纳米级钡铁氧体的原子力显微镜分析及微波性能的研究

采用溶胶-凝胶法制备掺杂钡离子的纳米六角晶型铁氧体.采用X衍射仪对其物相进行鉴定,利用原子力显微镜对不同方法制得的试样粒径进行了分析研究,最后用网络分析仪对铁氧体在1～6 GHz范围内的微波性能进行分析,结果表明:实验制得粉体为M型钡铁氧体,利用乙醇分散的稀浓度的试样能在原子力显微镜下很好地观察到颗粒的粒径,其平均粒径为52.68 nm左右,并且实验制得的纳米M型钡铁氧体具有较大的介电损耗和磁损耗,具有良好的吸波性能.     

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.     

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.     

La-Co共掺杂的M型锶铁氧体纳米纤维的制备和磁性能

以聚乙烯吡咯烷酮(PVP)和金属盐为原料,采用静电纺丝、溶胶-凝胶技术以及随后的热处理工艺,制备了La、Co共掺杂的M型锶铁氧体Sr1-xLaxFe12-xCoxO19(x=0.12)(SLFC)纳米纤维.利用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和超导量子干涉仪(SQUID)技术对纳米纤维样品的结构、形貌和磁学性能进行了观测,系统地研究了不同温度下样品的磁性能变化.结果表明:经过950°C焙烧2h后,得到纯相的M型锶铁氧体纳米纤维,纤维呈竹节状结构,直径约55nm;室温下测得矫顽力(Hc)为498.53kA·m-1,饱和磁化强度(Ms)为70.76A·m2·kg-1,剩磁(Mr)为36.35A·m2·kg-1,这比未掺杂SrFe12O19(SF)时纳米纤维的磁性能有明显的改善,并且与在相同温度下制得的相应纳米粉体样品相比,磁性能明显提高.     

Pd掺杂的纳米晶a-Fe2O3基CO敏感元件

采用共沉淀法制备了掺杂Pd和其它元素的纳米晶α-Fe2O3粉体,并制作了厚膜型CO敏感元件.用XRD、TEM和比表面积测定技术对合成的粉体进行了表征,考察了掺杂元素的种类和含量及焙烧温度对敏感元件的灵敏度的影响.结果表明,掺杂5％Sn4+和1％Pd2+,在450℃焙烧的α-Fe2O3对CO的气敏性最佳.     

Pd掺杂的纳米晶α-Fe_2O_3基CO敏感元件

采用共沉淀法制备了掺杂 Pd和其它元素的纳米晶α-Fe2 O3 粉体 ,并制作了厚膜型 CO敏感元件 .用XRD、TEM和比表面积测定技术对合成的粉体进行了表征 ,考察了掺杂元素的种类和含量及焙烧温度对敏感元件的灵敏度的影响 .结果表明 ,掺杂 5% Sn4 和 1 % Pd2 ,在 4 50℃焙烧的α-Fe2 O3 对 CO的气敏性最佳 .     

固相反应制备镍铁铜复合纳米氧化物粉体

镍铁铜复合氧化物属于改良的铁氧体材料。由于自然界的铁氧体材料化学成分和加工细度的局限性 ,而制约了铁氧体材料的进一步开发和利用。纳米材料特殊的超细特性导致了同种成分物质产生出异常性质[1 ] 而被科技界高度重视。因此研究制备不同类型的纳米铁氧体材料是当前铁氧体材料研究的热点。而采用什么方法 ,简单方便地制备出纳米铁氧体材料是研究问题的核心。目前所用的方法有物理法和化学法两大类 ,前者制备难度大、能耗和成本高 ,而且结果难以满意。后者利用化学反应 ,使制备过程容易、省时、节约。目前采用较多的方法有共沉淀法、溶胶…     

稀土掺杂的纳米TiO2分散性及光学性能研究

采用溶胶凝胶法在同一条件下制备REa+:Ti4+=0.02和0.10的稀土掺杂的纳米TiO2材料,其中REn+为Nd3+,Ce4+,La3+,Er3+四种稀土元素.通过TG-DTG,XRD,TEM,UV-Vis等测试方法对所制备的纳米TiO2进行焙烧温度、晶胞尺寸、晶粒形貌、谱学特性等方面的研究.研究表明,稀土掺杂的纳米TiO2径粒尺寸均在20 nm左右,少量稀土掺杂不但有利于TiO2颗粒的分散,而且有利于TiO2向金红石相转变.同时,由于表面修饰作用和晶场效应的影响,掺杂使纳米材料在可见光范围内有不同程度的"红移"现象,Ce4+掺杂的纳米TiO2在可见光的"红移"程度最强.稀土掺杂的纳米TiO2在农用膜和节能材料上可广泛运用.     

