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1.
Pt-loaded metal oxides [WO 3/ZrO 2, MO x/TiO 2 (MO x = WO 3, MoO 3, V 2O 5), WO 3 and TiO 2] equipped with interdigital Au electrodes have been tested as a NO x (NO and NO 2) gas sensor at 500 °C. The impedance value at 4 Hz was used as a sensing signal. Among the samples tested, Pt-WO 3/TiO 2 showed the highest sensor response magnitude to NO. The sensor was found to respond consistently and rapidly to change in concentration of NO and NO 2 in the oxygen rich and moist gas mixture at 500 °C. The 90% response and 90% recovery times were as short as less than 5–10 s. The impedance at 4 Hz of the present device was found to vary almost linearly with the logarithm of NO x (NO or NO 2) concentration from 10 to 570 ppm. Pt-WO 3/TiO 2 showed responses to NO and NO 2 of the same algebraic sign and nearly the same magnitude, while Pt/WO 3 and WO 3/TiO 2 showed higher response to NO than NO 2. The impedance at 4 Hz in the presence of NO for Pt-WO 3/TiO 2 was almost equal at any O 2 concentration examined (1–99%), while in the case of Pt/WO 3 and WO 3/TiO 2 the impedance increased with the oxygen concentration. The features of Pt-WO 3/TiO 2 are favorable as a NO x sensor that can monitor and control the NO x concentration in automotive exhaust. The effect of WO 3 loading of Pt-WO 3/ZrO 2-based sensor is studied to discuss the role of surface W-OH sites on the NO x sensing. 相似文献
2.
The humidity response characteristics of La doped BaTiO 3 with different sintered densities and room temperature electrical conductivities were investigated using complex impedance measurement. The samples with low density and high resistivity showed the large and nearly linear sensitivity to the change of humidity. The impedance spectra of samples, when exposed to high humidity, can exhibit microstructure-related features, even though they do not give rise to a noticeable characteristic change when exposed to low humidity. The observed impedance patterns were dependent upon the density, and hence the oxidation kinetics of BaTiO 3. 相似文献
3.
Impurities have great influence on the PTCR effect in BaTiO 3 ceramics, especially a donor and an acceptor. When Cd replaces Ba as equivalent impurity, neither donor nor acceptor does it act as. However, it was found that doping with either solid CdO or vapor one resulted in the enhancement of the PTCR effect of BaTiO 3-based semiconducting ceramics. The mechanism of the enhancement of the PTCR effect is also discussed. 相似文献
4.
A highly sensitive and fast responding CO sensor was fabricated from a sheet-like SnO 2. The SnO sheets were prepared by a room temperature reaction between SnCl 2, hydrazine and NaOH, and they were subsequently oxidized into SnO 2 sheets at high temperature (600 °C). The morphology and size of the SnO 2 sheets could be controlled during the formation of SnO, which influence the sensor response ( Ra/ Rg) and response time to a great extent. The sensor response of SnO nanosheets to 10 ppm CO was enhanced up to 2.34, and the 90% sensor response time could be reduced to 6 s, which are significantly higher and shorter than those of SnO 2 powders (1.57 and 88 s), respectively. The realization of both a high sensitivity and rapid response were explained in terms of rapid gas diffusion onto the entire sensing surface due to the less-agglomerated and very thin structure of SnO 2 nanosheets and the catalytic effect of Pt. 相似文献
5.
In 2O 3 nanoparticles were deposited by low-temperature metal organic chemical vapor deposition. The response of 10-nm thick In 2O 3 particle containing layers to NO x and O 2 gases is investigated. The lowest detectable NO x concentration is 200 ppb and the sensor performance is strongly dependent on the gas partial pressure as well as on the operating temperature. The sensor response towards 200 ppm of NO x is found to be above 10 4. Furthermore, the cross-sensitivity against O 2 is very low, demonstrating that the In 2O 3 nanoparticles are very suitable for the selective NO x detection. 相似文献
6.
Solid-electrolyte-based electrochemical SO x sensors fabricated with MgO-stabilized zirconia and Li 2SO 4---CaSO 4---SiO 2 (4:4:2 in molar ratio) exhibit fairly good sensing characteristics for 2–200 ppm SO 2 in air at 600–750 °C, with the e.m.f. responses following the Nernst equation for the two-electron reduction of SO 2. The 90% response and 90% recovery times to 20 ppm SO 2 are 10 s and 7 min at 650 °C, and 10 s and 3 min at 700 °C, respectively. It is further found that the sensor exhibits excellent selectivity to SO x in the coexistence of CO 2 and NO x, and good long-term stability. The sensor is simple in structure, easy to prepare, and quite tough chemically and mechanically. These features should ensure practical use for this SO x sensor. 相似文献
7.
