共查询到20条相似文献,搜索用时 15 毫秒
1.
The influence of potential on the anodic dissolution of SIMFUEL (doped uranium dioxide) has been characterized over the range 0-500 mV (versus SCE). Cathodic stripping voltammetry was used to determine the changes in surface reactivity of UO2 in neutral solutions after different anodic oxidation timescales. Scanning electron microscopy (SEM) was used to view the damage to the SIMFUEL electrode surface which was minimal at E < 200 mV but present as local pits and eroded grains after oxidation at higher potentials. Long-term anodic oxidation at potentials below 200 mV suggests that local acidification can develop within surface asperities in the fuel and pores in corrosion product deposits accumulated on the electrode surface. 相似文献
2.
The reaction of H2O2 on SIMFUEL electrodes has been studied electrochemically and under open circuit conditions in 0.1 mol l−1 NaCl (pH 9.8). The composition of the oxidized UO2 surface was determined by X-ray photoelectron spectroscopy (XPS). Peroxide reduction was found to be catalyzed by the formation of a mixed UIV/UV (UO2+x) surface layer, but to be blocked by the formation of UVI (UO22+) species on the electrode surface. The formation of this UVI layer blocks both H2O2 reduction and oxidation, thereby inhibiting the potentially rapid H2O2 decomposition process to H2O and O2. Decomposition is found to proceed at a rate controlled by desorption or reduction of the adsorbed O2 species. Reduction of O2 is coupled to the slow oxidative dissolution of UO2 and formation of a corrosion product deposit of UO3·yH2O. 相似文献
3.
The electrochemical reduction of hydrogen peroxide has been studied on uranium dioxide electrodes. The reduction kinetics are found to be influenced by dissolved carbonate/bicarbonate ions. The formation of hydrated UVI species on the electrode surface is avoided in carbonate solutions, allowing H2O2 reduction to proceed at less cathodic potentials than in carbonate-free solutions. At more cathodic potentials, the adsorption of carbonate ions on the active reduction sites inhibits the H2O2 reduction reaction. Over a narrow potential region, the reduction of peroxide is catalyzed by coadsoption of H2O2 and HCO3−/CO32−. The pH dependence of the H2O2 reduction reaction appears to be stronger in carbonate solutions than in solutions that do not contain carbonate. This can be attributed to the displacement of inhibiting CO32−/HCO3− adsorbed ions by OH−. 相似文献
4.
We report results on the adsorption and desorption of H2S on polycrystalline UO2 at 100 and 300 K, using ultrahigh vacuum X-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), and temperature programmed desorption (TPD). Our work is motivated by the potential for using the large stockpiles of depleted uranium in industrial applications, e.g., in catalytic processes, such as hydrodesulfurization (HDS) of petroleum. H2S is found to adsorb molecularly at 100 K on the polycrystalline surface, and desorption of molecular H2S occurs at a peak temperature of 140 K in TPD. Adsorption rates of sulfur as a function of H2S exposure are measured using XPS at 100 K; the S 2p intensity and lineshapes demonstrate that the saturation coverage of S-containing species is 1 monolayer (ML) at 100 K, and is 0.3–0.4 ML of dissociation fragments at 300 K. LEIS measurements of adsorption rates agree with XPS measurements. Atomic S is found to be stable to >500 K on the oxide surface, and desorbs at 580 K. Evidence for a recombination reaction of dissociative S species is also observed. We suggest that O-vacancies, defects, and surface termination atoms in the oxide surface are of importance in the adsorption and decomposition of S-containing molecules. 相似文献
5.
M.E. Broczkowski 《Electrochimica acta》2007,52(25):7386-7395
The anodic dissolution of UIVO2 has been studied at 60 °C in 0.1 mol dm−3 KCl using a range of electrochemical methods and X-ray photoelectron spectroscopy (XPS). The results were compared to previous results obtained at 22 °C. This comparison shows that the threshold for the onset of anodic dissolution (−400 mV versus SCE) is not noticeably changed by this increase in temperature. However, both the oxidation of the surface (to UIV/VO2+x) and the rate of anodic dissolution (as UVIO22+) leading to the formation of a UVIO3·yH2O deposit are accelerated at the higher temperature. The XPS analysis shows that the conversion of UV-UVI occurs at lower potentials at 60 °C. Consequently, once the surface becomes blocked by the presence of a UVIO3·yH2O deposit, rapid dissolution coupled to uranyl ion hydrolysis causes the development of locally acidified sites within the fuel surface at lower potentials at the higher temperature. 相似文献
6.
