Spinel

Spinels form an interesting class of compounds, finding applications in metal-ion batteries and as catalysts for metal−air batteries and fuel cells. Here, we report a fast, template-free solution combustion method to synthesize nanoscale zinc spinels for applications as cathodes in low-cost aqueous zinc-ion batteries and oxygen reduction reaction (ORR) catalysts. It leads to the formation of phase-pure spinels with near spherical nanoscale morphology. Three spinelsZnCo 2 O 4 (ZCO), ZnMn 2 O 4 (ZMO), and ZnMnCoO 4 (ZMCO)were investigated. ZMO and, for the first time, ZMCO were observed to show reversible Zn (de)insertion involving Mn 4+ /Mn 3+ redox couple with a first discharge capacity of 109.4 mAh/g (i.e., >99% of theoretical capacity). Further, these Zn-based spinels showed appreciable oxygen reduction reaction (ORR) electrocatalytic activity. The ORR activity in alkaline solution was characterized by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) using a rotating disk electrode (RDE) and was observed to be comparable to Pt/C with similar chronoamperometric stability. This enhanced ORR activity can be rooted to the optimal tuning of Co 3+ −O bond strength because of the presence of Mn 3+. This work presents a robust synthesis route to prepare ZnMnCoO 4 spinel acting as an economic cathode material for large-scale Zn-ion batteries for grid storage applications as well as an efficient and stable alternate ORR catalyst in alkaline solution.

Inorganic pigment of Co-Spinel was
synthesized by ultrasonic assisted co-precipitation method at different ultrasonic-treatment temperatures. The effect of ultrasonic treatment on reaction mechanism is also detailed. The colour analyses results indicated that the lowest b* value of -41.31 was observed at the ultrasonic treatment of 50°C. The synthesized bright blue powders were identified as Cobalt Aluminate Oxide (CoAl2O4, powder diffraction file number of 00-044-0160) in X-Ray diffraction (XRD) analyses. The colour
of synthesized compound was proved by adsorption peaks at the wavelengths of 550, 610 and 645 nm in UVVis spectroscopy (UV) results. The experimental results showed that spinels could be synthesized at higher crystallinity features by the use of ultrasonic treatment.

The slag's chromium leaching is one of the most pressing concerns in Electric Arc Furnace (EAF) carbon and stainless steels production. In recent years, many studies have aimed at understanding which properties (basicity, cooling speed) and phases (spinels, wustite, silicates) determine the Cr leaching, defining different indices (sp-factor, cs-factor) in order to forecast the slag's behavior compared to the leaching of this toxic metal. The literature suggests that spinel formation is usually a good way to fix Cr and prevent its leaching. However, in some conditions (high basicity, low amount of spinel-forming species) soluble Cr-bearing phases can be formed, i.e., Ca-chromite or unstable spinel. In these conditions, Cr can be leached easily, even if it is bound in a spinel structure. In this paper, the effects of basicity and impurities (Ca, Si) on the instability of Cr-spinel was investigated, with respect to slag mesh. The influence of basicity was also studied on Mg-wustite stability, which might contribute to the leaching of Cr. Different samples of carbon steel slag, suspected of forming unstable spinels, belonging to different steel grade production, were also investigated. Both granulated (4 mm) and milled (< 100 μm) slag were analyzed. Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM-EDS) analyses were carried out to measure the local chemical composition of Cr-bearing phases. This data was correlated with slag basicity (by X-Ray Fluorescence: XRF), spinel fraction (by X-Ray Diffraction: XRD), and Cr leaching (by Inductively Coupled Plasma Mass Spectrometry: ICP-MS). The main results indicate that the increase of the slag basicity implies an increase of the impurity content (Ca, Si) in the spinel, also over-saturated by Cr. This aspect, coupled with spinel geometrical features, seems to justify the unexpected Cr leaching of some slag samples. Basicity does not influence the chemistry of wustite, thus excluding it as an additional Cr leaching source.

In this research, modified sol gel synthesis is applied to prepare the nano spinel MgAl 2 O 4 . Effects of molar ratio of fuel to metal nitrates in the precursor solutions (1.5, 2) and subsequent calcination temperature (800, 1000 °C) on the powder characteristics are described. Gel formation, morphologies and specific surface area are characterized using DTA/TG, XRD, TEM and BET. The results indicate that the Gl/(metal nitrates) molar ratios has a strong effect on the formation of crystalline spinel MgAl 2 O 4 and higher temperature promote the increase of the crystallite size. According to TEM figures most of the particles calcined at 800 has sizes less than 30 nm.

