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1.
The Fray Farthing and Chen (FFC) and Ono and Suzuki (OS) processes were developed for the reduction of titanium oxide to titanium metal by electrolysis in high temperature molten alkali chloride salts. The possible transposition to CeO 2 reduction is considered in this study. Present work clarifies, by electro-analytical techniques, the reduction pathway leading to the metal. The reduction of CeO 2 into metal was feasible via an indirect mechanism. Electrolyses on 10 g of CeO 2 were carried out to evaluate the electrochemical process efficiency. Ca metal is electrodeposited at the cathode from CaCl 2–KCl solvent and reacts chemically with ceria to form not only metallic cerium, but also cerium oxychloride. 相似文献
2.
Polyaniline (PANI) synthesized by a potentiostatic method at 4 °C in 1 M HNO 3 with the polymerization charge density equal to/less than 0.45 C cm −2 was demonstrated to exhibit ideally capacitive characteristics (i.e. high reversibility and high-power property) with a high specific capacitance of 210 F g −1 for the application of electrochemical supercapacitors in NaNO 3. Influences of the polymerization charge density (i.e. the polymer loading) and the polymerization temperature on the capacitive characteristics of PANI films compared by both cyclic voltammetry and charge-discharge technique were reasonably correlated with their structural properties examined by X-ray photoelectron spectroscopy (XPS). The highest specific capacitance of a PANI film polymerized at 4 °C was attributed to its lowest density of structure defects. The surface morphology of these PANI films was examined by a scanning electron microscope (SEM). 相似文献
3.
The reduction and oxidation processes on platinum and glassy carbon electrodes in molten LiCl-KCl eutectic containing UCl 3 were investigated by cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS) in the temperature range 660-780 K. Two redox peaks have been observed in the cyclic voltammograms corresponding to the two redox reactions U(IV)/U(III) and U(III)/U which are found to be reversible and quasi-reversible, respectively. The reduction potentials of U(IV)/U(III) and U(III)/U are −0.325 and −1.490 V versus reference electrode (0.1 mol% AgCl in the LiCl-KCl), respectively at 700 K. Chronopotentiometric measurements confirm the three-electron transfer during the reduction of U(III) to U metal. Electrochemical impedance spectroscopy data at various potentials were interpreted either as diffusion, adsorption or reduction process by nonlinear fit of the impedance data to the simulated equivalent circuits. 相似文献
4.
Electrochemical reduction of solid Cr 2O 3, in the form of an assembled cathode of porous pellets attached to a current collector, to chromium powder was investigated in molten CaCl 2 and a molten equimolar mixture of CaCl 2 and NaCl. The study focused on the influence of pellets preparation conditions, cell voltages and temperatures on the reduction process. Analyses were reported of the characteristics of the current-time plots of the constant voltage electrolysis under different conditions, cyclic voltammograms of solid Cr 2O 3 in the molten equimolar mixture of CaCl 2 and NaCl, the microstructures and elemental compositions of the reduced pellets. Particularly, attention was given to the intermediate product of the electrolysis, calcium chromites of various stoichiometries, aiming to achieve a better understanding and optimisation of the reduction process. 相似文献
5.
The electrochemical behaviour of the Th(IV)/Th system was examined in molten LiF-CaF 2 medium on inert (molybdenum), reactive (nickel) and liquid (bismuth) electrodes in the 810-920 °C temperature range by several electrochemical techniques. Experimental results showed that (i) thorium fluoride was reduced in a single step exchanging 4 electrons and limited by thorium ions diffusion in the solution, (ii) the oxide ions induce the precipitation of Th(IV) in the form of thorium oxide (ThO 2), in a process involving as intermediate compound a soluble oxifluoride (ThOF 2), (iii) the reduction of thorium ions on reactive (Ni and liquid Bi) electrodes yields compounds Ni-Th and Bi-Th with a potential shift of around 0.7 V (for Ni and Bi) more anodic than the reduction of Th(IV) on inert substrate. 相似文献
6.
