Fe3O4 Layer Research Articles

Corrosion Behavior of Reinforcing Steel with Mill Scale in Concrete

Corrosion of reinforcing steel rebar is a main cause for losing the long-term reliability of concrete structures. When the rebar is corroded, the rust induces cracks and detachment of the cover concrete. On the rebars, the mill scale which is a thick oxide film is formed when the rebar is hot rolled. The role of mill scale on corrosion behavior of rebars in concrete has not been clarified, yet. In this study, the corrosion behavior of rebars with mill scale in concrete was studied using a new accelerated corrosion test we developed. Commercial rebars with 19 mm diameter, which have mill scale of several tens of micrometers in thickness, were used in this study. The corrosion behavior of rebars with and without mill scale in mortar was investigated. To remove the mill scale on the rebar surface, electrolytic polishing was carried out. The rebars with or without mill scale were embedded in mortar with 5.5 mm cover thickness and the sample was cured for 28 days. In order to prompt breakdown of passive film on the rebars, 2.06 M NaCl solution was mixed to the mortar. Using these samples, Hyperbaric-oxygen accelerated corrosion test (HOACT) was carried out [1]. In the HOACT, pressurized oxygen gas is supplied to the sample, and the oxygen reduction reaction on the steel surface is enhanced, which leads to the corrosion acceleration of the steel. In this study, the mortar-covered rebar samples were located in a high pressure gas chamber, and pressurized oxygen gas of 0.6 MPa was supplied. The periods of HOACT were 14, 28 and 56 days. After finishing the HOACT, the samples were embedded in resin, and then the cross section of the sample was observed using an optical microscope. The rust composition was analyzed using Raman spectroscopy measurement. The corrosion of the rebar with mill scale was more significant than that without mill scale. In the case of the sample with mill scale after 14-day HOACT, a rust layer was formed between the steel surface and mill scale, whereas no obvious corrosion was observed on the rebar without mill scale. To investigate the effect of the mill scale on the corrosion resistance of the rebar, anodic polarization measurements of the rebars with and without mill scale were carried out in a saturated Ca(OH)2 solution with Cl-. The pitting potential of the rebar with mill scale was more noble than that of the sample without mill scale. However, when the mill scale was scratched the pitting potential was significantly shifted to the less noble direction and it was below that of the rebar without mill scale. These results show that the mill scale improves the corrosion resistance of the rebar in mortar, whereas the corrosion resistance of the rebar becomes even worth than that of the rebar without mill scale when the mill scale contains defects. After 56-day HOACT of the sample with mill scale, two rust layers were observed above and beneath the mill scale. Raman spectroscopy revealed that the rust layer above the mill scale was mainly composed of a- and g-FeOOH, and the layer just beneath the mill scale was mainly composed of Fe3O4. The rust formed on the sample with mill scale during 14-day HOACT was monolayer just above the steel surface and it was composed only of Fe3O4. It is speculated that the Fe3O4 layer grows under the mill scale at the early stage of corrosion of a rebar. [1] K. Doi, S. Hiromoto, H. Katayama and E. Akiyama, Journal of the Electrochemical Society, 165(9), C582-C589 (2018).

Atomic layer deposition of thin films as model electrodes: A case study of the synergistic effect in Fe2O3-SnO2

Developing higher capacity electrode materials is a key challenge in battery advancement. Metal oxides undergoing conversion and/or alloying reactions offer high capacities, but suffer from volumetric changes and poor conductivities. However, combining several of these oxides can induce a synergistic effect, enhancing electrode characteristics. Using atomic layer deposition (ALD), carefully controlled model thin-film electrodes comprised of SnO2 and Fe2O3, and mixtures thereof are deposited to investigate length scales at which intermixing of the oxides is required to maximize this effect. ALD enables the synthesis of both intermixed structures and oxides where Fe, Sn, and O are mixed at the atomic scale and nanolaminated structures where Fe2O3 layer and SnO2 layers form a structure with well-defined interfaces. These model systems reduce the complexity of electrodes by eliminating the need for binders and additives and ensuring one-dimensional charge carrier diffusion. Using ALD enables us to study the influence of interfaces on electrode characteristics. It was found that intermixing of Fe2O3 and SnO2 at the atomic scale kinetically suppresses the alloying of Sn. In the nanolaminated superstructure, however, Sn alloying does take place, causing the well-defined interfaces to break down due to the volume changes brought about by alloying. As a consequence, the electrode capacity is rapidly fades, and thus, this structure type should be avoided. Here, the authors demonstrate that ALD is a unique tool with great potential for unraveling complex mechanisms in battery materials.