We report the bulk magnetic properties of a yet unexplored vanadium-based multi-valenced
spinel system, Zn3V3O8. A Curie–Weiss fit of our dc magnetic susceptibility χ(T ) data
in the temperature region of 140–300K yields a Curie constant C = 0.75 cm3Kmole−1 V−1,
θCW = −370 K. We have observed a splitting between the zero field cooled (ZFC) and
field cooled (FC) susceptibility curves below a temperature Tirr of about 6.3K. The value of
the ‘frustration parameter’ ( |θCW|
TN
∼ 100) suggests that the system is strongly frustrated. From
the ac susceptibility measurements we find a logarithmic variation of freezing temperature (Tf )
with frequency ν attesting to the formation of a spin glass below Tf . However, the value of the
characteristic frequency obtained from the Vogel–Fulcher fit suggests that the ground state is
closer to a cluster glass rather than a conventional spin glass. We explored further consequences
of the spin glass behavior and observed aging phenomena and memory effect (both in ZFC and
FC).We found that a positive temperature cycle erases the memory, as predicted by the hierarchical
model. From the heat capacityCP data, a hump-like anomalywas observed inCP /T at about
3.75 K. Below this temperature the magnetic heat capacity shows a nearly linear dependence
with T which is consistent with the formation of a spin glass state below Tf in Zn3V3O8.

LiMn 2 O 4 spinel cathode materials have been successfully synthesized by solid-state reaction. Surface of these particles were modified by nanostructured LiFePO 4 via sol gel dip coating method. Synthesized products were characterized by thermally analyzed by Thermogravimetric and Differential Thermal Analysis(TG/DTA), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) spectroscopy. The results of electrochemical tests showed that the charge/discharge capacities improved up to 120 mAh/g and charge retention of battery enhanced over %95. This improved electrochemical performance is caused by LiFePO 4 phosphate layer on surfaces of LiMn 2 O 4 cathode particles.

The synthesis of BaTiO3-MgFe2O4 composite powders by a Pechini-like one-pot process and resulting ceramic bodies is described herein. Phase formation during the decomposition of homogenous (Ba,Ti,Fe,Mg)-gels was monitored up to 1200 °C. Composite powders consisting of BaTiO3 and MgFe2O4 were obtained after decomposition at 700 °C for 1 h resulting in crystallite sizes of about 10 nm. The shrinkage and sintering behaviour of compacted powders were examined. Sintering at > 1200 °C leads to the formation of hexagonal BaTiO3 only for composites with a MgFe2O4 content of > 30 wt.%. SEM images of ceramic bodies reveal that the MgFe2O4 particles are surrounded by BaTiO3 crystallites. Magnetic measurements of both powders and corresponding ceramic bodies show ferrimagnetic behaviour with low coercivities. At high-field and low temperatures an additional small paramagnetic contribution was observed which increases with decreasing MgFe2O4 content and should be considered by the calculation of the saturation magnetization.
Finally, the frequency dependent variation of the relative permittivities of the composites was investigated.

During the 2018 Tucson gem shows, a range of greyish to greenish-blue to violet to purple spinels from Mozambique were displayed by one of the authors (MS) and Kobi Sevdermish (Advanced Quality, Ramat Gan, Israel). They started cutting the material in early 2017 and produced faceted stones from 2 mm in diameter up to 8 ct. About 3,000 carats of the larger stones have been cut. Seven spinels weighing 1.20–3.83 ct (Figure 28) were characterized by one of the authors (GB). Five of them were violetish purple to reddish purple with medium-to-dark tone and moderate to vivid saturation, and two of them were greenish-blue to blue with a dark tone and high saturation.

The Godzilla Megamullion, located in the Parece Vela Backarc Basin of the Izu–Bonin–Mariana (IBM) system, is the largest known example of an Oceanic Core Complex (OCC). Peridotites recovered from the megamullion are divided petrographically into fertile (e.g. lherzolites), depleted (e.g. harzburgites), and plagioclase-bearing groups (Ohara et al., 2003a). A total of 151 thin sections were studied from the Kairei KR03-01, Hakuho Maru KH07-02, and Yokosuka YK09-05 cruises. Melt stagnation is studied via the incidence of plagioclase-bearing peridotites and the major element chemistry of Cr-spinels in the plag-bearing samples. A distinct trend in melt stagnation is evident along the length of the megamullion representing a secular evolution in the entrapment of melts rising through the lithosphere. The distal (furthest from the termination of spreading), depleted portion of the mullion represents a robust mantle section that was still producing abundant melt and can be compared to typical oceanic spreading with its relatively “normal” percentage of plagioclase peridotites and average spinel Cr# of 0.35. The medial, fertile portion of the mullion represents a steep falloff in melt productivity represented by fertile spinel compositions (i.e. Cr# < 0.25) and the presence of plagioclase-free lherzolites. The proximal (closest to termination of spreading), heavily plagioclase impregnated portion (with spinel Cr#s covering nearly the entire range of abyssal peridotite spinel compositions) of the mullion then represents a period of increasing stagnation of melt into a lithosphere that was undergoing progressive thickening. We infer that the processes of mantle evolution through melt stagnation and impregnation, as evidenced by the systematic variations in plag–peridotites along Godzilla Megamullion, represent a possibly common way in which the mantle reacts to OCC formation. In this case, Godzilla Megamullion may represent an extreme endmember in OCC formation.

