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1.
The thermal behavior of Co xFe 3?xO 4/SiO 2 nanocomposites obtained by direct synthesis starting from nonahydrate ferric nitrate and hexahydrate cobalt nitrate in different ratios with and without the addition of 1,4-butanediol was studied. For the synthesis of Co xFe 3?xO 4 ( x = 0.5–2.5) dispersed in the silica matrix a wide Co/Fe molar ratio was used. The decomposition processes, formation of crystalline phases, gases evolvement and mass changes during gels annealing at different temperatures were assessed by thermal analysis. The absence of succinate precursor and a low mass loss were observed in the case of the gel obtained in the absence of 1,4-butanediol. In case of gels obtained using a stoichiometric ratio of Co/Fe, no clear delimitation between Co and Fe succinates was observed, while for samples with a Fe or Co excess, the formation of the two succinates was observed. The evolution of the crystalline phase after annealing (673, 973 and 1273 K) investigated by X-ray diffraction analysis and Fourier transformed infrared spectrometry revealed that in samples with Fe excess, stoichiometric Fe/Co ratio or low Co excess, the cobalt ferrite (CoFe 2O 4) was obtained as a single phase, while in samples with higher cobalt excess, olivine (Co 2SiO 4) as a main phase, cobalt oxide and CoFe 2O 4 as secondary phases were obtained after annealing at 1273 K. The SEM images confirmed the nanoparticles embedding in the silica matrix, while the TEM and X-ray diffraction data showed that the obtained nanoparticles’ size was below 10 nm in most samples. 相似文献
2.
Nanocomposites of ferrite and ferroelectric phases are attractive functional ceramic materials. In this work, the nanocomposite
Ni 1−x
Co
x
Fe 2O 4–BaTiO 3( x = 0.2, 0.3, 0.4, 0.5) fibers with fine diameters of 3 ~ 7 μm and high aspect ratios were synthesized by the organic gel-thermal
decomposition process from the raw materials of citric acid and metal salts. The structure, thermal decomposition process
and morphologies of the gel precursors and the resultant fibers derived from thermal decomposition of the gel precursors were
characterized by Fourier transform infrared spectroscopy, thermogravimetric differential thermal analysis, X-ray diffraction
and scanning electron microscopy. The magnetic properties of the nanocomposite fibers were measured by vibrating sample magnetometer.
The nanocomposite fibers of ferrite Ni 1−x
Co
x
Fe 2O 4 and perovskite BaTiO 3 are formed at the calcination temperature of 900 °C for 2 h. The average grain sizes of Ni 1−x
Co
x
Fe 2O 4 and BaTiO 3 in the nanocomposite fibers increase from about 15 nm to approximately 67 nm with the increasing calcination temperatures
from 900 to 1,180 °C. The saturation magnetization of the nanocomposite Ni 1−x
Co
x
Fe 2O 4–BaTiO 3( x = 0.2, 0.3, 0.4, 0.5) fibers increases with the increase of grain sizes of Ni 1−x
Co
x
Fe 2O 4 and Co content, while the coercivity reaches a maximum value at the single-domain size of about 65 nm of Ni 0.5Co 0.5Fe 2O 4 obtained at the calcination temperature of 1,100 °C. 相似文献
3.
