ε-Fe2O3 nanoparticles embedded in silica xerogel – Magnetic metamaterial

A novel method for synthesizing a new metamaterial based on ε-Fe₂O₃ nanoparticles immobilized in the xerogel matrix was proposed. Samples with different contents of ε-Fe₂O₃ nanoparticles dispersed in silica xerogel were synthesized by impregnation of as prepared hydrogel with iron (II) salts with the subsequent calcination. The structure and magnetic properties of the prepared composites were studied by transmission electron microscopy, X-ray diffraction, Mössbauer spectroscopy, and static magnetic measurements. The absence of other iron oxide polymorphs, controllable particle size distribution, and high ε-Fe₂O₃ nanoparticle concentration in combination with the weak interparticle magnetic interactions ensured the preservation of the unique magnetic properties of individual ε-Fe₂O₃ nanoparticles and allowed us to obtain a novel metamaterial. The high optical transparency and homogeneity of the prepared composites made it possible to detect the magnetic circular dichroism (MCD) of the magnetic silica xerogel, which is typical of the ε-Fe₂O₃-based systems.     

Nanofluids Containing γ-Fe2O3 Nanoparticles and Their Heat Transfer Enhancements

Homogeneous and stable magnetic nanofluids containing γ-Fe₂O₃ nanoparticles were prepared using a two-step method, and their thermal transport properties were investigated. Thermal conductivities of the nanofluids were measured to be higher than that of base fluid, and the enhanced values increase with the volume fraction of the nanoparticles. Viscosity measurements showed that the nanofluids demonstrated Newtonian behavior and the viscosity of the nanofluids depended strongly on the tested temperatures and the nanoparticles loadings. Convective heat transfer coefficients tested in a laminar flow showed that the coefficients increased with the augment of Reynolds number and the volume fraction.     

In situ synthesis of Fe3O4@SiO2 core–shell nanoparticles via surface treatment

Core–shell structured Fe₃O₄@SiO₂ nanoparticles were synthesized through a facile in situ surface-treatment process. Surface treatments of the as-prepared Fe₃O₄ nanoparticles with acid or base caused changes in the shape of spherical particles agglomerated into clusters. The morphological changes of the particles experienced an abrupt change depending on the concentration of the treated acid or base, and the magnetization properties and surface characteristics corresponding to these behaviors were studied. As a result, optimum surface-treatment conditions for depositing SiO₂ on the surface were established, and the derivation condition basically included the ideal environment for coating SiO₂. It was possible to coat SiO₂ using a sol–gel reaction without going through the removal of residual organics and a solvent displacement process. About 8?nm of a single coating layer was homogeneously formed due to excellent initial dispersibility of Fe₃O₄ nanoparticles according to the modified surface characteristics.     

Thermo-mechanical behaviors of epoxy resins reinforced with silane-epoxide functionalized α-Fe2O3 nanoparticles

In this work, α-Fe₂O₃ nanoparticles was synthesized, terminal-epoxide functionalized by using 3-glycidoxypropyltrimethoxysilane (GPS) coupling agent, characterized by FT-IR, X-ray diffraction, TGA and particle size analyzer and used in preparation of nanocomposites with epoxy resin (DGEBA) using different weight fractions (2–11 wt%). TEM and SEM were used to observe particle dispersion in the resin matrix and to investigate the fractured surface of nanocomposites for evidence of extrinsic toughening mechanism. The mechanical and thermo-mechanical properties of nanocomposites prepared from DGEBA and modified epoxide-terminated α-Fe₂O₃ were compared with the properties of untreated α-Fe₂O₃/DGEBA nanocomposites and neat DGEBA. The modified α-Fe₂O₃/DGEBA nanocomposites showed improvement in properties such as glass transition temperature (T_g) and tensile, flexural and impact strength. These improvements are due to better dispersion of epoxide-terminated α-Fe₂O₃ particles in the resin matrix and enhanced interfacial adhesion between DGEBA and α-Fe₂O₃ phases.     