Ultrafine SmFe 0.7Co 0.3O 3 powder, prepared by a sol–gel method, shows a single-phase orthogonal perovskite structure. The influence of annealing temperature upon its crystal cell volume, microstructure, electrical and ethanol-sensing properties was investigated in detail. When the annealing temperature increases from 600 to 950 °C, the unit cell volume of the SmFe 0.7Co 0.3O 3 sample reduces, and its average grain size increases. When the annealing temperature increases from 600 to 850 °C, the optimal working temperature and response to ethanol of the SmFe 0.7Co 0.3O 3 sensor increase, and the response–recovery time shortens. But when the annealing temperature further increases from 850 to 950 °C, there are decreases of the optimal working temperature and sensor response, and the response–recovery time is prolonged. The results indicate that, as for sensor response, its optimal annealing temperature is about 850 °C, and the sensor based on SmFe 0.7Co 0.3O 3 annealed at 850 °C shows the highest response S = 80.8 to 300 ppm ethanol gas, and it has the best response–recovery and selectivity characteristics. When the ethanol concentration is as low as 500 ppm, the curve of its optimal response versus concentration is nearly linear. Meanwhile, the influence mechanisms of annealing temperature upon the conductance, the optimal working temperature and sensor response for SmFe 0.7Co 0.3O 3 were studied. 相似文献
8.
Flexural In 2O 3 nanowires with high aspect ratios were synthesized via a hydrothermal–annealing route. The as-synthesized In 2O 3 nanowires had diameters of 30–50 nm and length up to several microns. Various reaction parameters, such as the kind of reagents, the time of hydrothermal treatment, annealing time and annealing temperature, were investigated by a series of control experiments. The as-synthesized In 2O 3 nanowires showed excellent gas-sensing properties to NO 2 in terms of sensor response and selectivity. 相似文献
9.
Potentiometric cell, Au/LiCoO 2 5 m/o Co 3O 4/Li 2.88PO 3.73N 0.14/Li 2CO 3/Au, has been fabricated and investigated for monitoring CO 2 gas. A LiCoO 2–Co 3O 4 mixture was used as the solid-state reference electrode instead of a reference gas. The idea is to keep the lithium activity constant on the reference side using thermodynamic equilibrium at a given temperature. The thermodynamic stability of the reference electrode was studied from the phase stability diagram of Li–Co–C–O system. The Gibb’s free energy of formation of LiCoO 2 was estimated at 500°C from the measured value of the cell emf. The sensors showed good reversibility and fast response toward changing CO 2 concentrations from 200 to 3000 ppm. The emf values were found to follow a logarithmic Nernstian behavior in the 400–500°C temperature range. CH 4 gas did not show any interference effect. Humidity and CO gas decreased the emf values of the sensor slightly. NO and NO 2 gases affect this sensor significantly at low temperatures. However, increased operating temperature seems to reduce the interference. 相似文献
10.
This paper describes the fabrication procedure as well as the sensing properties of new hydrogen sensors using Fe 2O 3-based thin film. The film is deposited by the r.f. sputtering technique; its composition is Fe 2O 3, TiO 2(5 mol%) and MgO(0–12 mol%). The conductance change of the film is examined in various test gases. The sensitivity to hydrogen gas is enhanced by treating the film in vacuum at 550 °C for 4 h and then in air at 700 °C for 2 h. The sputtered film is identified to be polycrystalline -Fe 2O 3 based on X-ray diffraction patterns. However, the surface layer is considered to be changed to Fe 3O 4 after heating in vacuum and then to γ-Fe 2O 3 after heating in air. The film is thus a multilayer one with a thin γ-Fe 2O 3 layer on a -Fe 2O 3 layer. The sensing mechanism is discussed based on measurements of the physical properties of the film, such as the temperature dependence of the sensor conductance, X-ray diffraction pattern, surface morphology, RBS (Rutherford back-scattering) spectrum and optical absorption spectrum. 相似文献
11.
Polypyrrole thin films have been deposited onto a glass substrate by the Langmuir-Blodgett technique to fabricate a selective ammonia (NH 3) gas sensor. The d.c. electrical resistance of the sensing elements is found to exhibit a specific increase upon exposure to different gases such as NH 3, CO, CH 4, H 2 in N 2 and pure O 2. The polypyrrole thin-film detector shows a considerable increase of resistance when exposed to NH 3 in N 2, and negligible response when exposed to comparable concentrations of interfering gases such as CO, CH 4, H 2 in N 2 and pure O 2. The calibration curve for NH 3 in N 2 at room temperature is measured in the concentration range from 0.01 to 1%. The relative change of the electrical resistance is about 10% for the lower detectable limit of 100 ppm of NH 3 in N 2. The sensitivity of the Langmuir-Blodgett polypyrrole towards ammonia is considerably higher than that of the electrochemical polypyrrole. The fast rise time and the high sensitivity of the detector are reported as a function of number of the polypyrrole layers. Long-term aging tests of the selective NH 3 gas sensor are performed. 相似文献
12.