Low Dimensional Magnetic Lattice and Room Temperature Magneto(di)electric Effect in Polyanion Ruddlesden-Popper Iron Oxides.

We have shown a new design strategy which exploits different oxyanions in a Ruddlesden-Popper (RP)-type phase to modulate the local crystal structure and magnetic lattice. Material (Sr4Fe2(SO4)0.5O6.5) with the larger voluminous oxyanion (SO4, S-O distance = 1.49 Å) as separating blocks between magnetic FeO layers shows a two-dimensional magnetic lattice. A three-dimensional magnetic lattice and spin reorientation transition is observed for the Sr4Fe2(CO3)O6, having CO3 (C-O distance = 1.25 Å), a smaller oxyanion, as a separating layer. Using mixed oxyanions (SO4 and CO3) in the central perovskite block of the RP3 phase, we have demonstrated a facile strategy to modulate the local crystal structure. The modulated displacement of the magnetic cations, which can break the local centrosymmetry, is suggested to originate the magnetodielectric effect near the magnetic ordering temperatures (higher than room temperature). Further, all CO3 containing samples show magnetodielectric coupling below room temperature due to the spin reorientation transition. The room temperature magnetodielectric effect coupled to the targeted local modulation of the crystal structure by oxyanions (in the absence of second-order Jahn-Teller active "distortion centers") opens a new door to the design of new multifunctional materials with the possibility for the room temperature application.

Curing epoxy with electrochemically synthesized NixFe3-xO4 magnetic nanoparticles

Fe3O4 magnetic nanoparticles (MNPs) were synthesized via cathodic electrodeposition in the form of undoped and Ni2+-doped MNPs, and their curing potential towards epoxy was discussed. Partial substitution of Fe2+ sites by Ni2+ cations in the general formula of NiXFe3-XO4 was confirmed by – X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), dispersive X-ray spectrometry (EDS), and vibrating sample magnetometry (VSM). Low-filled epoxy/Fe3O4 and epoxy/Ni2+-Fe3O4 nanocomposites containing 0.1 wt.% MNPs based on 100 parts by weight of epoxy resin were prepared and underwent nonisothermal differential calorimetry (DSC) at different heating rates (5, 10, 15, and 20 °C/min). The curability of the well-characterized nanocomposites of epoxy/Ni0.11Fe2.89O4 was qualitatively studied by the use of Cure Index. Overall, structural changes in Fe3O4 atomic structure resulting from the replacement of Fe2+ cations with Ni2+ had effect on epoxy curing reactions, as reflected in a shift in curing state from Poor for epoxy/Fe3O4 to Good for epoxy/Ni2+-doped Fe3O4 systems. This phenomenon was explained on account of the fact that Ni2+ dopants with their laminar structure tend to locate in the top layer of Fe3O4, which dramatically increases the activity of Fe3O4 to take electron pair of epoxy to open epoxy ring.

Interfacial reconstruction, exchange bias and photocurrent effect in epitaxial Fe3O4/Co3O4 spinel heterostructure

Fully spinel epitaxial Fe3O4/Co3O4 heterostructures were fabricated on the MgAl2O4 substrates by reactive magnetron sputtering, and the interfacial structure, magnetic and optical-electric properties were investigated. An interfacial CoxFe3-xO4 layer with a thickness of ~7 nm is formed between the Fe3O4 and Co3O4 layers through the interdiffusion. The interfacial CoxFe3-xO4 enhances the coercivity of the Fe3O4/Co3O4 heterostructures. The interfacial coupling between the ferromagnetic CoxFe3-xO4 and the antiferromagnetic Co3O4 also induces large exchange bias due to pinning effect. In addition, based on the strong optical absorption of the Co3O4 layer, the enhanced current (~79%) is achieved in the Fe3O4/Co3O4 heterostructures under irradiation of the 405-nm laser. Our work helps to understand the interfacial diffusion of the heterostructures, and reveals that the Fe3O4/Co3O4 heterostructures can be used in optical, electrical and magnetic multifunctional devices.

