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91.
K.O. RochaAuthor VitaeS.M. ZanettiAuthor Vitae 《Sensors and actuators. B, Chemical》2011,157(2):654-661
Nanocrystalline WO3/TiO2-based powders have been prepared by the high energy activation method with WO3 concentration ranging from 1 to 10 mol%. The samples were thermal treated in a microwave oven at 600 °C for 20 min and their structural and micro-structural characteristics were evaluated by X-ray diffraction, Raman spectroscopy, EXAFS measurements at the Ti K-edge, and transmission electron microscopy. Nitrogen adsorption isotherms and H2 Temperature Programmed Reduction were also carried out for physical characterization. The crystallite and particle mean sizes ranged from 30 to 40 nm and from 100 to 190 nm, respectively. Good sensor response was obtained for samples with at least 5 mol% WO3 activated for at least 80 min. Ceramics heat-treated in microwave oven for 20 min have shown similar sensor response as those prepared in conventional oven for 120 min, which is highly cost effective. These results indicate that WO3/TiO2 ceramics can be used as a humidity sensor element. 相似文献
92.
Detection of sulfur dioxide (SO2) at high temperature (600–750 °C) in the presence of some interferents found in combustion exhausts (NO2, NO, CO2, CO, and hydrocarbon (C3H6)) is described. The detection scheme involves use of a catalytic filter in front of a non-Nernstian (mixed-potential) sensing element. The catalytic filter was a Ni:Cr powder bed operating at 850 °C, and the sensing elements were pairs of platinum (Pt) and oxide (Ba-promoted copper chromite ((Ba,Cu)xCryOz) or Sr-modified lanthanum ferrite (LSF)) electrodes on yttria-stabilized zirconia. The Ni:Cr powder bed was capable of reducing the sensing element response to NO2, NO, CO, and C3H6, but the presence of NO2 or NO (“NOx”, at 100 ppm by volume) still interfered with the SO2 response of the Pt–(Ba,Cu)xCryOz sensing element at 600 °C, causing approximately a 7 mV (20%) reduction in the response to 120 ppm SO2 and a response equivalent to about 20 ppm SO2 in the absence of SO2. The Pt–LSF sensing element, operated at 750 °C, did not suffer from this NOx interference but at the cost of a reduced SO2 response magnitude (120 ppm SO2 yielded 10 mV, in contrast to 30 mV for the Pt-(Ba,Cu)xCryOz sensing element). The powder bed and Pt–LSF sensing element were operated continuously over approximately 350 h, and the response to SO2 drifted downward by about 7%, with most of this change occurring during the initial 100 h of operation. 相似文献
93.
Binary oxides of manganese and vanadium have been synthesized by solid state sintering, in which the mass ratio of the individual components Mn2O3 and VO2 have been varied from 90:10 to 5:95. The bulk ceramic samples were characterized by X-ray diffraction and scanning electron microscopy with energy dispersive X-ray analysis. The initial compositions either rich in Mn2O3 or in equi-proportion by mass with VO2 yield β-Mn2V2O7 or a new crystalline form of Mn2V2O7, with unit cell parameters: a = 7.73091 Å, b = 6.640788 Å, c = 6.70779 Å α = γ = 90° and β = 98.7086° which is designated as γ-Mn2V2O7. The compositions, richer in VO2 produce MnV2O6 co-existing with V2O5 the proportion of which increases with increase in VO2. The surface microanalysis shows a spherical-granular morphology in Mn2V2O7 structure and plate/rod-like structures co-existing with granular morphology in case of MnV2O6 together with V2O5. The electrical parameters of the negative temperature coefficient thermistors were determined. Depending on the constituent oxide composition, the NTC thermistors showed room temperature resistivity in the range of 6.52 × 102 to 6.1 × 106 Ω-cm. The thermistor constant and activation energy are in the range of 0.12–0.458 eV and 1393–4801 K, respectively. 相似文献
94.
