Microemulsion-based synthesis of porous zinc ferrite nanorods and its application in a room-temperature ethanol sensor

Porous zinc ferrite (ZnFe(2)O(4)) nanorods with a diameter of around 50?nm and a length of several micrometers have been synthesized by a microemulsion-based method in combination with calcination at 500?°C. The morphology and structure of the ZnFe(2)O(4) nanorods and its precursor (ZnFe(2)(C(2)O(4))(3) nanorods) were systematically characterized by x-ray powder diffraction, transmission electron microscopy, field emission scanning electron microscopy and high-resolution transmission electron microscopy. The formation mechanism for the porous ZnFe(2)O(4) nanorods is also discussed. Moreover, the porous ZnFe(2)O(4) nanorods were applied in a room-temperature ethanol sensor and exhibited much better sensing performance than ZnFe(2)O(4) nanoparticles.     

Preparation and gas-sensing characteristics of nanocrystalline spinel zinc ferrite thin films

Zinc ferrite is a promising sensor material. In this paper, thin films of nanocrystalline zinc ferrite were deposited on alumina substrates by nebulization of a 0.01-M solution of a mixture of ZnCl/sub 2/ and FeCl/sub 3/ in ethanol (Zn:Fe=1:2) followed by pyrolysis and annealing in flowing air. The resulting films were characterized by X-ray diffraction and scanning electron microscopy, and the gas-sensing properties of as-deposited films were also investigated.     

喷射共沉淀法制备纳米铁酸钴及气敏性能表征

尖晶石结构的复合氧化物已经成为一类重要的气体敏感材料.本文采用喷射共沉淀法制备了纳米铁酸钴,使用TG-DTA、XRD和TEM分析了结构特征.研究了纳米铁酸钴的气敏特性并探讨了气敏机理.     

The formation of zinc ferrite

The formation of zinc ferrite from zinc oxide and iron oxide is evaluated with high temperature X-ray diffraction experiments. Despite the problem of accurately determining the temperature of the part of the sample actually investigated, a kinetic analysis of the isothermal formation is shown to be possible. From these data the energy and entropy of activation are derived. It is further shown that neither corrections for grain growth during formation nor the presence of impurities have any influence on these results. On the other hand, the size of the reactant iron oxide particles is found to have a strong influence on both the energy and entropy of activation.     

Weight losses from zinc ferrite and nickel ferrite during sintering

The sintering in air of fully formed zinc ferrite and nickel ferrite is always accompanied by a loss of weight from the ferrite, caused by removal of some oxygen. Although the rate of weight loss from the ferrite has the same time and temperature dependence as the rate of shrinkage of the specimens, it is found that altering the loss of weight by changing the oxygen pressure has little effect on the sintering of fully formed ferrites. Criteria are established for the preparation of high density and high resistivity sintered ferrites.     

Reactive sintering of zinc ferrite

The reactive sintering of zinc ferrite, i.e. firing without previously calcining, has been studied using three types of iron oxide. The conversion into ferrite as well as the simultaneous densification were investigated upon variations in morphology and impurity content. The formation reaction is shown to be accompanied by a strong increase of the median pore size. This phenomenon appears responsible for the generally smaller density of the final material as compared with single-phase sintering. It is shown that reactive sintering is inevitably accompanied by expansion, irrespective of molecular volume variations. A calcining step appears indispensable for the preparation of the highest quality of ferrites.     

Magnetic structure of zinc ferrite

A detailed analysis of the available experimental data has been made for the ordered phase of ZnFe₂O₄. The abnormally lowT _N and the observed spin arrangement have been explained on the basis of the hybridization of orbitals on the oxygen ions which gives rise to an anisotropic exchange interaction. The variation of hyperfine field and susceptibility with temperature along with the zero point reduction of the magnetic moment indicate that the ZnFe₂O₄ is a two-dimensional antiferromagnet.     

锌铁氧体的合成及磁电性能

用化学共沉淀法制备了系列锌铁氧体微粉。借助于TG-DTA、XRD、SEM、VSM和PNA技术,对干凝胶的热分解过程、产物的物相、微观结构、磁性能和介电常数进行了研究。结果表明,随煅烧温度的提高,锌铁氧体微粉的粒径增大,磁性也增强;尖晶石结构的块状锌铁氧体具有负电阻率温度系数,而且随着煅烧温度的提高,介电常数减小。     

Highly sensitive and selective ethanol sensor based on micron-sized zinc oxide porous-shell hollow spheres

Zinc oxide (ZnO) porous-shell hollow spheres (PHS) were prepared by thermally oxidizing high-purity zinc powder in an oxygen-containing atmosphere, and its ethanol gas sensing properties were measured in the concentration range of 10–400 ppm. At the optimum operating temperature of 350 °C, a sensitivity of 0.25/ppm was obtained and the response–concentration curve was of high linearity. The response and recovery times were measured to be ～5–12 s and 8–13 s, respectively. The sensor was proved to be highly selective to ethanol. Our results indicate that ZnO PHS might be a promising material for fabricating practical ethanol sensors.     

Highly sensitive ethanol sensor based on zinc oxide-based nanomaterials with low power consumption

Journal of Materials Science: Materials in Electronics - Gas detection has a wide range of application needs in all walks of life, and a variety of gas sensors used in sensor nodes often use...     