Improving the SERS signals of biomolecules using a stacked biochip containing Fe2O3/Au nanoparticles and a DC magnetic field

This study proposes a magnetic biochip that uses surface-enhanced Raman scattering (SERS) for antigen detection. The biochip was a sandwich structure containing alternating layers of gold and magnetic Fe2O3 nanoparticles. Both single (Au/Fe2O3/Au) and multilayer (Au/Fe2O3/Au/Fe2O3/Au) chips containing Fe2O3 nanoparticles were fabricated to detect bovine serum albumin (BSA). The single-layer chip detected the BSA antigen at a signal-to-noise ratio (SNR) of 5.0. Peaks detected between 1000 and 1500 cm−1 corresponded to various carbon chains. With more Fe2O3 layers, bond resonance was enhanced via the Hall effect. The distribution of electromagnetic field enhancement was determined via SERS. The signal from the single-layer chip containing Au nanoparticles was measured in an external magnetic field. Maximum signal strength was recorded in a field strength of 12.5 gauss. We observed peaks due to other carbon–hydrogen molecules in a 62.5-gauss field. The magnetic field could improve the resolution and selectivity of sample observations.

Room temperature electric field control of magnetic properties for the α-Fe2O3/Fe3O4 composite structure

Abstract The raw nano α-Fe2O3 powders consisting of nanorods with 50–100 nm in length and 8–14 nm in width exhibit superparamagnetism. The vacuum annealing of the raw nano α-Fe2O3 at 400 °C for 3 h leads to ferromagnetic-like behaviors at room temperature (RT), due to the appearance of ferrimagnetic Fe3O4. The α-Fe2O3/Fe3O4 composite structure has an antiferromagnetic α-Fe2O3 layer and a ferrimagnetic Fe3O4 layer contains a certain amount of Fe2+ and oxygen vacancies. In addition, nano α-Fe2O3 annealed in H2 at 300 °C for 3 h completely become Fe3O4. Some magnetic properties of the α-Fe2O3/Fe3O4, such as magnetization, magnetic remanence (Mr), coercivity (Hc) and exchange bias (EB), can be modulated almost reversibly and non-volatilely by applied external RT electric field without loop current. However, for both the raw nano α-Fe2O3 and the Fe3O4, these magnetic properties cannot be modulated by applied external RT electric field. The electric field control of magnetic properties for the α-Fe2O3/Fe3O4 should be due to the mechanism of phase transition induced by migration and redistribution of oxygen vacancies within the interface of α-Fe2O3/Fe3O4.

Negative differential resistance and magnetotransport in Fe3O4/SiO2/Si heterostructures

The electronic transport and magnetotransport properties of Fe3O4/SiO2/Si heterostructures were investigated with a current source. Negative differential resistance is observed in Fe3O4/SiO2/p-Si heterostructures. The measurement circuit with four electrodes that I+ (I−) and V+ (V−) came into contact with the Fe3O4 (Si) layer introduces an in-plane transport into the heterostructures. By decreasing the temperature, the in-plane conductive channel switches from Fe3O4 to p-Si. However, the in-plane current is still carried by Fe3O4 in Fe3O4/SiO2/n-Si heterostructures. The formation of an accumulation layer in p-Si facilitates conductive channel switching (CCS), while the depletion layer in n-Si hampers the CCS. At 150 K, a magnetic-field-independent magnetoresistance (MR) in Fe3O4/SiO2/p-Si heterostructures manifests the conductive channel in the space charge region of p-Si. A positive MR generated from the increased electronic scattering in a trapezoidal space charge region reshaped by the magnetic field has been detected.

