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1.
The solubility of the system Pr 2O 3-SeO 2-H 2O at 100°C was studied. The fields of crystallization of Pr 2(SeO 3) 3·H 2O, PrH(SeO 3) 2, Pr(HSeO 3) 3 were established. The compounds obtained were identified by means of chemical, X-ray and thermal analysis. The thermal decomposition of Pr 2(SeO 3) 3·H 2O, PrH(SeO 3) 2, and Pr(HSeO 3) 3 was determined.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
2.
Nd 3+-doped precursor glass in the K 2O–SiO 2–Y 2O 3–Al 2O 3 (KSYA) system was prepared by the melt-quench technique. The transparent Y 3Al 5O 12 (YAG) glass–ceramics were derived from this glass by a controlled crystallization process at 750 °C for 5–100 h. The formation of YAG crystal phase, size and morphology with progress of heat-treatment was examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transformed infrared reflectance spectroscopy (FT-IRRS). The crystallite sizes obtained from XRD are found to increase with heat-treatment time and vary in the range 25–40 nm. The measured photoluminescence spectra have exhibited emission transitions of 4F 3/2 → 4I J ( J = 9/2, 11/2 and 13/2) from Nd 3+ ions upon excitation at 829 nm. It is observed that the photoluminescence intensity and excited state lifetime of Nd 3+ ions decrease with increase in heat-treatment time. The present study indicates that the incorporation of Nd 3+ ions into YAG crystal lattice enhance the fluorescence performance of the glass–ceramic nanocomposites. 相似文献
3.
The water activity and osmotic coefficients of the system { y NH 4NO 3+(1- y) KNO 3}(aq) has been measured at total molalities from 0.2 mol kg −1 to about saturation of one of the solutes for different ionic-strength fractions y of NH 4NO 3 with y=0.2, 0.5 and 0.8 at the temperature 298.15 K using the hygrometric method. The obtained data allow the deduction of the thermodynamic parameters. From these measurements, new Pitzer ionic mixing parameters are determined and used to predict the solute activity coefficients in the mixture. The results obtained are used to calculate the excess Gibbs energy at total molalities for different ionic-strength fractions of NH 4NO 3. 相似文献
4.
Reactivity of solid mixtures of crystalline V 2O 5 and basic compounds strongly increases at room temperature by means of water molecules adsorption process from a saturated atmosphere (100% RH). This is due, firstly, to a crystalline-amorphous V 2O 5 transformation and secondly to the formation of strongly acid V 2O 5 gels. In the present paper the evolution with time of the CaCO 3-V 2O 5 (11) mixture in the aforementioned conditions was studied by thermal analysis (TG, DTG and DSC), X-ray diffraction (XRD) and infrared spectroscopy (IR). The results confirmed the V 2O 5 gels formation which decomposed the basic CaCC 3 at room temperature through an acid-base mechanism reaction. A new crystalline compound was obtained which corresponded to a hydrated calcium metavanadate.This paper is a part of the L. Sobrados's PhD. 相似文献
5.
Crystallization of BaO–SrO–TiO 2– SiO2–Al 2O 3-based glass ceramics, prepared by sol–gel process, was evaluated in terms of the effect of sintering temperature on phase evolution and electrical properties. The characterization of the samples was performed by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) studies and impedance spectroscopy analysis. The XRD results demonstrate that fresnoite phase starts to crystallize at 700 °C and perovskite phase appears at 900 °C. The glass ceramic samples sintered at high temperatures contained three crystalline phases, including perovskite, feldspar and fresnoite. In addition, SEM observation showed that the average grain size increased and the porosity decreased with increasing sintering temperature. Furthermore, the measurement of impedance spectroscopy suggests that there is a minimum value of the activation energy associated with the sintering temperature of the glass ceramics. The possible explanation of the sintering temperature dependence was discussed. 相似文献
7.
