ß-Al2O3 synthesis from m-Al2O3

-Al₂O₃ formation fromm-Al₂O₃ was found by a new convenient technique. By thermal decomposition of a complex compound, trioxalatoaluminate Na _x (NH₄)_3–x [Al(C₂O₄)₃]yH₂O(0.091 x 0.333;y= 3), a very fine powder ofm-Al₂O₃ was formed. The decomposition process was examined by thermal analysis and X-ray diffraction and the phase relation of the system Na₂O-Al₂O₃ in the midtemperature region between 600 and 1200° C is discussed briefly. The tablet ofm-Al₂O₃ was fired at 1600° C for 30 min to prepare dense-Al₂O₃ ceramics, the apparent density of which was greater than 95% of the theoretical value. The sintered tablet was examined from the structural point of view and the electrical conductivity was measured by an a.c. method to verify that the procedure of the complex decomposition is a suitable technique for-Al₂O₃ synthesis.     

Synthesis of potassium beta-alumina by thermal decomposition of a complex

Potassium beta-alumina was synthesised from potassiumm-alumina by a new technique. Thermal decomposition of a complex, trioxalatoaluminate K _x (NH₄)_3–x [Al(C₂O₄)₃] ·3H₂O (0.091x 0.333), resulted in the formation of a fine powder of Km-alumina with mullite-like structure. The decomposition process was studied by thermal analysis and X-ray diffraction, and the phase relation of the K₂O-Al₂O₃ system is discussed in the mid-temperature region of 600–1200°C. The a.c. conductivity, the apparent density and the lattice parameters were measured. The complex decomposition was shown to be a suitable method for K-alumina synthesis.     

Shift of the Curie Point of Barium Titanate Ceramics with Sintering Temperature

Definite increases in the Curie point (T_C) of undoped and lanthanum- (La-) doped (<0.5 at.%) barium titanate (BaTiO₃) ceramics sintered at elevated temperatures in the range of 1300°-1450°C were observed. Both undoped and 0.3 at.% La-doped BaTiO₃ (chosen as a typical doping concentration to yield semiconducting materials) ceramics showed almost the same T_C behavior; their T_C values increased by ∼3.5°C as the sintering temperature was increased from 1300° to 1450°C. Semiconducting 0.3 at.% La-doped materials increased in room-temperature bulk resistivity and TC with increased sintering temperature. The bulk resistivity of the La-doped materials, which was obtained from complex impedance analysis, increased from ∼2 omega cm for the material sintered at 1350°C to ∼6 ω cm at 1450°C. The phenomenon of bulk resistivity increase with sintering temperature was observed in the materials with a doping concentration of ≥ 0.2 at.% La, but was not observed in those doped with <0.2 at.% La. The mechanisms of TC and the bulk resistivity increase observed in the present materials with increased sintering temperature are discussed based on various models found in the literature, particularly in terms of the defect chemistry in semiconducting BaTiO₃ ceramics and the influence of liquid phases present during sintering.     

Continuous production of acyl <Emphasis Type="SmallCaps">l</Emphasis>-ascorbates using a packed-bed reactor with immobilized lipase

Saturated acyl (6-O-caproyl, lauroyl, and myristoyl) and unsaturated acyl (6-O-oleoyl, linoleoyl, and arachidonoyl) l-ascorbates were continuously synthesized at 50°C using a system where a column packed with ascorbic acid powder and a packed-bed reactor with an immobilized lipase from Candida antarctica were connected in series. A productivity of 1.6–1.9 kg/L reactor·d was achieved for at least 11 d. The surface tension of the caproyl or lauroyl l-ascorbate in aqueous solution was measured at various temperatures and pH to estimate the critical micelle concentration (CMC) of the acyl l-ascorbate. The CMC values were independent of temperature but dependent on the pH. The value of the caproyl ascorbate increased with an increase in pH.     

FDTD method for site attenuation analysis of compact anechoic chamber using large‐cell concept

In this paper, the FDTD method has been applied to analyze the site attenuation of an anechoic chamber at 100 MHz or less where the ray tracing method is not applicable. To calculate site attenuation by a personal computer, the dipole antenna and the EM absorber were modeled using a large cell which was larger than the diameter of the antenna element and the thickness of the EM absorber. The equivalent diameter of the antenna element was determined so that the calculated site attenuation in free space agreed with that by the method of moments, and the equivalent dielectric constant and permeability of the absorber were determined so that the reflection coefficient agreed with that by the transmission theory. The site attenuation of the compact anechoic chamber was calculated for frequencies from 30 MHz to 100 MHz and compared with the measured one to confirm the validity of the proposed modeling method. The results indicated that the deviation between the calculated values and the measured ones was within 2 dB. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(4): 9–16, 2008; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20411     

Oxygen reduction at negatively charged iron porphyrins heat-treated and bridged by alkaline-earth metal ions

