Synthesis and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> magnetic composite nanoparticles by a one-pot process

Fe₃O₄@SiO₂ core–shell composite nanoparticles were successfully prepared by a one-pot process. Tetraethyl-orthosilicate was used as a surfactant to synthesize Fe₃O₄@SiO₂ core–shell structures from prepared Fe₃O₄ nanoparticles. The properties of the Fe₃O₄ and Fe₃O₄@SiO₂ composite nanoparticles were studied by X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. The prepared Fe₃O₄ particles were approximately 12 nm in size, and the thickness of the SiO₂ coating was approximately 4 nm. The magnetic properties were studied by vibrating sample magnetometry. The results show that the maximum saturation magnetization of the Fe₃O₄@SiO₂ powder (34.85 A·m2·kg–1) was markedly lower than that of the Fe₃O₄ powder (79.55 A·m2·kg–1), which demonstrates that Fe₃O₄ was successfully wrapped by SiO₂. The Fe₃O₄@SiO₂ composite nanoparticles have broad prospects in biomedical applications; thus, our next study will apply them in magnetic resonance imaging.     

核壳式磁性微球催化的Knoevenagel反应

Fe₃O₄@SiO₂-NH₂-CMC magnetic nanoparticles(MNPs) could be prepared by covalent modification method via the modification of sodium carboxymethyl cellulose (CMC). IR spectra could be used for the determination of Fe₃O₄@SiO₂-NH₂, Fe₃O₄@SiO₂-NH₂-CMC, Fe₃O₄@SiO₂-NH₂-CMC/MOF5, and Fe₃O₄@SiO₂-NH₂-CMC/IRMOF3 nanoparticles. The results showed that the polysaccharide modification and core-shell modification were successful. Knoevenagel condensation experiments exhibited that, as forFe₃O₄@SiO₂-NH₂-CMC/IRMOF3, the best conversion rate could be obtained.     

Size-controlled synthesis of Fe3O4 and Fe3O4@SiO2 nanoparticles and their superparamagnetic properties tailoring

Superparamagnetic properties and fine-tuning of colloidal Fe₃O₄nanoparticles are important for their widespread biomedical applications. Herein, colloidal Fe₃O₄nanoparticles(NPs) of different sizes(8–20 nm) were prepared,and their hydrophilization with SiO₂shell coating to be Fe₃O₄@SiO₂core-shell had been realized successively.The size of Fe₃O₄NPs was controlled by different heating rate...     

Synthesis and application of bilayer-surfactant-enveloped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles: water-based bilayer-surfactant-enveloped ferrofluids

Superparamagnetic carbon-coated Fe₃O₄ nanoparticles with high magnetization (85 emu·g-1) and high crystallinity were synthesized using polyethylene glycol-4000 (PEG (4000)) as a carbon source. Fe₃O₄ water-based bilayer-surfactant-enveloped ferrofluids were subsequently prepared using sodium oleate and PEG (4000) as dispersants. Analyses using X-ray photoelectron spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy indicate that the Fe₃O₄ nanoparticles with a bilayer surfactant coating retain the inverse spinel-type structure and are successfully coated with sodium oleate and PEG (4000). Transmission electron microscopy, vibrating sample magnetometry, and particle-size analysis results indicate that the coated Fe₃O₄ nanoparticles also retain the good saturation magnetization of Fe₃O₄ (79.6 emu·g-1) and that the particle size of the bilayer-surfactant-enveloped Fe₃O₄ nanoparticles is 42.97 nm, which is substantially smaller than that of the unmodified Fe₃O₄ nanoparticles (486.2 nm). UV–vis and zeta-potential analyses reveal that the ferrofluids does not agglomerate for 120 h at a concentration of 4 g·L-1, which indicates that the ferrofluids are highly stable.     

