首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The phase relationships in the Na2ZnP2O7–LiKZnP2O7 system are studied. They are represented by a mixture of the starting components in the subsolidus region. The eutectic was found at a temperature of 640°C and composition of 0.5LiKZnP2O7. The phase formation of this system is compared with the previously studied NaKZnP2O7–LiKZnP2O7 system. It is shown that a structural factor affects the geometry of the state diagrams.  相似文献   

2.
3.
4.
Mixed oxides with perovskite structure have been proposed as promising alternative for the solar fuel production via thermochemical redox cycles. For this work, the system La0.6Sr0.4Mn1?xAlxO3 (x?=?0 to 0.8) was selected according to its high thermal stability and rapid oxidation kinetics, and the influence of the Al/Mn ratio on the redox properties was investigated. The characterization of the five oxides samples with different Al content confirmed the high redox capacity and the favorable behavior of these materials in consecutive cycles, as analyzed thermogravimetrically. The results show that following reduction at 1300?°C in inert atmosphere up to 0.32 mmol g?1 of O2 are released, while a 10-cycle reaction test confirms the feasibility of long term operation with these perovskites. It was observed that the reduction extent was enhanced with increasing the Al-content, but the oxidation degree is maximum for compositions near x?=?0.5, corresponding to an O2 release of 0.318 mmol g?1 (δ?=?0.132). After selecting the compositions with more promising redox properties, additional reactions were performed in a lab-scale fixed bed reactor with injection of CO2 in the oxidation step at 900?°C in order to generate CO. In these tests, the most interesting results were obtained for the perovskite La0.6Sr0.4Mn0.6Al0.4O3, with reduction extent of 0.266 mmol?g?1, but the production of CO is in comparison significantly lower (0.114 mmol?g?1). Further studies are required to determine the best operation conditions for thermochemical cycles using those materials.  相似文献   

5.
Some photon interaction parameters such as mass attenuation coefficient, effective atomic number, half value layer, mean free path and electron density for 15ZnO–(17.5–x)Al2O3xFe2O3–67.5P2O5 glass system (x = 0, 7.5, 12.5, 17.5) and 15ZnO–(25–x)Al2O3xFe2O3–60P2O5 glass system (x = 0, 25) have been investigated in the photon energy range of 1 keV to 100 GeV. It has been observed that all the photon interaction parameters for the selected glass systems vary with the photon energy. Among the selected glass systems, the sample 15ZnO–25Fe2O3–60P2O5 glass system shows maximum values for mass attenuation coefficients, effective atomic numbers, electron densities and minimum values for mean free path and half value layer in the entire energy grid.  相似文献   

6.
It is shown that the phase heterogeneity of SiO2–Na2O–Al2O3 glass has a liquation and crystallization nature, the balance between which is determined by the conditions of their synthesis. An increase in the aluminum oxide content decreases the number of liquation and crystallization sites, and also the linear sizes of the crystalline formations without eliminating the phase separation due to the liquation. The area of metastable immiscibility in the SiO2–Na2O–Al2O3 system, which is determined by scanning electron microscopy, is probably wider than the area detected by the optical methods.  相似文献   

7.
The effect of the hydroisomerization conditions of the benzene-containing fraction of catalytic reforming gasoline on the yield and composition of products is studied on Pt/B2O3–Al2O3 and Pt/WO3–Al2O3 catalysts. These catalysts allow benzene to be completely removed from the raw material. At the same time, the greatest yields of liquid products are obtained with minimal losses of the octane number at 2 MPa, a mass feedstock hourly space velocity (MFHSV) of 2 h?1, and 325°C: 96.3 and 95.4 wt % on Pt/B2O3–Al2O3 and Pt/WO3–Al2O3 catalysts, respectively. The activity of the catalysts is maintained for 100 h during their operation.  相似文献   

8.
In this study, FeBxFe2?xO4 nanoparticles (NPs) were synthesized by the polyol method. The M–H hysteresis curves exhibit superparamagnetic characteristics that are both coercivity and remanent magnetization values are negligible. The particle size dependent Langevin function was applied to calculate the magnetic particle dimensions around 9 nm. The measured magnetic moments of NPs are in range of (1.52–2.2) µB and almost half or less with respect to 4 µB of bulk Fe ferrite. Magnetic anisotropy was specified as uniaxial and calculated effective anisotropy constants (K eff ) are between 43.3 × 104 and 19.4 × 104 emu/g. The UV–Vis diffuse reflectance spectroscopy and Kubelka–Munk theory were used to determine the optical properties. The estimated optical band gap values (2.15–2.48 eV) of FeBxFe2?xO4 NPs are bigger with respect to reported values (1.88–2.12 eV) for Fe3O4 NPs in the literature. The bigger E g values are mainly attributed to B concentration and partly to quantum confinement effect.  相似文献   

