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1.
NASICON dense ceramics were obtained from solid state reaction between SiO2, Na3PO4·12H2O and two different types of zirconia: monoclinic ZrO2 and the yttria-doped tetragonal phase (ZrO2)0.97(Y2O3)0.03. Higher temperatures were needed to obtain dense samples of the yttrium free composition (1265 °C). The electrical conductivity,
at room temperature, of the yttria-doped samples sintered at 1230 °C (0.20 S/m) is significantly higher than the value obtained
with the material prepared from pure ZrO2. The impedance spectra show that the differences in conductivity are predominantly due to the higher grain boundary resistance
of the undoped ceramics, probably due to formation of monoclinic zirconia and glassy phases along the grain boundary. Further
improvement of the electrical conductivity could be achieved after optimization of the grain size and density of grain boundaries.
A maximum conductivity value of about 0.27 S/m at room temperature was obtained with the yttria-doped samples sintered at
1220 °C for 40 h. Yttria-doped and undoped ceramics were tested as Na+ potentiometric sensors. The detection limit of the yttria-doped sample (10−4 mol/l) was one order of magnitude lower than the obtained with the undoped material.
Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2001. 相似文献
2.
The kinetics for the electrode reactions with oxygen and with NO and NO2 in the presence of oxygen has been studied for La0.8Sr0.2MnO3±δ-electrodes on stabilized zirconia (8 mol% Y2O3=YSZ) in the temperature range between 500°C and 900°C for oxygen partial pressures between 1 kPa and 20 kPa by means of electrochemical
methods (impedance, I-U characteristics) and temperature programmed desorption (TPD). For oxygen reduction below 900°C a mechanism
is proposed which describes the formation of peroxidic ions at the electrode surface and a subsequent rate-determining electron
transfer at the three-phase-boundary. At temperatures below 650°C the electrode reaction between NO and NO2 is much faster than the oxygen reduction. The results for the NO2-reduction to NO can be explained by a two-step mechanism consisting of a fast one-electron transfer to adsorbed NO2 at the electrode surface and a subsequent rate-determining transfer of the second electron to NO2 at the three-phase-boundary.
Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11 – 18 Sept. 1994 相似文献
3.
SOFCs are expected to become competitive devices for electrical power generation, but successful application is dependent
on decreasing working temperature from 1000 to 800 °C, without detrimental effects on resistance and on electrode processes.
This requires a reduction of the stabilized zirconia electrolyte thickness and an optimization of the electrodes, especially
the cathode, where losses are higher. Strontium doped lanthanum manganites are the most common materials tested as cathodes
for SOFCs working at high temperature (1000 °C). This cathode material presents high electronic and oxygen-ion conductivities,
a thermal expansion coefficient compatible with stabilized zirconia and good catalytic activity.
For thin film SOFC devices working at intermediate temperatures (less than 800°C), we have studied the optimization of this
type of cathode. Strontium doped lanthanum manganite has been deposited on yttria stabilized zirconia electrolyte substrates
by spray-pyrolysis and by RF sputtering. The electrode performances depend strongly on cathode microstructure, influenced
by processing conditions. With spray-pyrolysis processes, large porosity is expected. This is important for the supply of
oxygen, via O2 molecules through the pores to the triple phase boundaries, where the gas, the cathode and the electrolyte are in contact
and where oxygen reduction may occur. However, large porosity can have a nefaste effect on electronic conductivity. With RF
sputtering, denser films with higher electronic conductivity are obtained. But, in that case, the supply of oxygen occurs
via adsorbed O-atoms in a diffusion process through the cathode to the electrolyte. Spraypyrolysis and RF sputtering have
been compared relative to electrode properties.
Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997 相似文献
4.