Enhanced photocatalytic activity of electrochemically synthesized aluminum oxide nanoparticles

In this study, aluminum oxide (Al₂O₃) nanoparticles (NPs) were synthesized via an electrochemical method. The effects of reaction parameters such as supporting electrolytes, solvent, current and electrolysis time on the shape and size of the resulting NPs were investigated. The Al₂O₃ NPs were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, thermogravimetric analysis/differential thermal analysis, energy-dispersive X-ray analysis, and ultraviolet–visible spectroscopy. Moreover, the Al₂O₃ NPs were explored for photocatalytic degradation of malachite green (MG) dye under sunlight irradiation via two processes: adsorption followed by photocatalysis; coupled adsorption and photocatalysis. The coupled process exhibited a higher photodegradation efficiency (45%) compared to adsorption followed by photocatalysis (32%). The obtained kinetic data was well fitted using a pseudo-first-order model for MG degradation.     

Microwave absorption properties of SiC@SiO2@Fe3O4 hybrids in the 2-18 GHz range

To enhance the microwave absorption performance of silicon carbide nanowires (SiCNWs), SiO₂ nanoshells with a thickness of approximately 2 nm and Fe₃O₄ nanoparticles were grown on the surface of SiCNWs to form SiC@SiO₂@Fe₃O₄ hybrids. The microwave absorption performance of the SiC@SiO₂@Fe₃O₄ hybrids with different thicknesses was investigated in the frequency range from 2 to 18 GHz using a free-space antenna-based system. The results indicate that SiC@SiO₂@Fe₃O₄ hybrids exhibit improved microwave absorption. In particular, in the case of an SiC@SiO₂ to iron(Ⅲ) acetylacetonate mass ratio of 1:3, the microwave absorption with an absorber of 2-mm thickness exhibited a minimum reflection loss of -39.58 dB at 12.24 GHz. With respect to the enhanced microwave absorption mechanism, the Fe₃O₄ nanoparticles coated on SiC@SiO₂ nanowires are proposed to balance the permeability and permittivity of the materials, contributing to the microwave attenuation.     

Micro-analysis of high-temperature oxidation-resistance of a new kind of heat-resistant grid plate in grate-kiln

To further improve the oxidation-resistance of materials and reduce the cost of grid plates in grate-kiln, a new kind of heat-resistant grid plate was developed. The microstructure of this grid plate with a life more than 18 months was studied by XRD, SEM and EDS techniques. The results show that high hardness, high intensity and good impact property make the new kind of heat-resistant grid plate and its oxide film have a higher resistance to deformation and abrasion at 900-1000℃ Besides, small grain size is beneficial to form a complete protective oxide film. The oxide film composed of SiO₂ layer, Cr₂O₃ layer and Fe₂O₃ layer is rather thin and bonds closely with the backing. The forming of the chemical stable nickel-rich layer increases the density of Cr₂O₃ layer.     

Effect of chemical activation process on adsorption of As(V) ion from aqueous solution by mechano-thermally synthesized zinc ferrite nanopowder

Nanostructured ZnFe₂O₄ was synthesized by the heat treatment of a mechanically activated mixture of ZnO/α-Fe₂O₃. X-ray diffraction (XRD) and differential thermal analysis (DTA) results demonstrated that, after 5 h of the mechanical activation of the mixture, ZnFe₂O₄ was formed by heat treatment at 750°C for 2 h. To improve the characteristics of ZnFe₂O₄ for adsorption applications, the chemical activation process was performed. The 2 h chemical activation with 1 mol·L?1 HNO₃ and co-precipitation of 52%?57% dissolved ZnFe₂O₄ led to an increase in the saturated magnetization from 2.0 to 7.5 emu·g?1 and in the specific surface area from 5 to 198 m2·g?1. In addition, the observed particle size reduction of chemically activated ZnFe₂O₄ in field emission scanning electron microscopy (FESEM) micrographs was in agreement with the specific surface area increase. These improvements in ZnFe₂O₄ characteristics considerably affected the adsorption performance of this adsorbent. Adsorption results revealed that mechano-thermally synthesized ZnFe₂O₄ had the maximum arsenic adsorption of 38% with the adsorption capacity of 0.995 mg·g?1 in a 130 mg·L?1 solution of As(V) after 30 min of agitation. However, chemically activated ZnFe₂O₄ showed the maximum arsenic adsorption of approximately 99% with the adsorption capacity of 21.460 mg·g?1 under the same conditions. These results showed that the weak adsorption performance of mechano-thermally synthesized ZnFe₂O₄ was improved by the chemical activation process.     

