镧掺杂对大洋锰结核制备铁氧体磁性的影响

大洋锰结核又称铁锰结核、多金属结核,常见于4 000～6 000 m的海底沉积物表层,在世界各大洋底均有分布,预计总储量超过3×1012 t[1].天然锰结核含有Mn和Fe,以及Cu、Co、Ni、铂族和稀土等60多种金属元素,其中锰占20%～30%,铁约占3～20%[2].从化学成分而言,大洋锰结核与Mn-铁氧体(铁酸锰)十分接近.以锰结核为原料合成Mn-铁氧体可以为这种天然资源的开发利用提供新思路.     

On the consequences of mechanical activation of zinc and nickel ferrites

Mechanical activation of zinc and nickel ferrites was shown to affect their physicochemical properties. For example, the temperature of magnetic transition of activated zinc ferrite sharply increased, while that of activated nickel ferrite decreased. Variation in the magnetic properties of ferrites is not due to their reversal degree, but is caused by transfer of cation from tetrahedral- to the vacant octahedral-sites in the spinel structure. The cations are randomly distributed on the octahedral-sites producing new exchange-bound pairs. The disordering of the anion and cation sublattices, leading eventually to the X-ray-amorphous structure, is thought to be due to the plastic deformations in the course of mechanical activation.     

Mini-review: Ferrite nanoparticles in the catalysis

Recent applications of ferrite nanoparticles as catalysts in organic processes are reviewed. Catalytic applications include the use of mainly cobalt, nickel, copper, and zinc ferrites, as well as their mixed-metal combinations with Cr, Cd, Mn and sometimes some lanthanides. Core–shell nanostructures with silica and titania are also used without loss of magnetic properties. The ferrite nanomaterials are obtained mainly by wet-chemical sol-gel or co-precipitation methods, more rarely by the sonochemical technique, mechanical high-energy ball milling, spark plasma sintering, microwave heating or hydrothermal route. Catalytic processes with application of ferrite nanoparticles include decomposition (in particular photocatalytic), reactions of dehydrogenation, oxidation, alkylation, C–C coupling, among other processes. Ferrite nano catalysts can be easily recovered from reaction systems and reused up to several runs almost without loss of catalytic activity.     

Structure and morphology of spinel MFe2O4 (M=Fe, Co, Ni) nanoparticles chemically synthesized from heterometallic complexes

We synthesized magnetic spinel ferrites from trimetallic single-source precursors. Fe(II), Co(II), and Ni(II) ferrite nanoparticles in the range of 9-25 nm were synthesized by solvothermal decomposition of trimetallic acetate complex precursors in benzyl ether in the presence of oleic acid and oleylamine, using 1,2-dodecanediol as the reducing agent. For comparison, spinel ferrite nanoparticles were synthesized by stoichiometric mixtures of metal acetate or acetylacetonate salts. The nanoparticles (NP) were characterized by TEM, DLS, powder XRD, and Raman spectroscopy; and their magnetic properties were characterized by ZFC-FC and M(H) measurements. The ferrite-NP were more homogeneous and had a narrower size distribution when trimetallic complexes were used as precursors. As a consequence, the magnetic properties of these ferrite-NP are closer to the aimed room temperature superparamagnetic behavior, than are those of other ferrites obtained by a mixture of salts.     

Glass crystallization synthesis of ultrafine hexagonal M-type ferrites: Particle morphology and magnetic characteristics

This review concerns the synthesis and functional properties of ultrafine particles of M-type hexagonal ferrites prepared by the most advanced process of oxide glass crystallization. Hexaferrite phase formation during the heat treatment of multicomponent oxide glasses of various chemical compositions containing boron and/or silicon oxides as glass formers is considered. This route is useful to prepare assemblies of single-crystal strontium barium hexaferrite particles in the range of average particle sizes from tens of nanometers to several micrometers. The resulting glass ceramics and magnetic particle assemblies recovered from them are characterized by high coercive forces, approaching the theoretical limit for such compounds, and high magnetizations, close to the magnetization value for coarse-grained materials.     

M，W型六角钡铁氧体化学键性质和穆斯堡尔谱位移研究

利用电介质的平均能带模型研究了M型、W型六角铁氧体的化学成键性质,计算了各晶位的共价性的穆斯堡尔同质异能位移,结果与实验值一致,确定了Fe^2+在W型铁氧体中所占晶位。     

