Search

The oxidation behavior of 5 wt pct Cr (5Cr) ferritic steel in air at high temperatures has been investigated. A connected Cu-rich layer adjacently forms in inner oxidation layer (IOL) at 500 °C to 600 °C in addition to the formation of a continuous Cr-rich and Si-rich ribbon. Their synergistic effects imped growth of the Fe-rich oxide film towards the outer oxidation layer (OOL) and thus improve the oxidation resistance of 5Cr steel. With increasing oxidation temperature, the Cr, Si, and Cu oxide scales are gradually damaged and spallation of the oxide scale occurs at 1000 °C. Regarding the reaction kinetics, oxidation is controlled by oxygen inward diffusion. A gas-solid model is used to describe the oxidation behavior of 5Cr steel at 500 °C to 900 °C and there is good agreement with the experimental data. In particular, this model can predict the oxidation behavior and the typical results at 750 °C and 850 °C are provided. [ABSTRACT FROM AUTHOR]

Nanocrystalline Fe-Ni-P thin films have been prepared by electrodeposition method for different temperature. The structural, morphological, mechanical and magnetic properties are analyzed by different measurements. The structural and surface morphology of thin film were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD results showed all the electro deposited Fe-Ni-P films exhibits nanocrystalline FCC structure. The SEM pictures of Fe-Ni-P thin films show that the deposits of thin films are crack free, uniform and bright surface. The mechanical properties of Fe-Ni-P thin films have been analyzed by VHT. The electroplated Fe-Ni-P thin films were strongly adherent to the copper substrate. The VHT result of Fe-Ni-P thin films shows that thin film coated at high bath temperature has highest hardness value. Also VSM result shows that thin film coated at high bath temperature has higher magnetization value. This shows that the soft magnetic properties of Fe-Ni-P thin films are greatly enhanced by various temperatures. [ABSTRACT FROM AUTHOR]

Conventional Ceramic Reaction Methodology has been utilized for the preparation of M-type hexagonal ferrites of Sr0.35La0.40Ca0.25Fe11.6Co0.4O19 magnets. X-ray diffraction has been performed for phase determination of the magnetic powders. At calcination temperatures ranging from 1220 to 1330 ∘C, the synchronize compost of the magnetic powders comprised of M-type hexagonal ferrites together with a small amount of impurity phase such as α-Fe2O3 were co-existed. At calcination temperature above 1270 ∘C, single-phase M-type hexaferrites can be obtained. The particles seemed to be in a hexagonal plate-like mould which spread-out homogeneously were examined by field emission scanning electron microscopy. The magnetic edibility of the magnetic powders was intended by permanent magnetic measurement test equipment vibrating sample magnetometer. Magnetic properties, such as specific saturation magnetization, coercivity and remanence were temperature-dependent. However, with the increase of sintering temperature, i.e. above 1270 ∘C, saturation magnetization was increased while the coercivity showed reversed order. [ABSTRACT FROM AUTHOR]

Compared with other dual-phase (DP) steels, initial microstructures of cold-rolled martensite-ferrite have scarcely been investigated, even though they represent a promising industrial alternative to conventional ferrite-pearlite cold-rolled microstructures. In this study, the influence of the heating rate (over the range of 1 to 10 K/s) on the development of microstructures in a microalloyed DP steel is investigated; this includes the tempering of martensite, precipitation of microalloying elements, recrystallization, and austenite formation. This study points out the influence of the degree of ferrite recrystallization prior to the austenite formation, as well as the importance of the cementite distribution. A low heating rate giving a high degree of recrystallization, leads to the formation of coarse austenite grains that are homogenously distributed in the ferrite matrix. However, a high heating rate leading to a low recrystallization degree, results in a banded-like structure with small austenite grains surrounded by large ferrite grains. A combined approach, involving relevant multiscale microstructural characterization and modeling to rationalize the effect of the coupled processes, highlights the role of the cold-worked initial microstructure, here a martensite-ferrite mixture: recrystallization and austenite formation commence in the former martensite islands before extending in the rest of the material. [ABSTRACT FROM AUTHOR]

In this paper, the effect of Al 3+ substitution on the electrical and dielectric properties of Ni 0.25 Cu 0.20 Zn 0.55 Al x Fe 2-x O 4 ferrites with x = 0.0, 0.05. 0.10, 0.15 and 0.20, synthesized by solid state reaction has been reported. Using two probe method, the DC resistivity has been investigated in the temperature range from 30 °C to 300 °C. Activation energy was calculated from the Arrhenius plot. The electrical conduction is explained on the basis of the hopping mechanism. The frequency dependent dielectric properties of these spinel ferrites have been studied at room temperature by measuring AC resistivity, conductivity ( σ ac ), dielectric constant and dielectric loss tangent (tan δ ) in the frequency range between 1 kHz and 120 MHz. The study of dielectric properties showed that the dielectric constant and dielectric loss increased with increasing non-magnetic Al ions. The dependence of dielectric constant with frequency has been explained by Maxwell-Wagner interfacial polarization. Cole-Cole plots show semicircular arc(s) for the samples, and equivalent RC circuits have been proposed to clarify the phenomena involved therein. The analysis of complex impedance spectroscopy has been used to distinguish between the grain and grain boundary contribution to the total resistance. [ABSTRACT FROM AUTHOR]

