Synthesis of multielement ferrites and their silica composites

Ferrites of composition M_0.2Co_0.4Zn_0.4Fe₂O₄ with M = Cu²⁺, Mn²⁺ and Ni²⁺ were prepared by citrate complex method. Later, their composites with silica have also been obtained by a simple route. The citrate complex precursors of multielement ferrites were characterized by FTIR spectroscopy and thermal analysis, been found a similar behavior for the three systems. The thermal treatment (at 400, 600 and 800 °C) of precursors gives, as result, the spinel type cubic ferrite pure when the ions substituted were copper and nickel; when manganese was used an hematite phase was obtained as contaminant at 800 °C. The presence of all ions involved and the particle size was corroborated by EDX analysis and measured from a TEM micrograph, respectively. The magnetic parameters related to magnetic properties, magnetization and coercivity, were different depending of the chemical composition of the ferrite and the thermal treatment temperature, as it was expected. At room temperature, the values obtained were near to those reported for Co-ferrite in bulk. The synthesis route of the composites M_0.2Co_0.4Zn_0.4Fe₂O₄-SiO₂, proposed in this work, gives as result magnetic nanoparticles in an amorphous silica matrix. Their magnetic properties were depending on weight percentage of the magnetic phase in the composite.     

Characterization and preparation of nanocrystalline MgCuZn ferrite powders synthesized by sol–gel auto-combustion method

Nanocrystalline Mg–Cu–Zn ferrite powders were successfully synthesized through nitrate–citrate gel auto-combustion method. Characterization of the nitrate–citrate gel, as-burnt powder and calcined powders at different calcination conditions were investigated by using XRD, DTA/TG, IR spectra, EDX, VSM, SEM and TEM techniques. IR spectra and DTA/TGA studies revealed that the combustion process is an oxidation–reduction reaction in which the NO₃ ⁻ ion is oxidant and the carboxyl group is reductant. The results of XRD show that the decomposition of the gel indicated a gradual transition from an amorphous material to a crystalline phase. In addition, increasing the calcination temperature resulted in increasing the crystallite size of Mg–Cu–Zn ferrite powders. VSM measurement also indicated that the maximum saturation magnetization (64.1 emu/g) appears for sample calcined at 800 °C while there is not much further increase in M _s at higher calcination temperature. The value of coercivity field (H _c) presents a maximum value of 182.7 Oe at calcination temperature 700 °C. TEM micrograph of the sample calcined at 800 °C showed spherical nanocrystalline ferrite powders with mean size of 36 nm. The toroidal sample sintered at 900 °C for 4 h presents the initial permeability (μ _i) of 405 at 1 MHz and electrical resistivity (ρ) of 1.02 × 10⁸ Ω cm.     

Structural,textural, morphological,magnetic and electromagnetic study of Cu-doped NiZn ferrite synthesized by pilot-scale combustion for RAM application

The synthesis of the Ni_0.5-xZn_0.5-xCu_2xFe₂O₄ (x = 0; 0.10 and 0.15) ferrite with the differential of pilot-scale production by the combustion reaction method was investigated for RAM application purposes. Combustion temperatures ranging from 682 °C to 738 °C were observed. All ferrites were sintered at 1200 °C for 1 h. A comprehensive study of the influence of substitution with Cu²⁺ in a partial and proportional way to the Ni²⁺ and Zn²⁺ ions, doping mode little reported in the literature, and also of the sintering process over the structural, textural, morphological, magnetic and electromagnetic properties of NiZnCu ferrites was performed. The XRD patterns of the ferrites as synthesized revealed the formation of the cubic structure of the inverse spinel as majoritary phase, and traces of hematite and zinc oxide as segregated phases. After sintering, it was proven the single-phase formation of cubic spinel ferrite structure. The introduction of Cu led to a reduction in the lattice parameter, whose values ranged from 8.337 to 8.385 Å. The EDX results confirm the composition of oxides. The textural and morphological analyses confirmed the densest characteristic, with increase of particle size and reducing of surface area and pore volume after Cu-doping. All ferrites showed characteristics of soft ferrimagnetic material, where the increase in Cu content contributed to a slight reduction in saturation magnetization, whose values were of ~22–29 emu/g for the as synthesized ferrites and ~71–85 emu/g for the sintered ones. The best result of electromagnetic absorption in X-band was presented by the sintered ferrite with 0.3 mol of Cu, reaching an attenuation of 99.8% at 11.5 GHz frequency, thus confirming the efficiency of the pilot-scale combustion synthesis in obtaining a ferrite with great potential for RAM application.     