镝掺杂铁氧体纳米晶的制备、表征和磁性

采用化学共沉淀法制备出了镝掺杂铁氧体纳米晶, 利用透射电子显微镜(TEM)、X射线衍射仪(XRD)、傅立叶红外光谱仪(FTIR)、古埃磁天平、振动样品磁强计(VSM)、X射线能谱仪(EDX)等仪器对产物进行了表征, 研究了Dy^3＋掺杂量对铁氧体纳米晶的结构、磁性和粒度的影响. 结果表明: 适量稀土元素镝离子的掺杂可以提高尖晶石型铁氧体的磁性、降低矫顽力, 当n(Fe^3＋)∶n(Dy^3＋)＝14∶1时其磁性最强. Dy^3＋替代或充填进入了尖晶石晶格, 且主要占据B位. 掺杂了镝的铁氧体磁性纳米粒子粒度变小, 且分布更集中、均匀, 当Dy^3＋加入量为n(Fe^3＋)∶n(Dy^3＋)＝14∶1时铁氧体纳米粒子的平均粒径由掺杂前的14 nm降低到到8 nm. 这种具有超顺磁性的软磁铁氧体纳米晶可应用于纳米磁液领域.     

掺Ce提高（CoFe）3O4的矫顽力

采用添加剂湿法制备了掺入不同Ｃｅ含量的Ｃｅｘ（ＣｏＦｅ）３－ｘＯ４铁氧体。对产物的物相，形貌，磁性能研究表明，所得产物均为单一的尖晶石结构，一般情况下呈颗粒状，矫顽力随溶液中Ｃｅ＾４＋浓度的增加而增加。当溶液中含有Ｃｅ＾３＋和Ｃｅ（ＯＨ）４时，产物显示有部分棒状晶体，矫顽力有明显提高，且当「Ｃｅ＾３＋」占（「Ｃｅ＾３＋」＋Ｃｅ＾４＋「）总量的５％左右时所得产物矫顽力最大。     

Microstructural Characteristics and Magnetic Properties of Gadolinium-Substituted Cobalt Ferrite Nanocrystals Synthesized by Hydrothermal Processing

Gadolinium substituted cobalt ferrite nanocrystals with composition of CoFe_2?xGd_xO₄ (x = 0–0.04 in a step of 0.01) were prepared by a hydrothermal process and without subsequent annealing. X-ray diffraction, field-emission scanning electron microscopy, and vibrating sample magnetometer were used to investigate the effect of Gd³⁺ cation substitution on structural Characteristics and magnetic properties of cobalt ferrite nanocrystals. The X-ray diffraction analysis demonstrated that single phase spinel ferrites were obtained. The FE-SEM micrographs of the synthesized samples indicated the presence of two distinct groups of grains exhibiting different sizes and, more important, different shapes. The results of magnetic hysteresis at a room temperature showed that with an increase in gadolinium content, the coercive field decreased from 1250 Oe for x = 0 to 450 Oe for x = 0.03. In addition, it was observed that with substitutions of gadolinium cations, the values of saturation magnetization decreased.     

Vacancy contents and phase equilibria of Ti-substituted MnZn ferrite

Measurement of the divalent iron content in acid dissolved MnZn ferrites, fired in controlled atmospheres at various temperatures and quenched, allows calculation of cation vacancy contents. Addition of Ti⁴⁺ to these ferrites resulted in the introduction of vacancies at the rate of about 0 to 0.3 per Ti⁴⁺ depending on heat treatment conditions. Data are presented whereby the vacancy content with Ti⁴⁺ can be calculated based on the oxygen content of the undoped ferrite as available in the literature. Ti⁴⁺ stabilizes the hexagonal hematite-like structure and the phase boundary is presented as a function of Ti⁴⁺ and temperature. The vacancy contents at the phase boundary in Ti⁴⁺-doped ferrite as a function of temperature are in agreement with those calculated from the literature for undoped MnZn ferrites. Finally, the total oxygen content of coexisting spinel and hexagonal phases is presented.     

X型六角晶系钡铁氧体纳米晶的制备和表征

用硬脂酸凝胶法制备了Co₂-X型六角晶系钡铁氧体纳米晶,在750℃热处理得到的纳米晶形貌为球形,粒径范围为15～25nm.随着热处理温度的升高,粒子逐渐长大并呈块状.振荡样品磁强计测试结果表明,Co₂-X型六角晶系钡铁氧体纳米晶具有与常规体材料不同的磁性能,其比饱和磁化强度σ_s低于后者.产物的矫顽力、比饱和磁化强度随粒子的长大呈规律性的变化.     

Preparation and magnetic properties of Zn-Cu-Cr-La ferrite and its nanocomposites with polyaniline

Nanosized Zn(0.6)Cu(0.4)Cr(0.5)Fe(1.5-x)La(x)O(4) (x=0 - 0.06) ferrites doped with La are synthesized by a rheological phase reaction method. Polyaniline (PANI)/ferrite nanocomposites are prepared by in situ polymerization method. The structure, morphology and ferromagnetic property of ferrite powders and nanocomposites are characterized by X-ray powder diffractometer (XRD), transmission electron microscope (TEM), Fourier transform infrared spectra (FTIR), UV-visible spectroscopy (UV), thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM). The results indicate that the PANI and nanosized ferrite powders can be combined effectively. The polymers can reduce the agglomeration of nanosized ferrite particles to some extent, which is good for the dispersedness and stabilization of nanoparticles. The PANI/ferrite nanocomposites under applied magnetic field exhibit the hysteretic loops of the ferromagnetic nature. The magnetic properties of nanocomposites are tailored by controlling the ferrite content.     