吸波材料钡铁氧体BaFe12O19的制备

以Fe(NO3)3.9 H2O、Ba(NO3)2为基本原料,采用溶胶-凝胶法,在络合剂柠檬酸存在的条件下,通过调节pH值,制备了纯度高的片状M型六方晶系磁铅石型钡铁氧体BaFe12O19。采用X射线衍射(XRD)、电子显微分析(SEM)等对制备产物的物相、形貌和粒度进行了表征,优化制备工艺。结果表明,制备的钡铁氧体BaFe12O19纯度高,呈片状结构,片径一般1～50μm,其较佳的制备工艺条件为pH 4.5～7.0、煅烧温度850℃、保温时间为3 h,较传统钡铁氧体BaFe12O19的制备温度降低约200℃。     

化学自组装法制备钡铁氧体亚微空心球

描述了一种基于化学自组装制备钡铁氧体亚微空心球的新颖方法, 即以聚(苯乙烯-共-丙烯酸)乳胶粒子为模板, 利用酸醇相互作用, 将在聚乙二醇水溶液中得到的钡铁氧体前驱物包覆在模板粒子上, 形成聚(苯乙烯-共-丙烯酸)/钡铁氧体前驱物核壳纳米复合粒子. 复合粒子经历750 ℃的热处理, 可获得主晶相为BaFe12O19的钡铁氧体亚微空心球. 该空心球有可能在微波吸收、电磁流变等领域得到重要应用.     

Computer simulation to investigate magnetic and wave-absorbing characteristics of iron nanoparticles

Computer simulations were carried out to investigate the magnetic and wave-absorbing characteristics of iron nanoparticles. The magnetic properties were found to depend on the shape, aggregation, and array of the nanoparticles. Nanoparticle systems were simulated using a molecular dynamics (MD) method, and the resulting configurations were used to compute the magnetic properties of the systems. In this work, microdot magnetic dipoles were assumed to localize on the iron atoms of nanoparticles. The dynamics of these magnetic dipoles under an external magnetic field were simulated by solving the Landau-Lifshitz-Gilbert equation numerically. The energy loss of a system under an external magnetic field was computed from the hysteresis curve and was correlated with the wave-absorbing characteristic of the system. The findings suggested that the disk-shaped iron particles had a greater hysteresis loss energy than the ball-shaped iron particles. It was also found that the aggregation of nanoparticles apparently reduced the wave-absorbing characteristic of the system. All the outcomes were in good agreement with the experimental measurements.     

Annealing effect on the structural and magnetic properties of nickel ferrite thin films

Nickel ferrite is a soft magnetic material with inverse spinel structure. Soft ferrite films are used in microwave devices, integrated planar circuits, etc., because of their high resistivity. In this work, thin films of nickel ferrite were deposited on Si (100) substrate by using pulsed laser deposition (PLD) technique. The thickness of the film was measured by surface profilometer and also by X‐ray reflectivity (XRR). The films were annealed at three different temperatures to observe the effect on the structural and magnetic properties of the film. The films were characterised by X‐ray diffraction (XRD), Raman spectroscopy and vibrating sample magnetometer (VSM) to study the structural and magnetic properties. Copyright © 2010 John Wiley & Sons, Ltd.     

Mechanism of oxygen releasing of copper ferrite in the formation of the corresponding oxygen-deficient compound

Copper ferrite is a promising material for hydrogen production through thermochemical water splitting. In this work, the cation distribution of copper ferrite and the corresponding oxygen-deficient compound of spinel structure was analyzed based on the crystal structural chemistry theory. The mechanism of oxygen releasing of CuO, Fe₂O₃, CuFe₂O₄ and metal (M=Ni, Mn or Zn) doped copper ferrite in the process of temperature rising was investigated by differential thermal analysis-thermogravimetry (DTA-TG). By combining the theoretical analysis with experimental results, the mechanism of oxygen releasing of copper ferrite is proposed, which is different from that of other ferrites. For copper ferrite, the oxygen releasing caused by Cu(II)→Cu(I) plays a predominant role, while for other ferrites, the oxygen releasing resulting from Fe(III)·Fe(II) is dominant. Supported by the National Defense Fundamental Research Fund (Grant No. A1420080145)     

Synthesis and characterization of manganese–zinc ferrite obtained by thermal decomposition from organic precursors

Mn–Zn ferrites were obtained by the sol–gel autocombustion methods. The effect of the precursor used in the sol–gel autocombustion synthesis on the ferrite’s microstructure was examined. The as-obtained powders were characterized by XRD, FTIR, SEM, and TG/DTA. All ferrite powders obtained from different organic precursors, after gel autocombustion, were pure spinel phase, without secondary phases. The average crystallite size, estimated from Scherrer equation, was the smallest for ferrite obtained from a mixture of fuels/precursors (citric acid and EDTA). This ferrite powder has sponge-like microstructure with large pores, but it is less agglomerated than the material obtained from glycine as the fuel.     

