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1.
A series of α-Fe2O3/FeOOH nanostructures with different morphologies have successfully been synthesized based on K4[Fe(CN)6] at 140 °C by a novel hydrothermal method. The morphology and phase of α-Fe2O3/FeOOH can be controlled by adjusting the reaction time. UV–vis absorption spectrum, X-ray powder diffraction, and transmission electron microscopy analyses were used to characterize the resulting products. A detailed, rational mechanism is proposed for the formation of α-Fe2O3/FeOOH nanostructures. The potential applications of the as-synthesized α-Fe2O3/FeOOH nanoparticles with different morphologies on photocatalytic decomposition of salicylic acid were also investigated.  相似文献   

2.
Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu2P2O7 and Cu3(P2O6OH)2. α-Cu2P2O7 is reversibly transformed to β-Cu2P2O7 at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol−1. Enthalpies of formation from oxides of α-Cu2P2O7 and Cu3(P2O6OH)2 are −279.0 ± 1.4 kJ mol−1 and −538.8 ± 2.7 kJ mol−1, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol−1 and −4302.7 ± 6.7 kJ mol−1, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu3(P2O6OH)2, thus decreasing its thermodynamic stability.  相似文献   

3.
Protonic ceramic membrane fuel cells (PCMFCs) based on proton-conducting electrolytes have attracted much attention because of many advantages, such as low activation energy and high energy efficiency. BaZr0.1Ce0.7Y0.2O3−δ (BZCY7) electrolyte based PCMFCs with stable Ba0.5Sr0.5Zn0.2Fe0.8O3−δ (BSZF) perovskite cathode were investigated. Using thin membrane BZCY7 electrolyte (about 15 μm in thickness) synthesized by a modified Pechini method on NiO-BZCY7 anode support, PCMFCs were assembled and tested by selecting stable BSZF perovskite cathode. An open-circuit potential of 1.015 V, a maximum power density of 486 mW cm−2, and a low polarization resistance of the electrodes of 0.08 Ω cm2 was achieved at 700 °C. The results have indicated that BZCY7 proton-conducting electrolyte with BSZF cathode is a promising material system for the next generation solid oxide fuel cells.  相似文献   

4.
Fe2O3/SiO2 nanocomposites based on fumed silica A-300 (SBET = 337 m2/g) with iron oxide deposits at different content were synthesized using Fe(III) acetylacetonate (Fe(acac)3) dissolved in isopropyl alcohol or carbon tetrachloride for impregnation of the nanosilica powder at different amounts of Fe(acac)3 then oxidized in air at 400–900 °C. Samples with Fe(acac)3 adsorbed onto nanosilica and samples with Fe2O3/SiO2 including 6–17 wt% of Fe2O3 were investigated using XRD, XPS, TG/DTA, TPD MS, FTIR, AFM, nitrogen adsorption, Mössbauer spectroscopy, and quantum chemistry methods. The structural characteristics and phase composition of Fe2O3 deposits depend on reaction conditions, solvent type, content of grafted iron oxide, and post-reaction treatments. The iron oxide deposits on A-300 (impregnated by the Fe(acac)3 solution in isopropanol) treated at 500–600 °C include several phases characterized by different nanoparticle size distributions; however, in the case of impregnation of A-300 by the Fe(acac)3 solution in carbon tetrachloride only α-Fe2O3 phase is formed in addition to amorphous Fe2O3. The Fe2O3/SiO2 materials remain loose (similar to the A-300 matrix) at the bulk density of 0.12–0.15 g/cm3 and SBET = 265–310 m2/g.  相似文献   

