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1.
V. Kharton A. Kovalevsky E. Tsipis A. Viskup E. Naumovich J. Jurado J. Frade 《Journal of Solid State Electrochemistry》2002,7(1):30-36
Deficiency in the A sublattice of perovskite-type Sr1–
y
Fe0.8Ti0.2O3–δ (y=0–0.06) leads to suppression of oxygen-vacancy ordering and to increasing oxygen ionic conductivity, unit cell volume, thermal
expansion, and stability in CO2-containing atmospheres. The total electrical conductivity, predominantly p-type electronic in air, decreases with increasing
A-site deficiency at 300–700 K and is essentially independent of the cation vacancy concentration at higher temperatures.
Oxygen ion transference numbers for Sr1–
y
Fe0.8Ti0.2O3–δ in air, estimated from the faradaic efficiency and oxygen permeation data, vary in the range from 0.002 to 0.015 at 1073–1223 K,
increasing with temperature. The maximum ionic conductivity was observed for Sr0.97Fe0.8Ti0.2O3–δ ceramics. In the system Sr0.97Fe1–
x
Ti
x
O3–δ (x=0.1–0.6), thermal expansion and electron-hole conductivity both decrease with x. Moderate additions of titanium (up to 20%) in Sr0.97(Fe,Ti)O3–δ result in higher ionic conductivity and lower activation energy for ionic transport, owing to disordering in the oxygen sublattice;
further doping decreases the ionic conduction. It was shown that time degradation of the oxygen permeability, characteristic
of Sr(Fe,Ti)O3–δ membranes and resulting from partial ordering processes, can be reduced by cycling of the oxygen pressure at the membrane
permeate side. Thermal expansion coefficients of Sr1–
y
Ti1–
x
Fe
x
O3–δ (x=0.10–0.60, y=0–0.06) in air are in the range (11.7–16.5)×10–6 K–1 at 350–750 K and (16.6–31.1)×10–6 K–1 at 750–1050 K.
Electronic Publication 相似文献
2.
The oxidation of Ni100–xPx(7.3 at%<x<25.0 at%) powders in air in the temperature range 350–450°C was determined by kinetics and X-ray diffraction. The isothermal
kinetics was modeled using theGinstling–Brounstein equations. The oxidation process was found to be thermally activated with
activation energy 127.8 kJ mol–1 for x=7.3 at% to 157.7 kJ mol–1 for x=25.0 at%. It was found that the rate constants for x=7.3 at% were approximately 100 times lower than those for x=25.0 at%.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
We have been exploring the utilization of supported ceria and ceria–zirconia nano-oxides for different catalytic applications.
In this comprehensive investigation, a series of Ce
x
Zr1−x
O2/Al2O3, Ce
x
Zr1−x
O2/SiO2 and Ce
x
Zr1−x
O2/TiO2 composite oxide catalysts were synthesized and subjected to thermal treatments from 773 to 1073 K to examine the influence
of support on thermal stability, textural properties and catalytic activity of the ceria–zirconia solid solutions. The physicochemical
characterization studies were performed using X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy
(XPS), and high-resolution transmission electron microscopy (HREM), thermogravimetry and BET surface area methods. To evaluate
the catalytic properties, oxygen storage/release capacity (OSC) and CO oxidation activity measurements were carried out. The
XRD analyses revealed the formation of Ce0.75Zr0.25O2, Ce0.6Zr0.4O2, Ce0.16Zr0.84O2 and Ce0.5Zr0.5O2 phases depending on the nature of support and calcination temperature employed. Raman spectroscopy measurements in corroboration
with XRD results suggested enrichment of zirconium in the Ce
x
Zr1−x
O2 solid solutions with increasing calcination temperature thereby resulting in the formation of oxygen vacancies, lattice defects
and oxygen ion displacement from the ideal cubic lattice positions. The HREM results indicated a well-dispersed cubic Ce
x
Zr1−x
O2 phase of the size around 5 nm over all supports at 773 K and there was no appreciable increase in the size after treatment
at 1073 K. The XPS studies revealed the presence of cerium in both Ce4+ and Ce3+ oxidation states in different proportions depending on the nature of support and the treatment temperature applied. All characterization
techniques indicated absence of pure ZrO2 and crystalline inactive phases between Ce–Al, Ce–Si and Ce–Ti oxides. Among the three supports employed, silica was found
to stabilize more effectively the nanosized Ce
x
Zr1−x
O2 oxides by retarding the sintering phenomenon during high temperature treatments, followed by alumina and titania. Interestingly,
the alumina supported samples exhibited highest OSC and CO oxidation activity followed by titania and silica. Details of these
findings are consolidated in this review. 相似文献
4.
