Kinetics and Intermediate Phases in Epitaxial Growth of Fe3O4 Films from Deposition and Thermal Reduction

We have studied the growth of Fe3O4 (111) epitaxial films on Al2O3 (001) substrates using a pulsed laser deposition / thermal reduction cycle using an {\alpha}-Fe2O3 target. While direct deposition onto the Al2O3 (001) substrates results in an {\alpha}-Fe2O3 epilayer, deposition on the Fe3O4 (111) surface results in a {\gamma}-Fe2O3 epilayer. The kinetics of the transitions between Fe2O3 and Fe3O4 were studied by measuring the time constants of the transitions. The transition from {\alpha}-Fe2O3 to Fe3O4 via thermal reduction turns out to be very slow, due to the high activation energy. Despite the significant grain boundaries due to the mismatch between the unit cells of the film and the substrate, the Fe3O4 (111) films grown from deposition/thermal reduction show high crystallinity

Effect of PAO-based γ-Fe2O3 and surfactant concentration on viscosity characteristic

This is a preliminary study on the viscosity characteristics of polyalphaolefin (PAO)- based γ-Fe2O3 under zero magnetic fields. By varying the concentration of magnetic nanoparticles (MNPs), PAO-based γ-Fe2O3 with different concentrations were synthesized by co-precipitation method. The effect of this factor on the viscosity characteristic of γ-Fe2O3 (< 30 nm) was investigated on the basic of a series of rheological measurement. The use of oleic acid (OA) as a coating agent and surfactant was also investigated by varying its concentration. The results show the concentration of MNPs and the amount of OA has obvious effect on viscosity characteristics of PAO-based γ-Fe2O3. In the case of comparison between the concentrations of MNPs, higher concentration of MNPs increased the viscosity of the PAO-based γ-Fe2O3 and exhibit nearly Newtonian behavior. The large amount of OA also exhibits the increment on viscosity characteristic of MNPs. The experimental data were compared with the Bingham and Casson model and the results revealed that the rheology of the polyalphaolefin (PAO)-based γ-Fe2O3 fitted the Casson model better

Electronic structure of nanoscale iron oxide particles measured by scanning tunneling and photoelectron spectroscopies

We have investigated the electronic structure of nano-sized iron oxide by scanning tunnelling microscopy (STM) and spectroscopy (STS) as well as by photoelectron spectroscopy. Nano particles were produced by thermal treatment of Ferritin molecules containing a self-assembled core of iron oxide. Depending on the thermal treatment we were able to prepare different phases of iron oxide nanoparticles resembling gamma-Fe2O3, alpha-Fe2O3, and a phase which apparently contains both gamma-Fe2O3 and alpha-Fe2O3. Changes to the electronic structure of these materials were studied under reducing conditions. We show that the surface band gap of the electronic excitation spectrum can differ from that of bulk material and is dominated by surface effects.Comment: REVTeX, 6 pages, 10 figures, submitted to PR

Effects of Fe2O3 addition on the nitridation of silicon powder

The reaction of silicon powder and nitrogen was studied in the range of 1300-1400 C. When an addition of Fe2O3 was more than 0.8wt%, the reaction was linear and compared to samples with no Fe2O3, the reaction velocity increased 5 to 10 times. The reactions were mediated by the process of peeling and cracking in a thin layer of Si2N4 formed on the silicon particles or on the surface of the Fe-Si melts. As the addition of Fe2O3 increased, the reaction activation energy for highly pure samples decreased. Fe2O3 which exceeded the Si3N4 solubility limits was finally converted to d-Fe

α-Fe2O3 nanoparticles/vermiculite clay material: Structural, optical and photocatalytic properties

