共查询到20条相似文献,搜索用时 46 毫秒
1.
Klaartje De Buysser Philippe F. Smet Bart Schoofs Els Bruneel Dirk Poelman Serge Hoste Isabel Van Driessche 《Journal of Sol-Gel Science and Technology》2007,43(3):347-353
This paper describes the synthesis of ZrW2O8 by the use of an aqueous citrate-gel method in order to prepare a fine, pure and homogeneous oxide mixture suitable for ceramic
processing. The thermal expansion coefficient thus obtained for α-ZrW2O8 is −10.6 × 10−6 °C−1 (50–125 °C) whereas for the β-ZrW2O8 a value of −3.2 × 10−6 °C−1 (200–300 °C) is obtained. The advantages of the use of a sol–gel method is expressed in the very homogeneous end-products.
The paper describes crystallographic data, morphological structure and the thermal expansion properties of the ZrW2O8 material. Moreover, photoluminescence and photochromic properties specific to the precursor gel are described and analyzed.
These effects support our views that the precursors show homogeneity up to nanometer level. 相似文献
2.
New potassium-conducting solid electrolytes in the mixed gallate-ferrite systems (1 − x)Ga2O3 · xFe2O3 · 0.25TiO2 · K2O and 1.5[(1 − x)Ga2O3 · xFe2O3] · TiO2 · 2K2O are synthesized and studied. The electrolytes exhibit high ionic conductivity in the test temperature range of 300 to 750°C
(above 10−2 S/cm at 300°C and above 10−1 S/cm at 700°C). An increase in the conductivity with increasing concentration of iron in the specimens is a general tendency.
Possible reasons for the effect of Ga/Fe ratio in the structure of solid electrolytes on their transport properties are discussed. 相似文献
3.
A. S. Rozenberg E. I. Aleksandrova G. I. Dzhardimalieva A. N. Titkov A. D. Pomogailo 《Russian Chemical Bulletin》1993,42(10):1666-1672
The thermal decomposition of iron (III) acrylate, [Fe3O(CH2=CHCOO)6 · 3H2O]OH (FeAcr), a monomer with a complex cluster cation, has been studied at 200–370 °C. Thermal transformations of FeAcr occur
in two temperature regions. The rates of gas evolution in the low temperature region (200–300 °C) and the high temperature
region (300–370 °C) are described by first-order equations withk=4.2 · 1021exp[−59000/(RT)] s−1 andk=1.3 · 106exp[−30500/(RT)] s−1, respectively. A study of the qualitative and quantitative composition of the products of FeAcr thermolysis was carried out.
The thermal transformation of FeAcr is a complex process of dehydration, degradation, and polymerization in the solid phase
followed by decarboxylation of the metal-carboxyl groups of the polymer.
for part 33 see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1743–1750, October, 1993. 相似文献
4.
Polymer electrolyte systems were prepared for the first time by dissolution of amidomagnesium chlorides in poly(ethylene oxide),
(PEO). For the preparation, solutions of (hexamethyldisilylamido)magnesium chloride, (dimethylpyrrolyl)magnesium chloride,
(diisopropylamido)magnesium chloride, piperidinomagnesium chloride and morpholinomagnesium chloride were chosen. The composition
of these polymer electrolyte systems corresponds to the general formula R2NMgCl·P(EO)n·THF. Most work has been done with the system (hexamethyldisilylamido)magnesium chloride in PEO, (Me3Si)2NMgCl·P(EO)n·THF, with n= 3, 4, 5, or 7. The electrolytes have a soft rubber-like consistency. At 30 °C, electrical conductivities of 10−6–10−5 S/cm were found. The conductivities were measured in the temperature range 20–60 °C. Within this temperature range a linear
dependence of the logarithms of the conductivity on the inverse temperature was found and activation energies for the conducting
process of 30–60 kJ/mol were calculated. Using those polymer electrolytes with a high content of the amidomagnesium compound,
a reversible magnesium deposition takes place by cathodic reduction at potentials below −1.9 V vs. a Ag/AgCl reference electrode.
