Iron oxides

Top PDF Iron oxides:

In vitro bioactivity and stem cells attachment of three-dimensionally ordered macroporous bioactive glass incorporating iron oxides

In vitro bioactivity and stem cells attachment of three-dimensionally ordered macroporous bioactive glass incorporating iron oxides

is modi fied by the sedimentation of Ca and P while the nonmagnetic 3DOM BG forms the calcium phosphate by the ionic exchange following the Hench mechanism. The adult human adipose tissue derived stem cells (hADSCs) can be closely attached and well spread on the flat plate of all 3DOM BG/Fe and 3DOM BG. Without detectable cytotoxicity possibly induced by iron oxides, the osteoblast can be grown and proliferated. In addition to these bioactivity and biocompatibility, porous structures can allow their possible use in targeted drug delivery and magnetic properties of 3DOM BG/Fe can essentially be implemented in hyperthermia therapy.
En savoir plus

13 En savoir plus

In vitro bioactivity and stem cells attachment of three-dimensionally ordered macroporous bioactive glass incorporating iron oxides

In vitro bioactivity and stem cells attachment of three-dimensionally ordered macroporous bioactive glass incorporating iron oxides

is modi fied by the sedimentation of Ca and P while the nonmagnetic 3DOM BG forms the calcium phosphate by the ionic exchange following the Hench mechanism. The adult human adipose tissue derived stem cells (hADSCs) can be closely attached and well spread on the flat plate of all 3DOM BG/Fe and 3DOM BG. Without detectable cytotoxicity possibly induced by iron oxides, the osteoblast can be grown and proliferated. In addition to these bioactivity and biocompatibility, porous structures can allow their possible use in targeted drug delivery and magnetic properties of 3DOM BG/Fe can essentially be implemented in hyperthermia therapy.
En savoir plus

14 En savoir plus

Electrochemical dissolution and passivation phenomena of gold cyanidation from roasted ore in the presence of iron oxides

Electrochemical dissolution and passivation phenomena of gold cyanidation from roasted ore in the presence of iron oxides

158 Abstract This study investigates the electrochemical interactions between gold and roasted gold ore (RGO), with its associated oxide minerals serving as slurry, in an electrolyte saturated with atmospheric oxygen. Conventional cyanidation yielded a decrease of ~ 40% in the gold leach rate with magnetite slurry, while increases of 25% and 10% were observed for hematite and maghemite, respectively. These gold leach rates were obtained by applying cathodic Tafel slopes only. SEM-EDS, in the case of magnetite slurry, exhibited a high accumulation of iron oxides on the gold surface, which is an indication of slowdown in the gold leach rate. In the case of roasted gold ore slurry, lower amounts of iron oxides were detected with the association of calcium-magnesium coating. XPS results also exhibited a small amount of gold in the slurry of magnetite particles after leaching, i.e., suggesting the adsorption of gold by magnetite, which also justifies the slowdown in the gold leach rate. Magnetic separation tests of cyanidation tailings containing 20% Au resulted in a 4% (mass-pull) magnetic concentrate sample with 72% non-leached Au. Roasted gold ore, magnetic tailings, and synthetic maghemite electrodes exhibited a cathodic peak, suggesting the reduction of ferric to ferrous ions, which could be responsible for the slowdown of leach kinetics, whereas magnetic concentrate did not. Furthermore, when oxygen was bubbled, this peak disappeared in the case of roasted gold ore and synthetic maghemite, though magnetic tailings still exhibited the peak .
En savoir plus

235 En savoir plus

Characterization of iron oxides in mineral dust aerosols: Implications for light absorption

Characterization of iron oxides in mineral dust aerosols: Implications for light absorption