J. A. Caldern O. R. Mattos O. E. Barcia S. I. Crdoba de Torresi J. E. Pereira da Silva 《Electrochimica acta》2002,47(28):4531-4541
The electrodissolution of cobalt in carbonate/bicarbonate solutions was studied at room temperature by steady state polarisation, interfacial pH measurements and Raman spectroscopy. The active dissolution of cobalt leads to an initial CoO film formation. The metal passivation occurs by a slow transformation of the CoO into a Co3O4 oxide. The influence of HCO3− and CO32− anions was investigated. Two different parallel electrochemical processes were proposed to account for the anion role on the electrochemical steady state behaviour of cobalt in the studied solutions. 相似文献
7.
The influence of different metal oxide supports (i.e. ZrO2, ThO2, UO2, TiO2 and SiO2) on the performance of Ni- and/or Co-containing catalysts [Ni and/or Co/MO2 mole ratio (where M=Zr, Th, U, Ti or Si)=1.0] in the oxidative methane-to-syngas conversion at very low contact time (GHSV=5.2×105 cm3 g−1 h−1 at STP) was investigated. The nickel-containing ZrO2, ThO2 and UO2 catalysts (with or without pre-reduction by hydrogen at 500°C) showed good performance in the process; the order of their performance is NiO–ThO2>NiO–UO2>NiO–ZrO2. The NiO–TiO2 showed appreciable catalytic activity only after its reduction at 800°C. However, this catalyst and the NiO–SiO2 catalyst showed poor performance in the process. These two catalysts are also deactivated very fast, mostly because of sintering of Ni and/or formation of catalytically inactive binary metal oxide phases by solid–solid reaction at the high catalyst calcination and/or catalytic reaction temperature. Although the Ni-containing ThO2, UO2 and ZrO2 catalysts showed good performance, carbon deposition on them during the process is fast. However, because of the addition of cobalt to these catalysts (with Co/Ni=1.0), the rate of carbon deposition on them in the process is drastically reduced. This Co addition however resulted in a significant decrease in both the conversion and selectivity; the decrease in the selectivity was small. 相似文献
8.
Ousseïni Marou Alzouma Franck Marion Anne-Charlotte Robisson 《Ceramics International》2018,44(11):12073-12080
External lubrication is often used to complete compaction process of powder materials. The main goal of this method is generally to reduce the amount of admixed internal lubricant (Zinc stearate powder) within the raw material. The application of external lubricants enhances the density uniformity and the mechanical strength of the resulting compacts. This study investigates the effects of the external lubricant amount for UO2 powder compaction and the properties of the corresponding green pellets (corresponding to the compacts before sintering) without any admixed lubricant in the raw powder in order to evaluate the feasibility of this route in the case of nuclear powder. Results show that there is a quantity or number of layers from which the external lubricant applied on the die wall becomes detrimental to the friction index and the ejection force measured during the pressing cycle. The quality (surface defects, mechanical strength) of the green pellets can also be affected by the amount of lubricant. Thus the quantity and the thickness of the die wall lubricant must be optimized in order to assure an efficient mixed lubrication mode corresponding to the better lubrication mode in our study case. 相似文献
9.
This paper describes the synthesis and characterization of three-dimensional hybrid inorganic-organic networks prepared by a polycondensation reaction between Zr(O(CH2)3CH3)4 and polyethylene glycol 400 (PEG400). Eleven hybrid networks doped with varying concentrations of LiClO4 salt were prepared. On the basis of analytical data and FT-Raman studies it was concluded that these polymer electrolytes consist of inorganic-organic networks with zirconium atoms bonded together by PEG400 bridges. These polymers are transparent with a solid rubber consistency and are very stable under inert atmosphere. Scanning electron microscopy revealed a smooth glassy surface. X-ray fluorescence microanalysis with energy dispersive spectroscopy demonstrated that all the constituent elements are homogeneously distributed in the materials. Thermogravimetric measurements revealed that these materials are thermally stable up to 262 °C. Differential Scanning Calorimetry measurements indicated that the glass transition temperature Tg of these inorganic-organic hybrids varies from −43 to −15 °C with increasing LiClO4 concentration. FT-Raman investigations revealed the TGT (T=trans, G=gauche) conformation of polyether chains and allowed characterization of the types of ion-ion and ion-polymer host interactions in the bulk materials. The conductivity of the materials at different temperatures was determined by impedance spectroscopy over the 20 Hz-1 MHz frequency range. Results indicated that the materials conduct ionically and that their ionic conductivity is strongly influenced by the segmental motion of the polymer network and the type of ionic species distributed in the bulk material. Finally, it is to be highlighted that the hybrid network with a nLi/nO molar ratio of 0.0223 shows a conductivity of ca. 1×10−5 S cm−1 at 40 °C. 相似文献
10.
