Effects of the fuel type and fuel content on the specific surface area and magnetic properties of solution combusted CoFe2O4 nanoparticles

In this work, the different fuels (citric acid, glycine and urea) at the various fuel to oxidant ratios (ϕ=0.5, 0.75, 1 and 1.25) were used for solution combustion synthesis of CoFe₂O₄ nanoparticles. The phase evolution, microstructure, specific surface area and magnetic properties of the solution combusted CoFe₂O₄ nanoparticles were investigated by X-ray diffraction, thermal analysis, electron microscopy, adsorption-desorption isotherms and vibrating sample magnetometry techniques. The specific surface area of the combusted products decreased with the increase of fuel to oxidant ratio (ϕ), irrespective of the fuel type. However, the specific surface area for the glycine fuel was higher than the others, due to the higher combustion rate for releasing gaseous products. Furthermore, the solution combusted CoFe₂O₄ powders by the glycine fuel exhibited the higher saturation magnetization (63.6 emu/g) on account of their higher crystallinity and particle size.     

Effect of annealing on the structure and magnetic properties of CoFe2O4:SiO2 nanocomposites

The decomposition of succinate type precursors obtained by a modified sol-gel method using cobalt and iron nitrates, 1,4-butanediol and tetraethylorthosilicate, followed by the formation of single phase cobalt ferrite embedded in the silica matrix by annealing at 400–1100 °C was studied. The thermal analysis indicated the formation temperature of succinate type precursors, while the Fourier transform infrared spectroscopy (FT-IR) data confirmed the formation of the precursors in the pores of silica matrix. The formation of CoFe₂O₄ was investigated by X-ray diffraction and FT-IR, the size and shape of the nanoparticles by transmission electron microscopy, while the resulted microstructures by scanning electron microscopy. The crystallinity and crystallites size increased with the annealing temperature. The hysteresis loops revealed a direct relationship between annealing temperature and saturation magnetization in constant coercive field. The particle size of ferrite powders is critically dependent on the annealing temperature.     

Salt-assisted solution combustion synthesis of NiFe2O4: Effect of salt type

The effects of three types of salt including NaF, KCl, and NaCl on the properties of NiFe₂O₄ nanoparticles using salt-assisted solution combustion synthesis (SSCS) have been investigated. The synthesized powders were evaluated by SEM, TEM, FTIR, XRD, and VSM analysis. Also, the specific surface area (SSA), as well as size distribution and volume of the porosities of NiFe₂O₄ powders were determined by the BET apparatus. The visual observations showed that the intensity and time of combustion synthesis of nanoparticles have been severely influenced by the type of salt. The highest crystallinity was observed in the synthesized powder using NaCl. The SSA has also been correlated completely to the type of salt. The quantities of SSA was achieved about 91.62, 64.88, and 47.22 m²g^-1 for the powders synthesized by KCl, NaCl, and NaF respectively. Although the magnetic hysteresis loops showed the soft ferromagnetic behavior of the NiFe₂O₄ nanoparticles in all conditions, KCl salt could produce the particles with the least coercivity and remanent magnetization. Based on the present study, the salt type is a key parameter in the SSCS process for the preparation of spinel ferrites. Thermodynamic evaluation also showed that the melting point and heat capacity are important parameters for the proper selection of the salt.     

Hydrothermal synthesis,magnetic properties and characterization of CoFe2O4 nanocrystals

Magnetic cobalt ferrite (CoFe₂O₄) nanocrystals were synthesized via the hydrothermal method and the crystallite size was measured using Sherrer's equation. Instrumental broadening was a significant parameter for determining crystallite size. The effect of annealing time and calcination on crystallite size and magnetic properties was discussed. It was found that the coercivity was highly dependent on the crystallite size. As the crystallite size increased from 61 to 68.2 nm, room temperature coercivity increased from 1488 Oe to 1700 Oe, while high coercivity (5.2 kOe) was achieved at lower temperature (80 K). It was found that the presence of hematite could affect the crystallite size after calcination.     

