Spinel Particles Research Articles

Chemical Reaction of Glazed Refractory with Al-deoxidized Molten Steel

A high alumina refractory, glazed by typical ladle slag of CaO–MgO–Al2O3–SiO2 was investigated to understand the influence of the glazed refractory on the generation of non-metallic inclusions in Al-deoxidized molten steel at 1600°C. The variations of microstructure and chemistry of the glazed refractory with reaction time were studied. Thermodynamic analysis was simultaneously carried out to understand the complex chemical reactions. During the reaction between the glazed refractory and molten steel, two chemical reactions were observed: between glaze and molten steel, and between glaze and original refractory. By the chemical reactions, SiO2 in the glaze was reduced to [Si] by [Al] in molten steel. The glaze layer also gradually changed from the liquid CaO–MgO–Al2O3–SiO2 phase with small amount of embedded spinel particles to the liquid CaO–MgO–Al2O3 phase with embedded spinel and CaAl4O7 particles. Severe erosion was observed in the porous spinel area of a refractory. Spinel inclusions were found as major inclusions originated from the glazed refractory. The erosion mechanism of the glazed refractory was proposed in the present study.

Growth kinetics and microstructure characterization of oxide film formed on La-implanted Co-Cr alloy

The isothermal and cyclic oxidizing kinetics of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1000℃ in air by thermal-gravimetric analysis (TGA). Scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) were used to examine the morphology and structure of the oxide film after oxidation. Secondary ion mass spectrum (SIMS) method was used to examine the binding energy change of chromium caused by La-doping and its influence on formation of Cr2O3 film. Laser Raman spectrum was used to examine the stress changes within oxide films. It was found that lanthanum implantation remarkably reduces the isothermal oxidizing rate of Co-40Cr and improves the anti-cracking and anti-spalling properties of Cr2O3 oxide film. The reasons for the improvement were mainly that the implanted lanthanum reduces the grain size and internal stress of Cr2O3 oxide and increases the high temperature plasticity of oxide film. Lanthanum mainly exists in the outer surface of Cr2O3 oxide film in the forms of fine La2O3 and LaCrO3 spinel particles.

Thermal activation effect on catalytic systems MnO x /Al2O3 for deep oxidation of hydrocarbons

The effect of thermal activation, sharp increase in the catalytic activity of the system MnOx-Al2O3 in reactions of deep oxidation of CO and hydrocarbons after calcination of the catalyst at 900–1000°C was discovered and investigated. With the use of X-ray phase analysis, X-ray electron spectroscopy, EXAFS, IR spectroscopy, electronic spectroscopy of diffuse reflections, electron microscopy etc. it was established that the effect of thermal activation is related to reversible phase transitions in the system at heating and cooling. On cooling from 1100°C to 650°C disperse particles of cubic spinel of composition Mn2.1 − x · Al0.9 + xO4 are conserved on the corundum surface. On further cooling the spinel decomposes and finally the nanocristalline species of β-Mn3O*4 containing up to 15 at% of Al3+ form and govern the activity.

Powder and film of nickel and iron-layered double hydroxide: Elaboration in polyol medium and characterization

Two main reactions occur in polyol media: reduction and hydrolysis. In the case of systems with two easily reducible elements, Ni and Fe for instance, previous works have shown that bimetallic particles or the oxide spinel particles can be obtained. This paper shows that polyols can also be used to elaborate layered double hydroxides (LDH)–Ni–Fe. In this case, the hydrolysis ratio must be adjusted to avoid both reduction and oxolation reactions in favor of hydroxylation. The compound can be obtained either in powder or in gel forms. The gel enables elaboration of film by spin-coating process. The compound is poor-crystallized and exhibits a turbostractic character. Its interlamellar distance (12.89 Å) is slightly higher than that of a similar compound elaborated in aqueous solution via the titration method (12.02 Å). 57Fe Mössbauer spectrometry allows concluding the presence of HS Fe 3+ cations, which occupy two different octahedral sites. XRD and Mössbauer studies reveal interesting preferential orientation features of the film with an anisotropy of the crystalline grains having their c-axis perpendicular to the film.