Abstract For catalysts comprised of mixed manganese-chromium oxides MnxCr3-xO4 (x = 0.3–2.7) prepared by Pechini route with Ni and Ru supported by impregnation fundamental factors determining their performance in ethanol steam reforming have been elucidated using combination of structural (XRD, HRTEM), spectroscopic (UV–vis), surface science (XPS, FTIR spectroscopy of adsorbed CO) and kinetic (H2 and EtOH TPR, oxygen isotope heteroexchange with C18O2) methods. The most important feature is strong metal-support interaction stabilizing small clusters of metals/alloys and preventing carbon nucleation. The lattice oxygen mobility and reactivity increased with Mn content. The highest TOF was obtained for (Ni + Ru)–loaded oxide support containing cubic spinel phase of MnCr2O4 composition, which implies a positive effect of Ni-Ru interaction in mixed clusters on catalytic activity. This catalyst has also a high density of active sites, surface enriched by Mn and sufficient oxygen mobility providing coking stability, which makes it attractive for practical application.

Manganese aluminium spinel, MnAl 2 O 4 , is prepared by hot-pressing an equimolecular mixture of MnO and Al 2 O 3 at 1450°C. The spinel is characterized by the X-ray powder diffraction (XRD) method and by scanning electron microscopy (SEM). The X-ray data are indexed ...

Blue ceramic nano pigment of CoAl2O4 has been synthesized by a co-precipitation method. The reactions conditions (stirring time and stoichiometric ratio) for the preparation of precipitated compound and the calcination conditions (temperature and time) have been optimized for the proper particle synthesis. In addition, the effects of different capping agents (pyrrolidinone, N-cetyl-N,N,N-trimethylammonium bromide, triethylamine, and oleic acid) on the characteristic features of CoAl2O4 have been analyzed by X-ray diffraction and color analysis. Synthesized samples have been identified as spinel (CoAl2O4). The spectroscopic results indicate that minor changes have been seen and the desired electronic transitions in Co2+ in tetrahedral coordination have been achieved. The color performance of pigments has been increased and particle sizes have been decreased with the capping agent addition. The lowest b* values have been obtained in the TEA added samples. The crystallite sizes have be...

Nanostructure-related magnetic properties are investigated systematically for various mesoporous cobalt oxide (Co3O4) and cobalt ferrite (CoFe2O4) spinel phases. Synthesis of the materials by nanocasting offers the opportunity to obtain materials which are different from each other with respect to both specific surface area and crystallite size. As a result, the respective contributions of two types of interfaces, namely, “solid–gas” and “solid–solid” interfaces, to the magnetic ordering can be distinguished. Structural characterization of the porous materials by X-ray diffraction, N2 physisorption, and electron microscopy as well as investigation of the magnetic behavior (field-dependent magnetization and temperature-dependent susceptibility) are presented.

A vibronic photoexcitation band at approximately 230 nm was found at 13 K in reactor neutron- and electron-irradiated magnesium aluminate spinel (MgO.nAl2O3). Vibronic structure was found to be temperature dependent and became obscure at over 120 K. Huang Rhys factor S and Debye Temperature D were estimated from the temperature dependence of the 230 nm band by curve-fitting method using Debye approximation. Origin of the vibronic photoexcitation band was suggested as F center.

An in situ Raman spectroscopic study was conducted to investigate the pressure-induced phase transformation in the synthetic ZnCr 2 O 4 spinel up to pressures of 70 GPa at room temperature. Results indicate that ZnCr 2 O 4 spinel starts to transform to the CaFe 2 O 4 (or CaTi 2 O 4) structure at 17.5 GPa, and such a phase transformation is complete at 35 GPa. The coexistence of two phases over a wide range of pressure implies a sluggish mechanism upon phase transformation. No experimental evidence was observed to support the theoretical simulation with the dissociation of ZnCr 2 O 4 to ZnO and Cr 2 O 3 at 34 GPa. Moreover, enhancement of the intensity of the Raman peak at 642 cm\ \ 1 at either elevated pressures or temperatures is most likely caused by an enhanced order}disorder e4ect. Upon release of pressure, the recovered phase may exhibit an inverse spinel structure, which di4ers from the initial normal spinel structure.