The microstructure, mechanical properties, and hydrogen permeation behavior of hot rolled enamel steel were investigated. Three coiling temperatures were adopted to gain different sizes of ferrite grain and TiC precipitates. The results show that a large number of interphase precipitates of nano-sized TiC can be obtained at coiling temperatures of 650 and 700 °C, while a few precipitates are found in experimental steel when coiling temperature is 600 °C. The yield strength and ultimate tensile strength decrease with increasing coiling temperature, while elongation increases. The experimental steel has the best resistance to fish-scaling at coiling temperature of 700 °C, due to the large quantities of nano-sized interphase precipitates of TiC. [ABSTRACT FROM AUTHOR]

Demonstrates that an individual particulate form of BaFe[sub12]O[sub19] can be crystallized during heating of a raw material using an inorganic dispersing matrix phase. Change in the crystallization behavior with varying decomposition conditions; Resultant magnetic properties; Disadvantages of glass-crystallization method.

The effects of sintering temperature on microstructure, phase, electrical and magnetic properties of LiZn ferrites prepared by hot pressing methods were examined systematically. All the ferrites were spinel strustures sintered at the temperature above 1050°C. At higher than 1100°C, pores within the grains appeared due to the volatilization of lithium. The DC electrical resistivity ρ increased firstly and decreased dramatically because of the Fe2+formation. The magnetic properties showed that the saturation magnetization (Ms) increased and coercive field (Hc) decreased with the increasing temperature. The hot pressing method is proven an effective way to obtain the densified LiZn ferrites. [ABSTRACT FROM AUTHOR]

Various oxides of Al2O3, ZrO2-Y2O3, and Ta2O5 were coated on ferritic-martensitic steel for application as an environmental barrier layer. Sol-gel based coating was investigated to form the oxides by varying the coating parameters, such as the concentration of the precursors, the temperature of the curing, cycles of repeated runs, and additional heat-treatment. The obtained coatings revealed nano-sized granular structures. The surface morphologies were rough in alumina and zirconia, but appeared smooth in tantalum oxide. In the case of alumina and tantalum oxide, coated layers were mostly amorphous after pyrolysis at 750 °C. The crystalline phases were obtained after an additional heat-treatment at 950 °C. In the case of zirconia, a desirable oxide phase was formed when the samples were cured at 750 °C during the coating process. In addition to the heat-treatment after the coating, the repeated coatings were effective in crystallizing the coated layers and forming proper oxides. [ABSTRACT FROM AUTHOR]

The heating processes in ferrofluids in ac magnetic field depend on chemical composition, dimension, shape, magnetic properties of the nonoparticles, and rheological characteristics of the dispersing medium. By controlling these parameters, a maximum energy can be transferred to the medium. This paper was focused on determining the specific absorption rate (SAR) of a series of nanoparticles (NPs), with ferromagnetic properties at room temperature, dispersed in water to prove their possible use in medical applications. CoxFe3−xO4 (with \(x = 0.2\) –1 in steps of 0.2) magnetic fluids were synthesized by the coprecipitation method and subjected to an ac magnetic field with different amplitudes and distinct frequencies. X-ray difractometry and transmission electron microscopy were used to characterize the phase and microstructure of NPs. Vibrating sample magnetometer measurements denoted a ferrimagnetic behavior of the particles at room temperature and expected superparamegnetic behavior for ferrofluids. The values of SAR obtained using a calorimetric method, at fixed frequency, increased with strength of applied field and Co content being higher at low frequencies. The results are explained in terms of relaxation times, and the experimental data were compared with theoretical predictions. [ABSTRACT FROM AUTHOR]

New experimental data are reported relative to the development of banded structures in Mn-segregated Dual Phase steels during the austenite-to-ferrite transformation stage of their final heat treatment. Two types of ferrite are detected to grow simultaneously, i.e. allotriomorph and acicular ferrite, with distinct consequences on the topology of the final (ferrite + martensite) microstructure: allotriomorph ferrite sharpens the banded structure of ferrite and martensite between Mn-poor and Mn-enriched regions, respectively, whereas acicular ferrite favours more isotropic microstructures. Owing to an original image treatment procedure, the sharpness of banded structure is quantitatively analyzed for different heat treatment conditions. Results confirm those of previous works, but we propose to rather explain them by considering that a change in a heat treatment parameter results in a variation in the respective amounts of both ferrite types. [ABSTRACT FROM AUTHOR]

