Synthesis Of Spinel Research Articles

Synthesis of alumomagnesian spinel by mechanical activation method

The influence of the mechanical activation of the initial alumina and magnesium oxide powders on the formation of alumomagnesian spinel has been studied. It has been established that the mechanical activation of the starting powders accelerates the formation of alumomagnesian spinel, significantly reducing the temperature of the subsequent heat treatment.

Nanocrystalline Transition-Metal Gallium Oxide Spinels from Acetylacetonate Precursors via Solvothermal Synthesis.

The synthesis of mixed-metal spinels based on substituted γ-Ga2O3 is reported using metal acetylacetonate precursors in solvothermal reactions with alcohols as solvents at 240 °C. New oxides of Cr, Mn and Fe have been produced, all of which are formed as nanocrystalline powders, as seen by high-resolution transmission electron microscopy (HR-TEM). The first chromium-gallium mixed oxide is thus formed, with composition 0.33Ga1.87Cr0.8O4 ( = vacant site). X-ray absorption near-edge spectroscopy (XANES) at the chromium K-edge shows the presence of solely octahedral Cr3+, which in turn implies a mixture of tetrahedral and octahedral Ga3+, and the material is stable on annealing to at least 850 °C. An analogous manganese material with average chemical composition close to MnGa2O4 is shown to contain octahedral Mn2+, along with some Mn3+, but a different inversion factor to materials reported by conventional solid-state synthesis in the literature, which are known to have a significant proportion of tetrahedral Mn2+. In the case of iron, higher amounts of the transition metal can be included to give an Fe:Ga ratio of 1:1. Elemental mapping using energy dispersive X-ray spectroscopy on the TEM, however, reveals inhomogeneity in the distribution of the two metals. This is consistent with variable temperature 57Fe Mössbauer spectroscopy that shows the presence of Fe2+ and Fe3+ in more than one phase in the sample. Variable temperature magnetisation and electron paramagnetic resonance (EPR) indicate the presence of superparamagnetism at room temperature in the iron-gallium oxides.

Feasibility of aluminum recovery and MgAl2O4 spinel synthesis from secondary aluminum dross

The feasibility of aluminum recovery from secondary aluminum dross by extraction with NaOH solution and the subsequent synthesis of MgAl2O4 spinel by sintering the extracted slag were studied. The extraction percentage of soluble aluminum from the dross reached 80% at a temperature of 353 K, liquid-to-solid ratio of 12 mL·g−1, stirring speed of 300 r·min−1, and an extraction time of 15 min; the hydrolysis percentage of AlN reached 40% with an extraction time of 30 min. The activation energies of the soluble aluminum and AlN extracted from the dross were 7.15 and 8.98 kJ·mol−1, respectively, indicating that their kinetics were controlled by outer diffusion without a product layer. The extracted slag was sintered in the temperature range 1373–1773 K; MgAl2O4 spinel with a compressive strength as high as 69.4 MPa was produced in the sample sintered at 1673 K for 3 h. This value exceeds the threshold (40 MPa) prescribed by the National Standard for the Magnesia and Magnesia−alumina Refractory Bricks of China (GB/T 2275–2007). These results establish the effectiveness of aluminum recovery from secondary aluminum dross and subsequent MgAl2O4 spinel synthesis.

Low-cost synthesis of cubic spinel structured high efficient NiCo2O4/polyaniline nanocomposite for supercapacitor application

In this work, NiCo2O4 nanoparticles were synthesized by solution combustion method and NiCo2O4/PANI composite was prepared by physical blending method. The samples were od. The samples were characterized by Fourier transform infrared spectroscopy, x-ray diffraction analysis (XRD), scanning electron microscope (SEM), high- resolution transmission electron microscope (HRTEM) and Electrochemical studies such as Cyclic voltammetry (CV) and galvanostatic charge—discharge analysis. XRD peaks revealed the crystallite size of the NiCo2O4 and NiCo2O4/PANI composites. The samples were refined using Rietveld refinement method. The values of crystallite size and strain determined by W-H method were in good agreement with the results obtained in the Scherer method. FTIR confirmed the presence of respective functional groups. Morphology was studied by SEM and HRTEM images. The Morphological changes in Composite implied the enhanced electrochemical activity. The crystalline nature of NiCo2O4 and NiCo2O4/PANI nanoparticles observed by XRD study was further confirmed by SAED pattern of HRTEM images. The specific capacitance of the samples were calculated by CV and CP in three electrode configuration. Specific capacitance obtained for NiCo2O4 in 5 mV s−1 was 723 F g−1 and for NiCo2O4/PANI was 882 F g−1 from CV study. The maximum specific capacitance obtained for NiCo2O4 was 729 F g−1 and for the composite NiCo2O4/PANI was 887 F g−1 at the applied current density of 0.5 A g−1 through galvanostatic charge—discharge analysis. NiCo2O4/PANI composites showed potential and high performance, in which the maximum specific capacitance was exhibited.

