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1.
The two step oxidation of UO2+x and reduction of U3O8 powders observed during Differential Thermal Analysis (DTA) has been exploited to determine their Specific Surface Areas (SSAs). The results obtained by this method have been compared with the Braunauer, Emmett and Teller (BET) method and are found to be in good agreement in the SSA range of 2–4 m2/gm in the case of UO2+x obtained from ADU route and 4–8 m2/gm in the case of AUC route. A precision of ±0.1 m2/gm is obtained. The maximum temperature of oxidation and reduction of these oxides are dependent upon their preparative routes such as Ammonium Diuranate (ADU) and Ammonium Uranyl Carbonate (AUC).  相似文献   

2.
The oxidation of UO2 was investigated by TG, DSC and X-ray diffraction . UO2 samples were prepared by the reduction of UO3 at PH2 + PN2 = 100 + 50 mm Hg and 5°C min?1 up to 800°C. In order to obtain six UO2 samples with different preparative histories, UNH, UAH and ADU were used as starting materials and their thermal decomposition was carried out at 450–625°C for 0–9 h at an air flow rate of 100 ml min?1. α-UO3, γ-UO3, UO3 - 2 H2O, and their mixtures were obtained. The reduction of UO3 gave β-UO2+x with different x values from 0.030 to 0.055. The oxidation carried out at PO2 = 150 mm Hg was found to consist of oxygen uptake at room temperature. UO2 - U3O7 (Step I) and U3O7 → U3O8 (Step II). TG and DSC curves of the oxidation showed two plateaus and two exothermic peaks corresponding to Steps I and II. In the case of two of the samples, the DSC peak of Step II split into two substeps, which were assumed to be due to the different reactivities of U3O- formed from α-CO3 and that from other types of UO3. The increase in O/U ratio due to the oxygen uptake at room temperature changed from 0.010 to 0.042 except for a sample prepared from ADU which showed an extraordinarily large value of 0.445. TG curves showed an increase in O/U from room temperature to near 250°C for Step I and the plateau at 250–350°C where O/U was about 2.42, and showed a sharp increase in O/U above 350°C for Step II and the plateau above 100°C where O/U was 2.72–2.75. It is thought that the prepared UO2 had a defective structure with a large interstitial volume to accommodate the excess oxygen.  相似文献   

3.
Reduction of U3O8 was investigated for the recycling of spent oxide fuel from a commercial nuclear power plant. The possible reduction methods were proposed and compared. Based on the thermodynamic analysis, Li metal was selected as a reductant. The optimum reaction temperature for the reduction of U3O8 was investigated at the wider reaction temperature range. The adverse oxidation of U metal by Li2O at 1,000 °C was experimentally verified. Ellingham diagram was constructed to investigate the extent of the uranium oxides reduction when the reaction was carried out above melting point of U metal.  相似文献   

4.
Selective catalytic reduction (SCR) with ammonia has been considered as the most promising technology, as its effect deals with the NOX. Novel Fe-doped V2O5/TiO2 catalysts were prepared by sol–gel and impregnation methods. The effects of iron content and reaction temperature on the catalyst SCR reaction activity were explored by a test device, the results of which revealed that catalysts could exhibit the best catalytic activity when the iron mass ratio was 0.05%. It further proved that the VTiFe (0.05%) catalyst performed the best in denitration and its NOX conversion reached 99.5% at 270 °C. The outcome of experimental procedures: Brunauer–Emmett–Teller surface area, X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction and adsorption (H2-TPR, NH3-TPD) techniques showed that the iron existed in the form of Fe3+ and Fe2+ and the superior catalytic performance was attributed to the highly dispersed active species, lots of surface acid sites and absorbed oxygen. The modified Fe-doped catalysts do not only have terrific SCR activities, but also a rather broad range of active temperature which also enhances the resistance to SO2 and H2O.  相似文献   

5.
A yolk–shell-structured sphere composed of a superparamagnetic Fe3O4 core and a carbon shell (Fe3O4@HCS) was etched from Fe3O4@SiO2@carbon by NaOH, which was synthesized through the layer-by-layer coating of Fe3O4. This yolk–shell composite has a shell thickness of ca. 27 nm and a high specific surface area of 213.2 m2 g?1. Its performance for the magnetic removal of tetracycline hydrochloride from water was systematically examined. A high equilibrium adsorption capacity of ca. 49.0 mg g?1 was determined. Moreover, the adsorbent can be regenerated within 10 min through a photo-Fenton reaction. A stable adsorption capacity of 44.3 mg g?1 with a fluctuation <10% is preserved after 5 consecutive adsorption–degradation cycles, demonstrating its promising application potential in the decontamination of sewage water polluted by antibiotics.  相似文献   