A Self-propagating high-temperature synthesis process for the fabrication of Fe(Cr)-Al2O3 nanocomposite

Self-propagating high-temperature synthesis (SHS) was used to fabricate a Fe(Cr)-Al₂O₃ nanocomposite. The composite was fabricated by the reactions between the powders of Fe, Fe₂O₃, Cr₂O₃, and Al. The effect of blending ratio and mechanical activation of the initial powders and the precursor compressing pressure on the microstructure of the final product was studied by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The significance of the effect of each of the aforementioned parameters on the quality of the composite (assessed by measuring the compressive strength and wear resistance) was determined using a full-factorial design of experiments method. The results showed that the best molar powder ratio that produced the most homogeneous product through a sustainable SHS reaction was Fe:Fe₂O₃:Cr₂O₃:Al=10:1:1:4. A lower Fe content caused the Fe(Cr) phase to melt and separate from the rest of the materials.     

Microstructure characterization of a pressureless infiltrating oxidized SiCp preform by Al-8Mg

The microstructure of a pressureless infiltrating 55vol% oxidized SiC preform by Al-8Mg alloy was characterized by transmission electron microscopy (TEM), high resolution TEM (HRTEM), field emission scanning electron microscopy (FE-SEM), and X-ray diffraction. The TEM image of the interface between Al and SiC shows that the surface of SiC is covered by a rough nanocrystal layer of MgAl₂O₄, Al₂O₃, and Si, produced by the interfacial reaction of Al, Mg, and SiO₂ on the surface of SiC. The Al-SiC interface is also examined by HRTEM to be better understood how MgAl₂O₄ and Al₂O₃ are produced. Dendritic Al₂O₃ crystals are embedded in the pores of the composite generated from the mutual bonding of SiO₂ on the surface of SiC. Columnar AlN crystals of about 250 nm in length are bunched vertically on the SiC particle surface.     

Effect of Fe2O3 on the size and components of spinel crystals in the CaO-SiO2-MgO-Al2O3-Cr2O3 system

size of spinel crystals in the CaO-SiO₂-MgO-Al₂O₃-Cr₂O₃ system was investigated using lab experiments carried out in a carbon tube furnace. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD) were used to analyze the microstructure, components, and the mineral phases of synthetic slags. FactSage 7.1 was used to calculate the crystallization process of the molten slag. The results showed that the addition of Fe₂O₃ promoted the precipitation of spinel crystals and inhibited the formation of dicalcium silicate. The size of spinel crystals increased from 2.74 to 8.10 μm and the contents of chromium and iron in the spinel varied as the Fe₂O₃ addition was increased from 0 to 20wt%. Fe₂O₃ thermodynamically provided the spinel-forming components to enhance the formation of FeCr₂O₄, MgFe₂O₄, and Fe₃O₄. The addition of Fe₂O₃ increased the fraction of liquid phase in a certain temperature range and promoted diffusion by decreasing the slag's viscosity. Therefore, Fe₂O₃ is beneficial to the growth of spinel crystals in stainless steel slag.     

Isothermal reduction kinetics and mineral phase of chromium-bearing vanadium-titanium sinter reduced with CO gas at 873-1273 K

Reduction of chromium-bearing vanadium-titanium sinter (CVTS) was studied under simulated conditions of a blast furnace, and thermodynamics and kinetics were theoretically analyzed. Reduction kinetics of CVTS at different temperatures was evaluated using a shrinking unreacted core model. The microstructure, mineral phase, and variation of the sinter during reduction were observed by X-ray diffraction, scanning electron microscopy, and metallographic microscopy. Results indicate that porosity of CVTS increased with temperature. Meanwhile, the reduction degree of the sinter improved with the reduction rate. Reduction of the sinter was controlled by a chemical reaction at the initial stage and inner diffusion at the final stage. Activation energies measured 29.22-99.69 kJ/mol. Phase transformations in CVTS reduction are as follows:Fe₂O₃→Fe₃O₄→FeO→Fe; Fe₂TiO₅→Fe₂TiO₄→FeTiO₃; FeO·V₂O₃→V₂O₃; FeO·Cr₂O₃→Cr₂O₃.     