Controllable Synthesis of Hierarchical Rose-Like MnCo₂O₄ Spinel as Lithium-Ion Anode Materials.

Hierarchical rose-like structured MnCo₂O₄ spinel was synthesized via a facile solvothermal process using polyvinyl pyrrolidone (PVP) as the soft template, which was characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), etc. When evaluated as the anode materials for lithium ion batteries, the as-synthesized MnCo₂O₄ spinel exhibited excellent cycling performance and rate capacity. The initial discharge and charge capacity reached 1502 mA·h·g-1 and 1131 mA·h·g-1 at the current density of 100 mA·g-1, respectively.

One-step synthesis of in situ multilayer graphene containing MgAl2O4 spinel composite powders

Owing to its exceptional properties, graphene has been considered to be a new and promising reinforcement for oxide ceramics over the last few years. Herein, in situ multilayer graphene/MgAl2O4 composite powders with homogeneously distributed graphene were synthesized via one-step carbon-bed sintering with magnesium citrate serving as the source of both MgO and carbon. The products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The microstructure and synthesis mechanism of the products were characterized and discussed. The results indicated that graphene with 6–10 layers grows between or outside the MgAl2O4 grains. The carbon content of the products was 5.96 wt%. The crystallite size of carbon (La) of in situ graphene increased as temperature rose to 1400 ℃. The composite powders synthesized retained the size and morphology of the Al2O3 raw material, confirming the template mechanism of spinel synthesis.

One-step mild synthesis of Mn-based spinel MnIICrIII2O4/MnIIMnIII2O4/C and Co-based spinel CoCr2O4/C nanoparticles as battery-type electrodes for high-performance supercapacitor application

Two chromite spinel-based composite materials, MnIICrIII2O4/MnIIMnIII2O4/C and CoCr2O4/C are successfully synthesized by a solid-state conversion process via annealing MnCr-coordination compound and CoCr-coordination compound at 350 °C in air for 1 h, respectively. The two composite materials both show the morphology of nanoparticles, in which the spinels are embedded in carbon matrix into a continuous phase. The as-prepared composite materials are used as supercapacitor electrodes in basic electrolyte. The MnIICrIII2O4/MnIIMnIII2O4/C composite material possesses a high specific capacity of 184.0 mAh g−1 at a current density of 0.5 A g−1 with a superior rate capability of 138.3 mAh g−1 (75.2% retention) at 20 A g−1. Meanwhile, CoCr2O4/C nanoparticles also deliver a high specific capacity of 158.8 mAh g−1 at a current density of 0.5 A g−1 with a superior rate capability of 125.0 mAh g−1 (78.7% retention) at 20 A g−1. The good supercapacitive behaviors of the two composite materials are probably attributed to the characteristics of bimetallic compound and the presence of multiple valence states in the samples, giving rise to obvious redox responses. And the MnIICrIII2O4/MnIIMnIII2O4/C and CoCr2O4/C composites possess reversible electrochromism.

Rare earth oxide doping and synthesis of spinel ZnMn2O4/KIT-1 with double gyroidal mesopores for desulfurization nature of hot coal gas