The mixed aqueous electrolyte system magnesium and manganese sulfate has been studied with the hygrometric method at the temperature 298.15 K. The relative humidity of this system is measured at total molalities from 0.2 mol kg −1 to about saturation of one of the solutes for different ionic-strength fractions y of MgSO 4 with y=0.2, 0.5 and 0.8. The obtained data allow the deduction of new thermodynamic parameters. The experimental results are compared with the predictions of ZSR rule. From these measurements, the new Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture. The obtained results are used to calculate the excess Gibbs energy at total molalities for different ionic-strength fractions y of MgSO 4. 相似文献
8.
Glasses in the system Li 2O–SnO–B 2O 3 system were prepared by a melt-quenching method. Thermal and viscous properties and local structure of these glasses were investigated. The SnO–B 2O 3 glasses exhibited relatively low glass-transition temperatures ( Tg) around 350 °C and excellent thermal stability against crystallization. Viscosity measurements in the vicinity of Tg indicated that the glasses were considerably fragile compared to alkali borate glasses. Fraction of four-coordinated boron was maximized at the composition with 50 mol% SnO and that of nonbridging oxygen, which is not purely ionic in alkali borate systems but partially covalent, augmented with an increase in the SnO content. Correlation between glass properties and structure was discussed in the SnO–B 2O 3 binary system. 相似文献
9.
The rate constant of the reaction CF 3 + O 2 + M → CF 3O 2 + M has been measured as a function of temperature in the fall-off region between 1 and 10 Torr, by laser photolysis and time-resolved mass spectrometry. The values of the fall-off parameters measured at room temperature are in good agreement with previous values and the temperature dependence of k1(0) is reasonably well accounted for by the theoretical analysis proposed by Troe and co-workers. With M = N 2k1(0) = (1.9 ± 0.2) × 10 −29 ( T/298) (−4.7 ± 0.4) cm 6 molecule −2 s −1. Reliable values of k1(∞) cannot be derived from these low pressure measurements. The rate expression proposed, k1(∞) = (9 ± 2) X 10 −12 ( T/298) (0±1) cm 3 molecule −1 s −1, is consistent with a “broadening parameter” of the form Fc = exp(− T/395) and previous values reported at room temperature. 相似文献
11.
Lead free 0.95[(K 0.5Na 0.5) 1−xAg xNbO 3]–0.05LiSbO 3 (KNAN–LS) ceramics with x = 0, 0.02, 0.04, 0.06 and 0.08 have been synthesized by conventional solid state reaction route (CSSR). X-ray diffraction (XRD) analysis confirmed the transformation of mixed structure to pure tetragonal structure with the increase in Ag content in KNN–LS ceramics. The Curie temperature ( Tc) of the ceramics decreased from 385.5 °C to 331 °C with the increase in silver (Ag) content. The poling temperature was optimized for better piezoelectric properties. The KNAN–LS ceramics with x = 0.06 showed better piezoelectric and ferroelectric properties ( d33 = 227 pC/N, kp = 42.5%, Tc = 368 °C and Pr = 21.9 μC/cm 2). 相似文献
12.
The methods of X-ray diffraction analysis, thermogravimetric analysis, differential scanning calorimetry, and dilatometry are used to study special features of the structural-phase state of the 80 mass% ZrO 2(Y)–20 mass% Al 2O 3 plasmochemical powders (PCPs) and their effects on the sintering of composite ceramics. It is revealed that the ZrO 2(Y)–Al 2O 3 powder composite represents a mechanical mixture containing crystalline tetragonal zirconium dioxide and aluminum oxide nanoparticles, the latter found in an amorphous state and partially included into the ZrO 2(Y) lattice, thus forming metastable solid solutions of variable composition. Heating of the composite powder within the temperature range 740–1,000 °C reveals an exothermal effect associated with decomposition of metastable states of aluminum oxide. This is accompanied by the formation of the corundum-phase nuclei having subcritical dimensions. They achieve the critical sizes at higher temperatures T > 1200 °C, when α-Al 2O 3 is finally crystallized. The shrinkage response of the powder compacts during non-isothermal sintering is measured in a sensitive dilatometer. It is shown that the shrinkage curve consists of several stages that closely correlate with the concurrent structural-phase transformation in the composite ZrO 2(Y)–Al 2O 3 powder mixture. The decisive contribution into shrinkage during non-isothermal sintering of composite comes from the high-temperature stages with the maximum shrinkage rate at the temperatures 1,250 and 1,550 °C. It is found out that the regime of sintering the ultrafine PCPs ( T = 1,600 °C, t = 1 h) allows producing composite ceramic materials with a porosity of Q ≈ (5–7) %, microhardness H v = 12.3 GPa, and crack resistance К 1c = (10–11) MPa m 0.5. 相似文献
15.