In this work the new synthesis and magnetic properties of NiFe 2O 4/SiO 2 and Co 0.5Zn 0.5Fe 2O 4/SiO 2 nanocomposites using a water‐soluble silica precursor, tetraglycolatosilane (THEOS), by the sol‐gel method were reported. Nanocomposite were obtained by the thermal decomposition of the organic part at different annealing temperatures varying from 400 to 900 °C. Studies carried out using XRD, FT‐IR, TEM, STA (TG‐DTG‐DTA) and VSM techniques. XRD patterns show that NiFe 2O 4 and Co 0.5Zn 0.5Fe 2O 4 have been formed in an amorphous silica matrix at annealing temperatures above 600 and 400 °C, respectively. It is found that when the annealing temperature is up to 900 °C NiFe 2O 4/SiO 2 and Co 0.5Zn 0.5Fe 2O 4/SiO 2 samples show almost superparamagnetic behavior with a magnetization 4.66 emu/g and ferromagnetic behavior with a magnetization 10.11 emu/g, respectively. The magnetization and coercivity values of nanocomposites using THEOS were considerably less than previous reports using TEOS. THEOS as a silica matrix network provides an ideal nucleation environment to disperse ferrite nanoparticles and thus to confine them to aggregate and coarsen. By using THEOS over the currently used TEOS and TMOS, organic solvents are not needed due to the entire solubility of THEOS in water. Synthesized nanocomposites with adjustable particle sizes and controllable magnetic properties make the applicability of ferrites even more versatile. 相似文献
4.
In this study, catalytic performance of nanoferrites NiFe 2O 4 and Ni 0.3Zn 0.7Fe 2O 4 is reported. Nickel–ferrite and mixed nickel–zinc ferrite were successfully synthesized by combustion reaction using a conical reactor with production of 10 g per batch. Crystallinity and purity or quantitative analysis of the catalyst were checked by using X-ray diffraction and energy dispersive X-ray analysis. Surface chemistry was examined via Fourier transform infrared (FTIR) analysis; N 2 physisorption at 77 K was conducted to obtain textural properties of the catalyst; a thermogravimetric analysis, a scanning electron microscope and a transmission electron microscopy were used to check the thermal stability and morphology of the catalyst, respectively. The catalysts were used to convert soybean oil into biodiesel in a batch mode and the reaction mixture was analyzed using a pre-calibrated gas chromatograph (GC). The presence of a single-phase spinel structure in the synthesized nanoparticles was confirmed by the XRD results. The Ni 0.3Zn 0.7Fe 2O 4 had a lower surface area value of 71.5 m 2g −1 and higher saturation magnetization value of 31.50 emu/g than sample NiFe 2O 4 which had 87.6 m 2g −1 and 17.85 emu/g, respectively. Biodiesel yield of 94% was obtained with Ni 0.3Zn 0.7Fe 2O 4 and 49% was obtained with NiFe 2O 4. Better performance of Ni 0.3Zn 0.7Fe 2O 4 when compared to that of NiFe 2O 4 could be attributed to higher acidity of the former. Findings from this study suggest that the development of nickel-zinc ferrite nanoparticles as magnetic heterogeneous catalysts could provide an environmentally friendly platform for biodiesel production. 相似文献
5.
Dissolution rates of NiO, CoO, ZnO, α-Fe 2O 3 and the corresponding ferrites in 0.1 mol dm −3 oxalic acid at pH 3.5 were measured at 70 °C. The dissolution of simple oxides proceeds through the formation of surface metal oxalate complexes, followed by the transfer of surface complexes (rate-determining step). At constant pH, oxalate concentration and temperature, the trend in the first-order rate constant for the transfer of the surface complexes ( kMe; Me=Ni, Co, Zn, Fe) parallels that of water exchange in the dissolved metal ions ( k−w). Thus, the most important factor determining the rates of dissolution of metal oxides is the lability of Me-O bonds, which is in turn defined by the electronic structure of the metal ion and its charge/radius ratio. UV (384 nm) irradiation does not increase significantly the dissolution rates of NiO, CoO and ZnO, whereas hematite is highly sensitive to UV light. For ferrites, the reactivity order is ZnFe 2O 4>CoFe 2O 4?NiFe 2O 4. Dissolution is congruent, with rates intermediate between those of the constituent oxides, Fe 2O 3 and MO ( M=Co, Ni, Zn), reflecting the behavior of very thin leached layers with little Zn and Co, but appreciable amounts of Ni. The more robust Ni 2+ labilizes less the corresponding ferrite. The correlation between log kM and log k−w is somewhat blurred and displaced to lower kM values. Fe(II), either photogenerated or added as salt, enhances the rate of Fe(III) phase transfer. A simple reaction mechanism is used to interpret the data. 相似文献
6.
