Synthesis and characterization of ultrafine spinel ferrite obtained by precursor combustion technique

Nanoparticles of the spinel ferrite, Co_0.6Ni_0.4Fe₂O₄ have been synthesized by the precursor combustion technique. This synthetic route makes use of a novel precursor viz. metal fumarato hydrazinate which decomposes autocatalytically after ignition to yield nanosized spinel ferrite. The X-ray powder diffraction of the ??as prepared?? oxide confirms the formation of monophasic nanocrystalline cobalt nickel ferrite. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric and differential thermal analysis. The precursor has also been characterized by FTIR, and chemical analysis and its chemical composition has been fixed as Co_0.6Ni_0.4Fe₂(C₄H₂O₄)₃·6N₂H₄. The Curie temperature of the ??as prepared?? oxide was determined by ac susceptibility measurements.     

Synthesis of potassium ferrite by precursor and combustion methods

The thermolysis of potassium hexa(carboxylato)ferrate(III) precursors, K₃[Fe(L)₆]·xH₂O (L=formate, acetate, propionate, butyrate), has been carried out in flowing air atmosphere from ambient temperature to 900°C. Various physico-chemical techniques i.e. TG, DTG, DTA, XRD, IR, Mössbauer spectroscopy etc. have been employed to characterize the intermediates and end products. After dehydration, the anhydrous complexes undergo exothermic decomposition to yield various intermediates i.e. potassium carbonate/acetate/propionate/butyrate and α-Fe₂O₃. A subsequent decomposition of these intermediates leads to the formation of potassium ferrite (KFeO₂) above 700°C. The same ferrite has also been prepared by the combustion method at a comparatively lower temperature (600°C) and in less time than that of conventional ceramic method.     

Thermal, structural, magnetic and photoluminescence studies on cobalt ferrite nanoparticles obtained by citrate precursor method

Magnetic nanoparticles of cobalt ferrite have been synthesized by citrate precursor method. TG-DSC studies have been made to get the idea of the optimum temperature of annealing that could lead to the formation of nanoparticles. Annealing the citrate precursor was done at 450, 650, and 973?°C. The X-ray diffraction (XRD) studies and the scanning electron microscopy (SEM) have been used for characterization. The data from vibrating sample magnetometer and photoluminescence spectrometer (PL) have been analyzed for exploring their applications. Using the Scherrer formula, the crystallite size was found to be 25, 32, and 43?nm, respectively, using the three temperatures. The particle size increased with annealing temperature. Rietveld refinements on the X-ray (XRD) data were done on the cobalt ferrite nanoparticles (monoclinic cells) obtained on annealing at 650?°C, selecting the space group P2/M. The values of coercivity (1574.4?G) and retentivity (18.705?emu g^?1) were found out in the sample annealed at 650?°C while magnetization (39.032?emu g^?1) was also found in the sample annealed at 973?°C. The photoluminescence (PL) property of these samples were studied using 225, 330, and 350?nm excitation wavelength radiation source. The PL intensity was found to be increasing with the particle size.     

Synthesis of lithium ferrite by precursor and combustion methods: A comparative study

The thermal decomposition of lithium hexa(carboxylato)ferrate(III) precursors, (Li₃[Fe(L)₆]·xH₂O, L = formate, acetate, propionate, butyrate), has been carried out in flowing air atmosphere from ambient temperature upto 500 °C. Various physico-chemical techniques, i.e., TG, DTG, DTA, XRD, SEM, IR, Mössbauer spectroscopy, etc., have been employed to characterize the intermediates and end products. After dehydration, the anhydrous complexes undergo decomposition to yield various intermediates, i.e., lithium oxalate/acetate/propionate/butyrate, ferrous oxalate/acetate and α-Fe₂O₃ in the temperature range of 185–240 °C. A subsequent decomposition of these intermediates leads to the formation of nanosized lithium ferrite (LiFeO₂). Ferrites have been obtained at much lower temperature (255–310 °C) as compared to conventional ceramic method. The same nano-ferrite has also been prepared by the combustion method at a comparatively lower temperature (400 °C) and in less time than that of conventional ceramic method.     