These polymer electrolytes were found to be stable against oxidation up to about −0.3 V vs. Ag/AgCl.
Electronic Publication 相似文献
5.
F. Bousmina L. Zayani D. Ben Hassen-Chehimi N. Kbir-Ariguib M. Trabelsi-Ayedi 《Monatshefte für Chemie / Chemical Monthly》2003,4(10):763-768
The diagram of the ternary system Mg2+/Cl−, SO4 2−–H2O was established at 15°C by means of analytical and conductimetric measurements. Three compounds were found in this diagram, which are MgSO4·6H2O, MgSO4·7H2O, and MgCl2·6H2O. The solubility field of MgSO4·7H2O is important whereas those of MgSO4·6H2O and MgCl2·6H2O are small. The compositions (mass-%) of the two invariant points determined by the two methods are: MgSO4:MgCl2=2.73:33.80 and MgSO4: MgCl2=3.38:28.91. Both the measured and the calculated isotherm at 15°C have been used for modelling of the diagram Mg2+/Cl−, SO4 2−–H2O between 0 and 35°C. The polythermal invariant point was approximately located between 15 and 10°C. 相似文献
6.
N. V. Chukanov A. I. Kazakov I. V. Pekov A. A. Grigor’eva 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(12):2154-2159
The kinetics of cation exchange between natural amorphized microporous zirconosilicate terskite Na4ZrSi6O15(OH)2 · H2O and aqueous solutions of cesium fluoride was studied calorimetrically under isothermal conditions, in the temperature range
of 27.5 to 55.2°C, at CsF concentrations of 0.6–2.2 mol/l. The rate of the process was described by the first-order kinetic
equation with the rate constant k, h−1 = 3.1 × 103
C
CsF0.92 exp(−(21 ± 8) × 103/RT). Upon replacing Na+ with Cs+, the first-order equilibrium was observed to shift abruptly toward the Cs-substituted sorbent form, where Cs2O content after saturation was 25.5–29.1 wt %. The average heat of ion exchange Q
0 over the temperature range 27.5–32.4°C was shown to be ∼3.4 kJ per 1 mol of Na+ ions. We conclude that sorbents based on A-terskite are of practical interest for the processes of extracting 137Cs isotope from water. 相似文献
7.
In situ
developments of platelike spodumene–diopside grains were obtained by
controlled devitrification of the complex system Li2O–CaO–MgO–Al2O3–SiO2 glass. The crystallization mechanisms
of spodumene–diopside glass were measured by isothermal and non-isothermal
processes using classical and differential thermal analysis techniques. The
Avrami constant n was 2.0–2.1, indicating
two-dimensional crystal growth and platelike grains. The crystalline phases
precipitated first were high-quartzs.s., then transformed
to β-spodumene and diopside. The Flexural strength, fracture toughness
and thermal shock resistance (in 20°C water) increased from 145 MPa, 1.3
MPa m1/2, 800°C (pure spodumene) to 197 MPa,
2.9 MPa m1/2 and 920°C (spodumene–diopside)
with low thermal expansion coefficient (from 3∼9·10–7
to 11.8·10–7 K–1).
This mean in situ developments of platelike spodumene–diopside grains
reinforced the low thermal expansion coefficient glass-ceramics. 相似文献
8.