The effect of heat treatment on mechanical properties and microstructure of high-strength low-alloy ferrite-bainite pipe steels is studied. Specimens are heated in a laboratory furnace up to a temperature in the range 100-850°C. Dependences for the change in mechanical properties on heating temperature and the main features of steel structure are determined. TEM is used to study excess phase precipitation, including Nb and V carbonitrides, during heating. Unfavorable temperature ranges are determined for heating pipe steels with a ferrite-bainite structure. The results obtained may be used in industrial production and during development of new technology for thermomechanical treatment. [ABSTRACT FROM AUTHOR]

Abstract: The influence of different heat treatments on the magnetic and magnetoelastic properties of highly magnetostrictive CoFe2O4 has been investigated. The first order cubic anisotropy coefficient, coercive field, magnetostriction and high strain sensitivity were observed to decrease as the heat treatment temperature increased. The saturation magnetization of the samples on the other hand increased with increase in heat treatment temperature. These changes were not accompanied by any observable changes in crystal structure or composition and are indicative of migration of Co2+ from the octahedral sites (B-sites) to the tetrahedral sites (A-sites) and Fe3+ from the A-sites to the B-sites of the spinel structure. Different distributions of the cations at the two distinct lattice sites can strongly affect the magnetic and magnetoelastic properties of these materials. [Copyright &y& Elsevier]

Abstract: Differences in the microstructure and magnetic properties of highly magnetostrictive cobalt ferrite resulting from the effects of different vacuum sintering temperatures and times have been investigated. A vacuum environment was chosen to allow direct comparison of results with air-sintered samples which are more often reported in the literature. It was found that vacuum sintering resulted in the development of a solid solution second phase with composition Co1− x Fe x O4 (x∼0.33). There was a decrease in magnetostriction as a result of the formation of the second phase. Furthermore, differences in sintering temperatures were found to have a greater effect on the magnetostriction than differences in sintering times. It was found that the first order cubic anisotropy coefficient initially increased with both sintering temperature and time, before peaking and decreasing to its lowest measured value. The lowest anisotropy was therefore achieved with samples sintered at higher temperatures and longer times. [Copyright &y& Elsevier]

In the present work, the transformation characteristics of ductile iron austempered from intercritical austenitization temperature ranges were investigated. For this purpose, an unalloyed ductile cast iron containing 3.50 wt% C, 2.63 wt% Si and 0.318 wt% Mn were intercritically austenitized (partially austenitized) at various temperatures and then rapidly transformed to a salt bath held at the 365 °C for austempering for various times to produce dual matrix structure with different ausferrite volume fractions in ferrite matrix. A microstructure map was created to illustrate the transformation of products quantitatively as a function of austempering time for a particular intercritical and austempering heat treatment temperature and time. It was demonstrated that the total volume fraction of transformed phases was approximately constant for all austempering times after rapidly transforming samples from a particular intercritical temperature to austempering temperature. It was found out that the new ferrite (It is also called epitaxial ferrite) introduced into the intercritically austenitized structure during austempering and its content was dependent on the intercritical austenitizing temperature and austempering time. [ABSTRACT FROM AUTHOR]

Abstract: In this work strontium hexaferrite nano-crystalline powders were prepared by carbon monoxide heat treatment and re-calcination from conventionally synthesized powder. First strontium hexaferrite was obtained by the conventional route with calcination of strontium carbonate and hematite at 1100°C for 1h. Then strontium hexaferrite was isothermally subjected to carbon monoxide dynamic atmosphere at various temperatures and flows for different times. Optimum carbon monoxide heat treatment was achieved at 850°C with 20cm3/min flow for 0.5h. The resultant powder was then calcined at 900 and 1000°C for 1h. The single-phase strontium hexaferrite nano-crystalline powder was finally obtained after calcination at 1000°C. The phase identification of the powders was recorded by an X-ray diffractometer (XRD) with Cu Kα radiation. Morphology and size of the particles were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The magnetic properties were also measured by a vibration sample magnetometer (VSM). The results show a good enhancement in the coercivity by applying this method on the hexaferrite powder. [Copyright &y& Elsevier]

The factors responsible for shortening sublimation dehydration time for inorganic salts vis-à-vis products of organic nature have been examined. It has been found that substantial increase in temperature of the heat supplying surface may occur due to high-temperature process of thermal degradation of the salts, which follows the sublimation dehydration process; the time for drying granulated material diminishes vis-à-vis a monolithic layer; and the time for drying granulated material on a ribbed tray diminishes vis-à-vis the time for drying on a plane surface. Submitted to analysis are the factors increasing the time of sublimation of the materials and products: substantial thermal resistance develops because of loose adherence of the material to the tray (presence of gaps) and phase resistance appears during drying. Based on the obtained calculated and experimental data, an equation has been proposed for determination of the time of sublimation dehydration of prefrozen crystal hydrates of salts. [ABSTRACT FROM AUTHOR]