Influence of the thermal treatment in the crystallization of NiWO4 and ZnWO4

NiWO₄ and ZnWO₄ were synthesized by the polymeric precursor method at low temperatures with zinc or nickel carbonate as secondary phase. The materials were characterized by thermal analysis (TG/DTA), infrared spectroscopy, UV–Vis spectroscopy and X-ray diffraction. NiWO₄ was crystalline after calcination at 350 °C/12 h while ZnWO₄ only crystallized after calcination at 400 °C for 2 h. Thermal decomposition of the powder precursor of NiWO₄ heat treated for 12 h had one exothermic transition, while the precursor heat treated for 24 h had one more step between 600 and 800 °C with a small mass gain. Powder precursor of ZnWO₄ presented three exothermic transitions, with peak temperatures and mass losses higher than NiWO₄ has indicating that nickel made carbon elimination easier.     

Effect of the modifier ion on the properties of MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript> and ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> pigments

Magnesium and zinc ferrites have been prepared by the polymeric precursor method. The organic material decomposition was studied by thermogravimetry (TG) and differential thermal analysis (DTA). The variation of crystalline phases and particle morphology with calcination temperature were investigated using X-ray diffraction (XRD) and scanning electronic microscopy (SEM), respectively. The colors of the ferrites were evaluated using colorimetry. Magnesium ferrite crystallizes above 800°C, presenting a yellow- orange color with a reflectance peak at the 600–650 nm range, while zinc ferrite crystallizes at 600°C, with a reflectance peak between 650–700 nm, corresponding to the red-brick color.     

Nonstoichiometric Zn Ferrite and ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Composite Spheres: Preparation,Magnetic Properties,and Chromium Removal

Monodisperse and porous nonstoichiometric Zn ferrite can be prepared by a solvothermal method. Such non-Zn ferrite was used to be the precursor for synthesis of ZnFe₂O₄/Fe₂O₃ composite via calcination at 600°C for 3 h in air. X-ray powder diffractometer (XRD) and Energy Dispersive Spectrometer (EDS) proved the nonstoichiometry of Zn ferrite synthesized by solvothermal method and the formation of ZnFe₂O₄/Fe₂O₃ composite via calcination. TEM image showed that non-Zn ferrite spheres with wormlike nanopore structure were made of primary nanocrystals. BET surface area of non-Zn ferrite was much higher than that of ZnFe₂O₄/Fe₂O₃ composite. Saturation magnetization of non-Zn ferrites was significantly higher than that of ZnFe₂O₄/Fe₂O₃ composites. Calcination of non-Zn ferrite resulted in the formation of large amount of non-magnetic Fe₂O₃,which caused a low magnetization of composite. Because of higher BET surface area and higher saturation magnetization, non-Zn ferrite presented better Cr⁶⁺ adsorption property than ZnFe₂O₄/Fe₂O₃ composites.     

Structural evolution and magnetic properties of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanofibers by electrospinning

The SrFe₁₂O₁₉/poly (vinyl pyrrolidone) (PVP) composite fiber precursors were prepared by the sol-gel assisted electrospinning with ferric nitrate, strontium nitrate and PVP as starting reagents. Subsequently, the M-type strontium ferrite (SrFe₁₂O₁₉) nanofibers were derived from calcination of these precursors at 750–1,000 °C.The composite precursors and strontium ferrite nanofibers were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The structural evolution process of strontium ferrite consists of the thermal decomposition and M-type strontium ferrite formation. After calcined at 750 °C for 2 h the single M-type strontium ferrite phase is formed by reactions of iron oxide and strontium oxide produced during the precursor decomposition process. The nanofiber morphology, diameter, crystallite size and grain morphology are mainly influenced by the calcination temperature and holding time. The SrFe₁₂O₁₉ nanofibers characterized with diameters of around 100 nm and a necklace-like structure obtained at 900 °C for 2 h, which is fabricated by nanosized particles about 60 nm with the plate-like morphology elongated in the preferred direction perpendicular to the c-axis, show the optimized magnetic property with saturation magnetization 59 A m² kg⁻¹ and coercivity 521 kA m⁻¹. It is found that the single domain critical size for these M-type strontium ferrite nanofibers is around 60 nm.     