6.
The calcium fluoride solid electrolyte Galvanic cell: (-) Pt, U3O8(s) + UO2F2(s) + BaUF6(s) + BaF2(s) | CaF2(s) | NiO(s) + NiF2(s), Pt (+) was used to measure the standard molar Gibbs energy of formation of BaUF6(s). From the measured emf values of the cell and required Gibbs energy values from the literature, Δf G m° (T) of BaUF6(s) has been calculated. The pseudo-binary phase diagram of BaF2–UF4 system was calculated by minimization of Gibbs energies of the phases present in the system. The stability domain of BaUF6(s) has been calculated from the chemical potential diagram of Ba–U–F–O system at 800 K.  相似文献   

7.
Calcium aluminate (12CaO–7Al2O3) powder was synthesized using three methods, viz. Pechini, coprecipitation, and a new novel facile decomposition route starting from activated alumina and calcium nitrate precursors, then used as a support to prepare a series of 31 wt%Ni/12CaO–7Al2O3 catalysts by deposition–precipitation method. The resultant catalysts were tested in steam pre-reforming of natural gas at 400–550 °C, low steam-to-carbon (S/C) molar ratio of 1.5, and atmospheric pressure. The obtained samples were characterized by Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), hydrogen chemisorption, and CO2–temperature-programmed desorption (TPD). Experimental results showed that the basicity and morphology of the supports depended significantly on the synthesis method. Calcium aluminate synthesized using the new decomposition procedure showed surface area of 6.23 m2 g?1, while the surface area of those prepared by the Pechini and coprecipitation method were 1.38 and 3.76 m2 g?1, respectively. The catalytic properties of the 31 wt%Ni/12CaO–7Al2O3 catalysts were strongly influenced by the support preparation approach. The highest specific surface area (about 230 m2 g?1), smallest Ni particle size (8.86 nm), and highest nickel dispersion (7.48%) were observed for the catalyst whose support was synthesized by the decomposition method. Even at high gas hourly space velocity (GHSV) of 2 × 105 mL \({\text{g}}^{ - 1}_{\text{catalyst}}\) h?1, this catalyst exhibited around 100% C2H6 and C3H8 conversion at temperature above 500 °C. High catalytic stability during 60 h time on-stream was also shown. The TPO profiles of the spent catalyst demonstrated high resistance to carbon formation.  相似文献   

8.
A H3PW12O40/ZrO2 catalyst for effective dimethyl carbonate (DMC) formation via methanol carbonation was prepared using the sol–gel method. X-ray photoelectron spectra showed that reactive and dominant (63%) W(VI) species, in WO3 or H2WO4, enhanced the catalytic performances of the supported ZrO2. The mesoporous structure of H3PW12O40/ZrO2 was identified by nitrogen adsorption–desorption isotherms. In particular, partial sintering of catalyst particles in the duration of methanol carbonation caused a decrease in the Brunauer–Emmett–Teller surface area of the catalyst from 39 to 19 m2/g. The strong acidity of H3PW12O40/ZrO2 was confirmed by the desorption peak observed at 415 °C in NH3 temperature-programmed desorption curve. At various reaction temperatures (T?=?110, 170, and 220 °C) and CO2/N2 volumetric flow rate ratios (CO2/N2?=?1/4, 1/7, and 1/9), the calculated catalytic performances showed that the optimal methanol conversion, DMC selectivity, and DMC yield were 4.45, 89.93, and 4.00%, respectively, when T?=?170 °C and CO2/N2?=?1/7. Furthermore, linear regression of the pseudo-first-order model and Arrhenius equation deduced the optimal rate constant (4.24?×?10?3 min?1) and activation energy (Ea?=?15.54 kJ/mol) at 170 °C with CO2/N2?=?1/7 which were favorable for DMC formation.  相似文献   