S. Kurajica E. Tkalcec J. Sipusic G. Matijasic I. Brnardic I. Simcic 《Journal of Sol-Gel Science and Technology》2008,46(2):152-160
Nanosized zinc aluminate spinel (gahnite, ZnAl2O4) powders were prepared by sol−gel technique at low sintering temperatures. Aluminium-sec-butoxide [Al(OsBu)3] and zinc nitrate hexahydrate Zn(NO3)2 . 6H2O were used as starting materials. Gels with and without chelating agent were prepared. Ethyl-acetoacetate (C6H10O3) was used as a chelating agent in order to control the rate of hydrolysis of Al(OsBu)3. The dried gels and thermally treated samples were characterized by means of Differential Thermal Analysis and Thermo-Gravimetric
Analysis (DTA, TGA), X-ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR) and Transmission Electron Microscopy
(TEM). The surface area was measured by Brunauer-Emmet-Teller (BET) adsorption–desorption isotherms. It has been established
that chelation enables to obtain a transparent gel. The thermal evolution of gels was characterized by two crystallization
processes in the range 200–400 °C and 600–700 °C. Both processes yielded pure ZnAl2O4 as evidenced by XRD, i.e. zinc aluminate spinel powders were produced by gel heat-treatment at temperatures as low as 300 °C.
The average gahnite crystallite size for the samples sintered in the temperature range of 400–1000 °C has been calculated
from the broadening of XRD lines revealing that nanocrystalline powders were prepared. The surface areas measured for the
samples fired at 700 °C for 2 h were 43.1 and 62.6 m2 g−1, for sample without and with the chelating agent, respectively. TEM micrographs confirmed the nano-scale size of particles. 相似文献
9.
R. G. Bulgakov Yu. G. Ponomareva Z. S. Muslimov F. G. Valyamova R. A. Sadykov R. F. Tuktarov 《Russian Chemical Bulletin》2007,56(2):211-219
Fullerenyl radicals (FR) RC60
· and chemiluminescence (CL) are generated in the presence of O2 in C60—R3Al (R = Et, Bui) solutions in toluene (T = 298 K). The FR are formed due to the addition of the R· radical, which is an intermediate of R3Al autooxidation, to C60. Mass spectroscopy and HPLC were used to identify EtnC60Hm (n, m = 1–6), EtpC60 (p = 2–6), and dimer EtC60C60Et as stable products of FR transformations. As found by ESR, the EtC60
· radical (g = 2.0037) is also generated by photolysis of solutions obtained after interaction in the (C60— R3Al)—O2 system. In the presence of dioxygen, the FR is not oxidized but yields complexes with O2, which appear as broadening of the ESR signals. Chemiluminescence arising in the (C60—R3Al)—O2 system is much brighter (I
max = 1.86·108 photon s−1 mL−1) than the known background CL (I
max = 6.0·106 photon s−1 mL−1) for the autooxidation of R3Al and is localized in a longer-wavelength spectral region (λmax = 617 and 664 nm). This CL is generated as a result of energy transfer from the primary emitter 3CH3CHO* to the products of FR transformation: RnC60Hm, RpC60, and EtC60C60Et.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 205–213, February, 2007. 相似文献
10.
A two-dimensional network compound [Ce(DMF)4(H2O)][α-BW12O40]·H2O·(HDMA)2 (HDMA = protoned dimethylamine, DMF = N,N-dimethylformamide) was synthesized from α-H5BW12O40·nH2O, Ce(NO3)3·6H2O and DMF and characterized by IR, UV spectra and TG-DTA. The result of the X-ray single crystal diffraction indicates that
the crystal is monoclinic, space group P21/n, with unit cell dimensional: a = 1.1983(3), b = 2.4216(5), c = 1.9517(4) nm, β = 92.91(3)°, Z = 4, R
1 = 0.07710, wR
2 = 0.1416. Structural analysis indicates that every [Ce(DMF)4(H2O)]3+ building block is surrounded by three adjacent [α-BW12O40]5− polyanions, meanwhile, every [α-BW12O40]5− polyanion interconnects with three neighboring [Ce(DMF)4(H2O)]3+ subunits, by making use of which two-dimensional network structure can be constructed. The result of thermogravimetric analysis
manifests that the title compound has two-stage weight loss and the decomposition temperature of the title polyanionic framework
is 560°C. The electrochemical analysis shows the title polyanion has three-step redox processes in the pH = 4–7 media. 相似文献
11.