Corrosion and Carburization Behavior of Heat-Resistant Steels in a High-Temperature Supercritical Carbon Dioxide Environment

The corrosion behavior of heat-resistant steels, including T91, VM12, Super 304H, and Sanicro 25, in high-temperature supercritical carbon dioxide at 650 °C and 15 MPa for 1000 h was investigated. X-ray diffraction, Raman spectroscopy, and glow-discharge optical emission spectrometry were employed to characterize the corrosion products. The results showed that the weight gain of the investigated steels is in the order of T91 > VM12 > Super 304H > Sanicro 25. Compared with the dual layers of Fe3O4 and FexCr3−xO4 on T91 and VM12, the chromia-rich oxide scales on Super 304H and Sanicro 25 enhanced their corrosion resistance. Internal carburization zones were found underneath the oxide scales, indicating the presence of oxidation and carburization reactions in the supercritical carbon dioxide. Moreover, the total carbon uptake into the T91 and VM12 steels approximately followed a parabolic law with experimental time but followed a linear law for the austenitic heat-resistant steel Sanicro 25. A corrosion mechanism that couples oxidation and carburization is summarized and quantified for oxidation and carburization to determine the dominant reaction.

Synthesis and properties of a novel Fe<sub>3</sub>O<sub>4</sub>@MoO<sub>3</sub>@GdF<sub>3</sub>:Eu<sup>3+</sup> magnetic-luminescent bi-model imaging materials

The probe plays a key role in the process of the tumor diagnosis and image guided accuracy surgery, but its single-function, weaker luminescent intensity and high cost limitits application. Therefore, development of new type high-performance and multi-functional imaging materials has become an important research topic in the field of chemistry, materials science, life science and medicine. In recent years, researchers have found that magnetic-luminescent bi-functional nanoparticles can provide high-resolution, high-contrast images for precision medicine and are crucial for imaging applications. Among them, the design and synthesis of Fe3O4@REL (rare earth luminescence) magnetic-luminescent bi-functional nanoparticles have become the focus of current research. In this work, we demonstrated the nonmetallic plasmon induced enhancement of luminescence in a core-shell structured material, consisting of Fe3O4 as the core, GdF3: Eu3+ as the luminescence layer and MoO3 as the plasmonic layer. The novel Fe3O4@MoO3@GdF3:Eu3+ nanoparticles of MoO3 intermediate with local surface plasmon resonance (LSPR) effect were synthesized by solvothermal and precipitation method. And their structures, compositions and properties were analyzed. Enhancement mechanism of luminescence property and the interaction factors between the oxide layer and luminescence shell had been illuminated. The results of X-ray diffraction (XRD) analysis showed that the nanoparticles are composed of Fe3O4, single monoclinic MoO3 and orthorhombic GdF3:Eu3+. Transmission electron microscope (TEM) images showed that the obvious nanoparticles and MoO3 and GdF3:Eu3+ are deposited on the surface of Fe3O4 layer by layer. It showed that the shielding effect of homogeneous coating MoO3 spacer and the MoO3 with LSPR plays a role in enhancing the luminescence properties of the shell GdF3:Eu3+. The emission spectra showed that the strongest emission (593 nm) is due to the 5D0→7F1 forced electric dipole transition, and the other emission bands are observed at 556, 616 and 692 nm for 5D0 →7Fn, 5D0→7F2 and 5D0→7F4, respectively. The magnetic measurement results showed that the Fe3O4@MoO3@GdF3:Eu3+ nanoparticles possess excellent magnetic responsivity (25.9 emu/g) and redispersibility. MTT assays showed that the nanoparticles almost have no cytotoxicity or side effects in living cells. The magnetic resonance imaging of the sample gradually enhanced with the increase of the concentration, indicating that the effect of magnetic resonance imaging was corresponding to the concentration. The T 2 magnetic resonance imaging relaxation rate of the material was 0.9813 mg−1 m−1 s−1. In summary, the core-shell structured Fe3O4@MoO3@GdF3:Eu3+ nanoparticles have been prepared by a facile method. The nanoparticles have high emission intensity and magnetisation saturation value. Compared with Fe3O4@GdF3:Eu3+, luminescence intensity of Fe3O4@MoO3@GdF3:Eu3+ nanoparticles increased significantly. Therefore, the as-prepared core-shell structured bifunctional nanoparticles are feasibly applicable to simultaneous cell imaging and target drug delivery. This work can solve the property problem of the magnetic-luminescent bimodal imaging material and promote this kind of composite material applications in imaging and therapy of tumor, and optical confocal microscopy technology.