Photocatalysis is increasingly becoming a center of interest due to its wide use in environmental remediation. Hematite (-Fe2O3) is one promising candidate for photocatalytic applications. Clay materials as vermiculite (Ver) can be used as a carrier to accommodate and stabilize photocatalysts. Two different temperatures (500 degrees C and 700 degrees C) were used for preparation of -Fe2O3 nanoparticles/vermiculite clay materials. The experimental methods used for determination of structural, optical and photocatalytic properties were X-ray fluorescence (ED-XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS), N-2 adsorption method (BET), diffuse reflectance UV-Vis spectroscopy (DRS), photoluminescence spectroscopy (PL) and photocatalytic reduction of CO2, respectively. The data from XRD were confronted with molecular modeling of the material arrangement in the interlayer space of vermiculite structure and the possibility of anchoring the -Fe2O3 nanoparticles to the surface and edge of vermiculite. Correlations between structural, textural, optical and electrical properties and photocatalytic activity have been studied in detail. The -Fe2O3 and -Fe2O3/Ver materials with higher specific surface areas, a smaller crystallite size and structural defects (oxygen vacancies) that a play crucial role in photocatalytic activity, were prepared at a lower calcination temperature of 500 degrees C.Web of Science1211art. no. 188

Ionic and electronic dark decay of holograms in LiNbO3:Fe crystals

The lifetimes of nonfixed holograms in LiNbO3:Fe crystals with doping levels of 0.05, 0.138, and 0.25 wt % Fe2O3 have been measured in the temperature range from 30 to 180 °C. The time constants of the dark decay of holograms stored in crystals with doping levels of 0.05 and 0.25 wt % Fe2O3 obey an Arrhenius-type dependence on absolute temperature T, but yield two activation energies: 1.0 and 0.28 eV, respectively. For these crystals, two different dark decay mechanisms are prevailing, one of which is identified as proton compensation and the other is due to electron tunneling between sites of Fe2 + and Fe3 + . The dark decay of holograms stored in crystals with the doping level of 0.138 wt % Fe2O3 is the result of a combination of both effects

One pot solvothermal synthesis of organic acid coated magnetic iron oxide nanoparticles

Indexación: ScieloABSTRACT In this work we present the synthesis and characterization of iron oxide nanoparticles (IONPs), which were structurally and magnetically characterized. The use of iron salts and an organic acid (l-serine or ascorbic acid) as precursors under solvothermal conditions yielded these coated IONPs. The powder X-ray diffraction pattern of FeO-1 and FeO-2 is consistent with hematite (α-Fe2O3) and hematite-maghemite ((α-Fe2O3/γ-Fe2O3) respectively. The TEM analysis permits to estimate an average size of 10 nm for the FeO-1 sample. The magnetic characterization of the samples through the M(H) plots showed a very low coercivity value for both samples, being 53 Oe for FeO-1 and 10 Oe for FeO-2, indicating the very weak ferromagnetic character of the synthesized iron oxide species. Even though both organic acids under solvothermal conditions permit to obtain coated IONPs in one pot reaction, l-serine produces a more narrow-size distribution

Activity of alumina supported fe catalysts for N2O decomposition: Effects of the iron content and thermal treatment

Indexación: Scopus.The activity of Fe2O3/Al2O3 catalysts prepared by impregnation of Al2O3 with different amounts of Fe and calcination temperatures (650 and 900 °C) in the direct N2O decomposition reaction was studied. High calcination temperature was introduced to study the effect of "aging", which are the conditions prevailing in the process-gas option for N2O abatement. The catalysts were characterized by BET, XRD, UV-DRS, and H2-TPR. The incorporation of Fe promotes the alumina phase transition (g-Al2O3 to a-Al2O3) when the catalysts are calcined at 900 °C, which is accompanied by a decrease in the specifc area. The activity of the catalysts and the specifc surface area depend on Fe loading and calcination temperature. It was found that highly dispersed Fe species are more active than bulk type Fe2O3 particles. We conclude that Fe2O3/Al2O3 catalysts prepared by impregnation method are active in the decomposition of N2O, to be used at low or high reaction temperatures (tail-gas or process-gas treatments, respectively), as part of nitric acid production plant. © 2018 Sociedad Chilena de Quimica. All rights reserved.https://scielo.conicyt.cl/pdf/jcchems/v62n4/0717-9324-jcchems-62-04-3752.pd