CO oxidation activity. Both the compounds reversibly release lattice oxygen and exhibit excellent CO oxidation activity with 99% conversion below 200 degrees C. A bifunctional reaction mechanism involving CO oxidation by the extraction of lattice oxygen and rejuvenation of oxide vacancy with gas feed O-2 has been used to correlate experimental data. The performance of both the solid solutions has also been investigated for energy application by performing the water gas shift reaction. The present catalysts are highly active and selective towards the hydrogen production and a lack of methanation activity is an important finding of present study.