Silica-free hydrothermal synthesis of ε-Fe2O3 nanoparticles and their oriented attachment to nanoflakes with unique magnetism evolution

It is a general consensus that ε-polymorph of Fe₂O₃ is not easy to synthesize in the form of bare nano-sized objects owing to its significant thermal instability. Thus, a supporting medium (e.g., silica matrix in most cases) is always necessary for its successful high-temperature synthesis at the sacrifice of its yield. In this study, optimized amounts of protons and nitrate ions were employed in a hydrothermal synthetic route to facilitate the growth of pure ε-Fe₂O₃ nanoparticles. The absence of silica matrix ensured a high yield of ε-Fe₂O₃ product, and moderate reaction temperature of mere 200?°C was conducive to its scalable energy-efficient production. These ε-Fe₂O₃ nanoparticles exhibited large room-temperature coercivity of ca. 16.3?kOe, which was found to be degenerated to 36?Oe as prolonging the reaction time due to the phase and structure evolution. The preformed ε-Fe₂O₃ nanoparticles and post-formed α-Fe₂O₃ phase would co-align with each other to form nanoflakes for long-time reaction, being of a character of oriented attachment. The concomitant distorted lattice spacing and disordered atomic configuration not only contributed to the degeneration of ferromagnetism of ε-Fe₂O₃ phase, but also induced unique spin glass behavior.     

Novel iron-rich mullite solid solution synthesis using fused-silica and α-Al2O3 powders

An iron-rich mullite solid solution was synthesized by using α-Al₂O₃, fused-silica and Fe₂O₃ powders at elevated temperatures. The phase compositions and microstructures of the synthesized samples were characterized by X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and field emission scanning electron microscope (FESEM). The occurrence states of Fe²⁺ and Fe³⁺ at different temperatures were analysed by X-ray photoelectron spectroscopy (XPS). The influence and the reaction mechanism of Fe₂O₃ addition on the synthesis of the mullite solid solution were clarified. The results showed that with the addition of Fe₂O₃, a liquid-solid sintered state was formed at 1300–1400?°C, which leaded to a reduction in the mullitization temperature. After sintering at 1600?°C, the quantitative analysis showed that the mullite phase content was 100%. Meanwhile, the Fe^3+/2+ ions entered completely into the mullite to form a stable solid solution, which exhibited the crystal morphology of a spherical shape and a short columnar shape with a low aspect ratio. The crystal grains were interwoven and squeezed each other, showing good structural stability. The refractoriness under load (RUL) property of the sample sintered at 1700?°C was slightly higher than that of the sample sintered at 1600?°C.     

α-Fe2O3 nano-platelets prepared by mechanochemical/thermal processing

A new method to prepare plate-shaped Fe₂O₃ nanoparticles was investigated and their magnetic properties were characterised. First, Fe₂O₃ nanoparticles of ~ 6 nm in diameter were synthesised by mechanochemical processing, involving the solid-state exchange reaction Fe₂(SO₄)₃ + 3 Na₂CO₃ → Fe₂(CO₃)₃ + 3 Na₂SO₄ → Fe₂O₃ + 3 Na₂SO₄ +  3 CO₂ (g) effected by high-energy ball milling and subsequent heat treatment at 400 °C. Next, nano-platelets were grown from the nanoparticles by further heat treatment in a salt matrix at 700 °C. Removal of the salt and by-product phases after heat treatment led to well-dispersed platy haematite particles of 20-200 nm in diameter with aspect ratio of 4-10. The hematite nano-platelets were weakly ferromagnetic with coercivity of ~ 160 Oe and remanent magnetisation of 0.2 emu/g.     