Effects of strontium silicate on structure and magnetic properties of electrospun strontium ferrite nanofibers

The composite nanofibers of xSrSiO₃/(100 − x)SrFe₁₂O₁₉ (x = 0–13 wt%) with diameters around 110 nm have been prepared by calcination of the electrospun SrSiO₃/SrFe₁₂O₁₉/poly (vinyl pyrrolidone) (PVP) composite fibers at 800–900 °C. The composite nanofibers were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. After calcined at 800° the M-type strontium ferrite is formed and the strontium silicate exists as an amorphous state when the calcination temperature below about 950 °C. The addition of SrSiO₃ has an obvious suppression effect on the strontium ferrite grain growth and the ferrite grain size decreases from 66.9 to 33.5 nm corresponding SrSiO₃ content from 0 to 9 wt% in the composite. The specific saturation magnetization (Ms) of the xSrSiO₃/(100 − x)SrFe₁₂O₁₉ composite nanofibers exhibits a continuous reduction from 58.0 to 45.6 A m² kg⁻¹ with the increase of SrSiO₃ content from 0 to 13 wt%. With addition of SrSiO₃ from 0 to 13 wt%, the coercivity of the composite nanofibers obtained at 900 °C initially increases, reaching a maximum value 501.1 kA m⁻¹ at the silicate content 7 wt%, and then shows a reduction tendency with the strontium silicate content increase further up to 13 wt%. This influence on the coercivity by strontium silicate can be attributed mainly to the ferrite grain growth suppression and the non-magnetic phase barrier for the domains misalignment.     

Heat-induced changes in microstructure and magnetic properties of Co0.75Ni0.75[Fe(CN)6] · XH2O

Polycrystalline Co_0.75Ni_0.75[Fe(CN)₆]?·?XH₂O was prepared by coprecipitation. The coprecipitated powder was annealed in vacuum at 80°C, 100°C, and 130°C. Variation of microstructural and magnetic properties with different annealed temperatures was studied by Fourier-transform infrared, X-ray diffraction, and magnetization measurements. The differences in magnetic phase transition temperature, coercivity, remanence, and effective magnetization were studied in detail. The magnetic contribution mainly results from Fe^III–CN–Co^II/Ni^II and Fe^III–NC–Co^II/Ni^II because Fe^II–CN–Co^III/Ni^II carries no net spin. After annealing at 130°C, the microstructures Fe^III–CN–Co^II/Ni^II and Fe^III–NC–Co^II/Ni^II convert to Fe^II–CN–Co^III/Ni^II. Differences in magnetic properties may be attributed to heat-induced microstructural changes.     

Thermochemical studies on the formation and constitution of the zinc oxide—aluminium oxide system

This study is based on thermogravimetric (TG), differential thermal analysis (DTA) and chemical analysis of the ZnOAl₂O₃ system. The coprecipitation from mixed nitrate salt solutions of zinc and aluminium results in the formation of zinc basic carbonate and aluminium hydroxide, and is also a precursor to aluminate spinel (2ZnO·3Al₂O₃) only in the samples in which aluminium is present in near or above stoichiometric quantities. Grinding of the mixtures of individual precipitates maintains the similarity with coprecipitates in forming a “precursor”, but to a lesser extent. The endothermic peak in DTA at 275°C in some coprecipitated and mixed samples hints at the formation of a precursor since the individual precipitate does not have a peak at this temperature. The “precursor” to spinel obtained in the precipitation stage in some coprecipitated samples is freely soluble in 1 M HCl, and that obtained at 450°C is partially soluble which cannot be detected by the usual X-ray technique due to its highly disordered structure in amorphous state. The “precursor” is converted around 800°C to an actual spinel structure, which is almost insoluble in M HCl and is detectable by X-rays.     

The study of thermal,microstructural and magnetic properties of manganese–zinc ferrite prepared by co-precipitation method using different precipitants

Mn–Zn ferrite was prepared from the solution after acid leaching of spent batteries by co-precipitation method using ammonia oxalate, sodium carbonate and sodium hydroxide as precipitating agents. The co-precipitation process was performed at temperature of over 50 °C by continuous magnetic stirring. The precipitates were pre-sintered at 850 °C in air. Dilatometric study has revealed that lowest shrinkage (only 5.6%) showed a material obtained from an oxalate precipitant. After pressing and high-temperature sintering at 1325 °C, it showed both insufficient density and the presence of pores, which contribute to the deterioration in the magnetic properties of the ferrites: the low magnetic permeability value and high magnetic losses. Ferrite prepared from hydroxide and carbonate precipitant showed a much higher shrinkage, sintered density and much higher magnetic permeability compared with the ferrite prepared from oxalate precursor.     