The synthesis for a series of ferrite (M IIFe 2O 4) and cobaltite (M IICo 2O 4) spinels was investigated where M II is Mg, Co, Ni, Cu or Zn. The ferrites were prepared at a calcination temperature of 800 °C; the cobaltites at 500 °C. TG–MS
indicated that reduction of Co III to Co II occurs at ca . 800 °C, hence, the lower calcination temperature. For both the ferrites and the cobaltites, the evolution of water and CO 2 during the calcination suggests the presence of both species in the precipitates. The observed mass losses indicated that
the precursor basic carbonate precipitates for the cobaltite synthesis were predominantly carbonate, while the precursor basic
carbonate precipitates for ferrite synthesis were predominantly hydroxide in character. XRD data showed successful synthesis
of the ferrites with minimal contamination from the parent oxides, while the cobaltites were observed to be predominantly
of the spinel structure. 相似文献
7.
A series of Ni doped cobalt ferrite compounds with the formula Ni
χ
Co 1−χ
Fe 2O 4 where x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 were prepared using a hydrothermal method and subsequently sintered/annealed at 600
°C for 3 h. The influence of the Ni content on the lattice parameter, a, stretching vibration and the magnetization of specimens were subsequently studied. XRD and FTIR were used to investigate
structure and composition variations. All samples were found to have a cubic spinel structure. SEM was used to study morphological
variations. The results indicate that the average particle sizes are between 30–35 nm with a narrow size distribution along
with nanocrystals forming of regular octahedrons. A decrease in the peak to peak line width and increase in resonance field
with increasing Ni content were observed from ESR measurements. Based on ESR results, a core-shell type of formation was proposed
where the core is made up of undoped CoFe 2O 4 and the shell is Ni 2+ doped CoFe 2O 4.
相似文献
8.
Solid-phase synthesis of cobalt, nickel, copper, and zinc ferrites with spinel structure was performed from oxides of these metals and natural magnetite under the action of microwave radiation. The optimal conditions in which the corresponding ferrites can be formed were determined by varying the irradiation parameters affecting the reaction (magnetron power and reaction duration). It was found that the solid-phase interaction of oxides of Ni, Zn, Cu, Co(II) metals gives in practically acceptable yields metal-substituted ferrospinels (NiFe 2O 4, CoFe 2O 4, ZnFe 2O 4, CuFe 2O 4) constituting the main phase of the samples. A high capacity of the precursors and target synthesis products for absorption of the microwave radiation energy at a frequency of 2.45 GHz and its transformation into heat was demonstrated. This gives reason to use these compounds when preparing catalysts for microwave-stimulated reactions. 相似文献
9.
In this work the synthesis of CoFe 2O 4-SiO 2 and NiFe 2O 4-SiO 2 nanocomposites was studied via the sol–gel method, using the polymerized complex route. The polymerized precursors obtained
by the reaction of citric acid, ethylene glycol, tetraethylorthosilicate, ferric nitrate, and cobalt nitrate or nickel chloride
were characterized by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. NMR and IR spectra of the precursors,
without and with metallic ions, show the formation of polymeric chains with ester and ether groups and complexes of metal-polymeric
precursor. The nanocomposites were obtained by the thermal decomposition of the organic fraction and characterized by X-ray
diffraction (XRD) and vibrating sample magnetometry (VSM). XRD patterns show the formation of CoFe 2O 4 and NiFe 2O 4 in an amorphous silica matrix above 400 °C in both cases. When the calcination temperature was 800 °C the particle size of
the crystalline phases, calculated using the Scherrer equation, reached ∼35 nm for the two oxides. VSM plots show the ferrimagnetic
behavior that is expected for this type of magnetic material; the magnetization at 12.5 KOe of the CoFe 2O 4-SiO 2 and NiFe 2O 4-SiO 2 compounds was 29.5 and 17.4 emu/g, respectively, for samples treated at 800 °C. 相似文献
10.