α-Fe2O3空心球的溶剂热合成与表征

以FeCl3.6H2O为原料,乙醇为溶剂,采用聚乙二醇(PEG-400)辅助的溶剂热法制备了大小均匀的α-Fe2O3空心微球,其直径约为900 nm,粒径分布均匀。产物经X射线衍射仪(XRD)、扫描电镜(SEM)和透射电镜(TEM)进行了表征。     

Agglomeration of α-Al2O3 powders prepared by gel combustion

Ultrafine α-Al₂O₃ powders were prepared by a gel combustion method and the agglomeration characteristic of the resultant powders was studied. A variety of fine crystallite α-Al₂O₃ powders with different agglomeration structures could be obtained by altering the citrate-to-nitrate ratio γ and calcining the precursors at 1050 °C for 2 h. All the powders were of nearly equivalent crystallite size (60–80 nm) except for the P1 powder (113 nm) from the gel with γ = 0.033. The primary crystallites of the obtained α-Al₂O₃ powders were formed into large secondary particles with different degree of agglomeration. Except for the powder P1, the mean particle sizes from specific surface area and particle size distribution measurement increase with increasing citrate-to-nitrate ratio in the fuel-lean condition and decrease in the fuel-rich condition. Densities of alumina ceramics from powders P4 and P5 sintered at different temperatures were relatively low due to the wide particle size distribution.     

Synthesis of γ-Ga2O3-Al2O3 solid solutions by spray pyrolysis method

Synthesis of the γ-Ga₂O₃-Al₂O₃ solid solutions by spray pyrolysis was examined. Spherical particles were obtained using an aqueous solution of Al(NO₃)₃ and Ga(NO₃)₃ with HNO₃. For Ga-rich composition, γ-phase solid solutions were directly crystallized by the spray pyrolysis. For Al-rich composition, spray pyrolysis gave amorphous products unless a sufficient thermal energy was supplied during the spray pyrolysis. Subsequent calcination of the amorphous products gave γ-Ga₂O₃-Al₂O₃ solid solutions. However, physical properties of the solid solutions were affected by the spray pyrolysis conditions.     

Room temperature NO2 gas sensor based on PPy/α-Fe2O3 hybrid nanocomposites

Polypyrrole–iron oxide (PPy/α-Fe₂O₃) hybrid nanocomposite sensor films were prepared by spin coating method on glass substrate and characterized for structural and morphological properties by means of X-ray diffraction (XRD), Fourier transform infra red (FTIR) spectroscopy and scanning electron microscopy (SEM), which proved the strong interaction between polypyrrole and α-Fe₂O₃ nanoparticles. The gas-sensing properties of the hybrid nanocomposites were studied and compared with those of PPy and α-Fe₂O₃. It was found that PPy/α-Fe₂O₃ hybrid nanocomposites can complement the drawbacks of pure PPy and α-Fe₂O₃ to some extent. It was revealed that PPy/α-Fe₂O₃ (50%) hybrid sensor operating at room temperature could detect NO₂ at low concentration (10 ppm) with very high selectivity (18% compared to C₂H₅OH) and high sensitivity (56%), with better stability (85%). The sensing mechanism of PPy/α-Fe₂O₃ materials to NO₂ was presumed to be the synergism of PPy and α-Fe₂O₃ or the effect of p–n heterojunctions.     

Fe2O3/Ni2O3/Al2O3催化剂制备及其催化氧化靛蓝废水研究

以三氧化二铝为载体,采用浸渍沉淀法制备系列Fe2O3/Ni2O3/Al2O3催化剂。采用TG-DTA,XRD及ESEM等技术对催化剂进行表征,确定催化剂的最佳焙烧温度为460℃。以次氯酸钠为氧化剂,同时考察m(三氧化二镍)/m(三氧化二铝)、m(三氧化二铁)/m(三氧化二镍)、m(次氯酸钠)∶m(靛蓝废水)、pH对印染靛蓝废水处理的影响。结果表明:m(三氧化二镍)/m(三氧化二铝)=0.3,m(三氧化二铁)/m(三氧化二镍)=0.04,m(次氯酸钠)∶m(靛蓝废水)=1∶11,pH=7,反应温度为20℃,常压反应时间为2 h时,COD的去除率为95.3%。     