Perumal Elumalai Vladimir V. Plashnitsa Taro Ueda Masaharu Hasei Norio Miura 《Ionics》2006,12(6):331-337
The effect of thickness of oxide-sensing electrode (SE) on NO2 sensitivity of the planar sensor based on yttria-stabilized zirconia (YSZ) was examined at high temperatures. The sensitivity
of the sensor increased with decreasing thickness of SE, and the highest sensitivity was obtained by using the thinnest layer
of Cr2O3–SE (2.7 μm) at 700 °C. In the case of NiO–SE, the highest sensitivity was observed for the sensor using the 4-μm-thick SE
even at a high temperature of 850 °C. Based on the results of the measurements for the complex impedances, the polarization
curves, and the gas-phase NO2 decomposition catalysis, it was confirmed that the catalytic activity to the gas-phase NO2 decomposition on the oxide–SE matrix played an important role in determining the NO2 sensitivity of the present sensors. 相似文献
5.
Potentiometric sensors based on zirconia can be used for determining gaseous NO at temperatures between 400 and 480 °C. For
such mixed potential sensors, NO sensitive electrode materials such as CdMn2O4 and V2O5 have been described. In order to improve the cell voltage response, composite electrode materials based on V2O5-γ-Al2O3 were investigated. Sensors employing these materials show a better voltage response and an improved adhesion to the solid
electrolyte compared with pure V2O5. The optimal temperature was found to be 440 °C. The NO sensitivity is nearly independent on the oxygen partial pressure
in the gas.
Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001. 相似文献
6.
In potentiometric zirconia based sensors gold electrodes show a high sensitivity for hydrocarbons (HC's) when the measurements
are carried out in non equilibrated oxygen containing gas mixtures at temperatures <700 °C. This behaviour explained by mixed
potential theory is not stable and depends strongly on preparation and particularly on measuring conditions. To modify the
electrode behaviour composites consisting of gold and gallium oxide were investigated. Gold pastes with different amount of
Ga2O3 were prepared and screen printed on YSZ pellets. After sintering at defined temperatures between 900 and 950 °C the cells
were tested regarding the electrode behaviour in a C3H6, O2 gas mixture using a platinum air reference electrode. These composite electrodes show as compared with pure gold an enhanced
sensitivity at low propylene concentrations and a time-independent characteristic at high concentrations of C3H6. The optimal composition is found to be at 20 mass-% Ga2O3. This electrode can be treated in reducing gases at temperatures 850 °C without changing its characteristics.
Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000. 相似文献
7.
The non-stoichiometry and chemical diffusion coefficient of SrFe1−xCoxO3-δ have been measured by steady state and transient thermogravimetry in the temperature range 750–1200 °C at different oxygen
partial pressures. At high oxygen partial pressures, the chemical diffusion coefficient was in the range 1·10−4 – 7·10−4 cm2/s. This, combined with high concentration of disordered vacancies make these materials perhaps the fastest solid oxygen ion
diffusers known at high temperatures and high oxygen partial pressures. However, due to the high concentration of defects
in SrFe1−xCoxO3-δ the compound transforms from a cubic (disordered) perovskite to a brownmillerite type of structure under reduced oxygen partial
pressures below approx. 900 °C. Due to this phase transition, the mobility of oxygen vacancies in SrFe1−xCoxO3-δ decreases up to about an order of magnitude at 850 °C. We also observe an ordering effect at 1000 °C, although smaller in
size, and this is suggested to be due to short range ordering of four-coordinated polyhedra of Fe. For possible use as oxygen
separation membranes, phase stability against sulphur and carbon containing atmospheres is also discussed with respect to
the formation of carbonates and sulphates.
Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999. 相似文献
8.
Vladimir V. Plashnitsa Taro Ueda Perumal Elumalai Toshikazu Kawaguchi Norio Miura 《Ionics》2008,14(1):15-25
The nanostructured thin NiO films with the thicknesses of 30–180 nm were examined as a sensing electrode (SE) for the planar
mixed-potential-type yttria-stabilized zirconia (YSZ)-based NO2 sensor. The sensing characteristics were examined in the temperature range of 600–800 °C under the wet condition (5 vol.%
water vapor). Among the NiO-SEs tested, the 60 nm-thick NiO-SE sintered at 1,000 °C was found to give the highest NO2 sensitivity in the NO2 concentration range of 50–400 ppm accompanying with fast response/recovery at the operating temperatures of 600–700 °C. The
high NO2 sensitivity was attributed to the high catalytic activity for both electrochemical reactions of O2 and NO2 at the interface of NiO-SE/YSZ. The ultrathin gold layer with the thickness of about 60 nm was additionally formed on the
60 nm-thick NiO-SE to fabricate the laminated-type (60 nm NiO/60 nm Au)-SE. It was demonstrated that the use of this laminated
(NiO–Au)-SE improved both the sensitivity and the selectivity to NO2. 相似文献
9.