XRD studies on the nanosized copper ferrite powders synthesized by sonochemical method

Abstract Nanosized copper ferrite spinel particles have been prepared by a precursor approach with the aid of ultrasound radiation. Influence of various preparation parameters on the formation of copper ferrite was studied. The preparation parameters included concentrations of precipitation agents and copper salt, sonochemical reaction time, calcination temperature and time. The reactions of reaction for the formation of CuFe2O4 were explored by analyzing X-ray diffraction data obtained under different processing conditions.

Phthalic acid assisted nano-sized spinel LiMn 2O 4 and LiCr xMn 2− xO 4 ( x = 0.00–0.40) via sol–gel synthesis and its electrochemical behaviour for use in Li-ion-batteries

Nano-sized particles of spinel LiMn 2O 4 and LiCr x Mn 2− x O 4 ( x = Cr; 0.00–0.40) have been synthesized using phthalic acid as chelating agent for the first time by sol–gel method. When compared to solid-state synthesis method, the sol–gel route reduces heating time of synthesize and to obtain particles of uniform surface morphology. The synthesized samples were characterized through thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images of the parent compounds show nanospherical grains of LiMn 2O 4 when compared to chromium-doped ones. XRD patterns of LiMn 2O 4 ascertain amorphous nature and for high calcined LiCr x Mn 2− x O 4 single phase highly crystalline patterns were obtained. TEM images of the parent and chromium-doped spinel particles depict individual grain morphology with well-separated grain boundaries. LiCr 0.10Mn 1.90O 4 excels in discharge and cycling behaviour and offer higher columbic efficiency, when compared to un-doped LiMn 2O 4. Cyclic voltammograms of LiMn 2O 4 and LiCr x Mn 2− x O 4 exhibit oxidation and reduction peaks corresponding to Mn 3+/Mn 4+ and Cr 3+/Cr 4+.

A new composite material Li4Ti5O12–SnO2 for lithium-ion batteries

A new Li4Ti5O12–SnO2 composite anode material for lithium-ion batteries has been prepared by loading SnO2 on Li4Ti5O12 to obtain composite material with improved electrochemical performance relative to Li4Ti5O12 and SnO2. The composite material was characterized by X-ray diffraction and scanning electron microscopy. The results indicated that SnO2 particles have encapsulated on the surface of the Li4Ti5O12 uniformly and tightly. Electrochemical results indicated that the Li4Ti5O12–SnO2 composite material increases the reversible capacity of Li4Ti5O12 and has good cycling reliability. At a current rate of 0.5 mA/cm2, the material delivered a discharge capacity of 236 mAh/g after 16 cycles. It suggests the existence of synergistic interaction between Li4Ti5O12 and SnO2 and that the capacity of the composite is not a simple weighted sum of the capacities of the individual components. In the composite material, SnO2 can act as a bridge between the spinel particles to reduce the interparticle resistance and as a good material for the Li intercalation/deintercalation. Thus, electrochemical performance of the Li4Ti5O12 spinel can be improved by the surface modification with SnO2, and the stability of Li4Ti5O12 also serves to buffer the internal stress caused by the volume changes in lithium insertion and extraction reactions.

Synthesis of nickel zinc ferrite nanoparticle/organic hybrid from metalorganics

(Ni,Zn)Fe2O4 particle/organic hybrid was synthesized in situ from metalorganics below 100 °C. A mixture of nickel (II) acetylacetonate (NA), zinc acetylacetonate (ZA), and iron (III) 3-allylacetylacetonate (IAA) was hydrolyzed and polymerized yielding a spinel oxide particle/organic hybrid. X-ray diffraction analysis revealed that the crystallinity of spinel particles was dependent upon the hydrolysis conditions of NA-ZA-IAA. Nanocrystalline nickel zinc ferrite particles below 5 nm were uniformly dispersed in the organic matrix. The magnetization of hybrid increased with an increasing amount of water for hydrolysis. Nano-sized nickel zinc ferrite particle/organic hybrid showed a magnetization-applied field (BH) curve with no remanence above 40 K. The magnetization versus H/T curves from 40 to 100 K were superimposed on the same curve and satisfied the Langevin equation. The remanent magnetization and coercive field of the hybrid were 7.2 emu/g and 150 Oe, respectively, at 4.2 K. The absorption edge of the hybrid was blue-shifted compared with that of bulk ferrite.