Pb0.325Sr0.675Ti1-xMnxO3 ceramics (x?=?0, 0.001, 0.005, 0.01, and 0.05) were successfully prepared by traditional solid-state reaction method. It was found that the lattice constant calculated through Rietveld refinement initially increased and then decreased with increasing Mn content, which was attributed to the variation in valence state of Mn and Ti ions. The microstructure gradually varied from the coexistence of large grains and fine grains for x?=?0 to the uniform grain for x?=?0.05 by increasing the doping Mn ions. With increasing Mn content from x?=?0 to x?=?0.05, the Curie temperature (Tc) dramatically decreased from 25?°C to ??40?°C and dielectric maximum decreased from 27,100 to 13,200. Pb0.325Sr0.675Ti1-xMnxO3 ceramics with x?=?0.001 showed the lowest dielectric loss of 0.006 with a relatively high dielectric peak value of ~ 21,000. The grain boundaries resistance obtained from the complex impedance decreased with the increase of Mn content. The decrease in resistance was ascribed to oxygen vacancies and electronics produced by the change of ionic valence state. X-ray photoemission spectroscopy revealed that Ti ions were Ti4+ and the valences of Mn ions were deduced to be mainly in the form of Mn2+ and/or Mn3+ for ceramics with low content of Mn, while the Ti ions were in the form of Ti3+ and Ti4+ and Mn ions were diverse valence states with the coexistence of Mn2+, Mn3+, and Mn4+ for ceramics with x?=?0.01 and 0.05. 相似文献
11.
We investigate the effects of doping and annealing on the dielectric properties of metal ions doped TiO2 ceramics. Colossal permittivity (CP) above 104 was observed in single Nb ion doped TiO2, which was dominated by electron transport related interfacial polarization. Moreover, the CP can be dropped to 120 when simultaneously introducing Mn ion into the sample. The disappearance of CP behaviors maybe due to the multivalence of Mn which would inhibit the reduction of Ti4+ to Ti3+, and thus reduce delocalized electrons. Interestingly, the CP was recovered for the (Nb+Mn) co-doped TiO2 after post-sintering heat treatment in N2 atmosphere. The recovery of CP in the sample after annealing can be ascribed to the semiconducting grain and the insulating grain boundary, according to impedance spectroscopy. We therefore believe that this work can help us understand the mechanism of CP from a new perspective. 相似文献
12.
The Co3O4 film anodes for oxygen evolution were prepared by a thermal decomposition method and their anodic polarization characteristics were investigated in alkaline solutions. As a result, the polarization characteristics were found to be greatly affected by the kind of metal substrates used. Especially when Fe was used as a substrate, some Fe species were proved to be doped in the Co3O4 layer during the electrode preparation and the resulting electrodes showed the attractive character for oxygen evolution. 相似文献
13.
C.R. Mariappan P. Kumar A. Kumar S. Indris H. Ehrenberg G. Vijaya Prakash R. Jose 《Ceramics International》2018,44(13):15509-15516
We report on the ion transport properties of Li1+xZr2-xYx(PO4)3 (0.05?≤ x?≤?0.2) NASICON type nanocrystalline compounds prepared through a Pechini-type polymerizable complex method. Structural properties were characterized by means of powder X-ray diffraction, Raman spectroscopy and electron microscopy with selected area electron diffraction. Impedance spectroscopy was utilised to investigate the lithium ion transport properties. Y3+ doped LiZr2(PO4)3 compounds showed stabilized rhombohedral structure with enhanced total ionic conductivity at 30?°C from 2.87?×?10?7 S?cm?1 to 0.65?×?10?5 S?cm?1 for x=0.05 to 0.20 respectively. The activation energies of Li1+xZr2-xYx(PO4)3 show a decreasing trend from 0.45?eV to 0.35?eV with increasing x from 0.05 to 0.20. The total conductivity of these compounds is thermally activated, with activation energies and pre-exponential factors following the Meyer-Neldel rule. The tanδ peak position shifts to the high-frequency side with increasing yttrium content. Scaling in AC conductivity spectra shows that the electrical relaxation mechanisms are independent of temperature. 相似文献
14.