Oxygen ion transference numbers for Gd2−xCaxTi2O7
−δ (x=0.10–0.14) pyrochlore ceramics were determined at 973–1223 K by the modified e.m.f. and faradaic efficiency techniques, taking
into account electrode polarization, and from the results on oxygen permeation. The ion transference numbers vary in the range
0.95–0.98 in air, increasing when the temperature or oxygen partial pressure decreases. The activation energies for the ionic
and p-type electronic transport in air are 74–77 and 87–91 kJ/mol, respectively. The p-type conductivity and oxygen permeability
of Gd2Ti2O7-based pyrochlores can be adequately described by relationships common for other solid electrolytes. At temperatures below
1273 K under a gradient of 10%H2+90%N2/air, average ion transference numbers for doped gadolinium titanate are not less than 0.97. Thermal expansion coefficients
for Gd2−xCaxTi2O7
−δ ceramics, calculated from dilatometric data in air, are in the range (10.4–10.6)×10−6 K−1 at 400–1300 K. 相似文献
5.
H.-L. Liu S.-J. Liu Z.-L. Xiao Q.-Y. Chen D.-W. Yang 《Journal of Thermal Analysis and Calorimetry》2006,85(3):541-544
Excess molar enthalpies of binary mixtures for tributyl
phosphate (TBP)+methanol/ethanol were measured with a TAM air Isothermal calorimeter
at 298.15 K and ambient. The results for xTBP+(1–x)CH3OH
are negative in the whole range of composition, while the values for xTBP+(1–x)C2H5OH
change from positive values at low x to
small negative values at high x. The experimental
results have been correlated with the Redlich–Kister polynomial. IR
spectra of the mixtures were measured to investigate the effect of hydrogen
bonding in the mixture. 相似文献
6.
Lamonier J. F. Sergent N. Matta J. Aboukaïs A. 《Journal of Thermal Analysis and Calorimetry》2001,66(2):645-658
Thermal analysis has been used to investigate the crystallization of ZrxCe1-xO2 mixed oxides, prepared by co-precipitation of corresponding hydroxides. For x≤0.5, small crystals of CeO2, were formed at low temperatures (373 K). For x>0.5an exothermic peak at 420°C (693 K) was observed after calcination under a flow of air ofhydroxide samples. This peak
was associated with the formation of a ZrxCe1-xO2 solid solution (XRD) in a tetragonal phase (Raman).
The solids calcined at 700°C (973 K) present a reactivity towards the carbon black oxidation. The thermal analysis coupled
with a gas chromatograph (GC) were used to follow this reactivity. Simultaneous study of the activity (thermal analysis) and
the selectivity (GC) in CO or CO2 of the different catalysts revealed an important parameter: acatalyst-soot particle contact. We also obtained a more precise
comparison of ZrxCe1-xO2 oxides in the catalytic soot combustion.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
High energy ball-milling methods were employed in the synthesis of anatase-doped hematite xTiO2(a) · (1−x)α-Fe2O3 (x = 0.1, 0.5, and 0.9) ceramic system. The thermal behavior of as obtained ceramic system was characterized by simultaneous
DSC–TG. The pure anatase phase was found to be stable below 800 °C, but there is a 10.36% mass loss due to the water content.
Two exothermic peaks on DSC curves of pure anatase indicate the different crystallization rates. The pure hematite partially
decomposed upon heating under argon atmosphere. Ball-milling has a strong effect on the thermal behaviors of both anatase
and hematite phases. For x = 0.1 and 0.5, there is gradual Ti substitution of Fe in hematite lattice, and the decomposition of hematite is enhanced
due to the smaller particle size after ball-milling. The crystallization of hematite was suppressed as the enthalpy values
decreased due to the anatase-hematite solid–solid interaction. For x = 0.9, most of the anatase phase converted to rutile phase after long milling time. The thermal behavior of xTiO2(a) · (1−x)α-Fe2O3 showed smaller enthalpy value of the hematite transformation to magnetite and anatase crystallization due to the small fraction
of hematite phase in the system and hematite–anatase interaction, while the mass loss upon heating increased as a function
of milling time due to more water content absorbed by the smaller particle size. 相似文献
8.