5.
High-temperature proton conductors have wide applications in the areas of fuel cells, electrolysis and hydrogen separation. Barium zirconate-based materials are of interest due to their good stability and high protonic conductivity. The reported conductivity of these ceramic materials is generally less than 10−2 S/cm, even at high temperatures. This is not high enough for an electrolyte-supported device to achieve an ASR of less than 0.2 Ω cm2 therefore thin film electrolytes are required for successful application. As BaZrO3-based materials have to be sintered at temperatures as high as 1700 °C, this makes it difficult to find a suitable supporting electrode which will not undergo significant chemical reaction with the BaZrO3-based electrolyte during fabrication of the required electrode supported electrolyte. In this paper, proton-conducting BaZr0.8Y0.2O2.9 was successfully sintered at 1325 °C with a relative density of 96% via addition of 1 wt% ZnO. Fabrication of electrochemical cells using proton-conducting BaZr0.8Y0.2O2.9 as the electrolyte thus becomes possible. The formula of the 1 wt% ZnO added sample is Ba0.97Zr0.77Y0.19Zn0.04O3−δ which exhibits a tetragonal structure with space group P4/mbm (127); a=5.9787(1) Å, c=4.2345(1) Å, V=151.36(1) Å3. It was found that a solid solution was formed for a limited range of Zn doping. Conductivity has been studied as a function of atmosphere (air, dry and wet 5% H2/Ar) with the changes in bulk and grain boundary on changing atmosphere being monitored as a function of time. The total conductivity of Ba0.97Zr0.77Y0.19Zn0.04O3–δ is 1.0×10−3 S/cm above 600 °C therefore it may be used as a proton-conducting thin film electrolyte for efficient electrochemical devices at such temperatures. The grain boundary resistance is insignificant at high temperature for the well-sintered sample.  相似文献   

6.
Mesoporous YSZ–γ-Al2O3 membranes were coated on α-Al2O3 (Ø2 mm) tube by dipping the α-Al2O3 support tube into mixed sol consists of nano-size YSZ and bohemite particles followed by drying and calcination at 600 °C. Addition of bohemite in YSZ sol helped a good adhesion and uniform coating of the membrane film onto α-Al2O3 support. The quality of the mesoporous YSZ–γ-Al2O3 membranes was evaluated by the gas permeability experiments. The number of defects was minimized when the γ-Al2O3 content became more than 40%. Addition of γ-Al2O3 inhibited the crystal growth of YSZ, sintering shrinkage and distortion stress. Increase of calcination temperature and time results in the increase of pore size and N2 permeance. A hydrogen perm-selective membrane was prepared by filling palladium into the nano-pores of YSZ–γ-Al2O3 layer by vacuum-assisted electroless plating. Crystal growth of palladium was observed by thermal annealing of the membrane at 600 °C for 40 h. The Pd–YSZ–γ-Al2O3 composite membrane revealed improved thermal stability allowing long-term operation at elevated temperature (>500 °C). This has been attributed to the improved fracture toughness of YSZ–γ-Al2O3 layer and matching of thermal expansion coefficient between palladium and YSZ. Although fracture of the membrane did not occur, decline of H2 flux was observed when the membrane was exposed in 600 °C. This has been attributed to the agglomeration of palladium particles by crystal growth and dense packing into the pore networks of YSZ–γ-Al2O3 by elevation of temperature.  相似文献   

7.
Cu2+ binding on γ-Al2O3 is modulated by common electrolyte ions such as Mg2+, , and in a complex manner: (a) At high concentrations of electrolyte ions, Cu2+ uptake by γ-Al2O3 is inhibited. This is partially due to bulk ionic strength effects and, mostly, due to direct competition between Mg2+ and Cu2+ ions for the SO surface sites of γ-Al2O3. (b) At low concentrations of electrolyte ions, Cu2+ uptake by γ-Al2O3 can be enhanced. This is due to synergistic coadsorption of Cu2+ and electrolyte anions, and . This results in the formation of ternary surface species (SOH2SO4Cu)+, (SOH2PO4Cu), and (SOH2HPO4Cu)+ which enhance Cu2+ uptake at pH < 6. The effect of phosphate ions may be particularly strong resulting in a 100% Cu uptake by the oxide surface. (c) EPR spectroscopy shows that at pH  pHPZC, Cu2+ coordinates to one SO group. Phosphate anions form stronger, binary or ternary, surface species than sulfate anions. At pH  pHPZC Cu2+ may coordinate to two SO groups. At pH  pHPZC electrolyte ions and are bridging one O-atom from the γ-Al2O3 surface and one Cu2+ ion forming ternary [γ-Al2O3/elecrolyte/Cu2+] species.  相似文献   