Preparation and In Vitro Cellular Uptake Assessment of Multifunctional Rubik-Like Magnetic Nano-Assemblies.

Through self-assembly of nanoparticles into high-order and stable structures of cubic clusters, high drug-loading rubik-like magnetic nano-assemblies (MNAs), possessing folic acid targeting and strong magnetism-enhanced cellular uptake capabilities, were built. In this study, the core of the cubic drug assemblies consisted of four monodisperse superparamagnetic iron oxide nanoparticles coated with layers of oleic acid (Fe₃O₄@OA), simultaneously encapsulating fluorescein, and Paclitaxol (Flu-MNAs and PTX-MNAs) for imaging and therapeutic applications. To enable preferential tumor cellular uptake by the nanocarriers, the outermost layer of Fe₃O₄ was functionalized with the new dual-oleic acid-polyethylene glycol-folic acid polymer (FA-PEG-Lys-OA₂) as a "shell." The drug carriers exhibited excellent stability and biocompatibility, and showed high drug loading and excellent magnetic response In Vitro. Furthermore, preliminary evaluations of the drug carriers with Hela cells showed effective cellular targeting capability. In addition, the cubic assemblies enhanced anticancer efficiency for Hela cells compared to bare drugs. Especially, the applied external magnetic field further improved the uptake of the vectors, and thereby enhanced the inhibitory effect. In brief, all these results suggested that cubic assemblies could serve as potential strategies for targeted anticancer therapies.

Dry and lubricated friction behaviour of thermal spray low carbon steel coatings: Effect of oxidational wear

The development of thermal spray steel coatings for Al-Si engine blocks with wear resistant cylinder bores constitutes an important aspect of automotive lightweighting strategy. In this work tribological behaviour of low carbon steel cylinder bore coatings produced by a plasma transferred wire arc (PTWA) method were studied using samples sliding against CrN coated top compression ring samples. The focus of the work was to study the role of oxidational wear on the friction behaviour of spray coatings consisting of α-Fe splats delineated by thin FeO layers. In-situ Raman spectroscopy was employed to observe the oxide transformations that occurred during dry and lubricated sliding tests conducted using a reciprocating tribometer. Lubricated sliding tests were performed within a speed range of 0.02–0.92 m/s covering the boundary and mixed lubrication conditions using a Polyol ester, POE, base oil with and without zinc dialkyldithiophosphate (ZDDP) addition. The use of ZDDP containing POE led to the generation of an amorphous carbon tribolayer incorporating ZnS and FePO4 nano-crystals that inhibited sliding-induced Fe2O3 debris formation, and consequently resulted in a reduced wear rate, but the steady-state coefficient of friction (COF) was higher during the boundary lubricated sliding. According to the Stribeck curves generated, the prevention of oxidational wear by the formation of oil residue layer delayed the transition from the boundary lubrication to the mixed lubrication regime.

Corrosion behavior of Fe-Ni alloys in molten KF-AlF3-Al2O3 salts at 700 °C

The corrosion behavior of Fe-Ni alloys in molten 45KF-50AlF3-5Al2O3 (wt.%) at 700 °C was characterized in this study. After oxygen evolution, all of the Fe-Ni alloys formed a passivation film consisting of an outer Fe2O3 layer, an intermediate Fe3O4 layer, and an inner FeO layer. Because of the outward diffusions of nickel ions, a NiO layer formed in the passivation film when the 43Fe-57Ni alloy was passivated by O2. A solid-state reaction between Fe2O3 and NiO led to the formation of NiFe2O4 in the passivation film, which greatly promoted its corrosion resistance to the molten fluoride salts.