Diffusion behavior and distribution regulation of MgO in MgO-bearing pellets

In this paper, the diffusion behavior between MgO and Fe₂O₃ (the main iron oxide in pellets) is investigated using a diffusion couple method. In addition, the distribution regulation of MgO in MgO-bearing pellets is analyzed via pelletizing experiments. The results illustrate that MgO is prone to diffuse into Fe₂O₃ in the form of solid solution; the diffusion rate considered here is 13.64 μm·min-1. Most MgO content distributes in the iron phase instead of the slag phase. The MF phase {(Mg_1-x Fe_x)O·Fe₂O₃, x ≤ 1} is generated in the MgO-bearing pellets. However, the distribution of MgO in the radial direction of the pellets is inconsistent. The solid solution portion of MgO in the MF phase is larger in the outer layer of the pellets than in the inner layer. In this work, the approximate chemical composition of the MF phase in the outer layer of the pellets is {(Mg_0.35-0.77·Fe_0.65-0.23) O·Fe₂O₃} and in the inner layer is {(Mg_0.13-0.45·Fe_0.87-0.55) O·Fe₂O₃}.     

动态反应釜制备超顺磁性Fe3O4粒子及其DNA提取

使用动态反应釜制备得到磁性粒子,与静态反应釜相比单次制备量提高20倍;通过扫描电子显微镜（SEM）、傅立叶红外光谱（FT-IR）、X射线衍射（XRD）、振动样品磁强计（VSM）等手段对产物进行表征,证明获得了粒径200 nm左右的单分散Fe₃O₄粒子,并具有超顺磁性;对其表面进行SiO₂包覆,获得具有良好分散性的Fe₃O₄@SiO₂粒子。研究发现Fe₃O₄@SiO₂对DNA提取具有可重复利用性,并且质粒DNA吸附到Fe₃O₄@SiO₂上后可直接加入聚合酶链式反应（PCR）体系作为扩增模板。     

超顺磁性Fe3O4@SiO2空心亚微球的制备及其在质粒DNA分离纯化中的应用

采用溶剂热法合成超顺磁性空心亚微球,然后通过正硅酸乙酯水解-聚合反应,在亚微球表面包覆SiO₂,形成核壳结构Fe₃O₄@SiO₂空心亚微球。以该Fe₃O₄@SiO₂亚微球为分离介质,实现了大肠杆菌（E. coli）质粒DNA的高效、快速分离。     

Fabrication of Fe–TiC–Al2O3 composites on the surface of steel using a TiO2–Al–C–Fe combustion reaction induced by gas tungsten arc cladding

The aim of the present study was to fabricate Fe–TiC–Al₂O₃ composites on the surface of medium carbon steel. For this purpose, TiO₂–3C and 3TiO₂–4Al–3C–xFe (0 ≤ x ≤ 4.6 by mole) mixtures were pre-placed on the surface of a medium carbon steel plate. The mixtures and substrate were then melted using a gas tungsten arc cladding process. The results show that the martensite forms in the layer produced by the TiO₂–3C mixture. However, ferrite–Fe₃C–TiC phases are the main phases in the microstructure of the clad layer produced by the 3TiO₂–4Al–3C mixture. The addition of Fe to the TiO₂–4Al–3C reactants with the content from 0 to 20wt% increases the volume fraction of particles, and a composite containing approximately 9vol% TiC and Al₂O₃ particles forms. This composite substantially improves the substrate hardness. The mechanism by which Fe particles enhance the TiC + Al₂O₃ volume fraction in the composite is determined.     