8.
LiFe0.5Ti1.5O4 was synthesized by solid-state reaction carried out at 900 °C in flowing argon atmosphere, followed by rapid quenching of the reaction product to room temperature. The compound has been characterized by X-ray powder diffraction (XRD) and 57Fe Mössbauer effect spectroscopy (MES). It crystallizes in the space group P4332, a = 8.4048(1) Å. Results from Rietveld structural refinement indicated 1:3 cation ordering on the octahedral sites: Li occupies the octahedral (4b) sites, Ti occupies the octahedral (12d) sites, while the tetrahedral (8c) sites have mixed (Fe/Li) occupancy. A small, about 5%, inversion of Fe on the (4b) sites has been detected. The MES data is consistent with cation distribution and oxidation state of Fe, determined from the structural data.The title compound is thermally unstable in air atmosphere. At 800 °C it transforms to a mixture of two Fe3+ containing phases – a face centred cubic spinel Li(1+y)/2Fe(5−3y)/2TiyO4 and a Li(z−1)/2Fe(7−3z)/2TizO5 – pseudobrookite. The major product of thermal treatment at 1000 °C is a ramsdellite type lithium titanium iron(III) oxide, accompanied by traces of rutile and pseudobrookite.  相似文献   

9.
In this work we report about a new rare-earth oxoborate β-Dy2B4O9 synthesized under high-pressure/high-temperature conditions from Dy2O3 and boron oxide B2O3 in a B2O3/Na2O2 flux with a walker-type multianvil apparatus at 8 GPa and 1000°C. Single crystal X-ray structure determination of β-Dy2B4O9 revealed: , a=616.2(1) pm, b=642.8(1) pm, c=748.5(1) pm, α=102.54(1)°, β=97.08(1)°, γ=102.45(1)°, Z=2, R1=0.0151, wR2=0.0475 (all data). The compound exhibits a new structure type which is built up from bands of linked BO3- (Δ) and tetrahedral BO4-groups (□). The Dy3+-cations are positioned in the voids between the bands. According to the conception of fundamental building blocks β-Dy2B4O9 can be classified with the notation 2Δ6□:Δ3□=4□=3□Δ. Furthermore we report about temperature-resolved in situ powder diffraction measurements and IR-spectroscopic investigations on β-Dy2B4O9.  相似文献   

10.
The synthesis and characterization of a series of cobalt(III) complexes of the general type [Co(N2O2)(L2)]+ are described. The N2O2 Schiff base ligands used are Me-salpn (H2Me-salpn = N,N′-bis(methylsalicylidene)-1,3-propylenediamine) (13) and Me-salbn (H2Me-salbn = N,N′-bis(methylsalicylidene)-1,4-butylenediamine) (45). The two ancillary ligands L include: pyridine (py) 1, 3-metheylpyridine (3-Mepy) 2, 1-methylimidazole (1-MeIm) 3, 4-methylpyridine (4-Mepy) 4 and pyridine (py) 5. These complexes have been characterized by elemental analyses, IR, UV–Vis, and 1H NMR spectroscopy. The crystal structures of trans-[CoIII(Me-salpn)(py)2]PF6, 1, and cis-α-[CoIII(Me-salbn)(4-Mepy)2]BPh4 · 4-Mepy, 4, have been determined by X-ray diffraction. Examination of the solution and crystalline structures revealed that the outer coordination sphere of the complexes exerts a noticeable influence on the inner coordination sphere of the Co(III) ion. The electrochemical reduction of these complexes at a glassy carbon electrode in acetonitrile solution indicates that the first reduction process corresponding to CoIII–CoII is electrochemically irreversible, which is accompanied by the dissociation of the axial (R-py)–cobalt bonds. It has also been observed that the Co(III) state is stabilized with increasing the flexibility of the ligand environment.  相似文献   