Hugo B. Suffredini Giancarlo R. Salazar-Banda Luis A. Avaca 《Journal of Sol-Gel Science and Technology》2009,49(2):131-136
One of the key objectives in fuel-cell technology is to improve the performance of the anode catalyst for the alcohol oxidation
and reduce Pt loading. Here, we show the use of six different electrocatalysts synthesized by the sol–gel method on carbon
powder to promote the oxidation of methanol in acid media. The catalysts Pt–PbO
x
and Pt–(RuO2–PbO
x
) with 10% of catalyst load exhibited significantly enhanced catalytic activity toward the methanol oxidation reaction as
compared to Pt–(RuO2)/C and Pt/C electrodes. Cyclic voltammetry studies showed that the electrocatalysts Pt–PbO
x
/C and Pt–(RuO2–PbO
x
)/C started the oxidation process at extremely low potentials and that they represent a good novelty to oxidize methanol.
Furthermore, quasi-stationary polarization experiments and cronoamperometry studies showed the good performance of the Pt–PbO
x
, Pt–(RuO2–PbO
x
)/C and Pt–(RuO2–IrO2)/C catalysts during the oxidation process. Thus, the addition of metallic Pt and PbO
x
onto high-area carbon powder, by the sol–gel route, constitutes an interesting way to prepare anodes with high catalytic
activity for further applications in direct methanol fuel cell systems. 相似文献
9.
T. Kaljuvee M. Radin D. Astahhov Y. Pelovski 《Journal of Thermal Analysis and Calorimetry》2006,84(1):59-66
Coupled
TG-FTIR technique was used for identification of gaseous compounds evolved
at thermal treatment of six coal samples from different deposits (Bulgaria,
Russia, Ukraine). The experiments were carried out under dynamic heating conditions
up to 900°C at heating rates of 5, 10 or 50 K min–1
in a stream of dry air. The emission of CO2, H2O,
CO, SO2, COS, methane, methanol, formic acid, formaldehyde,
acetaldehyde, chlorobenzene was clearly identified in FTIR spectra of the
samples studied. The formation of ethanol, ethane, ethylene and p-xylene, at least on the level of traces, was also
identified. At the heating rate of 5°C min–1
the temperature of maximum intensities of the characteristic peaks of COS
was 270°C, of formaldehyde, formic acid, ethane and methanol 330°C,
of SO2, CO, acetic acid, ethylene and p-xylene
400°C and of chlorobenzene 500°C. At 10°C min–1
and 50°C min–1 these temperatures were
shifted, respectively, by 70–300°C and 150–450°C towards
higher temperatures and the respective absorption bands in FTIR spectra were,
as a rule, more intensive. 相似文献
10.
The structure, thermal expansion coefficient, and electroconductivity of YBa2(Cu1−x
Al
x
)3O6+δ (x = 0.0–0.9) were studied at 20 to 900°C in air. The most conducting compositions of YBa2(Cu1−x
Me
x
)3O6+δ (Me = Al, Co, Fe) were determined. The electrochemical activity of electrodes with the most conducting compositions of YBa2(Cu1−x
Me
x
)3O6+δ (Me = Al, Co, Fe) was studied in a wide polarization range in the contact with 0.9ZrO2 + 0.1Y2O3 solid electrolyte in air at the temperatures of 700 to 900°C.
Original Russian Text ? V.K. Gil’derman, I.D. Remez, 2009, published in Elektrokhimiya, 2009, Vol. 45, No. 5, pp. 612–615.
Published by report at IX Conference “Fundamental Problems of Solid State Ionics”, Chernogolovka, 2008. 相似文献
11.