Spinel cobalt ferrites (CoFe 2 O 4) with varying levels of substoichiometry were prepared via sol-gel synthesis with different combinations of citric acid, dextrose and PVP (polyvinylpyrrolidone). The gels, prepared from the metal nitrates, were dried at 110°C, further treated at 850°C and finally subjected to thorough structural and magnetic characterization in order to correlate the composition of the gel to the structural and magnetic properties displayed by the ferrites. The materials synthesized in the present work have shown to be rather irondepleted, reaching over 50% deficiency of the metal, which leaves the spinel lattice and forms Fe 2 O 3 instead. The fuel/oxidant ratio and the thermal behavior of the xerogels exert a direct influence on the compositional variation of the prepared spinels, which could in turn be correlated to the magnetic properties displayed by the particles. A maximum in coercivity of 2154.4 Oe was achieved without the application of any additive to the nitrate precursors. On the other hand, the magnetic remanence displayed by the ferrites shows a linear relationship to the iron content in their chemical formula. The results open up the possibility of fine-tuning the structural and magnetic properties displayed by the spinel product via careful control of the composition of the reaction medium.

Introduction. In the industrial production of pigments, the solid state reaction has been traditionally applied as a method to obtain complex oxides, such as pigmenting application spinels (formula AB2O4), which are synthesized through alternative routes, aiming to reduce costs and energy consumption in the production process. In this research work, the spinel type pigment CuCr2O4 was synthesized by the use of the in solution auto combustion method, through the citrate-nitrate, urea-nitrate and glycine-nitrate routes. Objective. To obtain spinel type structures by the use of the citrate-nitrate, urea-nitrate and glycine-nitrate auto combustion methods. Materials and methods. For the synthesis of the pigments in the different routes, the compounds (Cu(NO3)2.3 H2O), (Cr(NO3)3.9 H2O), (CH2NH2CO2H), (CO(NH2)2), (C6H8O7), (CuCO3. Cu(OH)2) and finally (III) (Cr2O3), were used. The pigments obtained were characterized by the use of several techniques such as X ray diffraction (DRX), scanni...

Nanostructure-related magnetic properties are investigated systematically for various mesoporous cobalt oxide (Co3O4) and cobalt ferrite (CoFe2O4) spinel phases. Synthesis of thematerials by nanocasting offers the opportunity to obtain materials which are different from each other with respect to both specific surface area and crystallite size. As a result, the respective contributions of two types of interfaces, namely, “solid–gas” and “solid–solid” interfaces, to the magnetic ordering can be distinguished. Structural characterization of the porous materials by X-ray diffraction, N2 physisorption, and electron microscopy as well as investigation of the magnetic behavior (field-dependent magnetization and temperaturedependentsusceptibility) are presented.

In the synthesized MgAl 2 O 4 ceramics, Raman scattering modes were detected due to the presence of random distribution of cations over structural positions (structural reversal effects). Irradiation by 10 MeV electron beam caused intensity redistribution of the fundamental bands in Raman spectrum. New optical absorption bands were registered. Observed features were attributed to the effect of radiation-induced 'ionic mixing' in cation sublattice. This effect is the formation of additional [Al] í µí±€í µí±” and [Mg] í µí°´í µí±™ anti-site defects. The obtained data on the defects in transparent ceramics are of interest for the creation of radiation-resistant electromagnetic radiation converters for alternative energy.

We report on the analysis of dendritic crystals present in the dark spot areas of blue‐and‐white Ming porcelains. Using Raman spectroscopy and scanning electron microscopy equipped with energy dispersive spectrometer, we were able to evidence Mn‐rich spinels. Small Mn‐based spinel crystals being highly sensitive to laser‐induced heating, we identified proper working conditions, avoiding excessive heating and damage. Local temperatures during Raman measurements were deduced from Stokes/anti‐Stokes intensity ratios. By analysing the behaviour of the A1g mode of Mn‐rich spinels, we were able to identify phases ranging from jacobsite‐like to hausmannite‐like compounds. Polarized Raman scattering was shown to provide a convenient means of discriminating between these two types of phases, as they display different symmetries. Inhomogeneities within the dendritic network, as evidenced by micro‐Raman measurements, highlight its gradual formation during the cooling phase of firing, depending of Fe3+ and Mn3+ availability. The presence of Mn‐based spinels is consistent with the use of a local Chinese Mn‐rich cobalt ore during the middle Ming Dynasty.

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