Oxidation behaviour of thin Ni/Al2O3 nanocomposite coatings electrodeposited on steel substrate

This paper presents investigations of the oxidation behaviour of nanocomposite Ni/Al2O3 coatings electrodeposited on steel substrates. The high-temperature processes of the coating oxidation were studied using the thermo-gravimetric analysis, scanning electron microscopy and XRD phase analysis. Simultaneous DSC-TGA oxidation experiments were conducted with continuous heating within the temperature range 200 °C–1200 °C and isothermally at 750 °C and 900 °C in oxygen flux. A proposed oxidation mechanism of Ni matrix nanocomposite coatings that includes diffusion of the substrate element was developed. The oxidation of the Ni/Al2O3 coating occurred via complex routes such as the outward diffusion of Ni and Fe ions and the inward diffusion of oxygen ions. The iron atoms diffused outward from the steel substrate through the Ni/Al2O3 coating to the surface and formed iron and nickel oxides layers. This thermally grown scale on the Ni/Al2O3 coating deposited on the steel substrate consisted of a Fe2O3 layer at the surface, a (Fe,Ni)3O4 spinel sublayer, and an inner NiO layer. Temperature-dependent isothermal kinetics at the steady-state stage of the oxidation process could be described by the linear growth law at 750 °C, while at 900 °C the quasi-linear growth rate is slightly decreased by the quadratic function of time.

Composition control and introduction of an Fe2O3 seed layer in metalorganic chemical vapor deposition of epitaxial BiFeO3 thin films

We investigated the compositional self-regulation and seeding effects of an Fe2O3 layer during the metalorganic chemical vapor deposition of epitaxial BiFeO3 thin films. The growth of the BiFeO3 films was explained in terms of the prior deposition of Fe2O3 and the subsequent incorporation of Bi2O3 into Fe2O3. The self-regulation of film composition was achieved by supplying excess Bi at high growth temperature. The introduction of an Fe2O3 seed layer as thin as 5 nm promoted homogeneous thin film growth and consequently reduced the leakage and its fluctuation as well as the compositional fluctuation. The seed layer also served to control the interfacial composition between BiFeO3 and SrRuO3.

Estudio comparativo de la nitrocarburación de los aceros AISI 4340 y AISI 347 mediante el proceso Tenifer-QPQ®

Este trabajo estudia las diferencias microestructurales y tribológicas de las capas formadas durante la nitrocarburación ferrítica del acero aleado AISI 4340 y la nitrocarburación austenítica del acero inoxidable estabilizado AISI 347. Las muestras se sometieron a distintos tiempos de inmersión en un baño de nitrocarburación (60, 75, 90, 105 y 120 min) a 580 ºC. Posteriormente se sometieron a un proceso de oxidación a 480 ºC para formar una capa de Fe3O4. Los estudios de la microestructura de la capa nitrocarburada se realizaron por microscopía electrónica de barrido (SEM), espectroscopía de dispersión de energías (EDS) y difracción de rayos X (XRD). Se estudió el desgaste y el coeficiente de fricción de las muestras nitrocarburadas y las muestras no tratadas mediante el ensayo pink-on disk. Los resultados muestran tres zonas bien diferenciadas en el acero AISI 4340: una capa de óxidos externa, una capa blanca o de combinación y zona de difusión. Sin embargo, no se detectó la presencia de la capa de combinación en el acero AISI 347. En ambos aceros, el coeficiente específico de desgaste (k) de las muestras nitrocarburadas fue aproximadamente treinta veces menor que el de las muestras de referencia.

Core-shell Mn3O4 nanorods with porous Fe2O3 layer supported on graphene conductive nanosheets for high-performance lithium storage application

In this study, a core-shell nanostructure Fe2O3 coated grass-like Mn3O4 supported on graphene has been designed and fabricated via a facile and convenient hydrothermal method and thermal treatment routes. The Fe2O3 coated Mn3O4 nanorods with diameter of 35–40 nm are convolved by flexible graphene, which form a three-dimensional conductive network. As an anode for lithium-ion batteries, the as-prepared composite delivers an initial discharge/charge capacity of 1939.2/1393.5 mAh g−1 with a promising coulombic efficiency of 71.9% and a reversible specific capacity of 795.4 mA g−1 after 400 cycles at a high current density, which exhibits an upward trend in the capacity after long-term cycling as well. Both of the cross-linked structure and the synergistic effect are contributed to the enhance lithium-storage performance and dynamic characteristic, which reveals that the electrode holds a great potential as an anode material for rechargeable Li-ion batteries.