Jose A. Vega 《Electrochimica acta》2010,55(5):1638-35
The effect of carbonate and bicarbonate anions on the oxygen reduction reaction was investigated in four alkaline solutions (pH ∼ 14) on a Pt disk type electrode with varying concentrations of carbonate and bicarbonate. The addition of carbonate and bicarbonate had two primary effects on the observed voltammetric behavior: i) The Tafel slope shifts positive with increasing carbonate/bicarbonate concentration, indicating that the carbonate anions may compete for surface adsorption sites; and ii) The dissolved oxygen concentration and diffusion coefficient are depressed with increasing anion concentration. Finally, adding CO2 to the cathode stream of an anion exchange membrane fuel cell caused an improvement in the device performance under fully hydrated conditions, suggesting that the fuel cell was operating at least partially under the carbonate cycle. 相似文献
15.
Peroxynitrous acid (ONOOH) was formed by the on-line rapid reaction of acidified hydrogen peroxide with nitrite in a simple flow system. A weak chemiluminescent (CL) signal was observed due to the production of singlet oxygen (1O2) when ONOOH reacted with NaOH, whereas the replacement of NaOH by Na2CO3 markedly enhanced the CL intensity. The predominant CL-enhanced pathway was achieved by the carbonate-catalyzed decomposition of peroxynitrite (ONOO−). Carbonate species was regenerated in the process, that is, carbonate acts as a catalyst. Based on the studies of CL and fluorescence spectra, a possible CL mechanism from the reaction of carbonate with ONOOH was proposed. In brief, ONOOH was an unstable compound in acidic solution and could be quenched into ONOO− in basic media. It was suggested that ONOO− reaction with excess HCO3− proceeded via one-electron transfer to yield bicarbonate ion radicals (HCO3√). The recombination of HCO3√ may directly generate excited triplet dimers of two CO2 molecules [(CO2)2*]. With the decomposition of this unstable intermediate to CO2, the energy was released by CL emission. The addition of uranine into carbonate solution caused enhancement of the CL signal, which was due to a part of excited triplet dimers of two CO2 molecules energy to transfer to uranine, resulting in two CL peaks. 相似文献
16.
Quoc Nghi Pham 《Electrochimica acta》2006,51(27):6186-6193
The potentiometric response of the Li+ ion-selective electrode based on the fast ion conductor Li3xLa2/3−xTiO3 (x = 0.10) membrane (named LLTO) as well as the impedance of the LLTO membrane/Li+ solution in either anhydrous or hydrated PC solvent have been carried out. A four-electrode configuration has been used for the investigation of the interfacial phenomenon. It has been shown that the LLTO membrane can be used to detect the Li+ activity in anhydrous solutions through a Li+ ion exchange mechanism. The potentiometric response shows a Nernstian behavior with a Li+ sensitivity of −72 mV/decade at 25 °C. This high sensitivity can be correlated to a localised hydroxylation of the oxide surface with the residual water present in the solution in combination to the Li+ exchange reaction. An apparent standard current density of 12 μA/cm2 and a charge-transfer coefficient of 0.29 have been determined. However, as water content in the electrolyte increases, the activity domain of the detection decreases to lead to the disappearance of the Li+ ion exchange mechanism in Li+ aqueous solution. This annihilation of the exchange process may be due to the predominant catalytic reaction of [Ti-O]− with H2O and/or to the formation of a water layer on the oxide surface. 相似文献
17.