The (1- x)BiFeO 3- xBaTiO 3 (short for (1- x)BFO- xBTO, x = 0.2–0.4) ceramics were prepared by solid-state reaction with microwave sintering (MWS) and conventional sintering (CS) methods. The crystal structure, microstructures, dielectric properties, ferroelectric properties, and magnetic properties of BFO-BTO ceramics sintered by MWS and CS were systematically investigated. It is found that the MWS can effectively decrease the grain size and enhance the compactness of BFO-BTO ceramics. The X-ray diffraction (XRD) results confirm that all ceramics exhibit a single perovskite structure, and the phase transforms from rhombohedral in BiFeO 3-rich compositions to pseudo-cubic phase gradually as x increases. Introducing BTO into BFO can strengthen its dielectric relaxation behavior. Compared with CS, the MWS samples have a lower remanent polarization ( Pr) and a smaller coercive field ( Ec) under the same electric field. Therefore, MWS contributes to the decrease of dielectric loss. Addition of BTO can contribute to the reduction of the coercive force ( Hc) of BFO-based ceramic, and so decrease the hysteresisloss. At the same time, its remanent magnetization ( Mr) value can be decreased by introducing BTO into BFO and using MWS method. The present research provides a route for decreasing the dielectric loss and hysteresis loss of BiFeO 3-based ceramics using the MWS method. 相似文献
16.
In the present study, results concerning luminescence and dielectric properties of Eu 2O 3 (0.5 wt% in excess) doped nano-crystallized KNbO 3 containing transparent glass-ceramics obtained from glass of composition 25K 2O–25Nb 2O 5–50SiO 2 (mol%) by varied heat-treatment duration at 800 °C have been analyzed and reported. The formed crystallization phase, crystallite size and morphology have been examined through XRD, FESEM, TEM and FTIRRS measurements. The observed steep increase in the dielectric constant ( ?) of glass-ceramics over the as-prepared glass is attributed to the formation of ferroelectric nano-crystalline KNbO 3 in glass matrix. The absorption spectra of all the samples have revealed the characteristic 4f–4f intraband absorption transitions of Eu 3+ ions. The measured photoluminescence spectra have exhibited emission transitions 5D 0, 1 → 7F j ( j = 0, 1, 2, 3 and 4) of Eu 3+ ions. The excited level lifetimes have been determined from measured fluorescence decay curves. The rare earth ion site symmetry (nearly Cv) has been understood based on the nature of the Stark splittings of emission bands detected in both Eu 3+: glass and Eu 3+: glass-ceramics. 相似文献
17.
Density of the water-ethylene glycol binary mixtures was measured in the entire range of compositions in the temperature range
278–333.15 K (6 values) at atmospheric pressure using a vibration densimeter. Mixtures with low concentrations of ethylene
glycol were studied at 15 temperatures in the range of 274–333.15 K. Excess molar volumes V
m
E
, the partial molar volumes of water -V
1 and ethylene glycol, -V
2, the coefficients of thermal volume expansion α of the mixture, the partial molar volume coefficients of thermal expansion
of water $
\bar V_1
$
\bar V_1
and ethylene $
\bar V_2
$
\bar V_2
were calculated. Excess molar volumes were described using the Redlich-Kister equation. The density ρ of the mixture was
found to increase with the increasing ethylene glycol concentration at all temperatures, but at low content of ethylene glycol
the dependence ρ = f(T) of the mixture at ∼276.5 K passed through a maximum. The coefficient α increases sharply in the composition range 0 <
x < 0.2, in the range 0.5 < x <1 remains almost unchanged, and at T > 277 K is positive for all compositions. The dependences $
\bar \alpha _1
$
\bar \alpha _1
= f ( x) and $
\bar \alpha _2
$
\bar \alpha _2
= f ( x) are complex in whole temperature range and are characterized by the presence of an extremum. V
m
E
values are negative at all temperatures, and upon increase in the temperature the deviation from ideality decreases ( x is the mole fraction of ethylene glycol). 相似文献
18.