Synthesis of nanosized ferrites from the thermolysis of strontium and barium hexa(formato)ferrates(III)

Summary The thermal analysis of strontium and barium hexa(formato)ferrates(III), M₃[Fe(HCOO)₆]₂^. xH₂O, has been carried out from ambient temperature to 800 °C. Various physico-chemical techniques, i.e., TG, DTG, DSC, XRD, IR, M?ssbauer spectroscopy, etc., have been employed to characterize the intermediates/end products. After dehydration, the anhydrous complexes undergo decomposition to yielda-Fe₂O₃and metal oxalate in the temperature range of 275-290 °C. A subsequent oxidative decomposition of metal oxalate leads to the formation of respective alkaline earth metal carbonate in successive stages. Finally, nanosized ferrites of Sr₂Fe₂O₅and BaFe₂O₄stoichiometry have been obtained as a result of a solid-state reaction betweena-Fe₂O₃and a fraction of MCO₃. The temperature of ferrite formation is much lower than possible in the conventional ceramic method.     

Preparation and thermal stability of trioxalatocobaltates of bivalent metals KM2+ [Co(C2O4)3]·xH2O

Trioxalatocobaltates of bivalent metals KM²⁺[Co(C₂O₄)₃]·x H₂O, with M²⁺ = Ba, Sr, Ca and Pb, have been prepared, characterized and their thermal behaviour studied. The compounds decompose to yield potassium carbonate, bivalent metal carbonate or oxide and cobalt oxide as final products. The formation of the final products of decomposition is influenced by the surrounding atmosphere. Bivalent metal cobaltites of the types KM²⁺CoO₃ and M²⁺CoO_3—x are not identified among the final products of decomposition. The study brings out the importance of the decomposition mode of the precursor in producing the desired end products.     

纯相和镍取代的Co_3O_4尖晶石催化剂用于N_2O直接分解(英文)

A series of NixCo1-xCo2O4(0 ≤ x ≤ 1) spinel catalysts were prepared by the co-precipitation method and used for direct N2O decomposition. The decomposition pathway of the parent precipitates was characterized by thermal analysis. The catalysts were calcined at 500 °C for 3 h and characterized by powder X-ray diffraction, Fourier transform infrared, and N2 adsorption-desorption. Nickel cobaltite spinel was formed in the solid state reaction between NiO and Co3O4. The N2O decomposition measurement revealed significant increase in the activity of Co3O4 spinel oxide catalyst with the partial replacement of Co2+ by Ni2+. The activity of this series of catalysts was controlled by the degree of Co2+ substitution by Ni2+, spinel crystallite size, catalyst surface area, presence of residual K+, and calcination temperature.     

SrSnO<Subscript>3</Subscript>:Nd obtained by the polymeric precursor method

In this work, the synthesis of Nd-doped SrSnO₃ by the polymeric precursor method, with calcination between 250 and 700 °C is reported. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After heat treatment, the material was characterized by XRD and infrared spectroscopy. Ester and carbonate amounts were strictly related to Nd-doping. According to XRD patterns, the orthorhombic perovskite was obtained at 700 °C for SrSnO₃ and SrSn_0.99Nd_0.01O₃. For Sr_0.99Nd_0.01SnO₃, the kinetics displayed an important hole in the crystallization process, as no peak was observed in HTXRD up to 700 °C, while a XRD patterns showed a crystalline material after calcination at 250 °C.     

Synthesis and properties of LiMIIPO4 (MII = Mg,Mn0.5Mg0.5, Co0.5Mg0.5) affected by isodivalent doping and Li-sources

NH₄M^IIPO₄·H₂O (M^II = Mg, Mn_0.5Mg_0.5, Co_0.5Mg_0.5) were synthesized by direct-precipitating method. The olivine-like LiM^IIPO₄ were successfully generated through the solid state reaction between the synthesized NH₄M^IIPO₄·H₂O precursors and two different Li-sources (Li₂CO₃ or LiOH·H₂O). The NH₄M^IIPO₄·H₂O and LiM^IIPO₄ compounds were confirmed by TG/DTG/DTA, AAS/AES, FTIR and XRD methods. The structural and morphological properties of LiM^IIPO₄ compounds were studied by XRD and SEM, respectively. The XRD reflection shifts of olivine-like LiM^IIPO₄ from the Li-source of Li₂CO₃ revealed changing toward higher diffraction angles than that of LiM^IIPO₄ from the Li-source of LiOH·H₂O. The XRD shifts of LiM_0.5Mg_0.5PO₄ (M = Mn or Co) compounds confirmed the formation of the single phase of isodivalent doping of Mn²⁺ and Co²⁺ ions according to the change in the lattice parameters and cell volumes. The morphological investigations of the LiM^IIPO₄ obtained from Li₂CO₃ system illustrated the grain-like shape particles having smaller size of about 150–400 nm on account of the sequential transformations of types: deammoniation, dehydration, polycondensation and decarbonization. Conversely, the larger size particles (300–700 nm) of the LiM^IIPO₄ obtained from LiOH·H₂O were observed due to the shorter transformation path through the reactions of types: deammoniation and dehydration without polycondensation and decarbonization.     