F. Capel C. Moure P. Durán A.R. González-Elipe A. Caballero 《Applied Physics A: Materials Science & Processing》1999,68(1):41-48
2 -doped YTZP ([%mol]3 Y2O3) compositions sintered in the temperature range of 1300 to 1450 °C, the tetragonal zirconia solid solutions field for the
ZrO2-Y2O3-TiO2 system was established. The solubility of TiO2 in YTZP was found to be about 12–[%mol]14 at 1450 °C. Structural characterization of the Ti-YTZP tetragonal zirconia solid
solutions was carried out using X-ray absorption spectroscopy (EXAFS and XANES) to provide information on the environment
of Ti atoms. The electrical behavior in air of the TiO2-doped tetragonal zirconia solid solutions was studied by impedance spectroscopy in the temperature range of 300 to 800 °C,
and it was found that the ionic conductivity decreases with increasing titania content. EXAFS and XANES results show that
as the Ti4+ ions dissolve into the tetragonal zirconia YTZP matrix, a displacement of Ti ions from the center of symmetry takes place,
leading to a non-random substitution of Ti4+ ions on Zr4+ lattice sites. Ti-O bond distances derived from EXAFS indicate that the Ti ion can be in a square-pyramidal arrangement,
i.e., fivefold oxygen-coordinated. As a consequence two kinds of cation–oxygen vacancy associations are created; the high-mobility
oxygen-vacancy–eightfold-coordinated cation (Zr4+) and the low-mobility oxygen-vacancy–fivefold-coordinated cation (Ti4+). This results in a decrease in the global concentration of moving oxygen vacancies and, therefore, in a decrease of the
electrical conductivity.
Received: 1 April 1998/Accepted: 28 September 1998 相似文献
10.
The catalytic oxidation of methane on polycrystalline palladium films was studied at 550-750°C and atmosheric total pressure.
The reaction was studied under both open and closed-circuit. Under open circuit, and when yttria-stabilized zirconia (YSZ)
was used as solid electrolyte, the technique of Solid Electrolyte Potentiometry (SEP) was used to monitor the thermodynamic
activity of oxygen adsorbed on the Pd electrode during reaction. The main products were those of complete oxidation, i.e.
CO2 and H2O. Under closed-circuit, the effect of electrochemical oxygen “pumping” to or from the catalyst was studied. Non-faradaic
(NEMCA) phenomena were observed but the reaction rate enhancement factors (A) were not as large as with previously studied
catalytic systems.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996. 相似文献
11.
Perumal Elumalai Vladimir V. Plashnitsa Taro Ueda Masaharu Hasei Norio Miura 《Ionics》2007,13(6):387-393
The effect of thickness of oxide-sensing electrode (SE) on NO2 sensitivity of the planar sensor based on yttria-stabilized zirconia (YSZ) was examined at high temperatures. The sensitivity
of the sensor increased with decreasing thickness of SE, and the highest sensitivity was obtained by using the thinnest layer
of Cr2O3–SE (2.7 μm) at 700 °C. In the case of NiO–SE, the highest sensitivity was observed for the sensor using the 4 μm-thick SE
even at high temperature of 850 °C. Based on the results of the measurements for the complex impedances, the polarization
curves, and the gas-phase NO2 decomposition catalysis, it was confirmed that the catalytic activity to the gas-phase NO2 decomposition on the oxide–SE matrix played an important role in determining the NO2 sensitivity of the present sensors.