Rietveld structure refinement,cations distribution and magnetic features of CoFe2O4 nanoparticles synthesized by co-precipitation,hydrothermal, and combustion methods

Cobalt ferrite nanoparticles were synthesized by chemical co-precipitation, hydrothermal and sol gel auto-combustion methods. X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM) and vibrating sample magnetometer (VSM) were used to investigate the structural characteristics and magnetic properties of cobalt ferrite nanocrystals. X-ray patterns revealed the production of a broad single cubic phase with the average crystallite size of 16, 18 and 178 nm for co-precipitation, hydrothermal and combustion methods, respectively. The FTIR measurements between 400 and 4000 cm⁻¹ confirmed the intrinsic cation vibrations of spinel structure. The FE-SEM micrographs of the synthesized samples indicated the presence of two distinct groups of grains exhibiting different sizes and, different shapes for hydrothermal route. The results of magnetic hysteresis at a room temperature showed that the magnetic properties depend on the particle size and shape of particles, whereas the role of particle size is more significant.     

Uniaxial anisotropy and enhanced magnetostriction of CoFe2O4 induced by reaction under uniaxial pressure with SPS

In this study, we have compared magnetic and magnetostrictive properties of polycrystalline CoFe₂O₄ pellets, produced by three different methods, focusing on the use of Spark Plasma Sintering (SPS). This technique allows a very short heat treatment stage while a uniaxial pressure is applied. SPS was utilized to sinter cobalt ferrite but also to make the reaction and the sintering (reactive sintering) of the same ceramic composition. Magnetic and magnetostrictive measurements show that the reactive sintering with SPS induces a uniaxial anisotropy, while it is not the case with a simple sintering process. The induced anisotropy is then expected to be a consequence of the reaction under uniaxial pressure. This anisotropy enhanced the magnetostrictive properties of the sample, where a maximum longitudinal magnetostriction of −229 ppm is obtained. This process can be a promising alternative to the magnetic-annealing because of the short processing time required (22 min).     

Microwave-assisted solution combustion synthesis of Fe3O4 powders

Magnetite (Fe₃O₄) powders were synthesized by solution combustion method at different fuel to oxidant ratios (ϕ = 0.5, 0.75, 1 and 1.5) using conventional and microwave ignition. The ignition method and fuel content affected the phase evolution, microstructure and magnetic properties of Fe₃O₄ powders as characterized by X-ray diffractometry, infrared spectroscopy, N₂ adsorption–desorption, electron microscopy and vibrating sample magnetometry techniques. Single phase Fe₃O₄ powders were only obtained using conventional ignition at ϕ value of 1, while the impurity phases such as α-Fe₂O₃ and FeO together with Fe₃O₄ phase were formed by microwave ignition. The bulky microstructure of conventionally combusted powders with specific surface area of 71.5 m²/g was transformed to disintegrated structure (76.5 m²/g) by microwave heating. The microwave combusted powders showed the highest saturation magnetization of 86.5 emu/g at ϕ value of 0.5 and the lower coercivity than that of conventionally combusted powders at all ϕ values, due to their larger particles.     

Chromium incorporated nanocrystalline cobalt ferrite synthesized by combustion method: Effect of fuel and temperature

Nanocrystalline CoCrFeO₄ samples were prepared by Cost effective and low temperature combustion method using different fuels as glycine, urea and polyvinyl alcohol and the effect of temperature on their physical properties has been studied. The thermal study of the precursor gels was done by using Thermogravimetric and Differential thermal analysis (TG-DTA). Occurrence of the cubic spinel phase for the samples was confirmed by the Rietveld analysis of X-ray diffraction (XRD) data. The refinement results also confirm that the cationic distribution over the tetrahedral and octahedral sites in the spinel lattice of samples is partially inverse. The magnetic studies indicate a superparamagnetic behaviour, showing an increase in the blocking temperatures with the particle size in case of all fuels. All the samples showed ferromagnetic behaviour and the nanoparticles prepared by using glycine as a fuel were found to have largest crystallite size and relatively stronger A–O–B interaction compared to others. Magnetization measurements exhibit non-collinear ferrimagnetic structure for the samples.     

