Morphological changes and their thermal conductivities of MgO crystals containing various impurities (B,Ca, Si)

MgO is industrially produced from seawater or dolomite as the raw material. MgO synthesized from seawater has a relatively low impurity concentration. However, these impurities strongly affect the fine structure and physical properties (especially the thermal conductivity) of MgO. In this research, the influence of impurity concentration on the MgO grain growth and its thermal conductivity was investigated. The processing conditions for MgO powder synthesis were optimized by a polymer complex method using magnesium nitrate hydrate, citric acid, ethylene diamine, and chemical compounds containing B, Ca, or Si, which are the main impurities of MgO produced from seawater. The morphology and phase composition of the MgO powders were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). The morphological changes and differences in the thermal conductivity of MgO crystalline systems containing impurities (B, Ca, and/or Si) were clarified, and the relationship between the fine structure of MgO crystals containing impurities and their thermal conductivities was described in detail.     

pH-independent fluorescent chemosensor for highly selective lithium ion sensing

Since lithium salts are used as pharmaceutically active compounds against manic-depressive psychosis, there is a demand to monitor the lithium concentration in blood in the narrow range of 0.6-1.2 mM effectively and safely. Here we report on an optical sensor approach for the determination of Li+, based on the design and synthesis of a novel lithium fluoroionophore KLI-1 and its polymer immobilizable derivative KLI-2, and the application to an optode. The novel lithium fluoroionophores rely on a tetramethyl "blocking subunit" bearing 14-crown-4 as a Li+-selective binding site and 4-methylcoumarin as a fluorophore, intramolecularly connected to show ICT-type wavelength shift for ratiometric fluorescence measurements. The fluoroionophores showed high selectivity for Li+ with binding-induced blue shift in the fluorescence spectra, no response to major biological interfering cations (K+, Ca2+, Mg2+), a selectivity of log kLi+,Na+ = -2.4 over Na+ in solution, and no response to pH in the range of pH 3-10. A hydrophilic optode membrane with KLI-2 immobilized also showed good selectivity for Li+, pH independence in the physiological range (pH 6-8), and fully reversible signal changes. KLI-1 and KLI-2 are excellent Li+ fluorescent chemosensors that can be applied to quantitative measurements of lithium in clinical samples, although possible interference from Na+ has to be considered at the lower therapeutic level of Li+.     

Effect of tin addition on mesoporous silica thin film and its application for surface photovoltage NO2 gas sensor

Self-ordered and structure-controlled transparent films of tin-modified mesoporous silica (Sn/Si ratio of 0.5-3%) were first prepared using a molecule surfactant template method employing spin coating. A surface photovoltage (SPV) NO(2) gas sensor was then fabricated using these self-ordered tin-modified mesoporous silica thin films based on a metal-insulator-semiconductor structure. Highly sensitive tin-modified mesoporous silica was obtained that could detect NO(2) gas concentrations of as low as 300 ppb at room temperature. The detection mechanism for NO(2) is believed to involve both the surface area, which contributes to the change in dielectric constant, and the amount of tin incorporated, which contributes to the change in charge. It was found that, in this SPV sensor, the optimal Sn/Si ratio of 0.5% delivered record-high sensing performance.     

Deoxidation of molten copper with a rotating graphite cylinder

The kinetics of deoxidation of molten copper by the “vacuum-suction degassing” (VSD) method is investigated. The molten copper is deoxidized by a rotating porous graphite tube immersed in the copper bath. The inside space of the porous graphite tube is evacuated so that the CO gas formed at the graphite-metal interface is removed through the tube wall. The experimental results suggest that the mass transfer of oxygen in the metal phase controls the reaction rate. The kinetic data are arranged with a first-order rate equation. At (ppm O)≥10, the rate constant increases by decreasing the porosity of the graphite and increasing the thickness of the tube wall. This result suggests that the suction of CO gas weakens CO bubble stirring and, thereby, the mass transfer at the tube-melt interface. However, when the rate of CO suction becomes comparable to or larger than the CO gas evolution rate, the effect of CO stirring becomes negligible. This situation appears under the conditions of high porosity and large wall thickness at (ppm O) ≥ 10. At the low oxygen concentration range of (ppm O) ≤ 4, the effect of CO stirring becomes negligible, regardless of the CO suction condition, because of the considerably low CO formation rate. The achievement of deoxidation by the VSD method is evaluated in connection with the final oxygen concentration.     