Synthesis of cobalt nickel ferrite nanoparticles via autocatalytic decomposition of the precursor

The chemistry, structure, and properties of spinel ferrites are largely governed by the method of preparation. The metal carboxylato-hydrazinate precursors are known to yield nanosized oxides at a comparatively lower temperature. In this study, we are reporting the synthesis of one such precursor, cobalt nickel ferrous fumarato-hydrazinate which decomposes autocatalytically to give cobalt nickel ferrite nanoparticles. The XRD study of this decomposed product confirms the formation of single-phase spinel, i.e., Co_0.5Ni_0.5Fe₂O₄. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric (TG), and differential scanning calorimetric (DSC) analysis. The precursor has also been characterized by FTIR, EDX, and chemical analysis, and its chemical composition has been determined as Co_0.5Ni_0.5Fe₂(C₄H₂O₄)₃·6N₂H₄.     

Synthesis of nanosized rubidium ferrite by thermolysis of ferricarboxylate precursors and combustion method

Nanosized pure rubidium ferrites have been successfully prepared by thermal decomposition of rubidium hexa(carboxylato)ferrate(III) precursors, Rb₃[Fe(L)₆]·xH₂O (L = formate, acetate, propionate, butyrate), in flowing air atmosphere from ambient temperature to 1000 °C. Various physico-chemical techniques i.e. simultaneous TG–DTG–DTA, XRD, Transmission Electron Microscope (TEM), IR and Mössbauer spectroscopy etc. have been employed to characterize the intermediates and end products. After dehydration, the anhydrous precursors undergo exothermic decomposition to yield various intermediates i.e. rubidium carbonate/acetate/propionate/butyrate and α-Fe₂O₃. A subsequent decomposition of these intermediates, followed by solid state reaction, lead to the formation of nanosized rubidium ferrite (RbFeO₂). The same nano-ferrite has also been prepared by the combustion method at a comparatively lower temperature and in less time than that of the conventional ceramic method (>1200 °C).     

Synthesis of nanosize particles of cobalt and nickel oxides from solutions

Rounded nanosize particles of Co₃O₄ and NiO were prepared by precipitation with ammonium carbonate from cobalt and nickel nitrate solutions. Cobalt and nickel oxides and their precursors were characterized by thermal and X-ray phase analyses, electron microscopy, and IR spectroscopy.     

纳米氧化铈、铁酸铜的乳化燃烧合成及其光催化性能

采用金属硝酸盐、硝酸铵和油相在乳化剂作用下制备成油包水的乳状液,以燃烧的方式制备了纳米氧化铈(CeO_2)和铁酸铜(CuFe_2O_4),并成功将它们负载到氧化石墨烯(GO)上.实验结果显示:以燃烧法合成的CeO_2和CuFe_2O_4纳米粒子较为纯净,平均粒径分别约为29.1和13.5nm;二者分别负载到GO上后,团聚现象得到一定程度改善,光响应能力得到增强.在汞灯照射下,催化剂GO-CeO_2、GO-CuFe_2O_4对罗丹明B的2h光降解率分别可达92.3%、98.1%.这表明所合成样品GO-CeO_2、GO-CuFe_2O_4具有优异的光催化活性.     

Micellar factors which play a role in the control of the nanosize particles of cobalt ferrite

Cobalt and iron (II) dodecylsulfate [Co(DS)₂ and Fe(DS)₂] form oil in water micelles. They have been used to make nanosize magnetic particles. The size of the particles is controlled by the surfactant concentration. The average size of the particles is determined by transmission electron microscopy, X-ray diffraction by small angle X-rays scattering and from simulation of magnetization curves. It varies from 2 to 5 nm, with less than 30% in polydispersity. By XANES, an increase in the formal oxidation degree of iron and cobalt ions with the increase in surfactant concentration has been observed. This could be correlated to the increase in the particle size with surfactant concentration.     

