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1.
The crystallization kinetics of Cs 2O–Fe 2O 3–P 2O 5 glasses containing 12.5–27 mol% Cs 2O were studied by using differential scanning calorimetry under nonisothermal conditions. Strong dependence of activation energy with temperature was observed, indicating the complex nature of the crystallization process. The various crystallization products were identified by X-ray diffraction technique. CsFeP 2O 7 was found to be the major crystalline phase in all cases. The overall activation energy obtained by classical model-free kinetic method was compared with that of isoconversional method; and from the results, the dependence of activation energy on extent of reaction and average temperature was delineated. 相似文献
2.
The effect of mechanical activation on the structure and thermal reactions of glasses has been studied on the example of Na–Al–Fe
phosphate glasses. These glasses are used in nuclear technology for immobilization of radioactive waste. The glasses were
activated by grinding in a planetary mill. Mechanical activation causes a decrease of the T
g temperature as well as of the glass crystallization temperature. The type of crystalline phases formed and the quantitative
proportions between them are changing. Analysis of inter-atomic interactions in the structure of glass was applied to explain
the observed regularities governing the crystallization of the activated glasses. 相似文献
3.
The glasses within composition as: (80 − x)V 2O 5/20Bi 2O 3/ xBaTiO 3 with x = 2.5, 5, 7.5 and 10 mol% have been prepared. The glass transition ( Tg) increases with increasing BaTiO 3 content. Synthesized glasses ceramic containing BaTi 4O 9, Ba 3TiV 4O 15 nanoparticles of the order of 25–35 nm and 30–46 nm, respectively were estimated using XRD. The dielectric properties over wide ranges of frequencies and temperatures were investigated as a function of BaTiO 3 content by impedance spectroscopy measurements. The hopping frequency, ωh, dielectric constant, ε′, activation energies for the DC conduction, Eσ, the relaxation process, Ec, and stretched exponential parameter β of the glasses samples have been estimated. The, ω h, β, decrease from 51.63 to 0.31 × 10 6 (s −1), 0.84 to 0.79 with increasing BaTiO 3 respectively. Otherwise, the Eσ, increase from 0.279 to 0.306 eV with increasing BaTiO 3. The value of dielectric constant equal 9.5·10 3 for the 2.5BaTiO 3/77.5V 2O 5/20Bi 2O 3 glasses-ceramic at 330 K for 1 KHz which is ten times larger than that of same glasses composition. Finally the relaxation properties of the investigated glasses are presented in the electric modulus formalism, where the relaxation time and the respective activation energy were determined. 相似文献
4.
In order to evidence the structural changes induced by CuO and V 2O 5 in the phosphate glass network and their modifier or former role, x(CuO·V 2O 5)(100 − x)[P 2O 5·CaO] glass system was prepared and investigated using Raman spectroscopy (0 ≤ x ≤ 40 mol%).Raman spectra of the studied glasses present the specific bands of the phosphate glasses at low concentration of transition metal (TM) ions, but at higher concentration ( x > 7 mol%) a strong depolymerization of the phosphate network appears; non-bridging oxygen atoms are involved in VOP and CuOP bonds and new short units are formed. For a high concentration of V 2O 5 ( x > 10 mol%) the Raman bands of V 2O 5 prevail in the spectra; this fact suggests that vanadium oxide imposes its structural units in the network acting thus as a network glass former.2D correlation analysis was also applied for the concentration-dependent Raman spectra in order to verify the assignments of the vibration modes and to find correlations in the changes induced by TM ions content. 2D correlation maps indicate a good correlation between the bands at ∼705 cm −1 assigned to POP stretching vibration and at ∼1175 cm −1 assigned to PO 2 groups which suggest the depolymerization of the phosphate network. The correlation between the 1270 cm −1 and 930 cm −1 bands also suggests that V 2O 5 oxide is responsible for PO bonds breaking and POV formation. 相似文献
5.
