The leaching of chalcopyrite with cupric chloride

A comparative study of electrochemical leaching and chemical leaching of chalcopyrite was performed mainly at 343 K to elucidate the leaching mechanism of chalcopyrite with CuCl₂. Also, the morphology of the leached chalcopyrite surface was studied by using a single chalcopyrite crystal. The leaching with CuCl₂ produced a porous elemental sulfur layer on the chalcopyrite surface, showing a similar morphology to that produced during leaching with FeCl₃. The leaching kinetics were found to be linear over an extended period, followed by an acceleration stage, as a result of an increase in the reaction surface area. The leaching rate of chalcopyrite was proportional to C(CuCl₂)^0.5, whereas it was inversely proportional to C(CuCl)^0.5. The mixed potential of chalcopyrite exhibited a 66 mV decade⁻¹ dependency upon C(CuCl₂), and—69 mV decade⁻¹ upon C(CuCl). Based on these observations together with other findings, an electrochemical mechanism involving the oxidation of chalcopyrite and CuCl ₋ ² and the reduction of CuCl⁺ was proposed. The Tafel plot between the mixed potential and the current density obtained by converting the rate of chemical leaching gave a straight line whose slope was in good agreement with that of the electrochemical leaching. These findings strongly support the electrochemical mechanism of chalcopyrite leaching with cupric chloride.     

Complete erasing of ghost images on computed radiography plates and role of deeply trapped electrons

Computed radiography (CR) plates made of europium-doped Ba(Sr)FBr(I) were simultaneously exposed to filtered ultraviolet light and visible light in order to erase ghost images, i.e., latent image that is unerasable with visible light (LIunVL) and reappearing one, which are particularly observed in plates irradiated with a high dose and/or cumulatively over-irradiated. CR samples showing LIunVLs were prepared by irradiating three different types of CR plates (Agfa ADC MD10, Kodak Directview Mammo EHRM2, and Fuji ST-VI) with 50 kV X-ray beams in the dose range 8.1 mGy—8.0 Gy. After the sixth round of simultaneous 6 h exposures to filtered ultraviolet light and visible light, all the LIunVLs in the three types of CR plates were erased to the same level as in an unirradiated plate and no latent images reappeared after storage at 0 °C for 14 days. With conventional exposure to visible light, LIunVLs consistently remained in all types of CR plates irradiated with higher doses of X-rays and latent images reappeared in the Agfa M10 plates after storage at 0 °C. Electrons trapped in deep centers cause LIunVLs and they can be erased by simultaneous exposures to filtered ultraviolet light and visible light. To study electrons in deep centers, the absorption spectra were examined in all types of irradiated CR plates by using polychromatic ultraviolet light from a deep-ultraviolet lamp. It was found that deep centers showed a dominant peak in the absorption spectra at around 324 nm for the Agfa M10 and Kodak EHRM2 plates, and at around 320 nm for the Fuji ST-VI plate, in each case followed by a few small peaks. The peak heights were dose-dependent for all types of CR samples, suggesting that the number of electrons trapped in deep centers increases with the irradiation dose.     

Remote sensing system for spatial electric field strength using free space light transmission

Most of the breakdowns in an electric power system are caused by lightning to the tower used for high‐voltage transmission wires. To avoid accidents due to lightning, it would be desirable to develop a measurement system for the spatial electric field distribution around the tower. We have developed a new system that can measure the electric field around the steel tower for electric power transmission by using an optical electric sensor. In conventional methods, the sensor is generally illuminated by light transmitted by optical fibers. On the other hand, the new measurement system illuminates the Pockels sensor directly by using a laser to measure the far electric field. Furthermore, our newly proposed feedback system makes it possible to measure the spatial electric field without concern for the change of Pockels sensor's operation point influenced by temperature change. This system is applicable as a remote sensing system to monitor the spatial electric field around a high‐voltage transmission line. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(2): 10–19, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20552     

Simulation of the oregonator model by using deterministic ARMS

We propose a deterministic method for simulating chemical reactions, deterministic abstract rewriting system on multisets (DARMS), which is based on the concept of mass action low. The feasibility and utility of DARMS are demonstrated by applying it to the oregonator, which is a well-known model of the Belousov-Zhabotinskii (BZ) reaction. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Reduction of in vitro allergenicity of buckwheat Fag e 1 through the Maillard-type glycosylation with polysaccharides

A major allergenic protein of buckwheat, Fag e 1 prepared from common buckwheat (Fagopyrum esculentum), was covalently linked with food-grade polysaccharides, arabinogalactan or xyloglucan through the controlled dry-heating at 60 °C under 65% relative humidity. The introduction of polysaccharide chain onto the molecular surface of Fag e 1 reduced the allergenicity of Fag e 1. The results revealed that the Maillard-type glycosylation of Fag e 1 with polysaccharides brought about a drastic reduction of the reactivity against human sera of buckwheat-allergy subjects, using immuno dot-blotting, QCM analysis and ELISA. In addition, the glycosylation of Fag e 1 yielded a great improvement of its surface functionality. Solubility of Fag e 1 at the neutral pH was substantially increased up to 13.5 times and 9.6 times by the conjugation with arabinogalactan and xyloglucan, respectively. Emulsifying properties of Fag e 1 were also improved by the glycosylation, of which both emulsifying activity and emulsion stability were more than 6 times higher than those of the native protein.     

Fracture Strength and Microstructure of β-SiAlON with Hafnia Addition

The influence of HfO₂ addition on the fracture strength and microstructure of ß-SiAlON ceramics sintered from Si₃N₄ and Al₂O₃ powders was investigated. The strength was increased by the addition of HfO₂, from ∼500 MPa to 700 MPa, and was almost constant from ambient temperature to 1300°C. Monoclinic HfO₂ grains that were distributed in the SiAlON grain boundaries had a flat shape (∼20 nm thick) and were surrounded by an amorphous phase. The aluminum concentration in ß-SiAlON in the samples with an Al₂O₃ starting composition of 15 wt% was decreased by the addition of HfO₂. The amount of secondary phases was very small at grain boundaries between the SiAlON grains; amorphous phases were observed infrequently at the triple points but were very small (∼20 nm). The effects of HfO₂ addition on the mechanism of the microstructure development and fracture strength are discussed.     

Carrier density control in the La2−x Sr1+x Cu2O6+y system

The effect of strontium and oxygen content variation is systematically studied in the La_2−x Sr_1+x Cu₂O_6+y system. The reason for the absence of superconductivity in this system is discussed.     

Organocatalytic Enantioselective Conjugate Addition of Malonic Acid Half Thioesters to Coumarin‐3‐carboxylic Acids Using N‐Heteroarenesulfonyl Cinchona Alkaloid Amides

We disclose herein an efficient enantioselective conjugate addition reaction between coumarin‐3‐carboxylic acids and malonic acid half thioesters (MAHTs). The reaction was catalyzed by N‐heteroarenesulfonyl Cinchona alkaloid amides to afford double‐decarboxylative conjugate addition products in good yield with high enantioselectivity. The reaction of various coumarin‐3‐carboxylic acids with MAHTs gave products in high yield with high enantioselectivity.