9.
A series of Co-modified Ce0.5Zr0.5O2 catalysts with different concentrations of Co (mass %: 0, 2, 4, 6, 8, 10) was investigated for diesel soot combustion. Ce0.5Zr0.5O2 was prepared using the coprecipitation method and Co was loaded onto the oxide using the incipient wetness impregnation method. The activities of the catalysts were evaluated by thermogravimetric (TG) analysis and temperature-programmed oxidation (TPO) experiments. The results showed the soot combustion activities of the catalysts to be effectively improved by the addition of Co, 6 % Co/Ce0.5Zr0.5O2 and that the 8 % Co/Ce0.5Zr0.5O2 catalysts exhibited the best catalytic performance in terms of lower soot ignition temperature (Ti at 349°C) and maximal soot oxidation rate temperature (Tm at 358°C). The reasons for the improved activity were investigated by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). These results revealed that the presence of Co could lower the reduction temperature due to the synergistic effect between Co and Ce, thereby improving the activity of the catalysts in soot combustion. The 6 % Co catalyst exhibited the best catalytic performance, which could be attributed to the greater amounts of Co3+ and surface oxygen species on the catalyst.  相似文献   

10.
It was established that heating to 90 °C of nitrate solutions of U, Np and Pu in the presence of hydrazine hydrate results in the formation of hydrated dioxides of these elements. On ignition under inert or reducing conditions in the temperature range of 280–800 °C hydrated uranium dioxide transmogrify into crystalline UO2. On ignition in air atmosphere UO2·nH2O turns into UO3 at 440 °C and into U3O8 at 570–800 °C. It was shown that thermolysis of the solution containing a mixture of uranium, neptunium and plutonium nitrates at 90 °C in the presence of hydrazine hydrate allows one to prepare hydrated dioxides (U, Np, Pu)O2·nH2O which on heating to ~300 °C transmogrify into crystalline product of UO2, NpO2 and PuO2 solid solution. The technique of preparation of solid solutions of U and Pu dioxides is very promising as simple and effective method of production of MOX-fuel for.  相似文献   

11.
Al(OPh)3 involving sterically hindered phenyl groups on ultrasonic assisted micro hydrolysis yielded a mixture of boehmite and bayerite as deduced from the FTIR and powder X-ray diffraction pattern. In the thermogravimetric trace, the complete removal of decomposable moieties of the hydrolyzed gel occurred around 530 °C. Calcining the gel at temperatures 600, 700, 800 and 900 °C showed crystalline tetragonal δ-Al2O3 to be the product at 900 °C as deduced from FTIR, 27Al NMR and PXRD techniques. δ-Al2O3 showed a surface area of 135 m2/g with rectangular bar like morphology with the sizes below 50 nm in the TEM images.  相似文献   

12.
Quartz (SiO2) glass was implanted with 5 × 1016 57Fe ions/cm2 at a substrate temperature of 500 °C, and annealed at temperatures between 700 and 950 °C. The implanted and annealed plates were characterized by conversion electron Mössbauer spectroscopy (CEMS), and measured by a Kerr effect magnetometer or a vibration sample magnetometer. Kerr effect measurement of as-implanted SiO2 glass showed ferromagnetism at room temperature. CEM spectrum of the as-implanted glass consisted of magnetic relaxation peaks of finely dispersed metallic Fe species, and paramagnetic doublets of Fe3+ and Fe2+ species. The sample heated at 700 °C contained large grains of metallic Fe and a lot of oxidation products of Fe2+ species. After oxidation at temperatures higher than 800 °C, the samples showed also ferromagnetism, which was attributed mainly to ferromagnetic ε-Fe2O3 precipitated in SiO2 matrix. Small amounts of α-Fe2O3 were produced at 950 °C. The results suggest that ion implantation and oxidation make a transparent ferromagnetic glass possible.  相似文献   

13.
Higher alcohol has been considered as a potential fuel additive. Higher alcohol, including C2–C4 alcohol was synthesized by catalytic conversion of syngas (with a ratio of CO/H2?=?1) derived from natural gas over modified Cu/ZnO/Al2O3 catalyst. Modified Cu/ZnO/Al2O3 catalysts promoted by alkali metal (Li) for higher alcohol synthesis (HAS) were prepared at different pH (6, 6.5, 7, 8, and 9) by co-precipitation to control Cu surface area and characterized by N2 physisorption, XRD, SEM, H2-TPR and TPD. The HAS reaction was carried out under a pressure of 45 bar, GHSV of 4000 h?1, ratio of H2/CO?=?1, and temperature ranges of 240 and 280 °C. It was found that the malachite phase of copper causes the size of copper to be small, which is suitable for methanol synthesis. Methanol and HAS share a common catalytic active site and intermediate. It was also found that the productivity to higher alcohol was correlated with Cu surface area.  相似文献   