The Na 2O–CaO–SiO 2 ternary glass–ceramic with the composition of 49 mass% Na 2O, 20 mass% CaO, and 31 mass% SiO 2 was prepared by the conventional method. The ternary glass–ceramic was characterized using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy techniques. The Na 2CaSiO 4 phase, having the cubic crystal system, with the crystallite size of 25.14 nm and lattice parameter of 0.7506 nm was determined from the XRD pattern. The activation energy of the glass–ceramic calculated from the DTA curves was found to be 162.02 kJ mol ?1. The Avrami exponent was found to be ~2 indicating a one-dimensional growth process. The mass loss percent from ambient temperature to 1,173 K is less than 1 %. The density was calculated to be 2,723 kg m ?3. The fine-grained microstructure with the particle sizes less than 1 μm was confirmed by the scanning electron microscope micrograph. 相似文献
6.
Thermal stability of PbO was studied. Reactivity of oxides in the systems PbO–M 2O 3 ( M = In, Fe) was investigated up to 650 °C. Using the DTA and XRD methods, parts of investigated ternary oxide systems, labelled by compounds: V 2O 5, Pb 8V 2O 13 and M 2O 3 ( M = In, Fe), have been divided into partial ternary systems. IR spectra of compounds Pb 2MV 3O 11 ( M = In, Fe) have been compared. 相似文献
7.
The effect of the SrO addition on the microstructure and structure of the glazes from the SiO2–Al2O3–CaO–MgO–K2O system was investigated in this study. The results were obtained by testing the ability of the frits crystallization, the stability of the crystallizing phases during the single-step fast-firing cycle depending on their chemical composition and the effect of addition of strontium oxide. Differential scanning calorimetry (DSC) curves showed that all glazes crystallized, and diopside and anorthite were mainly identified as dominant phases in the obtained glazes, while the size and amount of each depended on the amount of SrO introduced. The thermal characteristic of the frits was carried out using DSC, and crystalline phases were determined by X-ray diffractometry. The glaze microstructure was investigated by scanning electron microscopy and transmission electron microscopy. Additional information on the microstructure of frits was derived from spectroscopic studies in the mid-infrared range. 相似文献
8.
Multicomponent glasses from the SiO 2–P 2O 5–K 2O–MgO–CaO–CuO system acting as slow release fertilizers were synthesized by the melt-quenching technique. The influence of CuO and P 2O 5 addition on the structure of glasses was evaluated by FTIR, Raman, 31P, and 29Si MAS NMR spectroscopies. The studies showed that the Cu 2+ ions displacing Ca 2+ ions and Mg 2+ ions in the structure of glass prefer to associate with the phosphorus Q 1 species, forming the Q 0 species with chemically stable POCu bonds. This is accompanied by the reduction of the degree of polymerization of the phospho-oxygen sub-network, with a simultaneous increased degree of polymerization of the silico-oxygen sub-network of the silicate–phosphate glasses. 相似文献
9.
This paper reports on the preparation of SO 4 2?/Fe 2O 3–TiO 2–Nd 2O 3 (SFTN) by combustion method. The effect of Nd content on catalytic activity was investigated. The prepared materials doped and undoped by Nd were compared by means of TG-DTG, XRD, FT-IR, NH 3-TPD and TEM techniques. Results indicated that the introduction of Nd improved the catalytic activities of the catalysts. Catalytic activity of SFTN was the highest with 98.3 % menthol conversion when Nd content was at 2 wt%. The introduction of Nd stabilized the coordination bond between the sulfate irons and the metallic oxides, helping in the formation of solid acid sites, enhancing the dispersion of catalyst particles, and inhibiting the growth of catalyst particles under heating. 相似文献
10.