Modification of dielectric and mechanical properties of rubber ferrite composites containing manganese zinc ferrite

Spinel ferrites constitute an important class of magnetic materials. Polycrystalline ferrites are a complex system composed of crystallite grain boundaries and pores. Manganese zinc ferrites have resistivities between 0.01 and 10 Ω m. Making composite materials of ferrites with either natural rubber or plastics will modify the electrical properties of ferrites. Composite materials are ideally suited for many modern applications where ceramic materials have some drawbacks. The mouldability and flexibility of these composites find wide use in industrial and other scientific applications. Mixed ferrites belonging to the series Mn_(1−x)Zn_xFe₂O₄ (MZF) were synthesized for different ‘x’ values in steps of 0.2. These pre-characterized ceramic ferrites were then incorporated in a natural rubber matrix. The dielectric properties of the ceramic manganese zinc ferrite and RFC were also studied. A program based on G programming was developed with the aid of LabVIEW package to automate the dielectric measurements. The dielectric permittivity of the RFC were then correlated with that of the corresponding dielectric permittivity of the magnetic filler and matrix by a mixture equation, which helps to tailor properties of the composites.     

线面式电容传感器结构设计与传感特性研究

提出了一种基于自阻尼垂向测量参考的线面式电容传感器,对垂向运动中的残留水平位移进行精确测量。线面式电容传感器利用细丝电极作为直接垂向测量参考,消除了间接参考在其转换过程包含的系统误差;同时采用细丝末端的液体阻尼器保证细丝电极的稳定性。实验表明:在0.38~0.4pF范围内,线面式电容传感器的分辨力优于0.05μm,短期稳定性约为0.1μm。     

The magnetic behaviour of nanostructured zinc ferrite

We have investigated a series of nanostructured ZnFe₂O₄ samples produced by mechanical activation (mean particle sizes d ～50-8 nm) by variable temperature neutron diffraction measurements (2-535 K) supported by DC magnetisation measurements (4.2-300 K). The systematic increase in the mean inversion parameter (c ～0.04-0.43) with increasing milling time is accompanied by a gradual decrease in the occurrence of the long range antiferromagnetic ordering observed in the starting ZnFe₂O₄ material, as well as a gradual decrease in the related diffuse short range order peak. The neutron diffraction patterns of particles with d < ～15 nm and c> ～0.2 are consistent with the occurrence of ferrimagnetic order and exchange interactions of the type Fe³⁺A—O^2?—Fe³⁺ [B]. Diagrams summarising the magnetic regions of nanostructured ZnFe₂O₄ are presented. The magnetic behaviour overall agrees well with the enhanced magnetisation and ferromagnetic behaviour reported for nanostructured, ultrafine and thin films of ZnFe₂O₄ by other groups using mainly magnetisation and Mössbauer spectroscopy measurements.     

Gas sensing characteristics of MEMS gas sensor arrays in binary mixed-gas system

MOS gas sensor arrays based on MEMS gas sensor platforms were developed for the detection of carbon monoxide (CO), nitrogen oxides (NO_x) and ammonia (NH₃), and their gas sensing characteristics in binary mixed-gas system were investigated. Three gas sensing materials with nano-sized particles for these target gases, Pd–SnO₂ for CO, In₂O₃ for NO_x and Ru–WO₃ for NH₃ were synthesized using a sol–gel method. All the sensors showed good properties for their target gases at the optimum points for micro-heater operation. From the experimental data in MEMS gas sensor arrays in a binary mixed system, the gas sensing behavior and sensor response in mixed gas systems were scrutinized. The gas sensing behaviors to the mixed gas systems suggested that specific adsorption and selective activation of adsorption sites might occur in gas mixtures and offer the priority for the adsorption of specific gas. Thorough analysis of the sensing performance of the sensor arrays will make it possible to discriminate the components in gas mixtures as well as their concentrations.     

Precipitation of magnesium ferrite from MgO-FexO solid solutions

Debye-Scherrer X-ray powder photographs and photomicrographs of samples in the MgO-Fe _x O system have revealed the possible presence of spinodal decomposition.Samples of MgO doped with 4.99 cation % iron were quenched from high temperature into water. Debye-Scherrer photographs taken after quenching revealed the presence of satellite lines located adjacent to the main diffraction lines. These lines can be interpreted as due to a periodic fluctuation in lattice parameter. This periodic fluctuation has been described as one of the distinguishing features of spinodal decomposition.Microstructures of the samples in correlation with electrical conductivity measurements revealed two different types of precipitation depending on sample heat-treatment. The first type reveals MgFe₂O₄ precipitates at grain-boundaries. The second reveals a grainy precipitate network permeating the structure. The grainy network could be due possibly to growth of precipitates following an initial decomposition of the spinodal type.Based on a thesis submitted by S. K. Evans for the Ph.D. degree in ceramic engineering, University of Utah, September 1965.     

Reduced-temperature ethanol sensing characteristics of flower-like ZnO nanorods synthesized by a sonochemical method

Flower-like ZnO nanorods with diameters less than 15?nm were synthesized by a sonochemical method. The sensors fabricated from the nanorods exhibited excellent ethanol sensing properties. At the working temperature of 300?°C, their sensitivity was 176.8-100?ppm ethanol vapour. While the working temperature was reduced to 140?°C, they were still able to detect ethanol vapour at the ppm level. The reduced working temperature may be attributed to the small sizes of the nanorods.     

Superparamagnetic properties of thin films and small particles of magnesium ferrite

The magnetic properties of superparamagnetic thin films and small particles of magnesium ferrite obtained by thermal treatment of the iron films evaporated in vacuum on the