[ 54 ] In this study the iron oxide – clay aggregates were constructed by considering the aggregation of either hema- tite or goethite with kaolinite or illite resulting in four types of aggregates: hematite-illite (HI), hematite-kaolinite (HK), goethite-illite (GI), and goethite-kaolinite (GK). For each aggregate type, we considered the maximum, minimum and mean values of the volume fraction  that were determined from Fe/Al values measured for (1) total iron, (2) free iron, and (3) size-resolved free iron. Calculated values of  are presented in Table 7. These values were used to compute the spectral effective refractive indices of each type of aggre- gates employing the Bruggeman approximation and the refractive indices of individual end-members. Then the optical characteristics of aggregates were calculated and weighted with those of other species forming the external mixture to give its optical properties (see section 4). Here we model several different mixtures composed of light- absorbing (i.e., iron oxide – clay aggregates) and non- absorbing species (quartz and calcite). We also use the size-resolved data for Ni-WT, Ch-WT, and Tu-WT samples Table 7. Summary of Volume Fractions  of Iron Oxides in Illite- or Kaolinite-Containing Aggregates
En savoir plus

20 En savoir plus

Interactions of ribonucleotides with aluminium and iron oxides under varying environmental conditions

Interactions of ribonucleotides with aluminium and iron oxides under varying environmental conditions

! References : Feuillie et al, 2013, GCA 120 97–108; Halter & Pfeifer, 2001, C. Appl. Geochem.,16 (7-8), 793−802; Fukushi & Sverjensky, 2007, GCA 71 (15), 3717−3745; Cornell & Schwertmann, 2003, The iron oxides: structures, properties, reactions, occurence and uses, p 85-86; Sverjensky, 2005, GCA 69 (2) 225–257; Feuillie et al, 2015, Langmuir 31 (1) 240–248; He et al,

2 En savoir plus

Fouling of Steam Generator Tubes in Nuclear Power Plants : Investigation on the Preventive Effect of Polyacrylic Acid on Iron Oxides Deposition

Fouling of Steam Generator Tubes in Nuclear Power Plants : Investigation on the Preventive Effect of Polyacrylic Acid on Iron Oxides Deposition

The aim of this study was to evaluate the preventive nature of PAA on the fouling deposits (mainly composed of iron oxides) in SGs and to determine the action mechanism(s) of PAA on iron oxides. The investigation of the effect of PAA on magnetite suspensions and on the formation of deposit layers onto (pre-oxidized) Inconel 690TT tubes was conducted. This was performed in a dedicated biphasic loop reproducing the physico-chemical conditions of pressurized water reactor SGs. The results showed an increased iron concentration at the loop exit with the injection of PAA. Characterizations of the samples indicated the apparent diminution of oxide layer thickness and a change in oxide phase from magnetite to hematite at the liquid-steam interface region in the reactor. The study of these effects led us to the critical discussion of the hypotheses which can explain the underlying action mechanisms of PAA.
En savoir plus

13 En savoir plus

The effect of polyacrylic acid on iron oxides formed on steam generator tubes and on metallic copper present in pressurized water reactors

The effect of polyacrylic acid on iron oxides formed on steam generator tubes and on metallic copper present in pressurized water reactors

each test, we can conclude that the PAA effect on iron oxide is similar for both pH. In the other hand, for the ethanolamine conditioning, the observed iron content difference of 10 % between pH 9.1 and pH 9.4 is only due to the dispersion of the results (see Table 1). In an EPRI study [17], it is shown that the solution pH does not affect the effectiveness of PAA (OptiSperse PWR6600) over the range from pH 9.3 to 10.5 during steam generator wet layup. Therefore, a pH increase up to 10.5 at higher temperature, such as 275 °C, should be possible without modifying the PAA effect.
En savoir plus

17 En savoir plus

Decomposition of hydrogen peroxide and organic compounds in the presence of iron and iron oxides

Decomposition of hydrogen peroxide and organic compounds in the presence of iron and iron oxides

Unknown parameters in this model are the rate constants of reactions 11 and 12 and the concentration of total dissolved Fe(III).. First, increasing the amount of ferrihydrit[r]

182 En savoir plus

Prediction of isoelectric point of manganese and cobalt lamellar oxides : application to controlled synthesis of mixed oxides

Prediction of isoelectric point of manganese and cobalt lamellar oxides : application to controlled synthesis of mixed oxides