This artice was accidentally published twice. This is the second publication, please cite only the authoritative first one
which is available at . An additional erratum is available at .
An erratum to this article can be found at 相似文献
12.
An electrochemical cell composed of an yttria-stabilized zirconia disk and two layers cathode was used for nitrogen monoxide
decomposition. It was found that covering the Pt cathode by a mixture of oxygen ionic conductor (YSZ) and electronic conductor
(NiO) leads to enhancement of the performance of the electrochemical cell for NOx decomposition in the presence of excess oxygen. The decomposition activity was measured for the one-compartment cell oxide|(cathode)|YSZ|(anode)
by applying a DC voltage lower than 3.7 V in the temperature range 550–700 °C. The microstructure of the YSZ-NiO mixed oxide
electrodes was investigated in dependence of the cell operating condition and the working electrode sintering temperature.
The correlation between the microstructure of the mixed oxide electrode and conversion rate of NO was studied. The phenomenon
of self-optimization of the microstructure of the NiO-YSZ working electrode during the cell operation was observed and investigated.
Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000. 相似文献
13.
L. Bultel M. Hénault C. Roux E. Siebert B. Béguin F. Gaillard M. Primet P. Vernoux 《Ionics》2002,8(1-2):136-141
The catalytic activity of polycrystalline Pt deposited on Yttria Stabilized Zirconia (YSZ) for the oxidation of propane to
CO2 can be affected using the effect of Non-faradaic Electrochemical Modification of Catalytic Activity (NEMCA). It was found
that by applying positive overpotentials and thus, supplying O2- onto catalyst surface, up to 3.2-fold increase in the catalytic rate of C3H8 oxidation could be obtained at 365 °C. At 305 °C, no effect was evidenced. Using cyclic voltammetry and impedance spectroscopy,
we have shown the modifications induced by the addition of C3H8 on the kinetics of the 02, Pt/YSZ interface in the temperature range 300–400 °C. A decrease of the coverage of adsorbed oxygen species produced electrochemically
was evidenced as well as a decrease of the oxygen electrode reaction rate under anodic potential.
Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001. 相似文献
14.
This paper presents a formal analysis of the transport processes in yttria-doped zirconia under a temperature gradient. Due
to the simultaneous diffusion and drift of the species when the material is exposed to a thermodynamical potential gradient,
a kinetic demixing process appears on the cationic sublattice if the diffusion coefficients of the cations are different.
Experimental results obtained with yttria-doped zirconia are discussed on the basis of this analysis. They confirm that kinetic
demixing processes during cooling must be taken into account in the interpretation of the grain boundary conductivity of doped
zirconia.
Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000. 相似文献
15.
Doped bismuth ruthenates and bismuth ruthenate-stabilized bismuth oxide composites were studied as prospective cathode material
for solid oxide fuel cells. Symmetric cells were fabricated on gadolinium-doped ceria electrolytes and studied by electrochemical
impedance spectroscopy. Ca- and Ag-doped bismuth ruthenate electrodes (5–10 mol%) showed the same characteristic frequency
as undoped bismuth ruthenate but with higher activation energy and slightly better performance above ∼550 °C. At 700 °C, area-specific
resistance (ASR) of undoped, 5 mol% Ca and 5 mol% Sr-doped bismuth ruthenate electrode was 1.45, 1.24, and 1.41 Ωcm2, respectively. The change in ASR as a function of oxygen partial pressure and current bias suggests that the rate-limiting
steps for oxygen reduction in bismuth ruthenate systems are charge transfer and surface diffusion of dissociatively adsorbed
oxygen to triple phase boundaries. Introduction of the erbia-stabilized bismuth oxide (ESB) phase reduced both the rate-limiting
steps resulting in much improved electrode performance. At 700 °C, composite electrodes containing 31.25–43.75 wt% ESB exhibited
an ASR of 0.08–0.11 Ωcm2. 相似文献
16.