Co 0.5Ni 0.5(Gd/Nd) xFe 2-xO 4 (x ?= ?0.0 and 0.06) ferrites were prepared by the solid-state reaction method. These materials were characterized by XRD, FT-IR spectroscopy, and VSM techniques. The XRD analysis revealed the phase formation of all samples and their cubic spinel structure with the Fd-3m space group. Lattice constant was found to increase due to Gd and Nd ions substitution. However, the crystallite size was observed to decrease by the substitution effect. The FT-IR spectra showed the two vibrational frequency bands of the tetrahedral and octahedral sites. From the magnetic properties study, it was identified that the pure and Gd substituted Co 0.5Ni 0.5Fe 2O 4 ferrite showed a ferromagnetic behaviour. While the Nd substituted Co 0.5Ni 0.5Fe 2O 4 ferrite delivered a superparamagnetic behaviour. The substitution of Gd and Nd changed the values of the magnetic parameters of Co 0.5Ni 0.5Fe 2O 4 ferrite. An increase in the saturation magnetization (M s) value was observed due to substitution of Gd and Nd in Co 0.5Ni 0.5Fe 2O 4 ferrite, indicating that Gd and Nd substitution strengthen the supermagnetic interactions in Co 0.5Ni 0.5Fe 2O 4 ferrite. The highest value of M s was observed in Gd doped sample. 相似文献
11.
The spinel-type ferrites NiFe 2O 4 and Zn 0.5Ni 0.5Fe 2O 4 modified by lanthanide ions Eu 3+ and Tb 3+ were prepared by a sol—gel process with propylene oxide as a gelating agent. The phase homogeneity of the samples was tested by XRD and Mössbauer spectroscopy. Transmission electronic microscopy used for characterisation of the morphology of the samples revealed nanosized powdered samples with a narrow distribution of particle sizes. It was noted that the presence of Ln 3+ ions influenced the magnetic properties of nanosized NiFe 2O 4 and Ni 0.5Zn 0.5Fe 2O 4 ferrites. The dependence of the magnetic properties of the samples on the rare-earth doping may be explained by the different grain sizes. The saturation magnetisation tends to decrease with increasing rare-earth doping and decreasing crystallite size. A similar trend was observed for the coercive field, with the exception of the Tb 3+-doped Zn 0.5Ni 0.5Fe 2O 4 where it remained the same as in the pure ferrite. 相似文献
12.
Semiconducting nano-metal oxides (Fe3O4, Co3O4, NiO, CoFe2O4 and NiFe2O4) were synthesized by thermal decomposition of their oxalate precursors. Using DSC technique, effect of nano-metal oxides [5 m m?1 (%)] on the reaction pathway and mechanism of thermal decomposition of Ce2 (C2O4)3·10H2O in flowing atmosphere of N2 was investigated under linear non-isothermal condition. Performing the kinetic deconvolution method, physico-geometrical kinetic behavior of the two overlapping heat absorbing steps of both lower and higher temperature reactions was illustrated. Nano-Fe3O4 promoted the dehydration stages by lowering the Ea value to 35–36 kJ mol?1. Nano-Co3O4, nano-CoFe2O4 and nano-NiFe2O4 promoted the dehydration as well as decomposition stages of cerium oxalate decahydrate by decreasing the Ea value. Nano-NiO has shown retarding effect on both dehydration and decomposition stages. 相似文献
13.