Crystallographic characterization of silicon nitride ceramics sintered with Y2O3–Al2O3 or E2O3–Al2O3 additions

Silicon nitride ceramics were sintered using Y₂O₃–Al₂O₃ or E₂O₃–Al₂O₃ (E₂O₃ denotes a mixed oxide of Y₂O₃ and rare-earth oxides) as sintering additives. The intergranular phases formed after sintering was investigated using high-resolution X-ray diffraction (HRXRD). The use of synchrotron radiation enabled high angular resolution and a high signal to background ratio. Besides the appearance of β-Si₃N₄ phase the intergranular phases Y₃Al₅O₁₂ (YAG) and Y₂SiO₅ were identified in both samples. The refinement of the structural parameters by the Rietveld method indicated similar crystalline structure of β-Si₃N₄ for both systems used as sintering additive. On the other hand, the intergranular phases Y₃Al₅O₁₂ and Y₂SiO₅ shown a decrease of the lattice parameters, when E₂O₃ was used as additive, indicating the formation of solid solutions of E₃Al₅O₁₂ and E₂SiO₅, respectively.     

Al2O3/Fe2O3吸附剂脱除硫化氢的性能

采用共沉淀法制备了氧化铝改性的氧化铁吸附剂,并采用比表面积(BET)、X射线衍射(XRD)技术对吸附剂进行了表征。在固定吸附床上,考察了制备条件及吸附条件对吸附剂脱除硫化氢性能的影响。结果表明,引入氧化铝能显著提高氧化铁对硫化氢的吸附净化能力。氧化铁与氧化铝质量比为1∶0.5,造孔剂十六烷基三甲基溴化铵(CTAB)质量分数为2%,焙烧温度500℃时,采用共沉淀法的负载氧化铝吸附剂的吸附效果最好。在气速20 mL/min,吸附温度80℃时,脱硫率和穿透硫容可分别达到99.3%和105 mg/g,其穿透硫容比未经改性的活性氧化铁提高了49.8 mg/g。     

改善PEC用α-Fe2O3光阳极性能的策略

通过光电化学(PEC)电池将太阳能收集和储存为氢燃料,为未来的能源需求提供了一条清洁和可再生的途径。在多种常用材料中赤铁矿(α-Fe₂O₃)由于其来源丰富、价格低廉、优异的光稳定性等特点,近几十年来一直是研究热点。对PEC水分解用赤铁矿光阳极的最新进展进行了综述。首先,介绍了掺杂手段提高赤铁矿体相电导率。其次,介绍了负载助催化剂和沉积表面钝化层改善赤铁矿表面反应的有效途径。以及引入中间层促进界面传输3个方面进行了综述。展望了PEC水分解用赤铁矿光电极的发展前景和面临的主要挑战。     

Multiferroic ceramics in BaO–Y2O3–Fe2O3–Nb2O5 system

Multiferroic ceramics in BaO–Y₂O₃–Fe₂O₃–Nb₂O₅ system were synthesized and their dielectric, ferroelectric and magnetic properties were evaluated. XRD results showed that the ceramic composite consists of a major phase of tetragonal tungsten bronze structured Ba₂YFeNb₄O₁₅, and minor phases of monoclinic YNbO₄ and hexagonal Ba₃Fe₂Nb₆O₂₁. Three dielectric relaxations were observed in the temperature range from 125 to 575 K. The relaxor dielectric behavior in the temperature range from 125 to 350 K was attributed to the random occupation of Fe³⁺ and Nb⁵⁺ ions at B site of the tungsten bronze structure. The electrode polarization and the inhomogeneous structure contributed to the high-temperature and middle-temperature dielectric relaxations, respectively. Both the ferroelectric hysteresis loop and the magnetic hysteresis loop were measured, which suggested that the synthesized ceramic composite was a promising candidate of multiferroics.     