Acting mechanism of F,K, and Na in the solid phase sintering reaction of the Baiyunebo iron ore

The effect of F, K, and Na on the solid phase reaction of the Baiyunebo iron ore was investigated by differential thermal analysis (DTA) and X-ray diffraction (XRD). It has been identified that alkaline elements K and Na in the Baiyunebo ore instigate the formation of low melting point compounds Na₂SiO₃ and Na₂O·Fe₂O₃ and the generation of molten state in the solid phase sintering. Element F in the Baiyunebo ore facilitates the formation of cuspidine compound 3CaO·2SiO₂·CaF₂ in the solid phase reaction. The cuspidine compound is kept in solid as one of the final products through the entire sintering process due to its high melting point. In the sintering process, CaF₂ and SiO₂ react with CaO first and form 3CaO·2SiO₂·CaF₂ and 3CaO·2SiO₂, so the formation of ferrites, Na₂O·Fe₂O₃, and 2CaO·Fe₂O₃ is inhibited.     

Effect of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization behavior of glass-ceramics produced from naturally cooled yellow phosphorus furnace slag

CaO-Al₂O₃-SiO₂ (CAS) glass-ceramics were prepared via a melting method using naturally cooled yellow phosphorus furnace slag as the main raw material. The effects of the addition of Fe₂O₃ on the crystallization behavior and properties of the prepared glass-ceramics were studied by differential thermal analysis, X-ray diffraction, and scanning electron microscopy. The crystallization activation energy was calculated using the modified Johnson-Mehl-Avrami equation. The results show that the intrinsic nucleating agent in the yellow phosphorus furnace slag could effectively promote the crystallization of CAS. The crystallization activation energy first increased and then decreased with increasing amount of added Fe₂O₃. At 4wt% of added Fe₂O₃, the crystallization activation energy reached a maximum of 676.374 kJ·mol-1. The type of the main crystalline phase did not change with the amount of added Fe₂O₃. The primary and secondary crystalline phases were identified as wollastonite (CaSiO₃) and hedenbergite (CaFe(Si₂O₆)), respectively.     

Staged reaction kinetics and characteristics of iron oxide direct reduction by carbon

Staged reduction kinetics and characteristics of iron oxide direct reduction by carbon were studied in this work. The characteristics were investigated by simultaneous thermogravimetric analysis, X-ray diffraction (XRD), and quadrupole mass spectrometry. The kinetics parameters of the reduction stages were obtained by isoconversional (model-free) methods. Three stages in the reduction are Fe₂O₃→Fe₃O₄, Fe₃O₄→FeO, and FeO→Fe, which start at 912 K, 1255 K, and 1397 K, respectively. The CO content in the evolved gas is lower than the CO₂ content in the Fe₂O₃→Fe₃O₄ stage but is substantially greater than the CO₂ contents in the Fe₃O₄→FeO and FeO→Fe stages, where gasification starts at approximately 1205 K. The activation energy (E) of the three stages are 126–309 kJ/mol, 628 kJ/mol, and 648 kJ/mol, respectively. The restrictive step of the total reduction is FeO→Fe. If the rate of the total reduction is to be improved, the rate of the FeO→Fe reduction should be improved first. The activation energy of the first stage is much lower than those of the latter two stages because of carbon gasification. Carbon gasification and Fe_xO_y reduction by CO, which are the restrictive step in the last two stages, require further study.     

Effect of aluminum oxide on the compressive strength of pellets

Analytical-reagent-grade Al₂O₃ was added to magnetite ore during the process of pelletizing, and the methods of mercury intrusion, scanning electron microscopy, and image processing were used to investigate the effect of Al₂O₃ on the compressive strength of the pellets. The results showed that, as the Al₂O₃ content increased, the compressive strength of the pellets increased slightly and then decreased gradually. When a small amount of Al₂O₃ was added to the pellets, the Al₂O₃ combined with fayalite (2FeO·SiO₂) and the aluminosilicate (2FeO·2Al₂O₃·5SiO₂) was generated, which releases some iron oxide and reduces the inhibition of fayalite to the solid phase of consolidation. When Al₂O₃ increased sequentially, high melting point of Al₂O₃ particles hinder the oxidation of Fe₃O₄ and the recrystallization of Fe2O3, making the internal porosity of the pellets increase, which leads to the decrease in compressive strength of the pellets.