14.
Mesoporous TiO2 is prepared by sol–gel process with a triblock copolymer as an organic template and aqueous TiOCl2 solution as inorganic precursor. The XRD patterns reveal that only the anatase phase can be observed in mesoporous TiO2, regardless of the different calcining temperatures, and with increasing calcining temperature the grain size gradually increases. The grain sizes of TiO2 increased from 4.7 to 11.9 nm with calcining temperature increasing from 300 to 400 °C. The pore size and the surface area evaluated from the Barrett–Joyner–Halenda model and Brunauer–Emmett–Teller method indicated that the average pore sizes increased from 87 to 153 Å and specific surface areas decreased from 179.71 to 74.31 m2/g for 300–400 °C calcination. The relationship between the optical band gap (E g) and microstructure of anatase has been determined and discussed. The quantum confinement effect is observed at grain sizes lower than 10 nm, and the estimated E g shifts from 3.32 to 3.46 eV. These results suggest that there are potential applications of mesostructured TiO2 with nanocrystals in the design of optical devices and photocatalysts.  相似文献   

15.
Na2Ti3O7 ceramic materials have been widely used in sodium-ion battery applications with relative good results; however, there are still several studies that might be carried out in the improvement of the Na2Ti3O7 properties and the overall batteries’ performance. In this direction, we used sonochemical method following a thermal treatment in order to synthetized pure phase Na2Ti3O7 nanopowders. X-ray diffraction characterization revealed that Na2Ti3O7 is the primary phase in nanopowders and ceramic sample; although, a high level of amorphization was observed in the sonicated nanopowder without heat treatment process. Nanopowder-prepared ceramic sample showed a crystallite size of 50 nm after sintering at 900 °C for 1 h. The specific surface area, pore volume, and pore size were obtained from the B.E.T. measurements, being 51 m2 g?1, 0.07 cm3 g?1, and 55 Å, respectively. The capacitance values of the nanopowder-prepared ceramic sample were in the order of microfarad. The total energy of the system was used to determine relaxation time of the sample (τ 0 = 31 ms).  相似文献   

16.
Mn3O4 powders have been produced from Electrolytic Manganese Residue (EMR). After leaching of EMR in sulfuric acid, MnSO4 solution containing various ions was obtained. Purifying the solution obtained and then adding aqueous alkali to the purified MnSO4 solution, Mn(OH)2 was prepared. Two methods were employed to produce Mn3O4. One way was oxidation of Mn(OH)2 in aqueous phase under atmosphere pressure to obtain Mn3O4. The other way was roasting Mn(OH)2 precursors in the range of 500°C to 700°C. The prepared samples were investigated by using several techniques including X-ray powder diffraction (XRD), Fourier Transformation Infra-Red (FTIR) spectra, and Brunauer-Emmett-Teller (BET) specific surface area instrument. Particle distribution and magnetic measurements were carried out on laser particle size analyzer, vibrating sample magnetometer (VSM). Through XRD, FTIR and determination of total Mn content (TMC), the products prepared were confirmed to be a single phase Mn3O4. BET specific surface areas can reach to 32 m2 g−1. The results indicated that products synthesized by aqueous solution oxidation method had higher specific surface areas and smaller particle size than those prepared by means of roasting. However the products prepared using the above two methods showed no obvious differences in magnetic property.   相似文献   

17.
Fe@Fe2O3 core-shell nanowires were synthesized via the reduction of Fe3+ ions by sodium borohydride in an aqueous solution with a subsequent heat treatment to form Fe2O3 shell and employed as a cathode catalyst for non aqueous Li-air batteries. The synthesized core-shell nanowires with an average diameter of 50–100 nm manifest superior catalytic activity for oxygen evolution reaction (OER) in Li-O2 batteries with the charge voltage plateau reduced to ~3.8 V. An outstanding performance of cycling stability was also achieved with a cutoff specific capacity of 1000 milliampere hour per gram over 40 cycles at a current density of 100 mA g?1. The excellent electrochemical properties of Fe@Fe2O3 as an O2 electrode are ascribed to the high surface area of the nanowires’ structure and high electron conductivity. This study indicates that the resulting iron-containing nanostructures are promising catalyst in Li-O2 batteries.  相似文献   