Synthesis and neel temperature determination of ferrites from the MO−ZnO−Fe2O3 systems (M=Cu,Co and Ni)

The Curie (Neel) temperature is successfully determined by means of a simple magnetic device attached to the Q Derivatograph (MOM, Hungary), which is widely used in many laboratories. This possibility is demonstrated by a study of ferrite materials with general formula M_xZn_1?xFe₂O₄ (M=Cu, Co and Ni;x=0.0; 0.2; 0.4; 0.5; 0.6; 0.8; 1.0). X-ray phase analysis, Mössbauer spectroscopy and microscopic examinations revealed that the obtained ferrites are monophase samples. The mixed ferrites possess more strongly expressed magnetic properties than those of the individual ferrites; the maximum magnetic interaction in these ferrites is observed at different zinc contents.     

Synthesis and neel temperature determination of ferrites from the CuO−ZnO−Fe2O3 system

Conditions were established and individual and mixed ferrites with the general formula Cu_xZn_1?xFe₂O₄ (x=0; 0.1; 0.2; 0.3; 0.4; 0.5; 0.6; 0.7; 0.8; 1.0) were synthesized from the CuO?ZnO?Fe₂O₃ system. X-ray phase analysis, Mössbauer spectroscopy and microscopic examinations revealed that the obtained ferrites are monophase samples. A magnetic device was attached to the Q-Derivatograph (MOM, Hungary) and successfully used for sample investigation in a magnetic field, and in particular for Curie (Neel) temperature determination. The ferrite composition and the thermal treatment conditions were shown to correlate with the Neel temperature of the synthesized ferrites.     

CuFe2O4 nanomaterials: Current discoveries in synthesis,catalytic efficiency in coupling reactions,and their environmental applications

In the last few decades, there has been enormous growth in ferrite nanoparticles. Magnetic, optical, and electrical properties of ferrites gain consideration due to their use in various applications such as rechargeable lithium batteries, medical diagnostics, solar energy devices, and so forth. A vast increase in interest in ferrite nanoparticles has led them to be used as catalysts in various applications as they possess a large surface area-to-volume ratio. Furthermore, iron-based magnetic characteristics make it simple to retrieve catalysts by using an external magnet. Iron's catalytic potential, however, is far less than copper's. Therefore, the catalytic scope is substantially increased by substituting copper within the crystal lattice. Recently copper ferrite nanoparticles have caught the interest of numerous researchers due to low-cost magnetic material, stability under diverse conditions, and ease at which catalyst can be retrieved using an external magnetic field and utilized repeatedly. This review of data from year 2010 through 2022 emphasizes the synthesis method, structure, application in dyes degradation, catalytic potential in the number of coupling reactions, recyclability, and reusability of the magnetic catalyst.     

Utilisation of industrial waste for ferrite pigments production

Preliminary results of research focused on the utilisation of specific waste from metallurgical and mining activities to obtain ferrite pigments are presented. As a source of iron in the spinel-type ferrites with the general structure MFe₂O₄ (where M is a bivalent metal such as Ca and Zn), three types of industrial wastes were used: metallurgical slag from the production of non-ferrous metals and two types of AMD (acid mine drainage) sludge: one of natural origin (Fe-sediment) and the second one synthetically prepared from AMD (Fe-precipitate). This waste was homogenised by ZnO and CaCO₃ in various stoichiometric ratios n(Ca): n(Zn): n(Fe) and calcined at the temperature of 1000–1095°C. Mineralogical (XRD) analysis of the metallurgical slag pigments confirmed the formation of zinc ferrite and hematite only (Ca from reaction components entered into other phases). The ferric component of the AMD sludge (Fe-precipitate and Fe-sediment) formed a mixture of zinc ferrite, calcium ferrite, and hematite while increased calcination temperature supported the ferritic structure formation. Prepared pigments have no considerable colour differences; they were in brown colour tones. Pigments from the AMD sludge were more dark brown coloured than those from slag. Pigments were applied in an alkyd-resin paint and consequently basic anticorrosive tests were performed. Pigments obtained from metallurgical slag showed better anticorrosive properties than those from AMD. However, because of high Pb content in pigments from the slag (0.67–1.10 mass % Pb in pigments), utilisation of these pigments in coatings is problematic. Ferrite pigments from the AMD sludge, mainly that with zinc ferrite, have promising application in anticorrosive paints but optimisation of the preparation process is required.     