An attempt to improve electrical conductivity of the pyrolysed carbon-LiMn 2O 4− yS y (0 ≤ y ≤ 0.5) composites

An attempt to obtain conductive carbon layer (CCL) on the LiMn 2O 4 and LiMn 2O 4− y S y spinels, using the radical precipitation polymerization of acrylonitrile (AN) and styrene–acrylonitrile (SAN) in water suspension of the spinels followed, by pyrolysis of the composed precursors was made. In the case of PAN–spinel precursors the CCL on spinel particles was effectively formed. Phase transitions, as well as thermal and electrical properties of the carbon-sulphided spinel composites were characterized. An attempt with SAN copolymer failed due to the reaction between SAN and the spinels during pyrolysis, even in the argon stream.

High-strain-rate superplastic flow in tetragonal ZrO2 polycrystal enhanced by the dispersion of 30 vol.% MgAl2O4 spinel particles

The high-strain-rate superplasticity of a ZrO2–spinel composite exhibits a sigmoidal strain rate–stress relationship. At high strain rates, a strain rate sensitivity of m≈0.25 can be ascribed to the intervention of plastic deformation. At intermediate and low strain rates, the decreasing m-value from 0.5 to 0.25 with decreasing strain rate can be ascribed to a single flow mechanism of grain boundary sliding (GBS) accompanied by a threshold stress for intragranular dislocation nucleation. At intermediate strain rates, the apparent activation energy has a value of lattice diffusion of cations, suggesting that the rate of deformation is controlled by the rate of recovery of the dislocations, which contribute to the relaxation of stress concentrations exerted within ZrO2 grains by GBS.

Growing kinetics and structural characterization of oxide film formed on La-doped Co–40Cr alloy

The isothermal and cyclic oxidizing kinetics of Co–40Cr alloy and its lanthanum ion-implanted samples were studied at 1000 °C in air by thermal-gravity analysis (TGA). Scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM)) were used to examine the oxidized film's morphology and the structure after oxidation. Secondary ion mass spectrum (SIMS) method was used to examine the binding energy change of chromium caused by La-doping and its influence on formation of Cr 2O 3 film. Laser Raman spectrum was used to examine the tress changes within oxidized films. It was found that lanthanum implantation remarkably reduced the isothermal oxidizing rate of Co–40Cr and improved the anti-cracking and anti-spalling properties of Cr 2O 3 film. The reasons were that the implanted lanthanum reduced the grain size and internal stress of Cr 2O 3 oxide, increased the high temperature plasticity of oxidized film. Lanthanum mainly existed in the outer surface of Cr 2O 3 film in the forms of fine La 2O 3 and LaCrO 3 spinel particles.

Direct processing of porous nano-structured ZnO-CoO x films

Highly porous nano-structured films and powders of ZnO:Co (0–5 metal% Co) or ZnO:Co and (Zn,Co) 3O 4 (10–35% Co) particles were obtained by deposition of mixed Zn- and Co-methoxy-ethoxide precursors on spinning or non-spinning substrates, and heating to 600 °C. The Co- and Zn-methoxy-ethoxide solutions were prepared by metathesis of CoCl 2 and potassium methoxy-ethoxide, and reaction of diethylzinc and methoxy-ethanol, respectively. Compositions in the range 0–35% Co were investigated by IR spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and X-ray diffraction. The gels obtained consisted of hydrated amorphous oxo-carbonates and were of good elemental homogeneity in the TEM. Thermogravimetric analysis showed that all residual groups had been removed at 550–600 °C, 5 °C min − 1 . The materials heated to 600 °C contained ZnO of the hexagonal modification with cell-edges in close agreement with un-doped ZnO regardless of composition and temperature. TEM-EDS studies showed that the ZnO:Co and (Zn,Co) 3O 4 spinel particles were well mixed, of similar shape and size, ca 10–25 nm. Heating of the 10% Co sample to 800 °C decomposed the spinel phase and left Co-doped ZnO.