In this work, spinel ZnMn2O4/KIT-1 using KIT-1 with 3-dimensional wormhole-like channels as support was fabricated for hot coal gas desulfurization at high temperature via a sol-gel method. Effects of ZnMn2O4 contents, desulfurization temperature, rare earth oxide doping and steam volume on the desulfurization performances of ZnMn2O4/KIT-1 were investigated systematically. A superior sorbent of ZnMn(Ce)2O4/KIT-1 was obtained with the addition of 45%ZnMn2O4 and doping of CeO2, which was suitable for 550 °C desulfurization and endured a small impact of steam. Moreover, the crystal lattice replace between Ce3+ and Mn3+ facilitated the dispersion of active species and avoided Zn2+ converting to elemental Zn. The high sulfur capacity of ZnMn(Ce)2O4/KIT-1 was maintained after five consecutive desulfurization-regeneration cycles. The textural properties of sorbents were evaluated successively by means of XRD, BET, HRTEM, XPS, H2-TPR and TG/DSC techniques. Results revealed that the main active components in sorbent were robustly existed in form of ZnMn2O4 spinel which effectually prevented the vaporization of Zn in high temperature. Therefore, a low-cost sorbent of ZnMn(Ce)2O4/KIT-1 with the high BSC (171.7 mg S/g sorbent) has an excellent performance for H2S removal from hot coal gas.

Hybrid-coprecipitation vs. combustion synthesis of Mg-Al spinel based nanocatalyst for efficient biodiesel production

In this paper, hybrid-coprecipitation and combustion methods were used to synthesis MgAl2O4 spinel. Of interest was also to evaluate the effect of different synthesis methods on the characteristics and performance of MgO/MgAl2O4 catalyst in biodiesel production. Physicochemical characteristics of synthesized catalysts were evaluated by XRD, FESEM, surface particle size distribution (SPSD), EDX-Dot Mapping, BET-BJH and FTIR analysis. Moreover, the final performance of the samples was investigated in biodiesel production. The results of the XRD analysis showed that the highest crystallinity and crystal size belonged to the sample synthesized by the combustion method. Furthermore, the FESEM analysis showed that the sample synthesized by the combustion method had a unique morphology and the other samples had almost the same morphology. The BET-BJH analysis indicated that the least surface area and pore volume were related to the sample prepared by the combustion method. However, by perusing the samples in biodiesel production, it was found that the combustion prepared sample had the largest conversion value (95.7%) and great reusability (6 cycles). According to the total analysis, it can be said that the size and shape of the pores as well as the catalyst crystallinity are the most important specifications for biodiesel production.

Single step solid-state fusion for MgAl2O4 spinel synthesis and its influence on the structural and textural properties

Magnesium aluminate (MgAl2O4) spinel nanostructure has been synthesized using a single step solid-state fusion method, with citric acid as a surfactant. The samples prepared at different annealing conditions such as temperature and duration, were analyzed to study their effects on the structural, crystalline and textural properties of MgAl2O4 spinel, such as specific surface area, morphology, crystallite size and agglomeration. The prepared samples were characterized using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Increasing the annealing duration has insignificant influence on the crystallinity and the formation of spinel phase. However, with increasing annealing temperature, significant effects were observed, namely, decreasing specific surface area, increasing pore size and crystallite size, and increasing degree of agglomeration. Samples prepared at different annealing temperatures were then tested for catalytic methane steam reforming to understand their catalytic properties. It was found that the MgAl2O4 spinel with high surface area and small crystallite size showed good catalytic activity at 700 °C, with a steam to carbon ratio of 2.

Facile synthesis of CuFe2O4 crystals efficient for water oxidation and H2O2 reduction

Synthesis of a robust and bifunctional catalyst with earth-abundant element efficient for electrocatalytic reduction and oxidation is crucial in electrocatalytic energy conversion and storage. Herein we show that a facile method to synthesize CuFe2O4 crystals with octahedral shape as a bifunctional catalyst efficient for water oxidation and H2O2 reduction. These as-obtained CuFe2O4 catalysts exhibited high-performance for water oxidation (2.2 times current density higher than that of commercial RuO2), lower Tafel slope (∼50 mV dec−1), larger anodic current density and much enhanced electrochemical durability. Besides, the resulted CuFe2O4 catalyst was also efficient for electrocatalytic H2O2 reduction, it shows 5-fold increment of current density in the presence of 5 mM H2O2, high sensitivity and much improved stability. The cost-effective synthesis route holds great promise for the controllable synthesis of nanostructured spinel, and is expected to show promising applications in the generation of renewable energy.