A series of spinel-type Co xNi 1−xFe 2O 4 ( x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) magnetic nanomaterials were solvothermally synthesized as enzyme mimics for the eletroctrocatalytic oxidation of H 2O 2. X-ray diffraction and scanning electron microscope were employed to characterize the composition, structure and morphology of the material. The electrochemical properties of spinel-type Co xNi 1−xFe 2O 4 with different (Co/Ni) molar ratio toward H 2O 2 oxidation were investigated, and the results demonstrated that Co 0.5Ni 0.5Fe 2O 4 modified carbon paste electrode (Co 0.5Ni 0.5Fe 2O 4/CPE) possessed the best electrocatalytic activity for H 2O 2 oxidation. Under optimum conditions, the calibration curve for H 2O 2 determination on Co 0.5Ni 0.5Fe 2O 4/CPE was linear in a wide range of 1.0 × 10 −8–1.0 × 10 −3 M with low detection limit of 3.0 × 10 −9 M (S/N = 3). The proposed Co 0.5Ni 0.5Fe 2O 4/CPE was also applied to the determination of H 2O 2 in commercial toothpastes with satisfactory results, indicating that Co xNi 1−xFe 2O 4 is a promising hydrogen peroxidase mimics for the detection of H 2O 2. 相似文献
14.
Thick film of nanocrystalline Co 0.8Ni 0.2Fe 2O 4 was obtained by sol–gel citrate method for gas sensing application. The synthesized powder was characterized by X-ray diffraction
(XRD) and transmission electron microscopy. The XRD pattern shows spinel type structure of Co 0.8Ni 0.2Fe 2O 4. XRD of Co 0.8Ni 0.2Fe 2O 4 revels formation of solid solution with average grain size of about 30 nm. From gas sensing properties it observed that nickel
doping improves the sensor response and selectivity towards ammonia gas and very low response to LPG, CO, and H 2S at 280 °C. Furthermore, incorporation of Pd improves the sensor response and stability of ammonia gas and reduced the operating
temperature upto 210 °C. The sensor is a promising candidate for practical detector of ammonia. 相似文献
15.
以乙酰丙酮金属盐为前驱体,三乙二醇为溶剂,采用多元醇法制备了镍锌不同配比的Ni_xZn_(1-x)Fe_2O_4(x=0,0.3,0.5,0.7和1.0)铁氧体,并通过X射线衍射仪(XRD),透射电子显微镜(TEM)和振动样品磁强计(VSM)等对样品的结构、形貌、磁性能和磁热性能进行了表征。结果表明:Ni_xZn_(1-x)Fe_2O_4铁氧体分散性较好,尺寸均一,形状近似球形,平均粒径为4~5 nm。Ni_xZn_(1-x)Fe_2O_4纳米颗粒在室温下表现出亚铁磁性,饱和磁化强度随着镍含量的增加先增大后减小,当x=0.5时达到最大值29.38 emu·g~(-1)。在382k Hz交变磁场作用下,Ni_(0.5)Zn_(0.5)Fe_2O_4铁氧体温度可升温至313 K,表现出较好的磁热性能。 相似文献
16.
Nanostructured cobalt ferrite (CoFe2O4) has been synthesized by a two-step process, a facile ultrasonic-assisted solvothermal technique for Fe2Co-MOF preparation and subsequent calcination. X-ray diffraction (XRD) patterns confirm the formation of MIL-88A(Fe) structure of Fe2Co-MOF and the cubic spinel structure of CoFe2O4. Field emission scanning electron microscope (FESEM) images reveal that calcination process converts the spindle-like morphology of Fe2Co-MOF to yolk-shell CoFe2O4 microspheres. From Brunauer–Emmett–Teller (BET) analysis, the specific surface areas of 36.0 and 29.2 m2 g?1 are measured for Fe2Co-MOF and CoFe2O4, respectively. Vibrating sample magnetometer (VSM) analysis of CoFe2O4 displays high coercivity of 2500 Oe due to surface anisotropy. Conversion of Fe2Co-MOF to CoFe2O4 reduces the optical band gap from 1.92 to 1.77 eV. Electrochemical performance of Fe2Co-MOF and CoFe2O4 deposited on Ni foams (NFs) is examined by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) tests. Specific capacitances of 489.9 and 192.6 F g?1 have been achieved from GCD curves at a current density of 1 A g?1 for Fe2Co-MOF/NF and CoFe2O4/NF electrodes, respectively. Fe2Co-MOF/NF electrode exhibits more cyclic stability than CoFe2O4/NF electrode after 3000 cycles. 相似文献
17.