A 12 T magnetic field has been applied to the annealing process of a 0.81%C-Fe (wt.%). It is found that the magnetic field shifts the eutectoid carbon content from0.77wt.% to 0.83wt.%. The statistical thermodynamic calculations were performed to calculate the eutectoid temperature change by the magnetic field. Calculation shows that the increase of the eutectoid temperature by a 12 T field is 29°C. Synchrotron radiation measurements were performed to measure the pole figures of the samples and were analyzed by MAUD to determine the bulk texture of the ferrite phase in the field-treated and non-field-treated samples. Results show that although there is no specific preferred orientation appearing by applying the magnetic field, slight enhancement of <001> fiber component occurs in both the sample normal direction (ND) and the transverse direction (TD). This effect might be related to the magnetic dipolar interaction between Fe atoms in the transverse field direction. [ABSTRACT FROM AUTHOR]

The effect of intercritical heat treatments on the tensile properties of iron-based P/M steels was investigated. For this purpose, atomized iron powder (Ancorsteel 1000) was admixed with 0.3 wt.% graphite powder. Tensile test specimens were cold pressed at 700 MPa and sintered at 1120 °C for 30 min under pure argon gas atmosphere. After sintering, ∼20% pearlite volume fraction in a ferrite matrix was obtained. To produce coarse ferrite + martensite microstructures, the sintered specimens were intercritically annealed at 724 and 760 °C and quenched in water. To obtain fine ferrite + martensite microstructures, the sintered specimens were first austenitized at 890 °C and water-quenched to produce a fully martensitic structure. These specimens were then intercritically annealed at 724 and 760 °C and re-quenched. After the intercritical annealing at 724 and 760 °C and quenching, martensite volume fractions were ∼ 18% and 43%, respectively, in both the coarse- and fine-grained specimens. Although the intercritically annealed specimens exhibited higher yield and tensile strength than the as-sintered specimens, their elongation values were lower. Specimens with a fine ferrite + martensite microstructure showed high yield and tensile strength and ductility in comparison to specimens with a coarse ferrite + martensite microstructure. The strength values of specimens increased with increasing martensite volume fraction. [ABSTRACT FROM AUTHOR]

Nanocrystalline CuFe2O4 particles are prepared by wet chemical method. The particles of various sizes are obtained by heat treatment in the temperature range 773–1073 K. The room temperature Mössbauer spectrum for all samples shows the presence of both sextet and doublet indicating the presence of superparamagnetic fractions. The isomer shift, quadrupole splitting and hyperfine field values are found to change with particle size. However, these changes in Mössbauer parameters may also be due to the Jahn–Teller effect that essentially arises due to the migration of Cu2+ from tetrahedral sites to octahedral sites resulting in crystal structure change from cubic to tetragonal system. These aspects are studied by using Mössbauer spectroscopy and are correlated to the X-ray diffraction data. [ABSTRACT FROM AUTHOR]

The compiled knowledge in literature regarding the isothermal formation of austenite from different initial microstructures (pure and mixed microstructures), has been used in this work to develop a model for non-isothermal austenite formation in low-carbon steels (C < 0.2 wt%) with a mixed initial microstructure consisting of ferrite and pearlite. Likewise, calculations of relative change in length have been made as a function of temperature, and the differences between theoretical and experimental results have been analysed in 0.1C–0.5Mn low-carbon low-manganese steel. Experimental kinetic transformation, critical temperatures as well as the magnitude of the overall contraction due to austenite formation are in good agreement with calculations. [ABSTRACT FROM AUTHOR]

Presents information on a study which prepared a single phase strontium-lanthanum M-type ferrite fine particles through the chemical coprecipitation and subsequent heat-treatment methods. Experimental method; Result and discussion; Conclusion.

Studies hydrogen production by water splitting with manganese ferrite and calcium oxide. Synthesis of ferrites; Results and discussion on the study conducted.

Abstract: Nanocomposite of hard (BaFe12O19) and soft ferrite (Ni0.8Zn0.2Fe2O4) are prepared by the mixing of the individual ferrite components at appropriate ratio and subsequent heat treatment. Initially the microstructure of the individual phases is controlled by suitable processing. We have observed the exchange spring behavior in the soft–hard ferrite composite for the first time by tailoring the particle size of the individual phases and by suitable thermal treatment of the composite. It is found that the exchange interaction dominates over the dipolar interaction for smaller particle sizes of the soft ferrite. The magnetization of the composite showed hysteresis loop that is characteristic of the exchange spring system. This gives experimental proof for some theoretical modeling as well as paves way for developing magnet with higher (BH)max product based on ferrites. [Copyright &y& Elsevier]