11.
The thermal evolution and structural properties of fluorite-related δ-Bi2O3-type Bi9ReO17 were studied with variable temperature neutron powder diffraction, synchrotron X-ray powder diffraction and electron diffraction. The thermodynamically stable room-temperature crystal structure is monoclinic P21/c, a=9.89917(5), b=19.70356(10), c=11.61597(6) Å, β=125.302(2)° (Rp=3.51%, wRp=3.60%) and features clusters of ReO4 tetrahedra embedded in a distorted Bi–O fluorite-like network. This phase is stable up to 725 °C whereupon it transforms to a disordered δ-Bi2O3-like phase, which was modeled with δ-Bi2O3 in cubic Fmm with a=5.7809(1) Å (Rp=2.49%, wRp=2.44%) at 750 °C. Quenching from above 725 °C leads to a different phase, the structure of which has not been solved but appears on the basis of spectroscopic evidence to contain both ReO4 tetrahedra and ReO6 octahedra.  相似文献   

12.
The SrMn1−xFexO3−δ (x=1/3, 1/2, 2/3) phases have been prepared and are shown by powder X-ray and neutron (for x=1/2) diffraction to adopt an ideal cubic perovskite structure with a disordered distribution of transition-metal cations over the six-coordinate B-site. Due to synthesis in air, the phases are oxygen deficient and formally contain both Fe3+ and Fe4+. Magnetic susceptibility data show an antiferromagnetic transition at 180 and 140 K for x=1/3 and 1/2, respectively and a spin-glass transition at 5, 25, 45 K for x=1/3, 1/2 and 2/3, respectively. The magnetic properties are explained in terms of super-exchange interactions between Mn4+, Fe(4+δ)+ and Fe(3+)+. The XAS results for the Mn-sites in these compounds indicate small Mn-valence changes, however, the Mn-pre-edge spectra indicate increased localization of the Mn-eg orbitals with Fe substitution. The Mössbauer results show the distinct two-site Fe(3+)+/Fe(4+δ)+ disproportionation in the Mn- substituted materials with strong covalency effects at both sites. This disproportionation is a very concrete reflection of a localization of the Fe-d states due to the Mn-substitution.  相似文献   

13.
Asymmetrical thin membranes of SrCe0.95Y0.05O3−δ (SCY) were prepared by a conventional and cost-effective dry pressing method. The substrate consisted of SCY, NiO and soluble starch (SS), and the top layer was the SCY. NiO was used as a pore former and soluble starch was used to control the shrinkage of the substrate to match that of the top layer. Crack-free asymmetrical thin membranes with thicknesses of about 50 μm and grain sizes of 5–10 μm were successfully pressed on to the substrates. Hydrogen permeation fluxes (JH2) of these thin membranes were measured under different operating conditions. At 950 °C, JH2 of the 50 μm SCY asymmetrical membrane towards a mixture of 80% H2/He was as high as 7.6 × 10−8 mol/cm2 s, which was about 7 times higher than that of the symmetrical membranes with a thickness of about 620 μm. The hydrogen permeation properties of SCY asymmetrical membranes were investigated and activation energies for hydrogen permeation fluxes were calculated. The slope of the relationship between the hydrogen permeation fluxes and the thickness of the membranes was −0.72, indicating that permeation in SCY asymmetric membranes was controlled by both bulk diffusion and surface reaction in the range investigated.  相似文献   