Microstructural, chemical and electrical characteristics of Au/magnetite (Fe3O4)/n-GaN MIS junction with a magnetite interlayer

Magnetite (Fe3O4) layers were prepared on n-type GaN surface by the e-beam method and its microstructural and compositional characteristics were evaluated by XRD, XPS and TEM techniques. The XRD, XPS and TEM evaluations confirmed the formation of the Fe3O4 layer on the n-GaN surface. Then, the Au/Fe3O4/n-GaN metal/interlayer/semiconductor (MIS) junction was fabricated and its electrical properties investigated with the I-V and C-V approaches. The MIS junction showed a good rectification nature with a high barrier height (0.83 eV) compared to the SE (0.71 eV). This implies that the barrier height was markedly affected by the Fe3O4 layer. Further, the barrier height was extracted by means of Cheung's, Norde and ψS-V plot and it was found that the values are nearly matched with one another, indicating that the methods used were consistent and valid. The frequency-dependent properties of the MIS and SE junctions have also been discussed. The interface state density (NSS) of the MIS junction was found to be lower than the SE, indicating that the Fe3O4 layer plays a vital role in the decreased NSS. Based on the analysis, it can be concluded that the Fe3O4 layer is an apt material for the fabrication of new electronic device applications.

Exchange Bias Enhancement and Magnetic Proximity Effect in FeVO4-Fe3O4 Nanoparticles

We study the behavior of the exchange bias (EB) and the blocking temperature in an antiferromagnetic FeVO4–ferrimagnetic Fe3O4 nanocomposite system upon annealing in Ar atmosphere. Surprisingly, the blocking temperature of post-annealed samples increased to ∼ 50 K, more than two-fold compared the Neel temperature (TN = 22 K) of individual FeVO4 nanoparticles. This significant enhancement of the blocking temperature was accompanied by the corresponding increase of EB, from ∼ 50 Oe in as-prepared samples to ∼ 110 Oe in post-annealed samples. The temperature dependence of EB can be described by two approximately linear regions with different slopes, with an inflection point at T ∼ 21 K coinciding with the Neel temperature of FeVO4 nanoparticles. The region above the inflection point with non-zero EB is characterized by a weaker temperature dependence and is expanded well beyond TN. The x-ray photoemission spectroscopy measurements indicate that the surface of post-annealed Fe3O4 particles becomes oxygen deficient, which leads to a modification of the electronic, magnetic and morphological properties of the FeVO4/Fe3O4 interface. We associate this unusual behavior with a magnetic proximity effect, in which the ordering temperature of the antiferromagnetic FeVO4 nanoparticles and the corresponding exchange bias are strongly affected by the adjacent ferrimagnetic Fe3O4 layer.

Dissolution behaviour of limestone in converter slag: evolution of microstructure and reaction interface

ABSTRACTThe dissolution behaviour of limestone in converter slag at 1300–1400°C was studied, and the effects of the slag temperature and basicity were examined. The results showed that the increment of slag temperature was favourable to the formation of cracks and macropores in the generated lime, and the dissolution of the lime into liquid slag was promoted by the slag penetrating through these cracks and macropores. While the slag basicity increased from 0.5 to 1.0, the 2CaO·SiO2 phase gradually formed around the lime and became discontinuous due to the effusion of CO2 formed by limestone decomposition. Moreover, the thickness of the CaO–FeO layer sharply increased during the coexisting period of the limestone decomposition and the lime dissolution. After the complete decomposition of the limestone, a continuous 2CaO·SiO2 layer formed at the lime/slag interface and the growth rate of the CaO–FeO layer obviously decreased, which hindered the lime dissolution.