The influence of solvent composition in the sol-gel synthesis of cobalt ferrite (CoFe2O4): A route to tuning its magnetic and mechanical properties

This work presents a successful, environmentally-friendly route for tuning the magnetic and mechanical properties of CoFe₂O₄ sintered ceramics. The precursor powders were prepared from mixtures containing 100, 50 and 20% water, with the remaining volume composed of isopropanol. The synthesised powders were pressed into pellets and sintered at 1150 and 1200 °C. SEM micrographs indicate that the solvent exerts a major influence over the morphology of the ferrite grains. Vickers hardness shows a maximum for products from a medium containing 50% water, which could be directly related to the smaller average size of the CoFe₂O₄ grains. The coercivity of the pellets is strongly influenced by the reactional medium, with a maximum of 501.7 Oe (sample prepared at 20% water and fired at 1150 °C). This work opens up possibilities for fine tuning of the final properties of CoFe₂O₄ sintered ceramics, further enabling the utilisation of this material in advanced applications.     

Microwave-assisted solution synthesis,microwave sintering and magnetic properties of cobalt ferrite

A simple, soft, and fast microwave-assisted hydrothermal method was used for the preparation of nanocrystalline cobalt ferrite powders from commercially-available Fe(NO₃)₃?9H₂O, Co(NO₃)₂?6H₂O, ammonium hydroxide, and tetrapropylammonium hydroxide (TPAH). The synthesis was conducted in a sealed-vessel microwave reactor specifically designed for synthetic applications, and the resulting products were characterized by XRD, FE-SEM, TEM, and HR-TEM. After a systematic study of the influence of the microwave variables (temperature, reaction time and nature of the bases), highly crystalline CoFe₂O₄ nanoparticles with a high uniformity in morphology and size, were directly obtained by heating at 130?°C for 20?min using the base TPAH. Dense ceramics of cobalt ferrite were prepared by non-conventional, microwave sintering of synthesized nanopowders at temperatures of 850–900?°C. The magnetic properties of both the nanopowders and the sintered specimens were determined in order to establish their feasibility as a permanent magnet.     

Effect of fuel type on the microstructure and magnetic properties of solution combusted Fe3O4 powders

Porous magnetite (Fe₃O₄) powders were synthesized by solution combustion method using the glycine and urea at different fuel to oxidant ratios (ϕ). The combustion behavior depended on the fuel type as characterized by thermal analysis. The structure and phase evolution investigated by X-ray diffraction method showed nearly single phase Fe₃O₄ powders which were achieved only by using the glycine fuel at ϕ=1. The specific surface area and porous structures of the as-combusted Fe₃O₄ powders were characterized by N₂ adsorption-desorption isotherms and scanning electron microscopy, respectively. The surface area using the glycine fuel (62.6 m²/g) was higher than that of urea fuel (42.5 m²/g), due to different combustion reactions. Magnetic properties of the as-combusted powders were studied by vibration sample magnetometry which exhibited the highest saturation magnetization of 74 emu/g using the glycine fuel at ϕ=1 on account of its high purity and large crystallite size.     

Effect of lemon juice on microstructure,phase changes,and magnetic performance of CoFe2O4 nanoparticles and their use on release of anti-cancer drugs

Cobalt ferrite magnetic nanoparticles were synthesized and developed by a modified Pechini method using iron nitrate, cobalt nitrate, ethylene glycol (EG), and sucrose with different volumes of lemon juice (10, 20, 30, 40, 50, 60, and 70 ml) as the source of chelating agent as well as nonmagnetic elements such as Ca and Mg ions. The XRD patterns confirmed that all samples synthesized by different contents of extracted lemon juice had a cubic crystal structure with single-phase spinel. Scanning electron microscopy revealed that cobalt ferrite nanoparticles had a semi-spherical morphology. Also, the vibrating sample magnetometer indicated that the saturation magnetization of CoFe₂O₄ nanoparticles prepared with different values of extracted lemon juice increased from 18.6 emu/g for 10 ml extracted lemon juice to 75.7 emu/g for 50 ml extracted lemon juice, after which the saturation magnetization diminished. Afterwards, the CoFe₂O₄ nanoparticles were coated with polyethylene glycol (PEG) and doxorubicin (DOX) drugs, whereby drug delivery was detected at different pH levels. The CoFe₂O₄-PEG-DOX nanocomposite could release doxorubicin by more than 42% at pH = 5.4 in 75 h.     

