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2.
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
3.
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
4.
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
5.
The subject of the study was silicate–phosphate glasses of NaCaPO 4–SiO 2 system which are precursors of glass–crystalline materials. Glass–crystalline materials of NaCaPO 4–SiO 2 system obtained via crystallization of glasses belong to a group of the so-called bioactive materials. In order to obtain glass–crystalline materials with pre-established parameters, it is necessary to conduct crystallization of glasses at specific conditions. In order to design direct crystallization process properly, it is necessary to know the structure and microstructure of the glassy precursor. Microscopic investigation showed that liquation takes place in all the studied glasses. Based on DSC examinations, it has been found out that crystallization of the glasses of NaCaPO 4–SiO 2 system is a multistep process. The presence of several clearly separated exothermic peaks in DSC curves of investigated glasses makes it possible to crystallize only the separated phase with the matrix remaining amorphous or vice versa. Conducted detailed X-ray and spectroscopic studies of the materials obtained by heating in a gradient furnace (in the temperature specified on the basis of DSC) showed that separated phase and matrix crystallizes separately. Therefore, bioactive glass–crystalline materials can be obtained due to the existence of the phase separation phenomenon and pre-established sizes of the crystalline phase. 相似文献
6.
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
7.
Nano-composite TiO 2?CZrO 2 materials were prepared via sol?Cgel processes by hydrolysis of mixtures of titanium- and zirconium-containing alkoxides with TiO 2:ZrO 2 ratios of 1:2, 1:1, 2:1, and 10:1. Precipitated powders were dried at room temperature and annealed in ambient air at temperatures between 350 and 500?°C for 4?h. Pure TiO 2 and ZrO 2 powders were synthesized for comparison. Samples were characterized with X-ray diffraction (XRD) and X-ray absorption near edge fine structure (XANES). The detailed analysis of those data provides the crystalline and amorphous phase composition as well as the crystallite particle size. According to XRD and XANES analysis, only the two pure oxide samples and one of the composite samples with a composition TiO 2:ZrO 2?=?10:1, crystallized. Both titania containing powders, the pure TiO 2 and the TiO 2:ZrO 2?=?10:1 composite, were found to crystallize in the anatase structure. ZrO 2 was found to stay amorphous in the composites but crystalline in the pure oxide. In the crystallized composite TiO 2:ZrO 2?=?10:1 sample, the concentration of the amorphous phase remains larger than in pure TiO 2 samples, but the crystallite size was found to be nearly constant with increasing annealing temperature in contrast to the increasing particle size of pure TiO 2-samples. Pure TiO 2 precipitates are amorphous directly after preparation, however they crystallize after 6?month storage at ambient conditions by aging. Such an aging was not observed for the TiO 2:ZrO 2 composites. 相似文献
8.
The effect of pseudovacancies on the density of electronic states of valence electrons in AgGaS 2, CdGa 2S 4, and InPS 4 is studied both experimentally, by means of X-ray spectroscopy, and theoretically, by calculating the partial densities of electronic states using the local coherent potential. The compounds under study are the derivatives of the sphalerite structural type (doubled cell) with gradually increasing deficiency of metals from
to
and further to
, where
is a vacancy. The environment of the metal atoms remains tetrahedral, while that of the sulfur atoms changes with increasing number of vacancies from four (AgGaS 2) to three (CdGa 2S 4) and two (InPS 4). For the compounds under study, S K and P K X-ray emission and absorption spectra were recorded at a resolution of about 0.2 eV, and the local partial densities of states were calculated for all components of the compounds. The theoretical curves practically coincide in shape and energy position of fine structure elements with the corresponding experimental curves. This allowed reliable conclusions about the energy positions of electronic states at the top of the valence band and about the dependence of the S K emission and absorption spectra in the series of compounds under study on variation of the crystal structure and on the chemical composition of the nearest surroundings of sulfur atoms. 相似文献
9.
The boiling points of solutions of three-component systems formed by propanol-2 and propanoic acid esters are measured at different pressures by means of ebulliometry. The coefficients of the activity of the solutions’ components are measured using Wilson and nonrandom two-liquid (NRTL) equations. The results from calculations are in line with the experimental data. 相似文献
10.
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
11.