9.
With the aim of achieving a high-performance 0.5Li2MnO3·0.5LiMn0.5Ni0.5O2 material, a series of 0.5Li2MnO3·0.5LiMn x Ni y Fe(1−xy)O2 (0.3 ≤ x ≤ 0.5, 0.4 ≤ y ≤ 0.5) samples with low Fe content was synthesized via coprecipitation of carbonates. Its crystal structure and electrochemical performance were characterized by means of powder X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, galvanostatic charge/discharge testing, cyclic voltammetry, and electrochemical impedance spectra. Rietveld refinements with a model integrating R [`3] \overline{3} m and Fm [`3] \overline{3} m indicate that a low concentration of Fe incorporated in 0.5Li2MnO3·0.5LiMn0.5Ni0.5O2 decrease a disordered cubic domain of the composite structure. The preferential distribution of Fe in cubic rock-salt contributes to an unimaginable decrease of c-axis parameter of the predominant layered structure as the Fe content increases. Moreover, including Fe as a dopant can kinetically improve crystallization and also change the ratio of Mn3+/Mn4+ and Ni3+/Ni2+. As a result, 0.5Li2MnO3·0.5LiMn0.4Ni0.5Fe0.1O2 exhibits lower Warburg impedance and higher reversible capacity than the undoped material.  相似文献   

10.
Effects of ZnO–B2O3 (ZB) addition on the densification, phase evolution and microwaves dielectric properties of Ba4Sm9.33Ti18O54 (BST) ceramics for low-temperature fired applications have been investigated. The sintering temperature of BST ceramics can be effectively lowered to about 1000°C with introduction of ZB. Tungsten bronze like single phase is observed in the BST ceramics with 0.5 and 1.0% ZB. However, Sm2Ti2O7 secondary phase appears when ZB addition reaches 2%, and Sm2Ti2O7 phase gradually increases with the increase ZB addition. Microwave dielectric properties of the present ceramics are strongly dependent on phase constitution and density. Optimal microwave dielectric properties of ε = 63.4, Qf = 2830 GHz, τ f =–8.8 ppm/°C is obtained for BST ceramics with 1% ZB addition.  相似文献   

11.
In this study, oleylamine (OAm) capped FeMnyCoyFe2?2yO4 (0.0?≤?y?≤?0.4) nanocomposites (NCs) were prepared via the polyol route and the impact of bimetallic Co3+ and Mn3+ ions on the structural and magnetic properties of Fe3O4 was investigated. The complete characterization of FeMnyCoyFe2?2yO4@OAm NCs were done by different techniques such as XRD, SEM, TGA, FT-IR, TEM, and VSM. XRD analyses proved the successful formation of mono-phase MnFe2O4 spinel cubic products free from any impurity. The average crystallite sizes were calculated in the range of 9.4–26.4 nm using Sherrer’s formula. Both SEM and TEM results confirmed that products are nanoparticles like structures having spherical morphology with small agglomeration. Ms continued to decrease up to Co3+ and Mn3+ content of y?=?0.4. Although Mössbauer analysis reveals that the nanocomposites consist three magnetic sextets and superparamagnetic particles are also formed for Fe3O4, Co0.2Mn0.2Fe2.6O4 and Co0.4Mn0.4Fe2.2O4. Cation distributions calculation was reported that Co3+ ions prefer to replace Fe2+ ions on tetrahedral side up to all the concentration while Mn3+ ions prefer to replace Fe3+ ions on the octahedral.  相似文献   

12.
Vapor–liquid equilibria of binary components of the BrCF2COOCH3–CF3COOH–BrCF2COOH–CF3COOCH3 quaternary system have been studied experimentally at constant pressure. The experiments have been carried out on a modified Sventoslavskii ebulliometer. Using the Aspen Plus software package, the appropriate models have been selected and the vapor–liquid equilibria for six binary systems have been simulated.  相似文献   