Glasses with compositions 60Bi 2O 3–(40?x)B 2O 3–xGa 2O 3 ( x = 5, 10, 15, 20 mol%) are prepared by conventional melting method. The thermal properties are investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The results show that density, refractive index and optical basicity increase with the increase of Ga 2O 3. The glass transition temperature ( Tg), the onset crystallization temperature ( Tx), Δ T ( Tx? Tg) decrease with the content of Ga 2O 3. The cut-off edges in ultraviolet and infrared shift to longer wavelength with the increase of Ga 2O 3. On the other hand, the addition of Ga 2O 3 causes a progressive coordination number change of the boron atom from 3 to 4. XPS result indicates both Bi 5+ and Bi 3+ exist in 5 mol% Ga 2O 3 content, while Bi 5+ amounts decrease with the increase of Ga 2O 3 contents. The glass is mainly composed of [BiO 6], [BO 3], [BO 4] and [GaO 4] polyhedra. Glasses are supposed to have layer structure. [BO 3] triangle and [BO 4] tetrahedra may be located between the [GaO 4] tetrahedral and [BiO 6] octahedra to prevent crystallization and to compensate electric charge. 相似文献
11.
By means of the conventional quenching route, the glass series 33Na 2O– xSrO– xTiO 2–(50 ? 2 x)B 2O 3–17P 2O 5 ( x = 0–12.5 mol%) were prepared. The amorphous state of samples was verified by X-ray diffraction (XRD). Density, molar volume, micro-hardness, glass transition temperature ( T g), and crystallization temperature ( T c) parameters are determined for each glass. The results show that they depend strongly on the chemical compositions. The structure approach of the glasses is determined by Infrared spectroscopy (IR). This investigation highlights that the glassy-matrix contains various phosphate and borate structural units. The crystallization of the high-TiO 2 glasses by heat-treatments favors the formation of titanate phosphate Na 4TiO(PO 4) 2 or Sr 0.5Ti 2(PO 4) 3 along with Sr 3(PO 4) 2 inside the glass-matrix. 相似文献
12.
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
13.
Fe–N–C catalysts were prepared through metal-assisted polymerization method. Effects of carbon treatment, Fe loading, nitrogen
source, and calcination temperature on the catalytic performance of the Fe–N–C for H 2O 2 electroreduction were measured by voltammetry and chronoamperometry. The Fe–N–C catalyst shows optimal performance when prepared
with pretreated active carbon, 0.2 wt.% Fe, paranitroaniline (4-NA) and one-time calcination. The Fe–N–C catalyst displayed
good performance and stability for electroreduction of H 2O 2 in alkaline solution. An Al–H 2O 2 semi-fuel cell was set up with Fe–N–C catalyst as cathode and Al as anode. The cell exhibits an open-circuit voltage of 1.3 V
and its power density reached 51.4 mW cm −2 at 65 mA cm −2. 相似文献
14.
The phase equilibria in the solid state in the system FeVO 4?CCu 3V 2O 8 and FeVO 4?CCuO have been determined. Based on the obtained DTA and XRD analysis results and some additional research, a phase diagram in the whole subsolidus area of the system CuO?CV 2O 5?CFe 2O 3 has been worked out. Eighteen subsidiary subsystems can be distinguished in this ternary system. Basic properties of the obtained phases with howardevansite- and lyonsite-type structure have been investigated by DTA, IR, and SEM methods. 相似文献
15.
Glasses with composition 50Bi 2O 3–(50 ? x) B 2O 3– xGeO 2 ( x = 0, 5, 10, 15 mol%) were prepared by conventional melting method. The thermal properties were investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The results show that density, refractive index and optical basicity increase with the increase of GeO 2. The glass transition temperature ( Tg), onset crystallization temperature ( Tx) and Δ T ( Tx ? Tg) increase as well. The cut-off edges in ultraviolet and infrared shift to longer wavelength by the addition of GeO 2. Infrared, Raman and XPS results indicate that the glass network consists of [Bi–O 6] octahedron, [BO 3] triangle, [BO 4] tetrahedron and [GeO 4] tetrahedron and borate oxide mainly exists in [BO 3] units. XPS result indicates Ge 4+ ions form steady [GeO 4] tetrahedra units in the glass network and the number of non-bridging oxygens decreases with the addition of GeO 2. 相似文献
16.