14.
Ferroelastic β′-Gd2(MoO4)3, (GMO), crystals are formed through the crystallization of 21.25Gd2O3–63.75MoO3–15B2O3 glass (mol%), and two scientific curious phenomena are observed. (1) GMO crystals formed in the crystallization break into small pieces with a triangular prism or pyramid shape having a length of 50–500 μm spontaneously during the crystallizations in the inside of an electric furnace, not during the cooling in air after the crystallization. This phenomenon is called “self-powdering phenomenon during crystallization” in this paper. (2) Each self-powdered GMO crystal grain shows a periodic domain structure with different refractive indices, and a spatially periodic second harmonic generation (SHG) depending on the domain structure is observed. It is proposed from polarized micro-Raman scattering spectra and the azimuthal dependence of second harmonic intensities that GMO crystals are oriented in each crystal grain and the orientation of (MoO4)2− tetrahedra in GMO crystals changes periodically due to spontaneous strains in ferroelastic GMO crystals.  相似文献   

15.
La1−x(PO3)3:Tbx3+ (0<x0.6) were prepared using solid-state reaction. The vacuum ultraviolet (VUV) excitation spectrum of La0.55(PO3)3:Tb0.453+ indicates that the absorption of (PO3)33− groups locates at about 163 and 174 nm and the absorption bands of (PO3)33− groups (174 nm) and La3+–O2− (200 nm) and Tb3+ (213 nm) overlap each other. These results imply that the (PO3)33− groups can efficiently absorb the excited energy around 172 nm and transfer the energy to Tb3+. Under 172 nm excitation, the optimal photoluminescence (PL) intensity is obtained when Tb concentration reaches 0.45 and is about 71% of commercial phosphor Zn1.96SiO4:0.04 Mn2+ with chromaticity coordinates of (0.343, 0.578) and the decay time of about 4.47 ms.  相似文献   

16.
A novel BaCe0.4Zr0.3 Sn0.1Y0.2O3−δ (BSY) electrolyte membrane with thickness of 20 μm was fabricated on NiO-based anode substrate via a one-step all-solid-state method followed by a co-sintering at 1450 °C for 5 h. Chemical stability test demonstrated that BSY electrolyte showed adequate chemical stability against CO2 and H2O at intermediate temperature. Besides, the doping of Sn also enhanced the conductivity in humidified hydrogen. With Nd0.7Sr0.3MnO3−σ cathode and hydrogen fuel, the fuel cell generated maximum output of 320, 185 and 105 mW cm−2 at 700, 650 and 600 °C, respectively. The interfacial resistance of the fuel cell was studied under open circuit conditions and the short-term cell performance also confirmed the stability of BSY electrolyte membrane.  相似文献   

17.
Li2O–Cr2O3–GeO2–P2O5 based glasses were synthesized by a conventional melt-quenching method and successfully converted into glass-ceramics through heat treatment. Experimental results of DTA, XRD, ac impedance techniques and FESEM indicated that Li1.4Cr0.4Ge1.6(PO4)3 glass-ceramics treated at 900 °C for 12 h in the Li1 + xCrxGe2 − x(PO4)3 (x = 0–0.8) system exhibited the best glass stability against crystallization and the highest ambient conductivity value of 6.81 × 10−4 S/cm with an activation energy as low as 26.9 kJ/mol. In addition, the Li1.4Cr0.4Ge1.6(PO4)3 glass-ceramics displayed good chemical stability against lithium metal at room temperature. The good thermal and chemical stability, excellent conducting property, easy preparation and low cost make it promising to be used as solid-state electrolytes for all-solid-state lithium batteries.  相似文献   

18.
Among the perovskites, the rare earth manganites find application in several electrochemical devices because of their enhanced thermodynamic stability. In this paper, we present the results obtained on the preparation and characterization of La0.95MnO3+δ and Sm0.95MnO3+δ which were prepared by the solid state and sol–gel methods. XRD characterization of the manganites indicated that the crystal structure depends on the method of preparation and heat treatments. The ratio of Mn3+ to Mn4+ in these samples also depended on the method of preparation and heat treatments, as indicated by thermogravimetric (TG) and temperature programmed reduction (TPR) studies in Ar + 5% H2 atmosphere. The standard molar enthalpy of formation, which is a measure of the thermodynamic stability of these compounds were determined using an isoperibol calorimeter.  相似文献   