以乙二醇为溶剂,氯化铁、氯化钴、氯化镍和醋酸铵为反应试剂,采用溶剂热法制备纳米Ni xCo 1-xFe 2O 4( x=0、0.3、0.5、0.7、1)铁氧体空心微球,研究镍含量对铁氧体空心球的磁性与吸波性能的影响。借助X-射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、振动样品磁强计(VSM)和网络分析仪对试样的物相组成、微观形貌和电磁特性进行表征。结果表明制备的镍钴铁氧体为尖晶石结构,且形貌为空心球,粒径在200 nm左右。当 x=0时,镍钴铁氧体空心球饱和磁化强度最大为81.7 emu·g -1,反射损耗在1 658.8 MHz有最小值为-16.9 dB。 相似文献
18.
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 0.5Fe 2O 4. 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 0.5Fe 2(C 4H 2O 4) 3·6N 2H 4. 相似文献
19.
Nickel and iron substituted LaCoO 3 with rhombohedrally distorted perovskite structure were obtained in the temperature range of 600-900 °C by thermal decomposition of freeze-dried citrates and by the Pechini method. The crystal structure, morphology and defective structure of LaCo 1−xNi xO 3 and LaCo 1−xFe xO 3 were characterized by X-ray diffraction and neutron powder diffraction, TEM and SEM analyses and electron paramagnetic resonance spectroscopy. The reducibility was tested by temperature programmed reduction with hydrogen. The products of the partial and complete reduction were determined by ex-situ XRD experiments. The replacement of Co by Ni and Fe led to lattice expansion of the perovskite structure. For perovskites annealed at 900 °C, there was a random Ni, Fe and Co distribution. The morphology of the perovskites does not depend on the Ni and Fe content, nor does it depend on the type of the precursor used. LaCo 1−xNi xO 3 perovskites ( x>0.1) annealed at 900 °C are reduced to Co/Ni transition metal and La 2O 3 via the formation of oxygen deficient Brownmillerite-type compositions. For LaCo 1−xNi xO 3 annealed at 600 °C, Co/Ni metal, in addition to oxygen-deficient perovskites, was formed as an intermediate product at the initial stage of the reduction. The interaction of LaCo 1−xFe xO 3 with H 2 occurs by reduction of Co 3+ to Co 2+ prior to the Fe 3+ ions. The reducibility of Fe-substituted perovskites is less sensitive towards the synthesis procedure in comparison with that of Ni substituted perovskites. 相似文献
20.
Synchrotron based in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) techniques are used to study electronic and crystal structure changes of the carbon coated LiFe 1/4Mn 1/4Co 1/4Ni 1/4PO 4 (LiFe 1/4Mn 1/4Co 1/4Ni 1/4PO 4/C) cathode material for Li-ion batteries during the first charge. In situ Fe, Mn, Co and Ni K-edge XAS results revealed that the three voltage plateaus at ~3.6, 4.2 and 4.7 V vs. Li/Li + are attributed to the redox reactions of Fe 2+/Fe 3+, Mn 2+/Mn 3+ and Co 2+/Co 3+, respectively, while the apparent capacities above 4.9 V is not originated from the Ni 2+/Ni 3+ redox, but very likely from the electrolyte decomposition. Interesting phase transition behaviors of LiFe 1/4Mn 1/4Co 1/4Ni 1/4PO 4/C were observed with the formation of an intermediate phase and the solid solution regions. Combined in situ XAS and XRD techniques indicate fast electronic structural changes and slow bulk crystal structural changes. 相似文献
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