The present study investigates the interaction of NO2 gas and μ-carbido-bridged iron phthalocyanine (PcFeCFePc) films obtained by Langmuir–Blodgett (LB) and spin-coating (SC) techniques. The phthalocyanine bridged dimer under study belongs to the polynuclear unsubstituted phthalocyanines class and presents poor solubility: in contrast the corresponding N-base bis-adducts are soluble enough in organic solvents to be deposited by Langmuir–Blodgett and spin-coating techniques. The reaction with NO2 is monitored by visible spectra variation that shows identical behaviour for both kinds of films, indicating that the chemical reaction between the gas and the films is independent of the deposition method. The electrical conductivity change as a function of time with NO2 is instead dissimilar: for spin-coated films it shows a behaviour already observed for sandwich-type phthalocyanine whereas for LB films it resembles that of monomeric phthalocyanine. Such a response implies that the charges (holes) generated in the oxidation/reduction process are carried differently through the material, and we attempt to explain this behaviour taking into account the two different structural and morphological features induced by the two techniques. 相似文献
95.
Preparation, characterisation and applications of thin films for gas sensors prepared by cheap chemical method 总被引:1,自引:0,他引:1
The physical properties of pure and doped (Ni, Os, Pd and Pt) SnO2 thin films, prepared by using a chloride-based inorganic sol–gel route, have been reported. These properties were investigated by using differential scanning calorimetry and thermogravimetric (DSC/TG), FTIR, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. Microsensors for gas detection were also fabricated and tested in various atmospheres (nitrogen oxide, carbon monoxide, ethanol, methanol and methane). The dopants affected the coating properties depending on the formation of nanoparticles. Furthermore the gas-sensing properties towards reducing and oxidising gases were found to be dependent on the nature of doping element. An array consisting of the manufactured sensors has been arranged and examples of applications for “electronic nose” are given. 相似文献
96.
Abstract— Coatings of indium tin oxide (ITO) nanoparticles on different flexible polymer substrates were investigated with respect to the achievable sheet resistance and their electrical behavior under oscillatory bending. As substrate materials, polyethyleneterephthalate (PET), polyethylenenaphthalate (PEN), polyetheretherketone (PEEK), and polyimide (PI) were chosen, the surface resistances on the different polymer substrates were compared as a function of annealing temperature and surface topography. The surface topography, which has a strong influence on the surface resistance, was characterized by means of a white‐light confocal (WL‐CF) microscope. On the PET substrate, which exhibits the smoothest surface, the coating of ITO nanoparticles shows the lowest sheet resistance of 2 kΩ/□ for a layer thickness of 3 μm and an annealing temperature of 200°C. Furthermore, the electrical behavior of coatings of ITO nanoparticles under oscillatory bending was investigated using a special device. These coatings show a cyclic change of the conductivity which can be explained by an alternating compression and extension of crack flanks under the applied stress. Due to the growing number of cracks with increasing number of cycles, a decrease of the conductivity is observed in the bent state as well as in the balanced state. For a small bending radii, the decrease of the conductivity is stronger due to more cracks caused by the higher tensile stresses in the layer. The electrical behavior of the coatings of the annealed ITO nanoparticles on PET films under oscillatory bending was compared with commercially available sputtered ITO coatings. The annealed coatings of ITO nanoparticles demonstrate better electrical properties under oscillatory bending than coatings of sputtered ITO. The different electrical behavior under oscillatory bending can be related to differences in crack formation. 相似文献
97.
98.
99.
The oxidation behaviors of Ni-16Cr-xAl (x=4.5%, 9.0%, mass fraction) superalloy foams in air at 1000℃ were investigated. The effects of AI content on the resistance to high temperature oxidation were examined. The oxidation mechanisms of the foams were discussed. The results show that the resistance to the oxidation of the Ni-16Cr-xA1 based alloy at 1 000 ℃ increases with the content of A1 increasing from 4.5% to 9.0%. Complex oxide products are formed on the surface of the superalloy foams after the oxidation. Cr203 and A1203 are the predominant oxides for the scales of the foams with 4.5% A1 and 9% A1, respectively. Excellent high temperature oxidation resistance and superior pore conformation stability for the Ni-16Cr-xA1 based superalloy foam with 9% A1 can be mainly attributed to the formation of relatively continuous and protective A1203 oxides on the surface of the foam. 相似文献
100.
通过建立数值模型进行编程计算,分析了锅炉过热器/再热器管道在不同的管道几何尺寸、烟气温度、蒸汽流量和温度下,各个界面热流密度的变化情况。通过回归分析得到了热流密度与管道内壁侧氧化层厚度和运行时间的关系表达式,即热流密度的评估关系式。 相似文献