Pet'kov V. I. Orlova A. I. Kazantsev G. N. Samoilov S. G. Spiridonova M. L. 《Journal of Thermal Analysis and Calorimetry》2001,66(2):623-632
A5–4xZrxZr(PO4)3 (A=Na, K;0≤x≤1.25), Na1-xCd0.5xZr2(PO4)3 (0≤x≤1), Na5–xCd0.5xZr(PO4)3 (0≤x≤4) compositions which belong to the NZP structural family were synthesized using the sol-gel method. The lattice thermal
expansion of members of these rows were determined up to 600°C by high-temperature X-ray diffractometry. The axial thermal
expansion coefficients change from -5.8·10-6to 7.5·10-6 °C-1 (αa) and from 2.6·10–6 to 22·10–6 °C-1 (αc). These results, in addition to those for other NZP compounds allow us to explain their low thermal expansion. The mechanism
can be attributed to strongly bonded three-dimensional network structure, the existence of structural holes capable to damp
some of the thermal vibrations and anisotropyin the thermal expansion of the lattice.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
D. A. Medvedev T. A. Zhuravleva A. A. Murashkina V. S. Sergeeva B. D. Antonov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(9):1623-1627
The phase composition, linear thermal expansion coefficient, electroconductivity (in the temperature interval 600–900°C and
partial pressures of oxygen 10−5–0.21 atm) of solid-oxide materials based on gadolinium-barium cobaltite doped with 3d-elements BaGdCo2 − x
Me
x
O5 + δ, Me = Cu, Fe; x = 0.0, 0.2, …, 2.0 were investigated. The homogeneity regions of samples were established by means of X-ray phase analysis.
It was shown that the linear thermal expansion coefficient of cobaltite decreases with an increase in the copper or iron concentration.
It was established that the electroconductivity of BaGdCo2 − x
Me
x
O5 + δ decreases with an increase in x. We concluded that upon a decrease in p(O2), the electroconductivity of samples first decreases and then reaches a horizontal plateau. 相似文献
13.
K. A. Aly A. Dahshan Yasser B. Saddeek 《Journal of Thermal Analysis and Calorimetry》2010,100(2):543-549
The present paper reports on the effect of MoO3 on the glass transition, thermal stability and crystallization kinetics for (40PbO–20Sb2O3–40As2O3)100−x
–(MoO3)
x
(x = 0, 0.25, 0.5, 0.75 and 1 mol%) glasses. Differential scanning calorimetry (DSC) results under non-isothermal conditions
for the studied glasses were reported and discussed. The values of the glass transition temperature (T
g) and the peak temperature of crystallization (T
p) are found to be dependent on heating rate and MoO3 content. From the compositional dependence and the heating rate dependence of T
g and T
p, the values of the activation energy for glass transition (E
g) and the activation energy for crystallization (E
c) were evaluated and discussed. Thermal stability for (40PbO–20Sb2O3–40As2O3)100−x
–(MoO3)
x
glasses has been evaluated using various thermal stability criteria such as ΔT, H
r
, H
g and S. Moreover, in the present work, the K
r(T) criterion has been considered for the evaluation of glass stability from DSC data. The stability criteria increases with
increasing MoO3 content up to x = 0.5 mol%, and decreases beyond this limit. 相似文献
14.
V. A. Varnek V. V. Sokolov I. Yu. Filatova S. A. Petrov 《Journal of Structural Chemistry》2009,50(2):351-355
M?ssbauer spectroscopy is used to study the state of iron atoms in samples with a composition of CuCr1−x
Fe
x
S2 (x = 0.01–0.30). It is shown that at x ≤ 0.02 samples are solid solutions in which iron atoms have an oxidation number of 3+ and replace chromium atoms in octahedral
sites. When the iron concentration increases, the second phase — chalcopyrite CuFeS2 — forms along with the solid solution. The relative iron concentration in this phase increases from 11% at x = 0.03 to 52% at x = 0.30.
Original Russian Text Copyright ? 2009 by V. A. Varnek, V. V. Sokolov, I. Yu. Filatova, and S. A. Petrov
__________
Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 2, pp. 365–368, March–April, 2009. 相似文献
15.
P. Mošner K. Vosejpková L. Koudelka L. Beneš 《Journal of Thermal Analysis and Calorimetry》2012,107(3):1129-1135
The effect of TeO2 additions on the thermal behaviour of zinc borophosphate glasses were studied in the compositional series (100 − x)[0.5ZnO–0.1B2O3–0.4P2O5]–xTeO2 by differential scanning calorimetry, thermodilatometry and heating microscopy thermal analysis. The addition of TeO2 to the starting borophosphate glass resulted in a linear increase of glass transition temperature and dilatometric softening
temperature, whereas the thermal expansion coefficient decreased. Most of glasses crystallize under heating within the temperature
range of 440–640 °C. The crystallization temperature steeply decreases with increasing TeO2 content. The lowest tendency towards crystallization was observed for the glasses containing 50 and 60 mol% TeO2. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were Zn2P2O7, BPO4 and α-TeO2. Annealing of the powdered 50ZnO–10B2O3–40P2O5 glass leads at first to the formation of an unknown crystalline phase, which is gradually transformed to Zn2P2O7 and BPO4 during subsequent heating. 相似文献
16.