N. C. Dutta T. Iwasaki Y. Onodera 《Journal of Radioanalytical and Nuclear Chemistry》1999,242(1):203-205
A study of fixation of caesium on crystalline titania by co-precipitation was carried out. A maximum loading of ∼46wt% of
caesium was found to be incorporated in the titania matrix. High leach-resistivity of Cs cations was observed to be in the
order of 10−6–10−8 g.m−2.d−1 by Soxhlet flow refluxing at 97 °C of the composite material calcined at 800, 1000 °C for 48 hours. The analysis of X-ray
powder diffractions of the composite materials revealed that cesium was fixed in the crystal lattice of host titania with
the formation of new mineral phases of CsTi4O9 and Cs2Ti5O11. The results, taken together, implicate that a better fixation of caesium on titania can be achieved by calcination at 1000
°C for 48 hours. 相似文献
12.
The Er3+-doped Al2O3 nanopowders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC3H7)3]-derived γ-AlOOH sols with addition of the erbium nitrate [Er(NO3)3·5H2O]. The five phases of γ-(Al,Er)2O3, θ-(Al,Er)2O3, α-(Al,Er)2O3, ErAlO3, and Al10Er6O24 were detected with the 0–20 mol% Er3+-doped Al2O3 nanopowders at the different sintering temperature of 600–1200°C. The average grain size was increased from about 5 to 62 nm
for phase transformation of undoped γ-Al2O3→α-Al2O3 at the sintering temperature from 600 to 1200°C. At the same sintering temperature, average grain size was decreased with
increase of the Er3+ doping concentration. Infrared absorption spectra of γ-Al2O3 and θ-Al2O3 nanopowders showed the two broad bands of 830–870 and 550–600 cm−1, the three broad bands of 830–870, 750–760, and 550–600 cm−1, respectively. The infrared absorption spectra for the α-Al2O3 nanopowder showed three characteristic bands, 640, 602, and 453 cm−1. The two characteristic bands of 669 and 418 cm−1 for Er2O3 clusters were observed for the Er3+-doped Al2O3 nanopowders when Er3+ doping concentration was increased up to 2 mol%. The 796, 788, 725, 692, 688, 669, 586, 509, 459, and 418 cm−1 are the characteristic bands of Al10Er6O24 phase. 相似文献
13.
The phase and chemical compositions of the precipitates forming in the Sr(VO3)2-VOCl2-H2O system in the V4+/V5+ = 0.11–9 range at 80–90°C are reported. At pH 1–3 and V4+/V5+ = 0.25−9, the general formula of the precipitated compounds is Sr
x
V
y
4+ V12−y
5+O31−δ·nH2)(0.37 ≤ x ≤ 1.0, 1.7 ≤ y ≤ 3.0, 0.95 ≤ δ ≤ 2.1). Polyvanadates containing the largest amount of vanadium(IV) are obtained at an initial V4+/V5+ ratio of 9 and pH 1.9. Precipitation from solutions at pH 3 takes place only in the presence of the VO2+ ion, and the highest precipitation rate is observed at V4+/V5+ = 0.11. The process is controlled by a second-order reaction on the polyvanadate surface. Under hydrothermal conditions at
180°C, Sr0.25V2O5·1.5H2O nanorods are obtained from solutions with a V4+/V5+ molar ratio of 0.1 at pH 3. The nanorods, 30–100 nm in diameter and up to 2–3 μm in length, have a layered structure with
an interlayer spacing of 10.53 ± 0.08 ?. 相似文献
14.
Liang Zhao Xiaoru Zhao Jinming Liu An Zhang Danhong Wang Bingbo Wei 《Journal of Sol-Gel Science and Technology》2010,53(2):475-479
Anatase Ti0.94Nb0.06O2 (TNO) films were fabricated on glass substrates by sol–gel method using a dip-coating technique. The annealing treatment
was separated into two steps, first in air at 350–550 °C for 1 h and then in vacuum of 4.0 × 10−4 Pa at 550 °C for 1 h. The influence of vacuum annealing treatment to the electrical and optical properties was discussed.