Summary and conclusion To design novel layered materials, we have focused on a bottom-up strategy which consists of synthesizing various layered oxides, exfoliating them, and restacking them together. The restacking process can be especially difficult, since it relies on an electrostatic attraction between the particles. The aim of this study was to facilitate this step by predicting the surface charge (or zeta potential) and determining the IEP of exfoliated materials. The MUSIC model allowed characterization of the effect of exfoliation on charge surface of the particles. Starting from platelets with a high basal area percentage, exfoliation process has no impact on IEP value, as verified by experimental values. The main parameter to take into account is the mean oxidation state of the metal oxide. This means that it is sufficient to know the mean oxidation state of initial particles to predict the IEP, and thus determine a suitable pH for the restacking. Moreover, the restacked materials (of different ratios) also have an IEP predictable by the model, thus confirming the valid approach of the model. Because the model was first developed on iron oxides and was verified for an accurate prediction of manganese and cobalt oxides, is it is reasonable to think that it can be extended to other various oxides and hydroxides.
En savoir plus

16 En savoir plus

Cation-disordered oxides for rechargeable lithium battery cathodes

Cation-disordered oxides for rechargeable lithium battery cathodes

97 Oxygen loss from LNTMO20 can also be inferred from the cyclic voltammetry (CV) tests. Figure 3-12b shows the first cycle CV profile of LNTMO20. When the oxidation cutoff voltage is 4.1 V (red), we observe a main reduction peak at ~3.7 V and a minor reduction peak at ~2.7 V. However, when the cutoff is increased to 4.5 V (black), an additional reduction peak at ~2.2 V is observed in the CV profile, which is likely associated with reduction of a second TM species. This shows that charging above 4.1 V triggers a reaction which allows reduction of species that were previously not reducible. In the case of LNTMO20, reduction of Mo 6+ or Ti 4+ upon discharge is likely triggered by oxygen loss, similar to reduction of Mn 4+ that becomes possible in Li-excess Ni-Mn-Co oxides after oxygen loss. 40,97,128 Although the Mo or Ti XANES do not show a clear evidence of the decrease in the average Mo or Ti oxidation states after the first discharge (Figs. 3-10b, 10c), the apparent discrepancy between CV (or EELS) and XANES implies that oxygen loss may be significant at the surface but not in the bulk. Otherwise, XANES should detect the overall decrease in the average Mo or Ti oxidation state after the first discharge.
En savoir plus

127 En savoir plus

The global lightning-induced nitrogen oxides source

The global lightning-induced nitrogen oxides source

The parameterisation for maritime thunderstorms is based on observations in- dicating that marine thunderstorms with the same CTH have weaker updrafts, resulting in lower lightning frequ[r]

197 En savoir plus

Co–Ce Oxides Supported on SBA-15 for VOCs Oxidation

Co–Ce Oxides Supported on SBA-15 for VOCs Oxidation

The most active catalysts in all studied reactions are mono-component cobalt. The addition of cerium oxide worsens the catalytic activity in all three reactions studied. According to the literature data, the different parameters, such as the crystallite size, the reducibility of cobalt species, the type of support, the cobalt content, control the catalytic activity of the cobalt oxide-based catalysts for propane complete oxidation [ 24 – 27 ]. The interaction of the cobalt oxide species with the support is also very important because if the particle–support interaction is stronger, their reducibility decreases and as a consequence the activity drops down [ 28 , 29 ]. The main factors governing the catalytic activity of CH 4 and VOCs complete oxidation over Co3O4 and Co3O4–CeO2 binary oxides are high bulk oxygen mobility (through the Mars–van Krevelen mechanism) and formation of highly active oxygen [ 4 ]. Luo et al. [ 30 ] found that the surface lattice oxygen species are related to C3H8 oxidation and, the propane oxidation takes place on neighboring surface lattice oxygen sites in Co 3 O 4 or crystallites where propane molecule is activated.
En savoir plus