Synthesis of manganese-cobalt spinel via wet chemistry methods and its properties

Abstract Mn 1.2 Co 1.8 O 4 spinel was synthesized via co-precipitation and EDTA gel processes to optimize the performance of high-quality spinel protective-conducting films deposited on steel interconnects. In the case of co-precipitation, in which ammonium hydroxide, ammonium oxalate, and ammonium carbonate were used as precipitating agents, two procedures were applied. In the first one, which was conventional, the precipitating agent was introduced into a mixture of salts, while in the other one, filter paper pre-saturated with a mixture of salts was soaked in the precipitating solution. The calcinated powders prepared via both conventional co-precipitation with ammonium hydroxide and EDTA gel processes were pure cubic spinels. The remaining powders had a dual-phase composition with cubic and tetragonal phases. Aside from the sinter obtained from the powder prepared via conventional co-precipitation with ammonium carbonate, which had a composition of Mn 1.5 Co 1.5 O 4 , all sinters were Mn 1.2 Co 1.8 O 4 cubic spinels. The highest electrical conductivity at 1023 K was observed for the spinel obtained from the powder prepared via conventional co-precipitation with ammonium hydroxide (61.5 S cm −1 ), while the lowest conductivity was measured for the Mn 1.5 Co 1.5 O 4 spinel (14.7 S cm −1 ). The study confirmed that the Mn 1.2 Co 1.8 O 4 spinel prepared via conventional co-precipitation with ammonium hydroxide is a suitable material for the surface modification of ferritic stainless steel applied in IT-SOFC interconnects.

Synthesis of MgAl2O4 spinel by thermal plasma and its synergetic structural study

Bulk quantity of the MgAl2O4 spinels with specific composition has been synthesized by thermal plasma method. The process time and compositions of the feed are optimized for a desired stoichiometry. A structural co-relation has been derived from several set of experiments by major variation in the α-Al2O3 content in the feed material. Formation of desired phase with particular feed stoichiometry has been studied by X-ray diffraction pattern (XRD) analysis which is corroborated by Raman scattering analysis. A good structural co-relation between the XRD, Raman and Fourier transform infrared spectroscopy (FTIR) analysis was derived. Additionally, the electron probe microanalysis (EPMA) of the specific sample has been carried out to study the exact compositional distribution and the presence of additional impurity phases in the as-synthesized spinels. Finally, the micro mechanical behaviour of the as-synthesized spinels has been studied and well co-related with the structural data.

CVD synthesis of cobalt spinel for bio-butanol combustion

As potential substitutes for precious metals, cobalt spinel has been considered as a promising alternative catalyst for the low-temperature catalytic oxidation of biofuels. This work reports the one-step synthesis of cobalt spinel by a more elaborated approach named pulsed-spray evaporation chemical vapor deposition with a new feedstock of Co(acac)3 and toluene. The obtained samples were comprehensively characterized in terms of structure and morphology (XRD, FTIR, Raman and SEM), chemical composition (XPS and EDS) and the redox properties (TPR/TPO). The structural and morphological analysis indicates that the synthesized thin films are pure cubic Co3O4 with homogeneous matrix with well-defined facets and straight edges. Compared to the commonly used feedstock of Co(acac)2/ethanol, Co(acac)3/toluene could result in a much higher growth rate, more lattice oxygen on the surface and better re-oxidation property. The Co3O4 film exhibits attractive performance towards the deep oxidation of n-butanol by preventing the formation of CO and acetaldehyde. The relationship between the peculiar structure and properties of Co3O4 is highlighted. The surface basic sites, specific morphology and the redox properties are proposed to play synergistic roles in the reaction sequence.

Spinel Production1

Methods are described for producing aluminium-magnesium spinel by solid phase synthesis using commercial alumina and caustic magnesite. It is proposed to replace commercial alumina by dust deposited in the aspiration system for an aluminum hydroxide calcination rotary furnace that makes it possible to exclude the stage of milling alumina. Methods are provided for spinel synthesis in electric arc furnaces with block melting and pouring of a charge. The effect of the MgO/Al2O3 ratio in electrically melted material on its properties, method for adding a charge to an electric furnace during melting for pouring, features and properties of spinel materials with subsequent molded object sintering, are studied.

Synthesis and properties of binary spinels in a NiO–CuO–Fe2O3–Cr2O3 system

The conditions for the formation of a spinel structure from a NiO–CuO–Fe2O3–Cr2O3 oxide mixture using several technological approaches have been examined. Addition of KCl is accompanied with the formation of two spinel-like phases, whereas in the absence of KCl just one solid solution of nickel–copper ferrite–chromite with the structure of a cubic spinel is formed. At the temperature of thermal treatment of 900°C, the presence of an admixture phase of the delafossite (CuCrO2) type was established. The conditions for the fabrication of samples containing two spinel phases (cubic and tetragonal) characterized with the most developed surface and manifesting = increased catalytic activity in the reaction of the decomposition of an organic substance by hydrogen peroxide have been formulated. The studied features of spinel synthesis can be of interest for developing materials with an active surface promising for application as adsorbents of catalysts and sensors.