Isomorphous Catena Transition Metal Squarates [MII(C4O4)(dmso)2(OH2)2] (M = Co,Mn) and Magnetic Investigation into their Solid Solution M = CoxMn1–x

The crystal structures of two new isomorphous transition metal squarato complexes [M^II(C₄O₄)(dmso)₂(OH₂)₂] [M^II = Co^II (3d⁷), Mn^II (3d⁵); dmso = dimethylsulfoxide] and their magnetic properties are reported. The compounds feature two symmetrically independent chains, in which 1,3‐bridging squarato ligands connect cations in distorted octahedral surroundings of pseudo‐symmetry D_4h. From an equimolar solution of CoCl₂ · 6H₂O and MnCl₂ · 2H₂O a mixed‐metal coordination polymer crystallizes; it represents a solid solution and adopts the same structure as the corresponding monometallic compounds. The results of the diffraction experiment unambiguously proof the presence of both Co^II and Mn^II cations in either independent site albeit no precise ratio between the metal cations involved may be deduced from these findings. The difference in the magnetic properties between Co^II and Mn^II cations in the given ligand field has allowed us to establish their ratio in the solid solution more reliably than by X‐ray diffraction: Accounting for ligand field potential and spin‐orbit coupling of Co^II and regarding Mn^II as a pure spin system, the calculations yielded a fraction of 73 % Co^II in the mixed‐metal polymer. With respect to superexchange effects only weak antiferromagnetic interactions have been detected for the three coordination polymers.     

Chrysanthemum-like Co3O4 architectures: Hydrothermal synthesis and lithium storage performances

Three-dimensional chrysanthemum-like Co₃O₄ was prepared via a facile hydrothermal route without any template, and a subsequent calcination process. With a controlled concentration of the homogeneous precipitation agent, urea, a chrysanthemum-like precursor was hydrothermally obtained at 120 °C for 20 h, and the morphology was kept for Co₃O₄ after a subsequent calcination at 300 °C for 2 h. Co₃O₄ chrysanthemum-like architectures are assemblies of nanorods radiating from a common centre, and the nanorods consisted of interconnected nanoparticles with the size of about 30 nm. When tested as an anode material of Li-ion batteries, chrysanthemum-like Co₃O₄ presented a discharge capacity of ∼450 mA h/g after 50 discharge/charge cycles.     

Preparation and characterization of Ba<Subscript>2</Subscript>Co<Subscript>2</Subscript>Fe<Subscript>12</Subscript>O<Subscript>22</Subscript> ferrite via glucose sol–gel method

Ba₂Co₂Fe₁₂O₂₂ (Co₂Y) was synthesized by sol–gel method using glucose as chelating agent. X-Ray diffraction studies indicate that sintering temperature as low as 950 °C is sufficient to produce Co₂Y ferrites. Co₂Y ferrites calcined at 1,000 °C exhibit good magnetic prosperities in high frequency, with the resonance frequency up to 11 GHz and intrinsic permeability about 5 even at 6 GHz. The heat-treated temperature dependence of coercivity, initial permeability and resonance frequency is close related to the particle shape and size.     

Preparation of Monodisperse Ferrite Nanocrystals with Tunable Morphology and Magnetic Properties

The synthesis of monodisperse magnetic ferrite nanomaterials plays an important role in several scientific and technological areas. In this work, dibasic spinel MFe₂O₄ (M=Mg, Ni, Co, Fe, Mn) and polybasic spinel ferrite MCoFeO₄ (M=Mg, Ni, Mn, MgNi) nanocrystals were prepared by the calcination of layered double hydroxide (LDH) precursors at 900 °C, which was confirmed by X‐ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images demonstrate that the as‐obtained spinel ferrites present a single‐crystalline nature with uniform particle size and good dispersibility. The composition, morphology, and particle size can be effectively tuned by changing the metal ratio, basicity, reaction time, and temperature of the LDH precursors. In addition, these spinel ferrites show high magnetic saturation values in the range 21.7–84.3 emu g^?1, which maintain a higher level than the previously reported magnetic nanoparticles. Therefore, this work provides a facile approach for the design and fabrication of spinel ferrites with controllable nanostructure and improved magnetism, which could potentially be used in magnetic and biological fields, such as recording media, sensors, drug delivery, and intracellular imaging.