Especially, the role of air annealing treatment from 350 to 550 °C on the crystallization and the structure of the films was
analyzed. It is proved that the films annealed at 550 °C in air and then 550 °C in vacuum exhibited the minimum resistivity
of 19.3 Ω·cm and the average optical transmittance of about 75% in the visible range, indicating that the sol–gel method is a feasible
and promising method to fabricate TNO films. 相似文献
15.
Uniform particles of manganese compounds obtained by forced hydrolysis of manganese(II) acetate 总被引:1,自引:0,他引:1
M. Ocaña 《Colloid and polymer science》2000,278(5):443-449
Procedures for the preparation at low temperature (80 °C) of uniform colloids consisting of Mn3O4 nanoparticles (about 20 nm) or elongated α-MnOOH particles with length less than 2 μm and width 0.4 μm or less, based on
the forced hydrolysis of aqueous manganese(II) acetate solutions in the absence (Mn3O4) or the presence (α-MnOOH) of HCl are described. These solids are only produced under a very restrictive range of reagent
concentrations involving solutions of 0.2–0.4 mol dm−3 manganese(II) acetate for Mn3O4 and of 1.6–2 mol dm−3 Mn(II) and 0.2–0.3 mol dm−3 HCl for α-MnOOH. The role that the acetate anions play in the precipitation of these solids is analyzed. It seems that these
anions promote the oxidation of Mn(II) to Mn(III), which readily hydrolyze causing precipitation. The evolution of the characteristics
of the powders with temperature up to 900 °C is also reported. Thus, Mn3O4 particles transform to Mn2O3 upon calcination at 800 °C; this is accompained by a sintering process. The α-MnOOH sample also experiences several phase
transformations on heating. First, it is oxidized at low temperatures (250–450 °C) giving MnO2 (pyrolusite), which is further reduced to Mn2O3 at 800 °C. After this process the particles still retain their elongated shape.
Received: 19 October 1999 Accepted: 24 November 1999 相似文献
16.
F. Bousmina L. Zayani D. Ben Hassen-Chehimi N. Kbir-Ariguib M. Trabelsi-Ayedi 《Monatshefte für Chemie / Chemical Monthly》2003,134(5):763-768
Summary. The diagram of the ternary system Mg2+/Cl−, SO4
2−–H2O was established at 15°C by means of analytical and conductimetric measurements. Three compounds were found in this diagram,
which are MgSO4·6H2O, MgSO4·7H2O, and MgCl2·6H2O. The solubility field of MgSO4·7H2O is important whereas those of MgSO4·6H2O and MgCl2·6H2O are small. The compositions (mass-%) of the two invariant points determined by the two methods are: MgSO4:MgCl2=2.73:33.80 and MgSO4: MgCl2=3.38:28.91. Both the measured and the calculated isotherm at 15°C have been used for modelling of the diagram Mg2+/Cl−, SO4
2−–H2O between 0 and 35°C. The polythermal invariant point was approximately located between 15 and 10°C.
Corresponding author. E-mail: ariguib@planet.tn
Received October 16, 2002; accepted (revised) December 3, 2002
Published online April 24, 2003
RID="a"
ID="a" Dedicated to Prof. Dr. Heinz Gamsj?ger on the occasion of his 70th birthday 相似文献
17.
Qiang Li Liping Sun Lihua Huo Hui Zhao Jean-Claude Grenier 《Journal of Solid State Electrochemistry》2012,16(3):1169-1174
The performance of Ca2Fe1.4Co0.6O5–Ce0.9Gd0.1O1.95 (CFC–CGO) composite cathode has been investigated for potential application in intermediate-temperature solid oxide fuel
cells (IT-SOFCs). The composite cathodes are prepared and characterized by XRD and SEM, respectively. The electrochemical
properties of the composite cathodes are investigated using AC impedance and DC polarization methods from 500 to 700 °C under
different oxygen partial pressures. The polarization resistance (R
p) decreases with the increase of CGO content in the composite electrode. The addition of 40 wt.% CGO in CFC results in the
lowest R
p of 0.48 Ω cm2 at 700 °C in air. Oxygen partial pressure dependence study indicates that the charge-transfer process is the rate limiting
step for oxygen reduction reaction. CFC-40CGO composite cathode exhibits the lowest overpotential of about 67 mV at a current
density of 85 mA cm−2 at 700 °C in air. 相似文献
18.