Diethylenetriamine assisted synthesis of mesoporous Co and Ni-Co spinel oxides as an electrocatalysts for methanol and water oxidation

The electrocatalytic oxidation of small molecules such as methanol and water is the crucial part of energy storage/generation technologies such as fuel cell and metal-air batteries. However, the high overpotential, sluggish reaction dynamics and low stability of electrode materials are the main barriers in developing an excellent catalyst for the anodic electro-oxidation process. To overcome such problems, we developed an easy synthesis root for the preparation of novel mesoporous (MP) Co3O4 and NiCo2O4 using a template-free hydrothermal and subsequent annealing method. In which, we used diethylenetriamine as a complexing agent, which was able to control crystal growth of corresponding metal hydroxide, leading to the formation of a mesoporous structure. Results show that the MP-NiCo2O4 exhibits a current density of 10.0mAcm−2 even at a lower potential (286mV vs. Ag/AgCl) for methanol oxidation reaction compared to that of MP-Co3O4. On the other hand, both MP-Co3O4 and MP-NiCo2O4 display excellent electrocatalytic activity towards water oxidation with lower onset potential and overpotential (MP-Co3O4 ɳ10=302mV and MP-NiCo2O4 ɳ10=322mV). The excellent electrochemical performance suggests that this mesoporous MP-NiCo2O4 and MP-Co3O4 could be potential candidates for energy and environmentally related applications.

Synthesis and characterization of ZnAl2O4 spinel from Zn(II) and Al(III) carboxylates

In this paper, zinc aluminate (ZnAl2O4) nanoparticles were obtained by a new synthesis method, thermal decomposition of Zn(II) and Al(III) carboxylates mixture. Complex combinations were obtained in the redox reaction between Zn(NO3)2·6H2O, Al(NO3)3·9H2O, and 1,3-propanediol at ~130 °C. The mechanism of Zn(II) and Al(III) carboxylates formation and decomposition was observed by thermal analysis and Fourier transform infrared spectroscopy. Zn(II) carboxylate, Al(III) carboxylate, and Zn(II) and Al(III) carboxylates mixture were annealed at different temperatures. Metal oxides synthesized from carboxylates precursors in single metal systems crystallized very well at 400 °C (ZnO) and weak at 800 °C (Al2O3), as shown by X-ray powder diffractometry. Homogenous mixture of Zn(II) and Al(III) carboxylates heated at 400 °C has led to a mixture of amorphous ZnO and Al2O3, which reacted forming at 600 °C well-crystallized ZnAl2O4, with mean crystallites size of 14.2 nm. The decomposition of carboxylates precursors is an appropriate method to obtain ZnAl2O4 spinel as well-crystallized single phase at low temperatures.

A facile low-temperature synthesis of Li4Mn5O12 nanorods

The present work provides a facile novel method for the low-temperature synthesis of Li4Mn5O12 spinel, a lithium manganese oxide that can potentially be used for application as cathode material in rechargeable lithium ion batteries, in supercapacitors, in magnetic devices, etc. Pure Li4Mn5O12 has been prepared using pre-synthesized nanostructured MnOOH nanowires as manganese sources and lithium salt at fairly low temperature. XRD, FESEM, HRTEM, and ICP-MS results revealed the formation of perfect cubic phase Li4Mn5O12 nanorods. Based on the results obtained, a mechanism of formation of Li4Mn5O12 nanorod is proposed.

Study of the factors affecting the formation of copper–chromium/aluminum oxide compounds with a spinel structure

The effect of the Cr3+/Al3+ ratio on the crystallization temperature of mixed oxide compounds with a spinel structure and their structural features and morphological characteristics have been studied using a combination of physicochemical methods: thermal analysis, IR spectroscopy, X-ray powder diffraction, and electron microscopy. The role of temperature of synthesis and drying of Cu–Cr/Al hydroxy precursors in the formation of copper-containing spinels CuCrxAl2–xO4, where x = 0–2, has been elucidated. The results are of interest for selection of the optimal composition and conditions of synthesis and formation of copper-containing spinels for their practical use.