Substitutional, continuous solid solution of the general formula Y2–xYbxO3 was obtained from the mixture of Y2O3 and Yb2O3 oxides, for the first time by the mechanochemical method in a high-energy ball milling. The monophasic samples of nanocrystalline solid solution for x?>?0.00 and x?<?2.00 were examined by the methods: XRD, DTA, SEM, IR and UV–Vis–DR. As follows from the results, the solid solution crystallizes in cubic system and is isostructural with Y2O3 and Yb2O3. The solution is stable in the air atmosphere up to at least 900°C, and its decomposition temperature decreases with the increase in x, that is, with decreasing number of Yb3+ ions replacing Y3+ ions in the crystal lattice of Y2O3. The energy band gap estimated for the solid solution varies from?~?5.30 eV for x?=?0.50 to?~?4.90 eV for x?=?1.50, which means that it is an insulator. 相似文献
19.
Ceramic pigments based on Y 2O 3–Al 2O 3 system doped by cobalt as a colourant agent were synthesized by solid-state reaction at temperatures up to 1,400 °C. The reactivity of initial mixtures of components was improved by the mineralizer LiF and the mechanical activation in a planetary ball mill. The temperature region of the product formation was followed by the method of thermal analysis. The effect of the synthetic method on the phase composition of the products was studied by X-ray diffraction analysis. Studied pigment-application properties of the product include the measurement of optical properties in the visible region of light and particle size distribution. The simple solid-state reaction led to the formation of turquoise samples that contain mainly blue CoAl 2O 4 spinel and next to it also YAlO 3 perovskite and Y 3Al 5O 12 garnet phases. The mineralizer LiF promotes the formation of yttrium aluminium double oxides of sandy-yellow to grey–brown colour hue, although the samples also contain small amount of blue CoAl spinel phase. Intensive milling process did not results in CoAl spinel phase and the samples contain yttrium aluminium perovskite and cobalt oxide. Evaluation of Kubelka–Munk absorption as a function of the pigment concentration was found that hiding is complete by adding of 5 mass% of pigment to the ceramic glaze. Resulting colour hue of all pigment applications into ceramic glaze is blue. The size of particles lies in the range of 7–26 μm. 相似文献
20.
Wet vacuum impregnation method was applied in order to evaluate the possibility of the formation of the material in BaCe0.9Y0.1O3?δ–V2O5 system. Single-phase BaCe0.9Y0.1O3?δ samples, synthesised by solid-state reaction method, were impregnated with the solution of vanadium(V) oxide precursor. Multi-step, multi-cycle impregnation procedure was applied to enhance the impregnation efficiency. Partial decomposition of Y-doped BaCeO3 in contact with the solution of the precursor, resulting in the formation of vanadium containing phases (CeVO4 and BaV2O6) on the materials surface, was observed. However, the presence of vanadium was also confirmed for the inner parts of the materials. The synthesised materials were submitted for exposition test to evaluate their chemical stability towards CO2/H2O. All BaCe0.9Y0.1O3-based materials modified by impregnation revealed higher chemical stability in comparison with single-phase un-modified BaCe0.9Y0.1O3?δ, since the amount of barium carbonate formed during the exposition was significantly lower. The total electrical conductivity of the received multi-phase materials was generally slightly lower than for the reference BaCe0.9Y0.1O3?δ sample, since the presence of the additional phases had a blocking effect on materials conductivity. The values of BaCeO3 lattice parameters and the Seebeck coefficient did not show the modification of the defects structure of Y-doped BaCeO3 during applied synthesis procedure. 相似文献
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