An ordered network of tetrasodium tetra(4-sulphonatophenyl)porphyrin iron(III) chloride (FeTPPS₄Na₄), which exhibited a higher catalytic activity for oxygen reduction than Co and Ir(CO)TPPS₄Na₄, was fabricated by complexation with alkaline-earth metal ions. Heat treatment of these complexes enhanced their catalytic activity with the highest performance observed with Ba²⁺-FeTPPS₄. The onset potential for oxygen reduction (E_onset) was 720 mV vs. Ag|AgCl, which is almost the same as that for Pt-impregnated carbon black. The number of electrons, n, transferred during oxygen reduction at a Ba²⁺-FeTPPS₄-coated electrode, as determined by rotating ring-disc experiments, was 3.9 and suggests that oxygen was reduced to water. A neutral solution of FeTPPS₄Na₄ was acidified by the addition of barium ion, and the elemental ratio Fe:S:Ba in the resulting Ba²⁺-FeTPPS₄ complex was approximately 1:4:2.5. This suggests the formation of a highly ordered network with Fe sites bridged with barium ions in addition to the normal salt bridges between sulphonates. Catalytic oxidation reactions with nitric oxide and nitrite ion as the intermediate at the heat-treated Ba²⁺-FeTPPS₄ indicate the formation of Fe(IV) and Fe(IV) π-cation radicals or Fe(V). The agreement between the potential of Fe(IV) π-cation radical formation and E_onset suggests that the redox cycle of the Fe(III)/Fe(IV) π-cation radical provides a sufficient driving force for the observed 4-electron reduction of oxygen at the heat-treated Ba²⁺-FeTPPS₄ electrode.     

Photoelectrochemical response of poly(3-hexylthiophene) and poly(2,3-diethylquinoxaline-5,8-diyl) in aqueous media

The photoelectrochemical properties of poly(3-hexylthiophene) (P3HT) and poly(2,3-diethylquinoxaline-5,8-diyl) (PDEQx) thin films on ITO (indium-tin oxide) electrodes were investigated in aqueous media. Photoirradiation of the P3HT-coated electrode resulted in cathodic photocurrents in the presence of methyl benzoylformate, whereas the PDEQx-coated electrode generated stable anodic photocurrents in the presence of 2-mercaptoethanol. The action spectra indicate that photoexcitations of the polymers cause photoelectrochemical reactions. The films of P3HT and PDEQx exhibit a typical photochemical response of p- and n-type semiconducting materials, respectively.     

Improvement of grain refining efficiency for Mg–Al alloy modified by the combination of carbon and calcium

The effects of carbon and/or Ca on the grain refinement of the Mg–3Al alloy have been investigated in the present study. The grain size of the Mg–3Al alloy decreased steeply with increasing the Ca content when it was lower than 0.2%. And then, the grain size decreased slightly when the Ca content was increased to 0.5%. A remarkable grain refining efficiency could be obtained for the Mg–3Al alloy treated with only carbon. Further high grain refining efficiency could be obtained by the combination of 0.2%C and the optimal content (0.2%) of Ca. Therefore, Ca is an effective element to improve the grain refining efficiency for the Mg–Al alloys refined by carbon. The AlCO particles were observed in the samples refined whether by only 0.2%C or by the combination of 0.2%C and a little (less than 0.2%) Ca addition. These AlCO particles should be the potent nuclei for the Mg grains. However, the AlCOCa intermetallic particles were observed when Ca content was increased to 0.5%. Peculiar particles with duplex phases were found in this sample in such a state that AlCO coating film was formed on the surface of Al–Ca compounds. These particles should also be the potent nuclei for the Mg grains.     

Differential Negative Resistance and Piezoresistivity in Thin Semiconducting BaTiO3 Ceramic Bars

Thin, semiconducting barium titanate (BaTiO₃) ceramic bars, with a diameter of 10 to 20 μm, consisting of single grains joined together in series have been prepared to investigate the piezoresistivity in the materials, which was evaluated from their current ( I )-voltage ( V ) characteristics under the loading condition of various bending stresses. I-V characteristics of single grain boundaries in some of the materials were found to exhibit distinct differential negative resistance (DNR) at room temperature with its feature changing with stress. The DNR appeared on the I-V curves at an electric field of several volts per one grain, and has been confirmed to be connected with the transition of current between two conduction states in the grain boundary region. The obtained results indicate that this phenomenon cannot be interpreted by a rise in the temperature of the materials up to their positive temperature coefficient of resistivity (PTCR) region above the Curie point by Joule heating due to current flow, that is their self-heating effect. This newly observed DNR phenomenon has thus been tentatively interpreted by the morphological change in the ferroelectric domain structure in the vicinity of grain boundaries under mechanical and electric stresses, on an assumption that different configurations of ferroelectric domains yield different conduction states in the grain boundary due to a difference in the degree of surface acceptor charge compensation or the anisotropic carrier mobilities in the crystal.