Glass–ceramic in the MgO–Al 2O 3–SiO 2 system with crystallization ability of gahnite (ZnO·Al 2O 3) and mullite were synthesized. It was found that the glass–ceramic containing gahnite phase had desirable mechanical behavior and reached to an acceptable hardness and density. The compositions were designed based on magnesium oxide replacement (from MgO–Al 2O 3–SiO 2 glass–ceramic system) with zinc oxide. Glass–ceramics were characterized by DTA, X-ray diffraction and scanning electron microscopy. Heat treatment at 1100 °C cause form gahnite crystals in glass–ceramic. Microhardness increased with increasing gahnite crystals. To achieve good mechanical properties, the initially formed high gahnite phase must transform. 相似文献
12.
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
13.
The partial substitution of CaF 2 for CaO in the Na 2O–CaO–SiO 2–P 2O 5 system was conducted by the sol–gel method and a comparison of the glass–ceramic properties was reported. Based on thermogravimetric and differential thermal analysis, the gels were sintered with a suitable heat treatment procedure. The glass–ceramic properties were characterized by X-ray diffraction, fourier-transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectrometer and so on, and the bioactivity of the glass–ceramic was evaluated by in vitro assays in simulated body fluid. Results indicate that with the partial substitution of CaF 2 for CaO in glass composition, the volume density, apparent porosity, bending strength and microhardness of the glass–ceramics have been significantly improved. Furthermore, CaF 2 promotes glass crystallization which does not inhibit the glass–ceramic bioactivity. 相似文献
14.
Beryllium precipitation from the Cu-rich matrix in a Cu–2 mass% Be–0.2 mass% Mg alloy homogenized and quenched from 1073 K was studied by differential scanning calorimetry (DSC). The DSC traces showed two main exothermic effects, A and B, each comprising two subeffects: A 1 and A 2 , and B 1 and B 2 respectively. Effects A 1 and A 2 correspond to the precipitation of GP zones and subsequent overlapping and independent precipitation of the phase. Only at very low heating rates can be inherited from GP zones. Effects B 1 and B 2 correspond to heat evolved during transitions to the states with and phases, respectively. Heat effect A can be quantitatively described in terms of solid solubilities before and after precipitation, and of the precipitation heats of the phases involved. The heat content of the combined GP zone/ phase precipitation effect was proportional to the number of beryllium atoms precipitated, yielding an average value of 21 kJ mol –1 beryllium for beryllium precipitation. It was shown that the phase arises from the combined transition from states with GP zones and phases, whereas arises from the transition of states with and phases. The apparent activation energies associated with GP zones and , and phases are 1.16±0.08, 1.18±0.07, 1.37±0.08 and 1.74±0.09 eV, respectively. These values are discussed in terms of the mobility of dissolved atoms related to the concentrations of excess vacancies and solute-vacancy complexes, and the direction of plate-like precipitate growth (either normal or perpendicular to the plate). It is inferred that the main roles of magnesium are to decrease the amount and rate of GP formation, to enhance the volume fraction of and to suppress the discontinuous precipitation of .This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
15.
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
16.
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
17.
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
18.
To study the intramolecular Diels-Alder cycloadditon of 2H-chromen-2-one as a diene, a series of chiral N-allyl-N-benzylamides that contain a 2H-chromen-2-one moiety were designed for the synthesis of benzo[f]isoindol-1-ones via an intramolecular Diels-Alder and a subsequent retro-Diels-Alder cycloaddition with the expulsion of CO 2. Both the yield (80%-89%) and absolute stereocontrol of the tandem reaction were high when an electron-withdrawing group was attached to the dienophile. The double bond in the styrene substructure remained in the products could be further derivatized by dihydroxylation. 相似文献
19.
Journal of Thermal Analysis and Calorimetry - In situ composites are today being considered for industrial use, owing to the fewer production steps involved, lower production cost, and better... 相似文献
20.
The ignition temperatures and effective activation energies of the ignition limits of mixtures (40–70% H 2 + 60–30% CH 4) stoich + air over Rh were experimentally determined at a pressure of 1 atm in the temperature range 20–300 °C. Over an ignition-treated Rh surface, the ignition temperature of a mixture of 70% H 2 + 30% methane + air is 62 °C. This indicates the potential of using Rh to markedly lower the ignition temperature of fuels based on hydrogen–methane mixtures. 相似文献
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