Physicochemical properties of ZnCl 2-NaCl-KCl eutectic melt were studied at 200-300 °C for the first time. Firstly, it was reconfirmed that the eutectic composition is ZnCl 2:NaCl:KCl = 0.6:0.2:0.2 in mole fraction, and that the eutectic temperature is 203 °C. Then, the density, viscosity, and ionic conductivity of the ZnCl 2-NaCl-KCl eutectic melt were measured at 200-300 °C. At 250 °C, the density was 2.43 g cm −3, the viscosity was 42.0 cP and the ionic conductivity was 8.53 S m −1. The temperature dependencies of density and ionic conductivity were well fitted by the VTF equations with the same ideal glass transition temperature of 283 K (10 °C). It was found that the melt obeys the fractional Walden's rule which is explained by the decoupling effect. The electrochemical window of the melt was determined to be 1.7 V at 250 °C with the cathode limit being zinc metal deposition and the anode limit being chlorine gas evolution. 相似文献
7.
The composition and corrosion performance of galvanised steel treated by immersion in cerium nitrate solution was investigated by electrochemical techniques and surface analysis. The surface film consists of a mixture of Ce(III) and Ce(IV) compounds, being very rich in Ce(III) in the first instants of the deposition process and becoming gradually enriched in the more oxidised form, Ce(IV). The presence of this film on the surface hinders the corrosion reaction by reducing the rate of both the cathodic and the anodic reactions. The film becomes thicker but more uneven when the time of film growth increases, with the development of defects in the film, which in contact with electrolyte behaves anodic with respect to the covered areas of the surface. These thicker films have revealed lower resistance to corrosion initiation. 相似文献
8.
The electrochemical behaviour of SmF 3 is examined in molten LiF–CaF 2 medium on molybdenum and nickel electrodes. A previous thermodynamic analysis suggests that the reduction of SmF 3 into Sm proceeds according to a two-step mechanism: The second step occurs at a potential lower than the reduction potential of Li+ ions. Cyclic voltammetry, chronopotentiometry and square-wave voltammetry were used to confirm this mechanism and the results show that it was not possible to produce samarium metal in molten fluorides on an inert cathode (molybdenum) without discharging the solvent. The electrochemical reduction of SmF3 is limited by the diffusion of SmF3 in the solution. The diffusion coefficient was calculated at different temperatures and the values obtained obey Arrhenius’ law. For the extraction of the samarium from fluoride media, the use of a reactive cathode made of nickel leading to samarium–nickel alloys is shown to be a pertinent route. Cyclic voltammetry and open-circuit chronopotentiometry were used to identify and to characterise the formation of three alloys: liquid Sm3Ni and a compact layer made of SmNi3 and SmNi2. 相似文献
9.
Effects of NaI as an additive on electrodeposition of Al coatings in AlCl 3-NaCl-KCl(80-10-10 wt-%)molten salts electrolyte at 150°C were investigated by means of cyclic voltammetry,chronopotentiometry,scanning electron microscopy and X-ray diffraction(XRD).Results reveal that addition of NaI in the electrolyte intensifies cathodic polarization,inhibits growth of Al deposits and increases number density of charged particles.The electrodeposition of Al coatings in the AlCl 3-NaCl-KCl molten salts electrolyte proceeds via three-dimensional instantaneous nucleation which however exhibits irrelevance with NaI.Galvanostatic deposition results indicate that NaI could facilitate the formation of uniform Al deposits.A compact coating consisting of Al deposits with an average particle size of 3μm was obtained at a current density of 50 mA?cm ?2 in AlCl 3-NaCl-KCl molten salts electrolyte with 10 wt-%NaI.XRD analysis confirmed that NaI could contribute to the formation of Al coating with a preferred crystallographic orientation along(220)plane. 相似文献
10.
To improve the oxidation resistance of TiAl intermetallic compound under high temperature condition, cathodic co-deposition of Al-Cr and Al-Ni alloy was carried out by constant potential control or potential pulse control in AlCl 3-NaCl-KCl molten salt containing CrCl 2 and/or NiCl 2 at 423 K. Cathodic reduction of Ni and Cr starts at potential of 0.8 and 0.15 V versus Al/Al 3+ in the molten salt, respectively. The co-deposition of Al, Cr, and Ni occurred at potentials more negative than −0.1 V to form a mixture of intermetallic compounds of Cr 2Al, Ni 3Al, and Al 3Ni. Concentration of Cr in the deposit was enhanced to 43 at% at −0.1 V; however, concentration of Ni in the deposit was 6 at% at the same potential. The concentration of Ni further decreased with more negative potential to 1 at% at −0.4 V. The potential pulse technique enhanced the Ni concentration in the deposit to about 30 at%, due to anodic dissolution of Al content from the deposit at the higher side of potential on the potential pulse electrolysis. 相似文献
11.