V2O5、NiO、Fe2O3和钒渣对Al2O3/MgAl2O4的腐蚀机理

研究了V2O5、NiO、Fe2O3和钒渣对Al2O3和MgAl2O4尖晶石的腐蚀。把Al2O3和MgAl2O4试样分别同上述氧化物一起从室温加热到1 400℃、1 450℃和1 500℃,加热速率为10℃.min-1。用XRD和SEM对每个系统的腐蚀机理进行了分析。结果显示,所研究的氧化物对Al2O3的影响弱于对MgAl2O4的影响。氧化铝被NiO侵蚀形成NiAl2O4尖晶石,MgAl2O4尖晶石被V2O5侵蚀形成MgV2O6。本文还观察到钒渣中的成分Fe2O3、Mg、Ni、V和Fe分散到了Al2O3结构中。另一方面,Fe2O3、Ca、S、Si、Na、Mg、V和Fe分散到了MgAl2O4结构中。最后,把得到的结果与FactSage软件的预测结果进行了对比。     

Study of AC electrical properties of V2O5–P2O5–B2O3–Dy2O3 glasses

The AC conductivity of glass samples of composition 60V₂O₅–5P₂O₅–(35−x)B₂O₃–xDy₂O₃, 0.4≤x≤1.2 has been analyzed. The samples were prepared by the usual melt-quench technique. The prepared compounds were analyzed by X-ray diffraction (XRD) and thermo gravimetric–differential thermal analysis (TG/DTA). The activation energies were evaluated using glass transition temperature (T_g) and peak temperature of crystallization (T_c) from TG/DTA. The dependence of activation energy on composition was discussed. The electrical conductance and capacitance were measured over a frequency range of 20 Hz to 1 MHz and a temperature range of 303–473 K; these reveal semiconducting features based predominantly on an ionic mechanism. The dielectric and complex-impedance response of the sample is discussed. The relaxation time was found to increase with increasing temperature. Jonscher's universal power law is applied to discuss the conductivity. The electrode polarization was found to be negligible and confirmed from electrical modulus.     

凹凸棒石/γ-Fe2O3/碳纳米复合材料吸附有机物污染物研究

以凹凸棒石、废活性白土和铁盐溶液为材料,采用氢气气氛煅烧获得碳纳米复合材料,以DCP/BPA为有机污染物研究复合材料的吸附性能,并用高锰酸钾再生吸附饱和的吸附剂进行探索。结果表明,两种有机物的吸附均能符合Freundlich吸附模型;动力学吸附拟合中,两种有机物均能使用二级动力学方程拟合其吸附行为,且KBPA>KDCP,表明该材料能够较易吸附极性较弱的有机物;通过再生发现,再生后其吸附能力提高。因此,该复合材料较易吸附疏水性有机物、并可进行循环再生利用。     

基于Fe2O3的片状α-Al2O3包覆研究

首先以片状α-Al₂O₃为基质,以Fe Cl₃为铁源,采用液相沉积法制备了Fe₂O₃/α-Al₂O₃珠光颜料,并借助SEM、EDS、XRD等手段对制备的珠光颜料进行性能表征,考察了反应p H值、反应温度、铁盐浓度、添加剂用量等因素对片状α-Al₂O₃包覆率的影响,得到了制备铁系包覆片状α-Al₂O₃的最佳制备工艺参数,同时了解了各参数影响包覆率的主次顺序,并在此基础上着重探讨了六偏磷酸钠对包覆率产生影响的机理。结果表明：影响包覆率的主次顺序依次为反应p H值、反应温度、添加剂用量、铁盐浓度;在最优的工艺参数下制备出来Fe₂O₃/α-Al₂O₃的包覆率为20.93%;样品的表面形貌光滑平整且包覆完整。