Polyacrylamide (PAA) and amine-functionalized PAA (AFPAA) nanoparticles with disulfonated 4,7-diphenyl-1,10-phenantroline ruthenium (Ru(dpp(SO 3) 2) 3) have been prepared. The nanoparticles produced have a hydrodynamic radius of 20–25 nm. The amount of singlet oxygen (1O2) produced by Ru(dpp(SO3)2)3 as been measured using anthracene-9,10-dipropionic acid (ADPA). A kinetic model for the disappearance of ADPA, by steady state irradiation of Ru(dpp(SO3)2)3 at 465 nm, has been developed taking also into account a consumption not mediated by 1O2. This direct consumption of ADPA is evaluated by irradiating in the presence of NaN3 and is about 30% of the total. All the experimental results are very well described by the model developed, both for free Ru(dpp(SO3)2)3 and with this dye incorporated in the nanoparticles. It is found that the polyacrylamide matrix does not quench the 1O2 produced, allowing it to reach the external solution of the nanoparticles and react with ADPA. When the matrix possesses amine groups, AFPAA, the amount of 1O2 that reacts with ADPA is slightly reduced, 60%, but most of the 1O2 produced can still leave the particles and react with external molecules. The particles produced may therefore be used as sources of 1O2 in photodynamic therapy (PTD) of cancers. The fact that those nanoparticles do not quench significantly the 1O2 makes possible the future development of 1O2 sensors based on PAA nanoparticles with the appropriate sensor molecule enclosed. 相似文献
13.
NO 2 sensing properties of SnO 2-based varistor-type sensors have been investigated in the temperature range of 400-650°C and in the NO 2 concentration range of 15–30 ppm. Pure SnO 2 exhibited a weak nonlinear I– V characteristic in air, but clear nonlinearity in NO 2 at 450°C. The breakdown voltage of SnO 2 shifted to a high electric field upon exposure to NO 2 and the magnitude of the shift was well correlated with NO 2 concentration. Thus, SnO 2 exhibited some sensitivity to NO 2 as a varistor-type sensor. When SnO 2 particles coated with a SiO 2 thin film were used as a raw material for fabricating a varistor, the breakdown voltage in air was approximately the double that of pure SnO 2 and the sensitivity to 15 ppm NO 2 was enhanced slightly. However, the sensitivity to 30 ppm NO 2 decreased. The Cr 2O 3-loading on SnO 2 also led to an increase in the breakdown voltage in air, but the Cr 2O 3 addition was not effective for promoting the NO 2 sensitivity under the present experimental conditions. 相似文献
14.
We present an approach to optimize the specific response to gases by using specially prepared nanosized platinum on highly dense sputtered polycrystalline SnO 2. Structural and morphological analyses of the SnO 2 and platinum thin films were performed. Gas measurements were carried out with single chip thin-film SnO 2 sensor arrays on silicon substrates. Pt nanoclusters covering the sensitive layer significantly affect the O 3, CO and NO 2 sensitivities and the corresponding dynamic response. 相似文献
15.
The two major industrial sources of sulphur dioxide emissions are electrical generation and non-ferrous smelting. While flue-gas scrubbing and acid-plant technology are well established, continuous methods for the determination of SO 2 in these process streams are based on expensive conventional UV or IR spectroscopic instrumentation in which the gases must be conditioned prior to analysis. Additionally, there appears to be no reliable continuous low-maintenance method of analysis for SO 3 in gases. Solid-state sensors for the continuous real-time measurement of concentrations of SO 3 and SO 2 in process gas streams offer the possibility of monitoring the efficiency of flue-gas scrubbing, determining the concentrations of SO 3 in corrosion-susceptible ducting or in acid-plant conversion towers and guarding against excessive releases of SO 3 from acid-plant tail gas. The measurement of SO 2 and SO 3 in gases by solid-state electrochemistry is reviewed. The electrochemical cells are described, and wherever possible, the temperature and concentration ranges of the various solid-state devices reported in the literature are given. We conclude with a summary of the further requirements for a successful inexpensive commercial solid-state sensor for SO 3 and SO 2 measurement in process gas streams. 相似文献
16.