The electrochemical reduction of GdF 3 was studied in the LiF-CaF 2 eutectic (77/23 mol%) on a tantalum electrode for various GdF 3 concentrations in the 800-900 °C temperature range. A previous thermodynamic study showed that gadolinium trifluoride is reduced into metal in a one-step process:
12.
This work presents a study on the electrochemical properties of AmCl 3 in a molten LiCl-KCl eutectic, at a temperature range of 733-833 K. Transient electrochemical techniques, such as cyclic voltammetry and chronopotentiometry, on inert metallic tungsten working electrode have been used to investigate the reduction mechanism of Am 3+ ions. The results show that Am 3+ is reduced to Am metal by a two-step mechanism corresponding to the Am 3+/Am 2+ and Am 2+/Am 0 transitions. Formal standard potentials of Am 3+/Am 2+ ( versus Cl 2/Cl − at 733 K) and Am 2+/Am 0 ( versus Cl 2/Cl − at 733 K) redox couples as well as diffusion coefficients of Am 3+ and Am 2+ (2.4 × 10 −5 and 1.15 × 10 −5 cm 2 s −1 at 733 K, respectively) have been calculated at three different temperatures. In the studied range of temperature, the DAm3+/ DAm2+ ratio was found to be around 2. In addition, thermodynamic properties have been calculated for Am 3+ () and Am 2+ () and compared to thermodynamic reference data in order to estimate activity coefficients (Am 3+ = 4.7 × 10 −3 and Am 2+ = 2.7 × 10 −2 at 733 K) in the molten LiCl-KCl eutectic. 相似文献
13.
Ordered nanoporous carbon (ONC) was comprehensively tested for the first time as electrode material in lithium-ion battery. Structure characterization shows the order nanoporous structure and tiny crystallite structure of as-synthesized ONC. The electrochemical properties of this carbon were studied by galvanostatic cycling and cyclic voltammetry. Of special interest is that ONC gave no peak on its positive sweep of the cyclic voltammetry, which was different from other known anode materials. Besides, X-ray photoelectron spectroscopy (XPS) and XRD were also used to investigate the electrochemical characteristics of ONC. 相似文献
14.
The Li content and anion lattice of Li 4SiO 4 were modified to improve ionic conductivity. Li 2CO 3 and Si 3N 4 were mixed in a ratio of Li/Si?=?4.5 and heated in NH 3 at 820?°C, which resulted in the formation of the oxynitride, Li 4.1SiO 3.9N 0.1. Powder X-ray diffraction analyses revealed Li 4.1SiO 3.9N 0.1 and Li 4SiO 4 to be isostructural with a subtle variation in the lattice constants. Diffuse-reflectance absorption spectroscopy, however, showed a significant decrease in the band gap, from 5.6?eV in Li 4SiO 4 to 4.8?eV in Li 4.1SiO 3.9N 0.1. X-ray photoelectron spectra of the Li 1 s and Si 2 p levels revealed enhanced lattice covalency in Li 4.1SiO 3.9N 0.1 compared to the oxide phase. The ionic conductivity of Li 4SiO 4 and Li 4.1SiO 3.9N 0.1 were measured by ac impedance spectroscopy over the temperature range 100–400?°C. Non-linear fitting analysis of the equivalent circuit revealed that the ionic conductivity of Li 4.1SiO 3.9N 0.1 was approximately one order of magnitude higher than that of Li 4SiO 4. 相似文献
15.
The electrochemical behaviour of the Eu(III)/Eu(II) system was examined in the molten eutectic LiF–CaF 2 on a molybdenum electrode, using cyclic voltammetry, square wave voltammetry and chronopotentiometry. It was observed that EuF 3 is partly reduced into EuF 2 at the operating temperatures (1073–1143 K). The electrochemical study allowed to calculate both the equilibrium constant and the formal standard potential of the Eu(III)/Eu(II) system. The reaction is limited by the diffusion of the species in the solution; their diffusion coefficients were calculated at different temperatures and the values obey Arrhenius’ law. The second system Eu(II)/Eu takes place out of the electrochemical window on an inert molybdenum electrode, which inhibits the extraction of Eu species from the salt on such a substrate. 相似文献
16.
Sintered solid porous pellets of copper sulfide (Cu 2S) and Cu 2S/FeS were electrolysed at a cell voltage of 2.2-2.8 V to elemental Cu, S and Cu, Fe, S, respectively in molten CaCl 2-NaCl at 800 °C under the protection of argon gas. The process parameters for optimal electrolysis are presented. The electrolysis products are characterized by microscopic techniques and XRD. The product characteristics are linked to the process parameters. The direct electrolysis of the sulfide to copper with the emission of elemental sulphur offers an attractive green process route for the treatment of copper ore. 相似文献
17.