Role of Steric Hindrance in the Performance of Superplasticizers for Concrete

Interparticle potential energy calculations were performed to investigate the mechanisms by which a new class of concrete admixtures, generally referenced as poly(carboxylic acid)-type (PC) superplasticizers, which aid in dispersing cement particles, are formed. These calculations consisted of long-range Van der Waals, electrostatic, and steric interactions. The repulsive potential that resulted from electrostatic interactions was negligible, which would allow cement particles to flocculate in the absence of steric contributions. A model was developed to describe the adsorption behavior of these superplasticizers, which consisted of grafted polyethylene oxide (PEO) chains on a PC backbone on cement surfaces. Using this adsorption model, the influence of the length of the PEO molecular chain and the density per unit area on the steric contribution was quantified. Steric hindrance effects were the dominant stabilizing mechanism in this system. As expected, enhanced stability was observed with increasing adlayer thickness (and/or density). The results of this study may be useful in designing the molecular structure of this new and important class of dispersion aids for cement-based systems.     

Long-term results of emergency coronary artery bypass grafting

Growth of the thermoacidophilic Gram-positive bacterium Alicyclobacillus acidocaldarius strain ATCC 27009 on maltose resulted in the increased production of a protein with apparent molecular mass of 40 kDa. By metabolic labelling with 14C-palmitic acid, the 40-kDa protein was identified as a lipoprotein. The protein exhibited maltose-binding activity at pH 3.5, as demonstrated by chromatography on cross-linked amylose. Partial amino acid sequence analysis revealed that the 40-kDa protein corresponds to the product of an open reading frame downstream from the amylase gene (amy) that displays similarity to enterobacterial maltose-binding proteins.     

Synthesis of LiCoO2 from cobalt—organic acid complexes and its electrode behaviour in a lithium secondary battery

Well-crystallized, layered LiCoO₂ has been prepared by heating cobalt—organic acid complexes (such as malic acid and succinic acid) at 900 °C in air after preheating at 400 °C (2 h) and at 650 °C (6 h). LiCoO₂ obtained by this method shows a high (003) peak intensity and low (104) or (101) intensities in X-ray diffraction (XRD). The first discharge capacity of LiCoO₂ obtained from this method in ester-based electrolyte is 132 mA h g⁻¹ on cycling between 4.3 and 3.7 V. The value is larger than that obtained by the conventional method. X-ray diffraction studies and open-circuit voltage curves show the presence of at least two types of reaction. A two-phase reaction occurs in the region of 0.71<χ <1.0 in Li_xCoO₂. The lithiation proceeds as a homogeneous reaction together with expansion of the c-axis in the region of 0.47<χ<0.71. The expansion of the c-axis againstΔχ at x=0.56 corresponds well with the voltage jump observed in the charge/discharge curves.     

SiC microsphere derived from phenolic resin—Ethyl silicate heterogeneous precursors with carbothermic reduction

Heterogeneous precursors for SiC particles were synthesized from viscous phenolic resin and tetraethyl orthosilicate with hastening ethanol removal process in a concentrated state. In the pyrolysis products, spherical carbon domains with diameter of several micrometers were embedded in the SiO₂‐C matrix. After the carbothermic reduction process at 2073 K, SiC‐C spheres were obtained with an SiC yield of ～80%, while the carbon domains acted as templates of the SiC‐C spheres with complete disappearance of the SiO₂‐C matrix area. After the carbon burned out, some of the spheres possessed a hollow structure. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1612–1618, 2004     

Fusion safety and environmental R&D tasks in Japan

This paper aims at listing and evaluating the status of all the research and development (R&D) tasks necessary for the construction of a safe and environmentally benign fusion experimental reactor. At this time, it is not possible to define precisely the R&D tasks necessary for the licensing approval and those that are useful in improving safety but not necessarily required for licensing because the licensing procedure itself is still being discussed. Among the R&D tasks, the most important are considered to be those related to tritium safety, namely, those effective in reducing the uncertainty in tritium inventory in the plasma facing components and blanket, uncertainty in tritium permeation and leakage, and those to clarify tritium behavior in the containment and in the environment. The R&D tasks with second priority are judged to be those related to mobilization of the activation products such as activated erosion dust or the corrosion products. The volatilization of structural metal caused by the oxidation at high temperature seems to be highly unlikely but some experiments are needed to assure that this is the case.