Pure and doped lanthanum cobaltites obtained by combustion method

We report the synthesis of La_1−xSr_xCoO₃ nanopowders by solution combustion method using metal nitrates and -alanine (alanine method) or urea (urea method) as fuel. The influence of metal nitrates/organic substance molar ratio and the type of fuel was investigated. The isolated complex precursors were characterized by atomic absorption spectroscopy (AAS), FT-IR spectra and DTA–TG analysis. The La_1−xSr_xCoO₃ (x = 0–0.3) powders were characterized by X-ray diffraction (XRD), scanning electron microscopy–energy-dispersive X-ray analysis (SEM–EDX), as well as by specific surface area measurements. XRD patterns indicate the formation of single-phase LaCoO₃ (rhombohedral) when as-synthesized powders were calcined at 873 K, 3 h in the case of the alanine method and at 1073 K, 3 h for urea-based system. Also, strontium doped lanthanum cobaltites obtained by both methods at 1273 K are single phase with rhombohedral perovskite-like structure as XRD data have proved. SEM investigation of pure and doped lanthanum cobaltites reveal that the samples prepared by both methods have fine particles with tendency of agglomerates formation with different shapes, spongy aspect and high porosity. La_1−xSr_xCoO₃ nanopowders obtained by alanine method have larger specific surface area values than those prepared by urea method.     

Synthesis and morphological characterization of nanocrystalline powders obtained by a gas condensation method

The preparation of nanocrystalline powders of Fe and Fe50Ni50 has been performed by a gas-condensation method under pure helium atmosphere. The characterization of the prepared materials which was carried out by means of Transmission Electron Microscopy, X-rays diffraction and Mössbauer Spectrometry, evidences for the presence of oxide phases. Fe and FeNi based ultrafine particles are observed with a size comprised within the range 10–70 nm and they occur as clusters or chains.     

Studies on the magnetism of cobalt ferrite nanocrystals synthesized by hydrothermal method

Fe-Co/CoFe₂O₄ nanocomposite and CoFe₂O₄ nanopowders were prepared by the hydrothermal method. The structure of magnetic powders were characterized by X-ray diffraction diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermal gravity analysis (TGA) and differential thermal analysis (DTA) analysis, X-ray photoelectron spectrometry (XPS), and Fourier transform infrared spectra (FTIR) techniques, while magnetic properties were determined by using a vibrating sample magnetometer (VSM) at room temperature. The effects of hydrothermal reaction conditions on magnetic properties were also discussed in details. The values of saturation magnetization (M_s) and coercive fore (H_c) for Fe-Co/CoFe₂O₄ nanocomposite are 113 emu/g and 1.4 kOe, respectively. Furthermore, CoFe₂O₄ ferrite with a single-domain critical size of 70 nm was fabricated by controlling the hydrothermal reaction conditions carefully, which presents high coercive force (ca. 4.6 kOe) and high squareness ratio (ca. 0.65). One interesting thing is M_s value of CoFe₂O₄ ferrite with a diameter of 40 nm is 86 emu/g which is comparable to that of the bulk counterpart.     

Low sintering temperature of Mg-Cu-Zn ferrite prepared by the citrate precursor method

Mg-Cu-Zn ferrite was prepared through a wet synthetic method by a self-combustion reaction directly from a citrate precursor. The as-synthesized powders were sintered at 750 °C for only 2 h. XRD patterns and FTIR spectra confirm the formation of single phase Mg-Cu-Zn ferrite after combustion. To the best of our knowledge, this is the first time that Mg-Cu-Zn ferrite is sintered at such a low temperature. The sintering process increased the crystallinity of the solid and the domain sizes.     

Structural and spectroscopic characterization of Al2−x Cr x O3 powders obtained by polymeric precursor method

Al₂O₃ and Al_2−x Cr _x O₃ (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL^*a^*b^* color data). The obtained results allow to identify the γ-Al₂O₃ to α-Al₂O₃ phase transition. The single-phase α-Al₂O₃ powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al_2−x Cr _x O₃ are related to the γ to α-Al₂O₃ phase transition and the temperature and time range for such transition depends on the chromium content.     

SrZrO3 powders obtained by chemical method: Synthesis,characterization and optical absorption behaviour

Strontium zirconate (SrZrO₃) powders have been synthesized by the polymeric precursor method after heat treatment at different temperatures for 2 h in oxygen atmosphere. The decomposition of precursor powder was followed by thermogravimetric analysis, X-ray diffraction (XRD) and Fourier transform Raman (FT-Raman). The UV–vis absorption spectroscopy measurements suggested the presence of intermediary energy levels in the band gap of structurally disordered powders. XRD, Rietveld refinement and FT-Raman revealed that the powders are free of secondary phases and crystallizes in the orthorhombic structure.     

