超声喷雾共沉淀法制备纳米氧化锡粉体及其气敏性研究

采用超声波喷雾技术,以SnCl4·5H2O和CO(NH2)2为前驱体原料制备了氧化锡以及Ce稀土离子掺杂纳米粉体.详细地研究了超声喷雾条件、反应时间以及化学组分对纳米SnO2粉体的形貌和尺寸的影响规律,以及前驱体沉淀物脱水化学处理的条件.用XRD,TEM研究了所获纳米粒子的晶相和形貌.结果表明,制备的SnO2纳米粒子呈球状,尺寸在10～20 nm,纳米颗粒均匀,分散性好.以该粉体为基础制备了相应的气敏元件,测定了气体灵敏度与温度和稀土元素掺杂的关系.研究测试表明,纳米SnO2半导体气敏元件对NO2气体有着良好的响应-恢复特性,并且具有较高的灵敏度和较低的工作温度.稀土元素铈的掺杂能明显提高纳米SnO2粉体的气敏性能.     

Study of magnetic and structural properties of ferrofluids based on cobalt-zinc ferrite nanoparticles

Ferrofluids are colloidal systems composed of a single domain of magnetic nanoparticles with a mean diameter around 30 nm, dispersed in a liquid carrier. Magnetic Co_(1−x)Zn_xFe₂O₄ (x=0.25, 0.50, 0.75) ferrite nanoparticles were prepared via co-precipitation method from aqueous salt solutions in an alkaline medium. The composition and structure of the samples were characterized through Energy Dispersive X-ray Spectroscopy and X-ray diffraction, respectively. Transmission Electron Microscopy (TEM) studies permitted determining nanoparticle size; grain size of nanoparticle conglomerates was established via Atomic Force Microscopy. The magnetic behavior of ferrofluids was characterized by Vibrating Sample Magnetometer (VSM); and finally, a magnetic force microscope was used to visualize the magnetic domains of Co_(1−x)Zn_xFe₂O₄ nanoparticles. X-ray diffraction patterns of Co_(1−x)Zn_xFe₂O₄ show the presence of the most intense peak corresponding to the (311) crystallographic orientation of the spinel phase of CoFe₂O₄. Fourier Transform Infrared Spectroscopy confirmed the presence of the bonds associated to the spinel structures; particularly for ferrites. The mean size of the crystallite of nanoparticles determined from the full-width at half maximum of the strongest reflection of the (311) peak by using the Scherrer approximation diminished from (9.5±0.3) nm to (5.4±0.2) nm when the Zn concentration increases from 0.21 to 0.75. The size of the Co-Zn ferrite nanoparticles obtained by TEM is in good agreement with the crystallite size calculated from X-ray diffraction patterns, using Scherer's formula. The magnetic properties investigated with the aid of a VSM at room temperature presented super-paramagnetic behavior, determined by the shape of the hysteresis loop. In this study, we established that the coercive field of Co_(1−x)Zn_xFe₂O₄ magnetic nanoparticles, the crystal and nanoparticle sizes determined by X-ray Diffraction and TEM, respectively, decrease with the increase of the Zn at%. Finally, our magnetic nanoparticles are not very hard magnetic materials given that the hysteresis loop is small and for this reason Co_(1−x)Zn_xFe₂O₄ nanoparticles are considered as soft magnetic material.     

流动注射在线共沉淀HG-AFS测定痕量铅

建立了流动注射在线共沉淀HG-AFS测定痕量铅的分析方法。方法基于铅在碱性介质中与氢氧化镁共沉淀,沉淀收集在锥形沉淀腔中,用HCl溶洗沉淀和NaBH4反应,产生的氢化物被载气引入原子化器中进行测定。测定铅的RSD为3％(5ng/mL,n=10),检出限为0．01ng。检出限较直接进样降低了11倍。对国家标准物质中铅的测定结果与标准值相符。     

Permeability spectra of Co2Z hexaferrite compacts produced via a modified aqueous co-precipitation technique

Co₂Z hexaferrite materials possess intrinsically high permeability, zero field ferromagnetic resonance values (∼1 GHz), and have their magnetic orientation in the plane perpendicular to the c-axis. These characteristics make these materials practical for applications in low to mid ultra-high frequency and L-band microwave device designs. Due to the relatively large size of elements operating within these bands, it has become important to produce large amounts of Co₂Z type hexaferrite materials. A modified co-precipitation method has been proposed to produce scalable quantities of high quality Co₂Z hexaferrite particles, at ∼24 g/L. These particles have been thoroughly characterized by vibrating sample magnetometry (VSM) and X-ray diffraction (XRD) with regard to phase purity and magnetic properties. After formation and subsequent ball milling, to achieve single domain particles on the order of 0.5–2 um, particles were oriented and pressed into compacts inside a rotating field to ensure magnetization in plane. Samples then underwent VSM, XRD, and scanning electron microscopy to determine the orientation effect. In addition, the complex permittivity and permeability of these samples were measured as a function of applied field and processing conditions. The results show strong orientation in these compacts making them practical for a variety of device applications.     