U. Ahmadu A. O. Musa S. A. Jonah N. Rabiu 《Journal of Thermal Analysis and Calorimetry》2010,101(1):175-179
Sodium zirconium phosphate (NZP) composition Na1−x
Li
x
Zr2(PO4)3, x = 0.00–0.75 has been synthesized by method of solid state reaction method from Na2CO3·H2O, Li2CO3, ZrO2, and NH4H2PO4, sintering at 1050–1250 °C for 8 h only in other to determine the effect on thermal properties, such as the phase formation
of the compound. The materials have been characterized by TGA and DTA thermal analysis methods from room temperature to 1000 °C.
It was observed that the increase in lithium content of the samples increased thermal stability of the samples and the DTA
peaks shifted towards higher temperatures with increase in lithium content. The thermal stability regions for all the sample
was observed to be from 640 °C. The sample with the highest lithium content, x = 0.75, exhibited the greatest thermal stability over the temperature range. 相似文献
17.
Structural, magnetic and magnetotransport properties of La0.7−x
Ce
x
Ba0.3MnO3 (x = 0–0.4) have been investigated although some unreacted secondary phases of CeO2 were present. The rhombohedral structure (R-3c) forx = 0 transforms to orthorhombic with the space groupImma forx = 0.3. All samples showed ferromagnetic transition above 300 K and a negative magnetoresistance. For x>0.1, magnetization
data measured at 1 T showed a decrease at low temperatures (T < 50 K) due to antiferro-magnetic coupling between Ce-local moments and Mn-moments. Forx = 0.4, the resistivity showed a maximum around 200 K which corresponds to ordering temperature of cerium. Since these results
are similar to that observed in the Sr-containing La0.5−x
Ce
x
Sr0.5MnO3 (x = 0–0.4) system, we suggest that the cerium ions are in the trivalent state and the anomalous behaviour has been attributed
to a Kondo-like effect.
Dedicated to Prof J Gopalakrishnan on his 62nd birthday. 相似文献
18.
Violeta D. Kassabova-Zhetcheva Lilyana P. Pavlova Bisserka I. Samuneva Zara P. Cherkezova-Zheleva Ivan G. Mitov Mikhail T. Mikhov 《Central European Journal of Chemistry》2007,5(1):107-117
Structural and magnetic properties of Mg
x
Zn1−x
Fe2O4 powders have been studied with respect to the application for thermal cancer therapy (magnetic hyperthermia). Mg
x
Zn1−x
Fe2O4 (x=0.1–0.5) powders with particle sizes between 5 and 8 nm were produced by citrate method. The X-ray diffraction patterns
of the samples correspond to a spinel phase. The lattice constant and the volume of the elementary cell increase when x changes
from 0.1 to 0.5. The FTIR-spectra ascertain the spinel phase formation. The Mossbauer studies reveal the presence of extremely
small particles, which undergo superparamagnetic relaxation at room temperature. The core-shell model has been applied to
explain quadruple doublets. The quadruple splitting at “shells” is bigger than those at “cores” whereas the isomer shifts
remain close. Magnetic studies confirm the presence of extremely small particles that behave as superparamagnetic ones.
相似文献
19.
The thermal decomposition kinetics of nickel ferrite (NiFe2O4) precursor prepared using egg white solution route in dynamical air atmosphere was studied by means of TG with different
heating rates. The activation energy (E
α) values of one reaction process were estimated using the methods of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS),
which were found to be consistent. The dependent activation energies on extent of conversions of the decomposition reaction
indicate “multi-step” processes. XRD, SEM and FTIR showed that the synthesized NiFe2O4 precursor after calcination at 773 K has a pure spinel phase, having particle sizes of ~54 ± 29 nm. 相似文献
20.
Thermal decomposition of M(mal/fum)·xH2O (M=Mn, Co, Ni) has been studied in static air atmosphere from ambient to 500°C employing TG-DTG-DTA, XRD and IR spectroscopic
techniques. After dehydration the anhydrous maleate salts decompose to metal oxalate in the temperature range of 320–360°C,
which at higher temperature undergo an abrupt oxidative pyrolysis to oxides. The anhydrous fumarate salts have been found
to decompose directly to oxide phase. A comparison of thermal analysis reveals that fumarates are thermally more stable than
maleates. 相似文献