Untersuchungen zum Materialtransport bei der Bildung von Zink- und Nickelferrit aus den Metalloxiden. II. Über die Rolle der Gasphase für den Materialtransport bei der Ferritbildung

Studies on Material Transport during the Formation of Zinc and Nickel Ferrite from the Oxides. II. On the Role of the Gas Phase for the Material Transport during the Ferrite Formation. For the investigation of the material transport during the formation of zinc and nickel ferrite the tablets of the starting oxides were allowed to react at temperatures between 1100 and 1300°C. The vice versa diffusing cations of the oxides were determined in dependence on the distance of the reaction partners and the partial oxygen pressure by chemical analysis. The material transport and the mechanism of the ferrite formation is discussed under the aspect of the vapour pressures of the starting oxides. A partial material transport via zinc and nickel metal vapour, respectively, during the progress of these solid state reactions is proposed.     

Nano-crystalline Mn0.3Ni0.3Zn0.4Fe2O4 obtained by novel fumarato-hydrazinate precursor method

Carboxylate hydrazinate complex involving mixed metals have been synthesized and used as precursor for preparing the nanocrystalline Mn?CNi?CZn ferrite. Chemical composition of complex was fixed from chemical analysis results, infrared studies, thermogravimetric and differential scanning calorimetric analysis and isothermal weight loss studies. Nano-crystalline Mn?CNi?CZn ferrite particles obtained by thermal autocatalytic decomposition were characterized using X-ray diffraction studies, infrared spectral studies and TEM measurement. Two peaks in the region of 340?C420 and 550?C660?cm^?1 observed in the infrared spectrum of ??as synthesized?? oxide are characteristics of spinel ferrites. Average particle size of ??as synthesized?? Mn?CNi?CZn ferrite was found to be 10?nm. ??As synthesized?? Mn?CNi?CZn ferrite showed Curie point at 313?°C. Saturation magnetization (44.7?emu/g) observed for ??as synthesized?? Mn?CNi?CZn ferrite is lower than bulk material which is indicative of its nano-crystalline nature. Seebeck coefficient measurement has shown that the material exhibits n-type semiconducting behavior.     

Nanophase cobalt, nickel and zinc ferrites: synchrotron XAS study on the crystallite size dependence of metal distribution

Nanophase cobalt, nickel and zinc ferrites, in which the crystallites are in the size range 4-25 nm, were synthesised by coprecipitation and subsequent annealing. X-Ray absorption spectroscopy using synchrotron radiation (supported by X-ray powder diffraction) was used to study the effects of particle size on the distributions of the metal atoms over the tetrahedral and octahedral sites of the spinel structure. Deviations from the bulk structure were found which are attributed to the significant influence of the surface on very small particles. Like the bulk material, nickel ferrite is an inverse spinel in the nanoregime, although the population of metals on the octahedral sites increases with decreasing particle size. Cobalt ferrite and zinc ferrite take the inverse and normal forms of the spinel structure respectively, but within the nanoregime both systems show similar trends in being partially inverted. Further, in zinc ferrite, unlike the normal bulk structure, the nanophase system involves mixed coordinations of zinc(ii) and iron(iii) consistent with increasing partial inversion with size.     

The effect of cooling rate on the solidification and microstructure evolution in duplex stainless steel

The effects of the cooling rate on the solidification and microstructure evolution in the duplex stainless steel SAF 2205 was studied using DSC and light microscopy. A ferritoscope was used to measure the ferrite content. It was revealed that the cooling rate has an influence on the ??-ferrite nucleation temperature and the width of the solidification interval. Moreover, with an increase in cooling rate, the content of ??-ferrite increases, while the quantity of austenite in the ferrite matrix decreases and its morphology changes to acicular. A two-cycle DSC experiment made possible a more accurate interpretation of the collected data.     

Effect of precursor pH on structural,magnetic and catalytic properties of CoFe2O4@SiO2 green nanocatalyst

Research on Chemical Intermediates - Cobalt ferrite is a promising material for many therapeutic applications, photo-catalysis, gas detectors, high-density data storage, etc. Optimization of...     

Lipase Immobilized in Organic-Inorganic Matrices

Enzyme lipase was immobilized with ferrite powder and deposited in layers on glass slides from lipase to a solution of silicone alkoxides. The highest hydrolytical activity was observed with the magnetic lipase prepared by mixing the paste of ferrite powder and lipase with tetramethoxysilane, 3-aminopropyltriethoxysilane and propyltrimethoxysilane. In a mixed reactor, the particles of the magnetic lipase were desintegrated by mechanical stirring which caused loosing the lipase linked to magnetic material and resulted in a significant drop of activity after magnetic separation. Transparent layers were prepared by dip- or spin-coating from partially hydrolyzed tetraethoxysilane and solutions containing methyltriethoxysilane with 3-aminopropyltriethoxysilane or tetraethoxysilane with 3-mercaptopropyltriethoxysilane. The lipases immobilized in films with magnetic particles were active in tests with 4-nitrophenyl butyrate and were not inhibited by 0,0-dimethyl-0-(2,2-dichlor-vinyl)-phosphate.