Structure and magnetic properties of CoFe2O4/SiO2 nanocomposites obtained by sol-gel and post annealing pathways

The influence of the CoFe₂O₄ nanoparticles concentration in silica matrix on the structural and magnetic properties of xCoFe₂O₄/(100−x)SiO₂ nanocomposites with x=10, 30, 50, 70 and 90 was studied. Magnetic CoFe₂O₄ nanoparticles dispersed in silica matrix was obtained by sol-gel method, followed by annealing at 1100 °C. The X-ray diffraction pattern and FT-IR spectra revealed the single spinel ferrite structure for all samples. The FT-IR spectra also suggested the formation of the amorphous silica matrix. The results showed that the increase of cobalt ferrite concentration (x) in the silica matrix leads to high crystallinity, specific surface area and particle size. The magnetic CoFe₂O₄ nanoparticles have spherical shapes and size in the 6–35 nm range. The Mössbauer measurements were fitted with two Zeeman sextets, indicating that all the samples were completely magnetically ordered. The vibrating sample magnetometer studies showed that the saturation magnetization (Ms) and coercivity (Hc) of the CoFe₂O₄ nanocrystals embedded in silica matrix possessed a linear relationship with the mean crystallite size. Also, the saturation magnetization of the studied nanocomposites increases with the increase of cobalt ferrite concentration (x) in the silica matrix.     

CoFe2O4的制备及其活化过硫酸盐降解磺胺甲恶唑

采用简单的共沉淀法在不同煅烧温度下成功合成了一系列铁酸钴材料（CoFe2O4-X），通过SEM，XRD，BET，XPS等表征手段对其结构组成进行了分析，并将其用于活化过一硫酸盐（PMS）以降解磺胺甲恶唑（SMX）。考察了催化剂投加量、PMS用量、pH值和无机离子对SMX降解的影响。结果表明，550℃煅烧温度下获得的CoFe2O4-550具有最佳的催化性能，在最佳反应条件下，20 min内，SMX的降解率可高达95%，且TOC去除率可达80%。同时，CoFe2O4-550/PMS反应体系具有较广的pH适用范围（pH=5.00-9.00）。CoFe2O4-550催化剂可磁性回收，具有较好的稳定性和重复使用性。自由基淬灭实验表明，在该降解反应过程中产生了大量的SO4-?和?OH自由基，并提出了相应的催化降解机理。这项工作将为有效处理含有SMX化合物的废水提供一种新思路。     

Magnetic interactions and hysteresis loops study of Co/CoFe2O4 nanoparticles

Co/CoFe₂O₄ nanoparticles with the mean size of 8.8, 10.8 and 16.9 nm were prepared by thermal decomposition of metal salts in the presence of citric acid. The X-ray diffraction patterns and Rietveld refinements confirmed coexistence of Co-ferrite and metallic cobalt phases in the nano-powders. Scanning electron microscope images showed an increase in particles aggregates mean diameter with increasing the annealing temperature. Magnetic hysteresis loops showed a demagnetization jump at low fields, which was attributed to different reversal fields of ferrite and the cobalt phases. Field-dependent behavior of maximum magnetization (M_max), remanence (M_r), squareness (S) and coercivity (H_c) were studied through minor loops measurements. The calculated S value of the loops showed a maximum, between anisotropy and coercive fields. A sharp increase in H_c of larger particles was observed with increasing the applied field when compared to smaller particles. Henkel plots showed that the samples are interacting. Negative deviation of Henkel plots from linear behavior and negative δm plots revealed the dominant role of dipole–dipole interactions in the nano-aggregates.     