Synthesis of alkali-metal cobalt kambaldaite by precipitation method

Alkali-metal cobalt kambaldaite (alkali-metal cobalt carbonate hydroxide hydrate; ideal structure, M₂Co₈(CO₃)₆(OH)₆ · 6H₂O; M-CoKBL) was prepared by the addition of a cobalt nitrate solution into a solution containing a large excess of alkali-metal bicarbonate followed by aging at 50 °C for 2–3 h. Hydrated alkali-metal ions are present in the channels of the kambaldaite structure; therefore, we tried to ion-exchange the K-CoKBL sample with various metals. However, collapse of the kambaldaite structure took place easily because of low pH of the ion-exchange solution. The catalytic activity of Co₃O₄ obtained by the calcination of “ion-exchanged” K-CoKBL was dependent on the residual potassium content in the catalyst.     

Synthesis of size-controlled cobalt ferrite particles with high coercivity and squareness ratio

Cobalt ferrite particles with diameters ranging from a few micrometer to about 15 nm were synthesized using a modified oxidation process. The fine control of the particle size was achieved by introducing various concentrations of Fe(3+) ions at the beginning of the reaction. Among the particle sizes obtained by using this method, particles with a grain size of about 36 nm showed a magnetization (M(s)) of 64 emu/g and a maximum coercivity (H(c)) of 2020 Oe at room temperature. The corresponding squareness ratio was found to be 0.53.     

Preparation and characterization of LiCoO2 by hydrazine-based precursor method

Journal of Thermal Analysis and Calorimetry - In this paper, LiCoO2 was prepared by combustion method. A hydrazine-based precursor was synthesized by four different routes using hydrazine hydrate...     

Nickel ferrite spinel as catalyst precursor in the dry reforming of methane:Synthesis,characterization and catalytic properties

Dry reforming of methane by CO2 using nickel ferrite as precursor of catalysts was investigated.Nickel ferrite crystalline particles were prepared by coprecipitation of nitrates with NaOH or ammonia followed by calcination,or by hydrothermal synthesis without calcination step.The textural and structural properties were determined by a number of analysis methods,including X-ray diffraction (XRD),Raman spectroscopy and X-ray photoelectron spectroscopy (XPS),among which X-ray diffraction (XRD) was at room and variable temperatures.All synthesized oxides showed the presence of micro or nanoparticles of NiFe2O4 inverse spinel,but Fe2O3 (hematite) was also present when ammonia was used for coprecipitation.The reducibility by hydrogen was studied by temperature-programmed reduction (TPR) and in situ XRD,which showed the influence of the preparation method.The surface area (BET),particle size (Rietveld refinement),as well as surface Ni/Fe atomic ratio (XPS) and the behavior upon reduction varied according to the synthesis method.The catalytic reactivity was investigated using isopropanol decomposition to determine the acid/base properties.The catalytic performance of methane reforming with CO2 was measured with and without the pre-treatment of catalysts under H2 in 650-800 C range.The catalytic conversions of methane and CO2 were quite low but they increased when the catalysts were pre-reduced.A significant contribution of reverse water gas shift reaction accounted for the low values of H2 /CO ratio.No coking was observed as shown by the reoxidation step performed after the catalytic reactions.The possible formation of nickel-iron alloy observed during the study of reducibility by hydrogen was invoked to account for the catalytic behavior.     

Synthesis and characterization of epoxy resin-montmorillonite nanocomposites obtained by frontal polymerization

Frontal polymerization, a method that allows to convert a monomer into a polymer exploiting the exothermicity of the self-same polymerization reaction, has been conveniently used for the easy and fast preparation of epoxy resin-montmorillonite nanocomposites. The obtained materials have shown characteristics similar or even better than those prepared by the conventional polymerization routes. The synthetic methods and the thorough characterization of the obtained nanocomposites are described. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2204–2211, 2007