Synthesis and characterization of Ni-Zn ferrite nanoparticles

Nickel zinc ferrite nanoparticles Ni_xZn_1−xFe₂O₄ (x=0.1, 0.3, 0.5) have been synthesized by a chemical co-precipitation method. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, electron paramagnetic resonance, dc magnetization and ac susceptibility measurements. The X-ray diffraction patterns confirm the synthesis of single crystalline Ni_xZn_1−xFe₂O₄ nanoparticles. The lattice parameter decreases with increase in Ni content resulting in a reduction in lattice strain. Similarly crystallite size increases with the concentration of Ni. The magnetic measurements show the superparamagnetic nature of the samples for x=0.1 and 0.3 whereas for x=0.5 the material is ferromagnetic. The saturation magnetization is 23.95 emu/g and increases with increase in Ni content. The superparamagnetic nature of the samples is supported by the EPR and ac susceptibility measurement studies. The blocking temperature increases with Ni concentration. The increase in blocking temperature is explained by the redistribution of the cations on tetrahedral (A) and octahedral (B) sites.     

Synthesis and optical properties of Cr doped ZnS nanoparticles capped by 2-mercaptoethanol

Nanoparticles of Zn_1−xCr_xS (x=0.00, 0.005, 0.01, 0.02 and 0.03) were prepared by a chemical co-precipitation reaction from homogenous solutions of zinc and chromium salts. These nanoparticles were sterically stabilized using 2-mercaptoethanol. Here a study of the effect of Cr doping on structural, morphological and optical properties of nanoparticles was undertaken. Elemental analysis, morphological, structural and optical properties have been investigated by energy dispersive analysis of X-rays (EDAX), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-visible spectroscopy .EDAX measurements confirmed the presence of Cr in the ZnS lattice. XRD showed that ZnS:Cr nanoparticles crystallized in zincblende structure with preferential orientation along (1 1 1) plane. The average sizes of the nanoparticles lay in the range of 3-6 nm and lattice parameters were in the range of 5.2-5.4 Å. Lattice contraction was observed with an increase of Cr concentration. The particle size and lattice parameters obtained from TEM and SAED images were in agreement with the XRD results. The absorption edge shifted to lower wavelengths with an increase in Cr concentration as per UV-Vis spectroscopy. The band gap energy values were in the range of 3.85-4.05 eV. This blueshift is attributed to the quantum confinement effect.     

新颖氧化镁纳米带共沉淀法合成与表征

氧化镁是一种具有重要工业用途的物质,在催化、陶瓷、塑料和橡胶等领域有着广泛的应用.当尺寸细化至纳米量级后,因纳米材料所特有的体积效应和表面效应,纳米氧化镁在低温烧结、微波吸收、催化性能等众多方面呈现出许多不同于本体材料的热、光、电、力学和化学特性,因而引起了人们广泛的研究兴趣[1,2].其中氧化镁纳米线、纳米带、纳米管等一维纳米结构材料以其新颖的结构形式及与之相关的性能,近年来更为引人关注.     

磁性固体超强酸SO42-/ZrO2-Al2O3-Fe3O4的制备与性能研究

利用化学共沉淀法将磁性基质与固体酸组装制备磁性纳米固体超强酸催化剂,利用XRD、Raman、TG-DSC、M?ssbauer、TEM、HRTEM等手段对样品性质进行表征。结果表明：磁性基质的引入赋予固体超强酸以超顺磁性;Fe₃O₄、Al₂O₃粒子弥散在ZrO₂基质中,烧结过程中阻碍了扩散传质的进行以及晶界移动,抑制了ZrO₂晶体生长,稳定了四方晶相(T-ZrO₂);样品粒径分布集中,平均约为32 nm;HRTEM显示T-ZrO₂晶体生长取向于(101)方向,晶面间距d(101)=0.29 nm;Hammett指示剂法测得经600 ℃焙烧后产物的酸强度H_o＜-13.8,酸强度大于浓硫酸(H_o=-11.93)。以柠檬酸三丁酯的合成作为磁性固体超强酸SO₄^2-/ZrO₂-Al₂O₃-Fe₃O₄催化剂的探针反应,结果表明外磁场的引入提高了柠檬酸的转化率。