Optimizing liquid phase promotion effect by modifying powder specific surface area in Si4+/Mg2+ co-doped transparent Yb:YAG ceramics

Utilizing the Si⁴⁺/Mg²⁺ co-doping has been considered an effective approach to fabricate highly transparent ceramics. However, the optimum doping concentration has been reported with considerable uncertainties. In this work, highly transparent Yb:YAG ceramics were obtained via the solid-state method and the sintering behavior is discovered to be closely related to both the doping concentration of Si⁴⁺/Mg²⁺ and the specific surface area (S_BET) of powders. S_BET is effectively modified by setting the ball-milling time, where the maximum S_BET (30.914 m²/g) is achieved with 24 h ball-milling time. With increasing S_BET, less Mg²⁺ is required for better optical properties. When S_BET equals 30.914 m²/g, the highest in line transmittance @ 1100 nm of 84.85% is obtained with Si⁴⁺/Mg²⁺ doping concentrations of 0.50 wt% and 0.05 wt%, respectively. The relation between S_BET and optimum doping concentration is explained by the different magnitudes of liquid phase promotion required for different contact areas between powder particles.     

微波辅助溶液燃烧法制备MgAl_2O_4粉体

将硝酸镁、硝酸铝、尿素按物质的量比为1 2 6.66制得透明混合前驱液,用低温燃烧技术与微波加热技术相结合的方法制备了高纯度、低团聚的镁铝尖晶石(MgAl2O4)粉体。研究了燃烧反应过程中,微波输出功率(200、400、600、700 W)对Mg Al2O4粉体晶体结构、形貌及比表面积的影响。结果表明:微波高效加热方式导致燃烧反应瞬间产生大量气体,促进了Mg Al2O4超细颗粒的形成。同时,随着微波输出功率的增加,尿素氧化加速,利于MgAl2O4晶粒的生长发育。在微波功率700W,微波时间2 min的条件下,可制备结晶完整,粒度分布均匀(平均晶粒尺寸为56.03 nm)的Mg Al2O4粉体。     

The effect of reaction temperature on the structural and magnetic properties of nano CoFe2O4

Nano cobalt ferrites (CoFe₂O₄) were co-precipitated at various reaction temperatures (60, 70 and 80 °C) for 1 h. The reaction temperature greatly influenced the crystallite size and the magnetic behaviours of the nano CoFe₂O₄. The mean crystallite size ranged from 9 to 15 nm with the increase in the reaction temperature and the intensity of metal oxide vibrations at 568–550 cm⁻¹ were also inclined. The synthesized samples were in the stoichiometric ratio of 1:2 (Co:Fe) with roughly spherical morphology. The synthesized cobalt nanoferrites exhibited ferromagnetism at room temperature and 5 K, and the saturation magnetization increased from 6.4 to 20 emu/g with the crystallite size.     

Biomimetic fabrication of mulberry-like nano-hydroxyapatite with high specific surface area templated by dual-hydrophilic block copolymer

Novel porous and mulberry-like hydroxyapatite (HAp) nanoparticles with three-dimensionally hierarchical microstructures were developed by using the dual-hydrophilic block copolymer poly(methacrylate acid)-b-poly[N-(2-methacryloylxyethyl) pyrrolidone] (PMAA-b-PNMP) as the template. It was found that the morphology and Ca/P ratio of synthesized HAp was highly related to the concentration of block copolymer and solution pH, respectively. The morphological evolution of HAp nanoparticles in different conditions was investigated systematically by scanning electron microscopy (SEM), transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM), powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The possible mechanism of PMAA-b-PNMP assisted mulberry-like HAp formation was also proposed based on the time-dependent TEM results. Attributing to the high specific surface area (SSA) of 119 m² g⁻¹, these mulberry-like HAp nanoparticles exhibited excellent adsorption ability for Congo Red (CR). The maximum adsorption capacity was 467 mg g⁻¹ according to the Langmuir monolayer adsorption model.