Electrochemical sensors using tubular yttria-stabilized zirconia (YSZ) and oxide sensing electrode (SE) were fabricated and
examined for NOx detection at high temperatures. The mixed-potential-type NOx sensor using ZnO-SE gave the highest sensitivity to NOx among other single-type oxides tested as SEs in the temperature range of 600–700 °C. The response of the ZnO-attached device
was a linear for the logarithm of NO2 (NO) concentrations from 40 to 450 ppm. The sensing mechanism of the sensor was discussed on the basis of the gas adsorption-desorption
behavior, the catalytic activity data, and electrochemical behavior for oxides examined. 相似文献
17.
A.V. Osipov P. Patzner P. Hess 《Applied Physics A: Materials Science & Processing》2006,82(2):275-280
The growth of ultra-thin (<6 nm) silicon-dioxide films on Si(100):H, Si(111):H, and a-Si:H surfaces in a dry oxygen atmosphere
(0.1–10 Pa) at low temperatures (35–200 °C) was investigated. Oxidation was induced by pulsed F2-laserradiation at 157 nm. The thickness and composition of the growing films were monitored in real time by spectroscopic
ellipsometry in the photon energy range of 1.15–4.75 eV. The kinetics of low-temperature oxidation was similar for the Si
surfaces investigated and differs from that of high-temperature thermal oxidation (900–1200 °C) that can be described by the
Deal–Grove model. To explain the faster growth at the initial stage, it is proposed that oxidation occurs by diffusion of
oxygen atoms O and/or ions O-rather than oxygen molecules. The recombination of diffusive species to oxygen molecules limits their penetration into the
bulk. A diffusion model is developed for low-temperature oxidation which takes into account the recombination process of the
diffusive species. Good agreement between theory and experiment is found. The activation energy of diffusion of the active
species was found to be 0.15 eV, in agreement with previous results and recent calculations for O- ions.
PACS 82.65.+r; 07.60.Fs; 81.65.Mq; 82.50.Hp 相似文献
18.
The electrochemical reduction and nucleation process of Si4+ on an electrical steel electrode in the eutectic LiF–NaF–KF molten salt were investigated at 750 °C, by means of cyclic voltammetry
and chronoamperometry technique. Silicon was electrodeposited on steel, and Fe3Si was formed by the diffusivity of silicon on the electrode surface. The electrochemical reduction of Si4+ process in single-step charge transfer and the cathode process was reversible. The electrocrystallization process of silicon
is controlled by progressive three-dimensional mechanism. The diffusion coefficient was calculated to be 5.42 × 10−7 cm2/s by chronopotentiometry at experimental conditions. 相似文献
19.
The distinctive features of the low-frequency internal friction Q
−1(T) of (Cu-Sn)-Nb composites at high temperatures (up to 400°C) are investigated for strains in the range 10−5–10−4. Considerable hysteresis of Q
−1(T) in the heating-cooling cycle is recorded, including the presence of a minimum at ∼175°C when the sample is heated to 400°C
and two peaks P
2 (at 280°C) and P
1 (at ∼100°C) when the sample is cooled from 400°C. The activation energy of the anomalous internal friction background (up
to 175°C), the oxygen diffusion parameters, and the oxygen concentration in the niobium fibers (all of which govern the peak
P
2) are calculated, and the value and temperature dependence of the yield point of the bronze matrix (which govern the peak
P
1) are estimated.
Zh. Tekh. Fiz. 68, 114–117 (November 1998) 相似文献
20.
P. A. Vakhrushin M. V. Vishnetskaya A. I. Kokorin 《Russian Journal of Physical Chemistry B, Focus on Physics》2012,6(1):169-172
The catalytic oxidation of dodecane by air oxygen on a mixed vanadium-molybdenum oxide (V2O5 · MoO3, 40 mol % MoO3) was studied over the temperature range 300–350°C. The reaction at 300–330°C occurred on oxygen vacancies with the rupture
of C-H bonds and formation of α-acid. Oxidation above 350°C occurred with the splitting of the C-C bond and formation of two
and more acids. Singlet oxygen 1O2 generated in the oxidation of oxide catalyst lattice oxygen participated in the reaction. A possible mechanism of the process
was considered. 相似文献