In situ synthesis of lithium ferrite nanoparticle/polymer hybrid

Lithium ferrite particle/organic hybrid was synthesized in situ from iron–organic and lithium–organic compounds below 100 °C. Spinel ferrite particle/organic hybrid was synthesized by hydrolyzing a mixture of iron (III) 3-allylacetylacetonate (IAA) and lithium acrylate (LA). X-ray diffraction analysis revealed that the crystallinity of spinel particle was dependent on the polymerization treatment and the hydrolysis conditions. The saturation magnetization of hybrid increased with increasing methylhydrazine and water amount of hydrolysis. Nanocrystalline lithium ferrite particle about 5 nm was dispersed in the organic matrix. The hybrid showed neither remanence nor coercive force at room temperature. The magnetization versus field/temperature H/T curves from 100 to 300 K were superimposed on the same curve and satisfied the Langevin equation. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curve revealed that the blocking temperature was about 75 K. The remanent magnetization and coercive field of the hybrid were 8.9 A·m2/kg and 26.3 kA/m, respectively, at 10 K.

Watching the crystallisation of complex oxides by in situ X-ray techniques

Abstract We report here the results from recent studies where in situ X-ray techniques have been employed to follow the structural evolution of complex oxide materials from amorphous precursors. Specifically we detail how combined X-ray absorption spectroscopy/X-ray diffraction (XAS/XRD) allowed us to obtain new insight into the heat-induced crystallization of industrially important bismuth molybdate catalysts (Bi2O3·nMoO3 where n = 3, 2 or 1 corresponding to the α, β and γ-phases) and nano-sized spinel (CoAl2O4) particles from amorphous zeolites. In addition we illustrate the power of the energy dispersive diffraction technique (EDXRD) to follow the evolution of bismuth molybdate phases in a real autoclave via low temperature (

Microstructural examination in high-strain-rate superplastically deformed tetragonal ZrO2 dispersed with 30 vol% MgAl2O4 spinel

The role of MgAl2O4 spinel particle dispersion for attaining high-strain-rate superplasticity (HSRS) was examined in tetragonal ZrO2. Microstructural examination shows that the dispersed spinel particles provide the following positive factors to ZrO2 simultaneously: (i) stable fine grain size by retarding grain growth due to pinning effect; and (ii) enhanced accommodation due to accelerated lattice diffusivity caused by the dissolution of aluminum and magnesium into ZrO2 from the spinel particles, and accelerated relaxation of stress concentrations exerted by grain boundary sliding through dislocation motion. These positive factors make it possible to attain HSRS in ZrO2.

Ductility and fracture toughness of molybdenum with MgAl 2O 4 additions

New interest in controlling the ductility of molybdenum follows from the hope that multiphase Mo–Si–B alloys may represent the next generation of gas-turbine blade materials. While the addition of MgAl 2O 4 spinel particles up to 5 vol.% has been previously found to improve the tensile ductility of molybdenum, the present study indicates that there is no corresponding improvement in the fracture toughness. Based on these results, the ductilizing effect is attributed to the associated reduction in grain size, rather than the actual presence of the spinel particles. For spinel additions >2.5 vol.%, the additional crack initiation sites associated with the brittle particles embrittle the molybdenum and hinder the ductilizing grain size effect, resulting in a decrease in ductility beyond 2.5 vol.% spinel. Thus, it would appear that controlling the molybdenum grain size, rather than adding spinel particles, is a more effective means of controlling ductility of molybdenum when fracture occurs intergranularly.

Effects of Coating with Gold on the Performance of Nanosized LiNi0.5Mn1.5O4 for Lithium Batteries

The electrochemical behavior of an Au-coated nanospinel in lithium cells was studied at two different temperatures (25 and ) and at five charge/discharge rates (C/6, C/4, 2C, 4C, and 8C). Two different coating methods were tested and the resulting products characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. One method, which involved treatment with in the presence of HCOH as reductant, resulted in poorer cell performance irrespective of the particular charge/discharge regime used, probably by effect of the attack on the material degrading its surface during the coating process. The other coating method involved evaporating Au on the spinel, the effect of coating on cell performance being dependent on both temperature and the charge/discharge rate. Thus, low rates (C/6, C/4) increased the capacity delivered by the cell at by ca. 20% relative to the bare spinel. This beneficial effect can be ascribed to the coating layer altering the electrolyte decomposition and the spinel particles being protected from attack by the species formed in the electrolyte decomposition. At high rates (2C, 4C), however, electrolyte decomposition played a minor role and crossing of the gold layer by lithium ions raised an energy barrier to be overcome. Under these conditions, the capacity delivered by the cell was markedly degraded irrespective of the temperature used.