15 En savoir plus

The adsorption of nitrogen oxides on crystalline ice

The adsorption of nitrogen oxides on crystalline ice

Fig. 7. Correlation of dipole moment (Lide, 2001-2002) and the ex- perimentally found adsorption enthalpy for NO, NO 2 , HONO and HNO 3 . bonds. The strength of a hydrogen bond depends on the ca- pability of an ice surface to act as hydrogen bond donor and the dipole moment of the nitrogen oxide. The capability of the crystalline ice used in this study to form hydrogen bonds, which is determined by the number of free OH groups on the surface, should be sufficient for the coverage of nitrogen ox- ides below a mono layer in this work. First of all, FTIRAS measurements indicated a free OH coverage on crystalline ice to be approximately one-sixth of that on amorphous ice (Schaff and Roberts, 1996). And secondly, even after anneal- ing at 258 K the polycrystalline character of the ice spheres used in our work, whose grain boundaries might posses free OH groups, is preserved. Finally, despite the annealing, sur- face defects facilitating free OH groups might be present on the surface. Assuming that hydrogen bonding is relevant for adsorption of nitrogen oxides on ice, the overall bond strength of the molecules to the surface should scale with the dipole moment. Figure 7 shows a correlation of dipole mo- ments and the adsorption enthalpy determined in this study.
En savoir plus

14 En savoir plus

The global lightning-induced nitrogen oxides source

The global lightning-induced nitrogen oxides source

Received: 16 January 2007 – Published in Atmos. Chem. Phys. Discuss.: 22 February 2007 Revised: 24 May 2007 – Accepted: 9 July 2007 – Published: 24 July 2007 Abstract. The knowledge of the lightning-induced nitro- gen oxides (LNO x ) source is important for understanding and predicting the nitrogen oxides and ozone distributions in the troposphere and their trends, the oxidising capacity of the atmosphere, and the lifetime of trace gases destroyed by reactions with OH. This knowledge is further required for the assessment of other important NO x sources, in par- ticular from aviation emissions, the stratosphere, and from surface sources, and for understanding the possible feedback between climate changes and lightning. This paper reviews more than 3 decades of research. The review includes labo- ratory studies as well as surface, airborne and satellite-based observations of lightning and of NO x and related species in the atmosphere. Relevant data available from measurements in regions with strong LNO x influence are identified, includ- ing recent observations at midlatitudes and over tropical con- tinents where most lightning occurs. Various methods to model LNO x at cloud scales or globally are described. Previ- ous estimates are re-evaluated using the global annual mean flash frequency of 44±5 s − 1 reported from OTD satellite data. From the review, mainly of airborne measurements near thunderstorms and cloud-resolving models, we conclude that a “typical” thunderstorm flash produces 15 (2–40)×10 25 NO molecules per flash, equivalent to 250 mol NO x or 3.5 kg of N mass per flash with uncertainty factor from 0.13 to 2.7. Mainly as a result of global model studies for various LNO x parameterisations tested with related observations, the best estimate of the annual global LNO x nitrogen mass source and its uncertainty range is (5±3) Tg a − 1 in this study. In spite of a smaller global flash rate, the best estimate is es- sentially the same as in some earlier reviews, implying larger flash-specific NO x emissions. The paper estimates the LNO x accuracy required for various applications and lays out strate- gies for improving estimates in the future. An accuracy of Correspondence to: U. Schumann
En savoir plus

86 En savoir plus

Direct electroreduction of oxides in molten fluoride salts

Direct electroreduction of oxides in molten fluoride salts

2 at 850 ◦ C for TiO 2 and TiO. The electrochemical behaviour of these oxides was studied by linear sweep voltammetry: a current corresponding to the oxide reduction was evidenced for TiO 2 , SnO 2 and Fe 3 O 4 . After galvanostatic electrolyses, a complete conversion was obtained for all oxides, except TiO, and the structure of reduced Ti and Fe samples had a typical coral-like structure while dense drops of Sn were recovered (Sn is liquid at operating temperature). After TiO electrolysis, a thin external metallic titanium layer was detected, acting as a barrier for the oxide ion diffusion and no complete reduction can be achieved. This could be explained by a Pilling–Bedworth ratio around 1 for Ti/TiO.
En savoir plus

7 En savoir plus

Resupply of mesopelagic dissolved iron controlled by particulate iron composition

Resupply of mesopelagic dissolved iron controlled by particulate iron composition

Remineralization of upper ocean particles: Implications for iron biogeochemistry. Dust deposition: iron 295[r]