Hongbo Guan Pei Wang Biying Zhao Yuexiang Zhu Youchang Xie 《Frontiers of Chemistry in China》2007,2(2):204-208
Nanometer MgO samples with high surface area, small crystal size and mesoporous texture were synthesized by thermal decomposition
of MgC2O4 · 2H2O prepared from solid-state chemical reaction between H2C2O4 · 2H2O and Mg (CH3COO)2 · 4H2O. Steam produced during the decomposition process accelerated the sintering of MgO, and MgO with surface area as high as
412 m2 · g−1 was obtained through calcining its precursor in flowing dry nitrogen at 520°C for 4 h. The samples were characterized by
X-ray diffraction, N2 adsorption, transmission electron microscopy, thermogravimetry, and differential thermal analysis. The as-prepared MgO was
composed of nanocrystals with a size of about 4–5 nm and formed a wormhole-like porous structure. The MgO also had good thermal
stability, and its surface areas remained at 357 and 153 m2·g−1 after calcination at 600 and 800°C for 2 h, respectively. Compared with the MgO sample prepared by the precipitation method,
MgO prepared by solid-state chemical reaction has uniform pore size distribution, surface area, and crystal size. The solid-state
chemical method has the advantages of low cost, low pollution, and high yield, therefore it appears to be a promising method
in the industrial manufacture of nanometer MgO.
Translated from Chinese Journal of Catalysis, 2006, 27(9): 793–798 (in Chinese) 相似文献
19.
Fu Qiang KeNing Sun NaiQing Zhang ShiRu Le XiaoDong Zhu JinHuo Piao 《Journal of Solid State Electrochemistry》2009,13(3):455-467
A-site-deficient perovskite cathode material La0.58Sr0.4Co0.2Fe0.8O3 − δ
(L58SCF) is coated on the yttria-stabilized zirconia electrolyte by screen-printing technique. Several key fabrication parameters
including selection of additives (binder and pore former), effect of coating thickness, sintering temperature and time on
the microstructure, and electrochemical performance of cathode are investigated by scanning electron microscopy and electrochemical
impedance spectroscopy. We study the microstructure and the electrochemical property of the cathode with different kinds of
additives. Results show that the cathode possesses fine microstructure, enough porosity, and ideal electrochemical property
when polyvinyl butyral serves as both binder and pore former in the cathode. The cathode with three screen-printing coats
(thickness 28 ± 7 μm, weight 6.07 ± 0.72 mg cm−2) sintering at 1,000 °C for 2 h shows lower polarization resistance of 0.183 Ω cm2 at 800 °C. Based on the optimized parameters, the polarization resistances of the L58SCF–Ce0.8Gd0.2O1.9 – δ
composite cathode display the R
p values of 0.067 Ω cm2 at 800 °C, 0.106 Ω cm2 at 750 °C, 0.225 Ω cm2 at 700 °C, and 0.550 Ω cm2 at 650 °C. 相似文献
20.
Homopolymerization of methyl methacrylate (MMA) was carried out in the presence of triphenylstibonium 1,2,3,4-tetraphenyl-cyclopentadienylide
as an initiator in dioxane at 65°C±0·l°C. The system follows non-ideal radical kinetics (R
p
∝ [M]1·4 [I]0·44
@#@) due to primary radical termination as well as degradative chain-transfer reaction. The overall activation energy and average
value ofk
2
p
/k
t
were 64 kJmol−1 and 0.173 × 10−3 1 mol−1 s−1 respectively 相似文献