The effects of pretreatment of catalyst on its surface properties and the HDS activity of a 0.49% Ru/Al 2O 3 catalyst were studied in a single-pass, differential microreactor. The surface properties of the catalyst were measured by NH 3-TPD and XPS analysis. The Ru/Al 2O 3 catalyst was pretreated in three ways: reduced in H 2 (Ru-R catalyst), oxidized in air and subsequently reduced in H 2 (Ru-OR catalyst), or sulfided in H 2S/H 2 (Ru-S catalyst). Three types of peaks (low, middle, and high temperatures) were observed in the NH 3-TPD study. The predominant high-temperature peak was observed for both the Ru-OR and Ru-S catalyst, pretreated at 300°C. Mass spectrometry showed that the high-temperature peak in NH 3-TPD consisted of N 2 and H 2 formed from the decomposition of NH 3 on the ruthenium sites. NO adsorption of unsaturated Ru species was related to the low-temperature peak in the NH 3-TPD. The XPS analysis showed that the peaks at 279.9 eV, 280.6 eV, and 282.5 eV were ascribed to metallic ruthenium, RuO 2, and RuO 3, respectively. The low-, middle-, and high-temperature peaks were assigned to RuO 2, acid sites on alumina, and metallic Ru, respectively. Metallic ruthenium was effective in the HDS of thiophene and the decomposition of NH 3. 相似文献
18.
We report results on the adsorption and desorption of H 2S on polycrystalline UO 2 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. H 2S is found to adsorb molecularly at 100 K on the polycrystalline surface, and desorption of molecular H 2S occurs at a peak temperature of 140 K in TPD. Adsorption rates of sulfur as a function of H 2S 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
19.
Titania photocatalysts were synthesised by the molten salts method by reaction of a titanium precursor with three different alkali metal nitrates (LiNO 3, NaNO 3, KNO 3). The titania powders obtained have been characterised using TEM, XRD, BET and UV-Vis absorption spectroscopy. Their photoactivities were evaluated by degrading a commercial sulfonylurea herbicide, Prosulfuron ®. It has been found that the rate constants increased in the following order: Li 2 prepared in KNO3, with a rate constant 1.4 times smaller than that of P25. The effect of calcination was also studied, especially for the sample prepared in NaNO3 (TiO2[Na]). An improvement in photocatalytic activity was observed when TiO2[Na] was calcined in the region of 700–800 °C. Even though the photocatalytic activities obtained did not exceed or even equal to that of Degussa P25, nevertheless, this study constitutes the first attempt to synthesise titania photocatalysts by the molten salts method. 相似文献
20.
Electrochemical codeposition of Mg, Li, and Zn on a molybdenum electrode in LiCl-KCl-MgCl 2-ZnCl 2 melts at 943 K to form Mg-Li-Zn alloys was investigated. Cyclic voltammograms (CVs) showed that the potential of Li metal deposition, after the addition of MgCl 2 and ZnCl 2, is more positive than the one of Li metal deposition before the addition. Chronopotentiometry measurements indicated that the codeposition of Mg, Li, and Zn occurs at current densities lower than −0.78 A cm −2 in LiCl-KCl-MgCl 2 (8 wt.%) melts containing 1 wt.% ZnCl 2. Chronoamperograms demonstrated that the onset potential for the codeposition of Mg, Li, and Zn is −2.000 V, and the codeposition of Mg, Li, and Zn is formed when the applied potentials are more negative than −2.000 V. X-ray diffraction (XRD) indicated that Mg-Li-Zn alloys with different phases were prepared via galvanostatic electrolysis. The microstructure of typical α + β phase of Mg-Li-Zn alloy was characterized by optical microscope (OM) and scanning electron microscopy (SEM). The analysis of energy dispersive spectrometry (EDS) showed that the elements of Mg and Zn distribute homogeneously in the Mg-Li-Zn alloy. The results of inductively coupled plasma analysis showed that the chemical compositions of Mg-Li-Zn alloys are consistent with the phase structures of the XRD patterns, and that the lithium and zincum contents of Mg-Li-Zn alloys depend on the concentrations of MgCl 2 and ZnCl 2. 相似文献
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