39 En savoir plus

Transition metal oxides for combustion and depollution processes

Transition metal oxides for combustion and depollution processes

8 6.3 Oxidation of carbon monoxide CO, which is highly toxic, is an important constituent of the automotive exhaust gases and its abatement is crucial not only to limit the environment pollution but also to prevent health damage or death. The CO molecule is also inevitably produced in the reforming process which aims to generate hydrogen. When hydrogen is produced to feed a proton-exchanged membrane fuel cell, few ppm of CO can cause dramatic poisoning of the electrode. Low-temperature CO oxidation is then essential to prevent the deactivation of the cell. It certainly makes the catalytic CO oxidation one of the most investigated catalytic reactions. Precious metals such as Au, Pt, Pd, and Rh supported catalysts are highly active for catalytic CO oxidation. However the increasing price as well as decreasing reserves of noble metals makes essential the development of cheaper catalysts constituted of more abundant metals but with comparable catalytic activity. Transition metal oxide catalysts appear as very interesting alternative of the noble metal-based catalysts and reviews regularly update the works which report a better comprehension of the catalytic mechanism as well as the optimization of the transition metal oxide- based formulation with improved catalytic performances [16]. Cobalt, Cerium, Manganese, Iron and Copper oxides are among the most studied samples for catalytic CO oxidation.
En savoir plus

58 En savoir plus

Tritium trapping by metal oxides in radioactive wastes

Tritium trapping by metal oxides in radioactive wastes

SUMMARY: Fusion facilities like ITER will produce radioactive waste during operation and dismantling phase. A part of those waste generated by this fusion machine are tritiated waste that have to be managed. One of the main issues in tritiated waste management is the confinement of tritium which presents a good ability to diffusion. One of the solutions is to trap the tritium degassed from waste directly in waste drums. In containers tritium is under gaseous form (HT and T2), tritiated water vapor (HTO and T 2O) and some traces of organic bounded tritium species (OBT). As a hydrogen isotope, HT and T2 conversion in HTO and T2O is possible thanks to a reaction with a mix of metal oxides MnO 2 and Ag2O [2] and tritiated water can be adsorbed on molecular sieve [5]. This paper aims at describing a methodology of developing a trapper, with an experimental part to obtain results on trapper efficiency and a modeling part to forecast impact of trapper on tritium release rate from waste drum.
En savoir plus

11 En savoir plus

Nanostructured zinc and tin oxides for gas sensors

Nanostructured zinc and tin oxides for gas sensors

ACKNOWLEDGMENTS: PRES, Région Midi-Pyrénées (NELI program -Nez Electronique Intégré-), BPI France and Sigfox SA for « Object’s World » project funding, and V. Collière (TEMSCAN Toulouse ) for SEM and TEM images. Nanostructured zinc and tin oxides for gas sensors J. Jonca, 1 A. Ryzhikov, 1 M. L. Kahn, 1 K. Fajerwerg, 1,2 P. Menini, 2, 3 A. Chapelle, 2, 3 C. H. Shim, 3,4 A. Gaudon, 4 P. Fau 1,2

2 En savoir plus

Nanosized iron and iron–cobalt spinel oxides as catalysts for methanol decomposition

Nanosized iron and iron–cobalt spinel oxides as catalysts for methanol decomposition

particle size effect [74] . The bulk catalysts are built of crystallites of high degree of crystallinity and low content of structural defects. On the contrary, the supported catalysts exhibit low degree of crystallinity, the particles are ultra dispersive and correspondingly with higher degree of structural defects typical of particles with superparamagnetic behavior. In addition, the results of magnetic measurements and Mo¨ssbauer spectra reveal a wide particles size distribution at room temperature. In the course of reduction and catalytic test the support protects the oxide character of the catalysts by pores screening effect and strong interaction between the nanosized particles and the support. The smaller difference between the catalytic activity of all supported samples and especially between both binary oxides compared to the corresponding non-supported ones could be due to different ions distribution in the spinel structure after their deposition on the activated carbon. For the latter materials, the presence of cobalt ions, mainly in tetrahedral position (which as mentioned above are not responsible for the catalytic activity) could be assumed and this supposition is also confirmed by the low value of the inversion degree obtained in this case.
En savoir plus

12 En savoir plus

Show all 921 documents...