化学共沈法による超微粒子Ｃｏフェライトの作製と鉄貯蔵蛋白質フェリチンへの内包の試み

Recently, there advances the collaboration of magnetics and life science fields. We focused on iron storage protein ferritin, which has a cavity of 6∼8 nm in a diameter after the removal of iron oxide from inside of it. Magnetic ferritin can be expected when ultrafine cobalt ferrite particle could be included in the cavity of ferritin because balk CoFe2O4 have large magnetocrystalline magnetic anisotropy constant K1 and suitable high magnetization. In this research, the morphology and magnetic properties of ultrafine cobalt particles less than 12 nm in diameter prepared by the coprecipitation method have been investigated. The X-ray diffraction data and TEM observations indicate that cubic-structured spinel particles are formed in granular shape in the reaction condition of pH 9∼13 and the temperatures 60∼105°C. For example, 7.3 nm particles in diameter, which are as small as the diameter of the cavity of ferritin, have been obtained successfully at a pH of 10 at 60°C for 0.5 hour reaction. Saturation magnetization and coercivity of the particles 6∼8 nm are 20∼40 emu/g and are less than 30 Oe at 300 K, respectively. Furthermore, after the removal of iron oxides from ferritin, the inclusion of ultrafine cobalt ferrite particles have been attempted. The change of UV-vis spectrum after the reaction might indicate the inclusion of ultrafine cobalt particle in the cavity of ferritin.

Electrochemical properties of LiNi 0.5Mn 1.5O 4 films prepared by spin-coating deposition

Highly uniform films of pure LiNi 0.5Mn 1.5O 4 spinel were obtained by spin-coating stoichiometric amounts of Mn(CH 3COO) 2 and Ni(CH 3COO) 2 dissolved in de-ionized water, and Li( i-OC 3H 7) dissolved in a 1:2 CH 3-COOH/ i-C 3H 7OH mixture, onto an Au substrate. The resulting gel was transformed into a spinel by calcining at variable temperatures from 400 to 800 °C. The deposits, thus, obtained were characterized by scanning electron microscopy (SEM), and X-ray diffraction and X-ray photoelectron spectroscopy (XPS), and their electrochemical properties determined from potentiostatic and galvanostatic measurements. The spinel formed at 400 °C, with an earthworm-like shape, the origin of which was ascribed to the formation of a layer of undecomposed organic components. At 800 °C, the film exhibited markedly improved in crystallinity and the spinel particles adopted a polyhedral shape of submicron size with well-defined edges and faces, thus, reducing the interparticle connectivity. Nickel atoms were found to occur in two chemical environments, namely: as Ni 2+ and Ni 3+, the former being the major component. The potentiostatic curves obtained were consistent with the spinel formula as they exhibited two well-defined peaks in the 4.6–4.8 V region associated to Ni 2+ → Ni 3+ → Ni 4+ processes. Also, both potentiostatic curves and galvanostatic curves were consistent with a reversible Li insertion/extraction reaction; however, the cells exhibited significant overcharge that was probably due to electrolyte decomposition catalyzed by gold. The thin deposits obtained were found to deliver capacities around 148 mAh g −1 and to efficiently retain them upon extended cycling. However, the coulombic efficiency of the deposits was rather low (around 50% at the 50th cycle). Increasing the film thickness, raised the coulombic efficiency to 85% but decreased the delivered capacity, probably through increased resistance of the electrode; however, capacity retention on cycling was maintained.

Effects of metal source in metal substitution of lithium manganese oxide spinel

Usefulness of W substitution for improvement of battery performance of LiMn 2O 4 cathode was investigated. Small amounts of tungsten were incorporated into LiMn 2O 4 spinel instead of available Mn. For this purpose, two sources of tungsten (metallic W or WO 3) were examined. W concentration and source have significant influence on both morphology and electrochemical behavior of W-substituted LiMn 2O 4 spinels. W substitution of LiMn 2O 4 spinel can lead to the formation of uniform spinel particles and improved battery performance. Cyclic voltammetric behaviors of the samples were examined in an aqueous solution, and Li diffusion process was investigated for different cases. The best case was the LiW 0.01Mn 1.99O 4 spinel prepared from metallic W powder, as exhibits excellent rate capability, but better cycleability was observed for the LiW 0.01Mn 1.99O 4 spinel prepared from WO 3. This means that because of significant influence of the dopant source, this parameter should be chosen in respect with the desire improvement.