19.
In this paper, we have reported the preparation of low cost γ-Al2O3 membrane on a macroporous clay support by dip-coating method. For the synthesis of γ-Al2O3 top layer on the support, a stable boehmite sol is prepared using aluminium chloride salt as a starting material by sol–gel route. The structural properties of the composite membrane as well as γ-Al2O3 powder is carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption–desorption isotherm data, Fourier transform infrared analysis (FTIR) and dynamic light scattering (DLS) analysis. The mean particle size of the boehmite sol used for coating is found to be 30.9 nm. The pore size distribution of the γ-Al2O3–clay composite membrane is found to be in the range of 5.4–13.6 nm. Separation performance of the membrane in terms of flux and rejection of single salts solution such as MgCl2 and AlCl3 as a function of pH, salt concentration and applied pressure is also studied. The rejection and flux behavior are found to be strongly dependent on electrostatic interaction between the charged molecules and γ-Al2O3–clay composite membrane. The intrinsic rejection has been determined by calculating the concentration at membrane surface (Cm) using Speigler–Kedem model. It is found that the observed rejection shows anomalous trend with increase in applied pressure and the intrinsic rejection increases with increase in applied pressure, a trend typical of the separation of electrolyte through charged membranes. At acidic pH, both the salt solution shows higher rejection. With increase in the salt concentration, observed rejection of salt decreases due to the enhanced concentration polarization. The maximum rejection of MgCl2 and AlCl3 is found to be 72% and 88%, respectively for salt concentration of 3000 ppm.  相似文献   

20.
Lithiation of O-functionalized alkyl phenyl sulfides PhSCH2CH2CH2OR (R = Me, 1a; i-Pr, 1b; t-Bu, 1c; CPh3, 1d) with n-BuLi/tmeda in n-pentane resulted in the formation of α- and ortho-lithiated compounds [Li{CH(SPh)CH2CH2OR}(tmeda)] (α-2ad) and [Li{o-C6H4SCH2CH2CH2OR)(tmeda)] (o-2ad), respectively, which has been proved by subsequent reaction with n-Bu3SnCl yielding the requisite stannylated γ-OR-functionalized propyl phenyl sulfides n-Bu3SnCH(SPh)CH2CH2OR (α-3ad) and n-Bu3Sn(o-C6H4SCH2CH2CH2OR) (o-3ad). The α/ortho ratios were found to be dependent on the sterical demand of the substituent R. Stannylated alkyl phenyl sulfides α-3ac were found to react with n-BuLi/tmeda and n-BuLi yielding the pure α-lithiated compounds α-2ac and [Li{CH(SPh)CH2CH2OR}] (α-4ab), respectively, as white to yellowish powders. Single-crystal X-ray diffraction analysis of [Li{CH(SPh)CH2CH2Ot-Bu}(tmeda)] (α-2c) exhibited a distorted tetrahedral coordination of lithium having a chelating tmeda ligand and a C,O coordinated organyl ligand. Thus, α-2c is a typical organolithium inner complex.Lithiation of O-functionalized alkyl phenyl sulfones PhSO2CH2CH2CH2OR (R = Me, 5a; i-Pr, 5b; CPh3, 5c) with n-BuLi resulted in the exclusive formation of the α-lithiated products Li[CH(SO2Ph)CH2CH2OR] (6ac) that were found to react with n-Bu3SnCl yielding the requisite α-stannylated compounds n-Bu3SnCH(SO2Ph)CH2CH2OR (7ac). The identities of all lithium and tin compounds have been unambiguously proved by NMR spectroscopy (1H, 13C, 119Sn).  相似文献   

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