Cobalt nano-particles have been prepared by reducing divalent cobalt species in an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide at room-temperature. Potentiostatic cathodic reduction of divalent cobalt species was conducted on a platinum mesh electrode at −2.0 V vs. Ag/Ag(I) in the ionic liquid, resulting in the change of color of the ionic liquid from purple to black. The transmission electron microscope observation of the ionic liquid after the potentiostatic cathodic reduction showed formation of cobalt nano-particles with the diameters from 2 to 10 nm.
Primary alumina is used as the raw material as well as the sorbent for fluoride in aluminum electrolysis. Secondary alumina is the product of primary alumina after absorbing fluoride in exhaust pot gas. The fluorine and mass loss during heating secondary alumina was measured to study the fluoride desorption process of alumina. It was found that during the heating of secondary alumina, HF emission was always combined with H2O escape at approximately 740°C or below. 47% fluorine in secondary alumina desorbed in the form of HF at 30–740°C, while the rest 53% desorbed in the form of chiolite at 740–1100°C.
The electrochemical behavior of graphite anode in KF-KBF4 molten salt at 500°C was studied by means of cyclic voltammetry, electrochemical impedance spectroscopy and chronopotentiometry techniques in this present work. The results showed that I-type “CF” compound is formed at 1.5 V vs. Pt-QRE, and II-type “CF” compound is formed at 2.1 V, while fluorine gas is formed at 4.9 V. The electrochemical reaction at 1.5 V is quasi-reversible, while the electrochemical reaction at 2.1 V is irreversible. The resistance of II-type “CF” compound is higher than I-type “CF” compound, and the value of charge transfer coefficient (β) for electrochemical formation II-type “CF” compound is calculated to be 0.26.
The molten state of simulated high-level waste glass and the behavior of ruthenium element in the melt were investigated by using synchrotron radiation based X-ray imaging technique. Melting, generating and moving of bubbles, condensation and sedimentation of ruthenium element were observed dynamically in continuous 12-bit gray-scale images from the CCD camera. X-ray intensity was obtained easily by digitalizing gray-scale values in the image. The existence of ruthenium element, which is one of the most important insoluble residues in the recycle process of spent nuclear fuels, is emphasized as a black color in the CCD image at X-ray energy higher than the Ru K-edge. The position sensitive imaging X-ray absorption fine structure (XAFS) measurement was also performed to clarify a chemical state of ruthenium element in the melt.
The anodic dissolution of copper was examined in oxygenated sulfuric acid solution. A characteristic property of the anodic process is that the oxidation process Cu → Cu2+ involves the detectable intermediate Cu+, which should disproportionate into Cu and Cu2+ in the thermodynamic equilibrium state. On the other hand, H2O2 was formed during anodic dissolution in oxygenated solution by the reaction of Cu+ with O2. The intermediate Cu+ and the byproduct H2O2 were detected in this study using a rotating ring-disk electrode. The anodic dissolution process including the role of oxygen was elucidated through the detection of Cu+ and H2O2. The decrease in the activity of Cu+ in the presence of O2 involved a negative shift of the partial current of Cu → Cu2+ (or Cu+), and resulted in a negative shift of the corrosion potential with increasing stirring rate of the solution. In addition, Cu+ was found to be not a transient intermediate, but rather, a thermodynamic equilibrium species. The acceleration of the corrosion rate in the presence of O2 was elucidated successfully to be due to the couple of the partial currents for Cu → Cu+ and O2 → H2O2.
For use of the large-sized Ni-MH battery in the social-infrastructure, it is important to improve its self-discharge suppression and overdischarge resistance as well as its high-power and long cycle-life performances. The use of the RE0.9Mg0.1Ni3.9Al0.2 alloy as the negative electrode of a Ni-MH battery effectively suppressed the self-discharge compared to the use of the conventional AB5-type alloy. Meanwhile, a carbon-coated Ni(OH)2 prepared using a fluid-bed coating method exhibited a better overdischarge resistance than that using the conventional CoOOH-coated one. The Co, which is an expensive rare metal, is completely removed from the Ni-MH battery using these Co-free electrodes. The Co-free Ni-MH battery combines several good battery characteristics, such as a low self-discharge and overdischarge resistance.
Direct electrolytic reduction of SiO2 was investigated in molten CaCl2 at 1123 K as a fundamental study to develop a continuous process for solar-grade Si production. Several different types of SiO2 granules, as well as SiO2 pellets, were successfully reduced to Si on the bottom cathode of a Si plate. Three parameters were varied in the reduction of SiO2 granules: electrode potential, layer thickness of the SiO2 granules, and SiO2 particle size. The reduction rate was evaluated by the magnitude of the reduction current. The main factor determining the reduction rate was the diffusion of O2− ions inside the reduced porous Si layer filled with the electrolyte. Another factor which influenced the reduction rate was the contact resistance between Si granules.
Carbon nanotubes (CNTs) which are directly grown on nanoporous alumina templates by chemical vapor deposition are modified by acid-treatment or/and annealing and then a negative electrode is obtained. Next, alumina is deposited onto the nanoporous alumina templates with the grown as well as modified CNTs by a chemical liquid phase deposition method and then a positive electrode is obtained. Finally, the negative electrode coated with solid electrolyte polymerized by changing weight ratios between iron(III) p-toluenesulfonate hexahydrate-6 H2O and 3,4-ethylenedioxythiophene is assembled with the positive electrode into an aluminum capacitor. The capacitance of the aluminum capacitor reaches a maximum at 6 of the weight ratio between iron(III) p-toluenesulfonate hexahydrate-6 H2O and 3,4-ethylenedioxythiophene. Furthermore, the highest capacitance as well as operation potential of the aluminum capacitor and the lowest leakage current density of the aluminum capacitor at the 10000th cycle of potential cycling are obtained by the CNTs being treated with acid and annealed. Moreover, the decreasing rates of the capacitance as well as operation potential of the aluminum capacitor and the increasing rate of the leakage current density of the aluminum capacitor for the raw CNTs are quicker than those for the CNTs treated with acid or/and annealed.