Evaluation of the catalytic effect of ZnO as a secondary phase in the Ni0.5Zn0.5Fe2O4 system and of the stirring mechanism on biodiesel production reaction

In search of efficient ways to produce biodiesel under environmentally friendly conditions, catalytic reactions have been explored with emphasis on replacing homogeneous by heterogeneous catalysis with the use of new catalyst types, such as the spinel ferrites, which are described as a viable option, since they are stable, highly active, inexpensive, reusable, and allow the easy recovery of the reaction medium through the application of magnetic fields. In this context, the present work proposes to contribute to the consolidation of the catalytic viability of the Ni_0.5Zn_0.5Fe₂O₄ system obtained by combustion reaction, because although previous studies indicate the catalytic effectiveness of this system in polyphasic form, the present work seeks as differential to evaluate the influence of the secondary phases and magnetization of the Ni-Zn system in the conversion to biodiesel, and for this purpose, it aims to evaluate the catalytic effect of ZnO formed as secondary phase and obtained concomitantly in the Ni-Zn ferrite synthesis, besides evaluating the effect of the stirring mechanism used in biodiesel production reaction by the ethyl transesterification of soybean oil. The synthesized Ni-Zn ferrites and ZnO sample were characterized by X-ray diffraction (XRD), nitrogen adsorption textural analysis (BET), particle size distribution, and then, tested in two reactor types, one with magnetic stirring, and another of mechanical stirring, to observe the magnetization effect of the material, and the characterization of the obtained biodiesels by gas chromatography (GC) and acidity index. The performed catalytic tests showed that the Ni-Zn ferrites promoted excellent ester conversions with values near and above 94%, thus confirming that although ZnO also promotes good ester conversion (83.9%), the catalytic effectiveness of the Ni-Zn ferrite is evident and independent of secondary phases. Moreover, the catalytic tests performed in the magnetic stirring reactor using the Ni-Zn ferrites as catalysts made it possible to realize that their magnetic properties may be interference in the catalytic effectiveness, being this, a more determining factor than the surface characteristics.     

Thermomagnetometric analysis of lithium ferrites

In this work, the magneto-phase transitions in pure lithium (Li_0.5Fe_2.5O₄), lithium–zinc (Li_0.4Fe_2.4Zn_0.2O₄) and lithium–titanium (Li_0.6Fe_2.2Ti_0.2O₄) ferrites were studied by the thermogravimetric analysis in magnetic field, which is known as the thermomagnetometry method. The ferrites were prepared by the solid-state synthesis from oxides and carbonates. The Curie point of magnetic phase in ferrites and their composite mixtures was determined from the derivative thermogravimetric curve in the region of ferrite mass change associated with the ferrimagnet–paramagnet transition in the magnetic phase. The method based on the analysis of ferrite mass change at Curie temperature was developed to estimate the ferrite phase concentrations in composite magnetic materials.

     

Magnetic properties of binary and ternary mixed metal oxides NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> and Zn<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> doped with rare earths by sol—gel synthesis

The spinel-type ferrites NiFe₂O₄ and Zn_0.5Ni_0.5Fe₂O₄ modified by lanthanide ions Eu³⁺ and Tb³⁺ 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 Ln³⁺ ions influenced the magnetic properties of nanosized NiFe₂O₄ and Ni_0.5Zn_0.5Fe₂O₄ 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 Tb³⁺-doped Zn_0.5Ni_0.5Fe₂O₄ where it remained the same as in the pure ferrite.     

Preparation of Magnesium,Cobalt and Nickel Ferrite Nanoparticles from Metal Oxides using Deep Eutectic Solvents

Natural deep eutectic solvents (DESs) dissolve simple metal oxides and are used as a reaction medium to synthesize spinel‐type ferrite nanoparticles MFe₂O₄ (M=Mg, Zn, Co, Ni). The best results for phase‐pure spinel ferrites are obtained with the DES consisting of choline chloride (ChCl) and maleic acid. By employing DESs, the reactions proceed at much lower temperatures than usual for the respective solid‐phase reactions of the metal oxides and at the same temperatures as synthesis with comparable calcination processes using metal salts. The method therefore reduces the overall required energy for the nanoparticle synthesis. Thermogravimetric analysis shows that the thermolysis process of the eutectic melts in air occurs in one major step. The phase‐pure spinel‐type ferrite particles are thoroughly characterized by X‐ray diffraction, diffuse‐reflectance UV/Vis spectroscopy, and scanning electron microscopy. The properties of the obtained nanoparticles are shown to be comparable to those obtained by other methods, illustrating the potential of natural DESs for processing metal oxides.