18.
Neodymium(III) peroxotitanate is used as a precursor for obtaining Nd2TiO5. The last one possesses numerous valuable electrophysical properties. TiCl4, Nd(NO3)3·6H2O and H2O2 in mol ratio 1:2:10 were used as starting materials. The reaction ambience was alkalized to pH = 9 with a solution of NH3. The obtained neodymium(III) peroxotitanate and intermediate compounds of the isothermal heating were proved by the help of quantitative analysis and infrared spectroscopy (IRS). It has Nd4[Ti2(O2)4(OH)12]·7H2O composition. The absorption band observed in IRS at 831 cm?1 relates to a triangular bonding of the peroxo group of Ti, at 1062 cm?1—terminal groups Ti–OH and at 1491 and 1384 cm?1—the bridging OH?-groups Ti–O(H)–Ti. Nd2TiO5 was obtained by thermal decomposition of neodymium(III) peroxotitanate. The isothermal conditions for decomposition were determined on the base of differential thermal analysis, thermogravimetric and differential scanning calorimetry results in the temperature range of 20–1000 °C. The mechanism of thermal decomposition of Nd4[Ti2(O2)4(OH)12]·7H2O to Nd2TiO5 was studied. In the temperature range of 20–208 °C, a simultaneous decomposition of the peroxo groups by the separation of oxygen and hydrate water is conducted and Nd4[Ti2O4(OH)12] is obtained. From 208 to 390 °C, the terminal OH?-groups are separated and Nd4[Ti2O7(OH)6] is formed. In the range of 390–824 °C, the bridging OH?-groups are completely decomposed to Nd2TiO5. The optimal conditions for obtaining nanocrystalline Nd2TiO5 are 900 °C for 6 h and 20–80 nm.  相似文献   

19.
Nano-crystalline La0.8Sr0.2Co0.5Fe0.5O3±δ powder has been successfully synthesized by microwave assisted sol–gel (MWSG) method. The decomposition and crystallization behavior of the gel-precursor was studied by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analysis. From the result of FT-IR and X-ray diffraction patterns, it is found that a perovskite La0.8Sr0.2Co0.5Fe0.5O3±δ was formed by irradiating the precursor at 700 W for 3 min, but the well-crystalline perovskite La0.8Sr0.2Co0.5Fe0.5O3±δ was obtained at 700 W for 35 min. Morphological and specific area analysis of the powder were done by transmission electron microscopy (TEM), scanning electron microscope (SEM) and Brunauer–Emmett–Teller (BET). The surface areas measured was 38.9 m2/g and the grain size was ∼23 nm. Electrochemical properties of pure LSCF cathode on YSZ electrolyte at intermediate temperatures were investigated by using AC impedance analyzer, which shows a low area specific resistance (0.077 Ω cm2 at 1073 K and 0.672 Ω cm2 at 953 K). Moreover, the synthesis period of 20 h usually observed for conventional heating mode is reduced to a few minutes. Thus, the MWSG method is proved to be a novel, extremely facile, time-saving and energy-efficient route to synthesize LSCF powders.  相似文献   

20.
Nickel aluminates were prepared by sol–gel and impregnation methods and calcined at 1100 °C. The sol–gel made samples were prepared with different amounts of nickel (Ni/Al molar ratio equal to 0, 0.25, 0.5, and 0.75) and aging times (24 and 48 h). The samples were characterized by X-ray diffraction, induced couple plasma, nitrogen physisorption, transmission and scanning electron microscopy, and ammonia temperature programmed desorption (NH3-TPD). In the sol–gel made samples, only the NiAl2O4 structure of nickel aluminate was defined, while for impregnation, NiAl10O16 was formed as well. The sol–gel made samples had low specific surface areas (7.7–12.4 m2/g), but a sample prepared by impregnation method had higher specific surface area (67.2 m2/g). The surface acidity density decreased by increasing the amount of nickel and was the lowest for impregnation method.  相似文献   

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