Xiao-Liang Xia 《Electrochimica acta》2010,55(19):5301-1846
Gd2(Zr1−xNbx)2O7+x (0 ≤ x ≤ 0.2) ceramics are prepared via the solid state reaction process at 1973 K for 10 h in air. Gd2(Zr1−xNbx)2O7+x (x = 0.1, 0.2) ceramics exhibit an ordered pyrochlore-type structure, whereas Gd2Zr2O7 has a defective fluorite-type structure. The electrical property of Gd2(Zr1−xNbx)2O7+x ceramics is investigated by electrochemical impedance spectroscopy over a frequency range of 10 Hz to 8 MHz from 623 to 923 K. The electrical conductivity obeys the Arrhenius equation. The grain conductivity of Gd2(Zr1−xNbx)2O7+x ceramics varies with doping different Nb contents, and exhibits a maximum at the Nb content of x = 0.1 in the temperature range of 623-923 K. The conductivity in hydrogen atmosphere is a little bit higher than in air in the temperature range of 723-923 K, which indicates that the doping of Zr4+ by Nb5+ can increase the proton-type conduction and reduce the oxide-ionic conduction. The conduction of Gd2(Zr1−xNbx)2O7+x is not a pure oxide-ionic conductor. 相似文献
18.
Nripesh Kumar Alok Shukla Nitin Kumar Sushrisangita Sahoo Sugato Hajra R.N.P. Choudhary 《Ceramics International》2018,44(17):21330-21337
Nowadays, much attention is paid for the development of lead-free complex or mixed metal oxides, which can be utilized for multi-functional devices. This communication provides the information on synthesis (by mixed oxide route) and physical properties (structural, electrical and ferroelectric) of the polycrystalline sample of Bi(Fe0.9La0.1)O3 Analysis of the phase formation and basic crystal data of the material using X-ray diffraction (XRD) technique shows an orthorhombic symmetry with well-defined cell parameters. It has been shown that a small amount (10%) of La substitution at the Fe site of BiFeO3 suppresses the impurity phase usually observed during phase formation of BiFeO3. The average crystallite size, calculated through applying Scherrer's technique, was found to be 68?nm. For the study of surface morphology (grain size and distribution) of the compound, the scanning electron microscope (SEM) was used. The grains of different dimension were found homogeneously distributed at the entire surface of the sample. The La substitution strongly affects the capacitive (dielectric) and resistive (electrical) characteristics of bismuth ferrite in a wide range of frequency and temperature. The contributions of grains and grain boundaries in the capacitive as well as in the resistive properties of the material at different temperatures and frequencies were studied by means of the impedance spectroscopy technique. This study has provided numerous useful and interesting data which may find potential industrial applications. 相似文献
19.
A general, physico-chemical analysis of mass transfer rate promotion in the system CO2-potassium carbonate-water-promoter is presented. Different possible mechanisms of promoter action including homogeneous catalysis, “shuttle” mechanism and surface reactions are discussed and classified. A unified picture of promoter chemistry is presented, showing that differences between inorganic and organic promoters are predominently quantitative, not qualitative.The “shuttle” mechanism is analyzed for absorption. The analysis leads to the prediction that the CO2 mass transfer rate may be influenced by the liquid hold up. This is related to the fact that, although the reaction in the interface region may be fast enough to enhance the mass transfer rate, the different reaction in the bulk may not be fast enough to maintain chemical equlibrium. This complex type of chemical absorption process has not been considered previously in the literature. 相似文献
20.
Pitting corrosion of Pb in Na2CO3 solutions (pH=10.8) containing NaNO3 as a pitting corrosion agent has been studied using potentiodynamic anodic polarization, cyclic voltammetry and chronoamperometry techniques, complemented with scanning electron microscopy (SEM) examinations of the electrode surface. In the absence of NO3−, the anodic voltammetric response exhibits three anodic peaks prior to oxygen evolution. The first anodic peak A1 corresponds to the formation of PbCO3 layer and soluble Pb2+ species in solution. The second anodic peak A2 is due to the formation of PbO beneath the carbonate layer. Peak A2 is followed by a wide passive region which extends up to the appearance of the third anodic peak A3. The later is related to the formation of PbO2. Addition of NO3− to the carbonate solution stimulates the anodic dissolution through peaks A1 and A2 and breaks down the dual passive layer prior to peak A3. The breakdown potential decreases with an increase in nitrate concentration, temperature and electrode rotation rate, but increases with an increase in carbonate concentration and potential scan rate. Successive cycling leads to a progressive increase in breakdown potential. The current/time transients show that the incubation time for passivity breakdown decreases with increasing the applied anodic potential, nitrate concentration and temperature. 相似文献