Li 2O–Al 2O 3–SiO 2 glass-ceramics were prepared with Ta 2O 5 as nucleating agent, the crystallization mechanism and microstructure evolution were investigated by DTA, XRD, and SEM technologies. With increasing amount of Ta 2O 5 from 2 to 6 mol%, the crystallization activation energy decreased from 297.73 to 218.66 kJ mol ?1, while the crystallization index increased from 1.76 to 3.39. In addition, the cluster of dendritic crystals and lamellar structure obtained in T-2 glass-ceramics indicated a typical two-dimensional crystallization mechanism, and the formation of spherical β-quartz solid solution in T-4 specimens, with average size of 50–70 nm, was mainly due to bulk crystallization mechanism. It was considered that Ta 2O 5 promoted the nucleation and crystallization of LAS glass by precipitating the crystalline precursor phase of Ta 2O 5, which acted as nuclei for the subsequent crystal growth. Eventually, the diffusion and crystallization process, microstructure morphology, as well as the secondary grain growth were also investigated. 相似文献
17.
The article presents a simple method that can be used to get the concentration of various species in mixed-modifier borate glasses. By using the fraction of four coordinated boron in xCaO (30 − x)Na 2O70B 2O 3 (0 ≤ x ≤ 27.5 mol%) and xCaO(40 − x)Na 2O60B 2O 3 glasses (10 ≤ x ≤ 40 mol%), the concentration of BO 4− and asymmetric BO 3 units related to each modifier oxide could be determined. CaO has a greater tendency to form asymmetric BO 3 units in the first glass series, while Na 2O has the ability to form BO 4 units to a greater extent. In xCaO(40 − x)Na 2O60B 2O 3 glasses, BO 4− and asymmetric BO 3 units are formed at the same rate from Na 2O and CaO. The fraction of four coordinated boron, can be predicted by treating the studied glasses as if they are mixtures of Na 2O–B 2O 3 and CaO–B 2O 3 matrices. The change in N4 is due to change in the relative concentration of these matrices. 相似文献
18.
Several commercially available supports were examined for cyclization of monoethanolamine to aziridine, and SiO 2 was found to yield the best results. The obtained results indicated that selectivity of aziridine was mainly influenced by support. The catalysts were characterized by NH 3-TPD and XRD. It was found that SiO 2 with lower acidity could inhibit the intermolecular condensations, and thus favored the formation of aziridine. The Cs 4P 2O 7 phase was confirmed as the active site in the supported cesium phosphate catalyst. The reaction parameters were also optimized and a yield of 52% aziridine was obtained over 200?h. Thus, a continuous process for the cyclization of monoethanolamine to aziridine has been established. 相似文献
19.
To evaluate the thermal stability of materials, various criteria have been used. Not only the simple parameters, as characteristic temperatures, but also the combined criteria E/ RT p , k f ( T) and criterion based on the length of induction period of crystallization have been taken into account. Four gels with the composition Li 2O–2SiO 2– nTiO 2 ( n = 0.00, 0.03, 0.062, and 0.1) were prepared and the validity of the criteria was tested by applying them to these gels. The results indicate that thermal stability of the studied gels decrease with amount of TiO 2. 相似文献
20.
The kinetics of alkaline hydrolysis of 2-chloroquinoxaline (QCl) with hydroxide ion was investigated spectrophotometrically
at different percentages of aqueous–organic solvent mixtures with acetonitrile (10–60% v/v) and with dimethylesulphoxide (10–80%)
over the temperature range from 25 to 45 °C. The reaction was performed under pseudo first order conditions with respect to
2-chloroquinoxaline (QCl). An increase in the percentage of organic solvent (v/v) has different effects on the reaction rate
constants, presumably due to hydrogen bond donor and acceptor differences of the media and other solvatochromic parameters.
The data were discussed in terms of the Kamelt-Taft parameter and E
T(30). A nonlinear relation between the logarithm of the rate constant and reciprocal of the dielectric constant suggests the
presence of selective solvation by the polar water molecules. Activation parameters Δ H
#, Δ S
# and Δ G
# were determined and discussed. 相似文献
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