The barium–strontium–titanate (BST, Ba 0.64Sr 0.36TiO 3) thin films have been prepared by the sol–gel method on a platinum-coated silicon substrate. The resulting thin films show very good dielectric and pyroelectric properties. The dielectric constant and dissipation factor for Ba 0.64Sr 0.36TiO 3 thin film at a frequency of 200 Hz were 592 and 0.028, respectively. The dependence of the capacitance as a function of the voltage shows a strongly non-linear character, and two peaks characterizing spontaneous polarization switching can be clearly seen in this curve, indicating that the films have a ferroelectric nature. The capacitance changed from 495 to 1108 pF with the applied voltage in the −5 to +5 V range at a frequency of 100 kHz. The peak pyroelectric coefficient at 30 °C is 1080 μC/m 2 K. The pyroelectric coefficient at room temperature (25 °C) is 1860 μC/m 2 K, and the figure-of-merit of this film is 37.4 μC/m 3 K. The high pyroelectric coefficients and the greater figures-of-merit of Ba 0.64Sr 0.36TiO 3 thin films make it possible to be used for thermal infrared detection and imaging. 相似文献
17.
Nanocrystalline gamma iron oxide (γ-Fe 2O 3) has been synthesized at room temperature through sonication-assisted precipitation technique. The key in obtaining γ-Fe 2O 3 at room temperature lies in exploiting high-power ultrasound (600 W). The gas-sensing properties to n-butane of pure γ-Fe 2O 3 were investigated by studying the electrical properties of the sensor elements fabricated from the synthesized powder. The maximum response (90%) of the sensor to 1000 ppm n-butane at 300 °C can be explained on the basis of catalytic activity of the nanocrystallites. The response and recovery time of the sensor to 1000 ppm n-butane were less than 12 s and 120 s, respectively. 相似文献
18.
Oxide semiconductors have been examined to develop NO x sensors for exhaust monitoring. Titania doped with trivalent elements, such as Al 3+, Sc 3+, Ga 3+ or In 3+, has a good sensitivity and selectivity to NO between 450 and 550 °C, and shows rapid response. A sensor probe for monitoring exhaust NO x has been fabricated. Many kinds of interference gases, such as C 3H 6, CO and SO 2, have been found to have only a slight influence on the sensor response to NO. The influence of O 2 and H 2O is also negligible, except for the cases of 0% H 2O and fuel-rich conditions. In accordance with these results, the sensor probe operates satisfactority in the exhaust gas of various combustion conditions without interference from the various kinds of gas species in the exhaust gases. 相似文献
19.
LaFEO 3 and Ca xLa 1−xFeO 3 ceramic powders have been prepared by the coprecipitation method from La(NO 3) 3, Fe(NO 3) 3 and Ca(NO 3) 2 aqueous solutions. The orthorhombic perovskite phases of LaFeO 3 and Ca xLa 1−xFeO 3 are characterized by X-ray diffraction patterns. The sensors fabricated with those powders have high sensitivity to alcohol. Partial substitution of La 3+ in LaFeO 3 with Ca 2+ can enhance the sensitivity of the materials to reducing gases. The resistance of an LaFeO 3 sensor in air, vacuum and alcohol-containing air has been measured. Complex impedance spectroscopy has been used to try and analyse the gas-sensing mechanism. According to the experimental results, it can be deduced that the surface adsorptive and lattice oxygen govern the sensing properties of LaFeO 3 and Ca xLa 1−xFeO 3 ceramics. 相似文献
20.
In our earlier study, we reported that at 300 °C, a 2.0 wt.% CeO 2-doped SnO 2 sensor is highly selective to ethanol in the presence of CO and CH 4 gases [F. Pourfayaz, A. Khodadadi, Y. Mortazavi, S.S. Mohajerzadeh, CeO 2 doped SnO 2 sensor selective to ethanol in presence of CO, LPG and CH 4, Sens. Actuators B 108 (2005) 172–176]. In the present investigation, we report the influence of ambient air humidity on the ethanol selective SnO 2 sensor doped with 2.0 wt.% CeO 2. Maximum response to ethanol occurs at 300 °C which decreases with the relative humidity. The relative humidity was changed from 0 to 80% for different ambient air temperatures of 30, 40 and 50 °C and the response of the sensor was monitored in a 250–450 °C temperature range. As the relative humidity in 50 °C air increased from 0 to 30%, a 15% reduction in the maximum response to ethanol was observed. A further increase in the relative humidity no longer reduced the response significantly. The presence of humidity improved the sensor response to both CO and CH 4 up to 350 °C after which the extent of improvement became smaller and at 450 °C was almost diminished. The sensor is shown to be quite selective to ethanol in the presence of humid air containing CO and CH 4. The selectivity passes a maximum at 300 °C; however it declines at higher operating temperatures. 相似文献
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