13.
Oxide based optical glass materials has important potential material in many applications from fiber optic to sensor due to the high transparency and amourphous structures. The objective of this study is to synthesize the novel optical glass materials based on the bismuth and aluminum contents to be able to determine the physical, chemical and mechanical properties by considering the systematic experimental steps. In this study, Bi2O3–Al2O3 based tellurite optical glasses have been prepared by using conventional melt quenching method as a function of the both Bi2O3 and Al2O3 compositions. There is a strong interactions between the glass former and modifier ions that might effect on the structure and mechanical properties. During the experimental steps, thermal, structural and mechanical properties of the prepared glass materials have been determined considering the DTA/DSC, FT-IR spectroscopy, SEM and Vicker’s hardness techniques, respectively. Thermal parameters, like glass transition, Tg, onset, Tx, crystallization, Tp, and melting, Tm, temperatures were obtained by using DTA scan.  相似文献   

14.
The results of the studies of the conditions of the liquid-phase synthesis of highly dispersed xerogels with a low degree of agglomeration and precursor nanopowders (~10–12 nm) based on zirconium dioxide in the ZrO2–HfO2–Y2O3(CeO2) system are presented. The thermal decomposition of xerogels and formation of crystalline solid solutions with the structure of fluorite are investigated. The optimal conditions for the solidification of nanodispersed powders for fabricating compact ceramics based on solid solutions of ZrO2 and the physical–chemical properties of these ceramics are studied.  相似文献   

15.
The results of the studies of the process of fabricating ceramic filtration membranes in the system ZrO2(Y2O3)–Al2O3 are presented. The phase compositions of the precursor powders and sintered ceramics have been investigated and their porous structures have been determined. Two stages of the implementation of the technology were demonstrated: fabrication of substrates with an open porosity ranging from 20 to 47% and pore sizes in the 100–300 nm range, as well as the deposition of nanocrystalline aluminum oxide layers on them. It has been established that the pore size distribution in the membrane layer of α-Al2O3 is unimodal (from 30 to 100 nm).  相似文献   

16.
Ultrafast pump-probe and transient photoluminescence spectroscopy were used to investigate carrier dynamics in β-Ga2O3 nanowires converted to β-Ga2O3/Ga2S3 under H2S between 400 to 600 °C. The β-Ga2O3 nanowires exhibited broad blue emission with a lifetime of 2.4 ns which was strongly suppressed after processing at 500–600 °C giving rise to red emission centered at 680 nm with a lifetime of 19 μs. Differential absorption spectroscopy reveals that state filling occurs in states located below the conduction band edge before sulfurization, but free carrier absorption is dominant in the β-Ga2O3/Ga2S3 nanowires processed at 500 to 600 °C for probing wavelengths >500 nm related to secondary excitation of the photo-generated carriers from the mid-gap states into the conduction band of Ga2S3.  相似文献   

17.
Vitrification in the Ga2S3–GeS2–PbF2 system is considered. The physicochemical properties of glasses, such as density, microhardness, electroconductivity, refraction index, and transmission percentage of specimens in visible and IR ranges of spectrum are studied; differential thermal analysis is carried out; and Raman and electron paramagnetic resonance spectra are investigated.  相似文献   

18.
A study has been made on the effects of the amount of silicon nitride and graphite on the physicomechanical properties of Al2O3–Si3N4–C composites for lining purposes. Adding 2.5–5.0 wt.% silicon nitride and 0.5 wt.% reactive alumina improves the properties, raises their apparent density, and increases the mechanical strength, while reducing the open porosity. Optimized compositions have been determined for refractory materials of Al2O3–Si3N4–C composition, and it has been found that to attain the higher values of physicomechanical properties the amount of graphite should constitute 5–10 wt.%.  相似文献   

19.
The thermal behavior of ammonioborite (NH4)3[B15O20(OH)8] · 4H2O is investigated using thermal X-ray diffraction, differential thermal analysis (DTA) in air and vacuum, and thermogravimetry. It is shown that the decomposition of the mineral (dehydration, dehydroxylation, deammoniation) proceeds in several stages, and the dehydration is accompanied by the amorphization. The thermal expansion of ammonioborite is sharply anisotropic. As in the case of other hydrous pentaborates, the thermal expansion is maximum in the direction in which pentaborate groups alternate with ammonium cations.  相似文献   

20.

Abstract  

The Rh/α-Al2O3 catalyst was modified by CeO2 in order to improve the thermal stability and the carbon deposition resistance during the CO2 reforming of methane The carbon formation was determined by TPO, TEM and Raman spectroscopy. Characterization results showed that the incorporation of Ce in the support inhibits the carbon deposition, increasing the useful life and the stability of the Rh base catalysts.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号