Nonisothermal gravimetric investigation on kinetics of reduction of magnesia by aluminum

An investigation of the reduction of magnesia by aluminum was carried out using a nonisothermal gravimetric technique under an argon atmosphere, in the temperature range from 1273 to 1873 K. The mixture of magnesia and aluminum powders was formed into a pellet under various isostatic pressures. It was found that magnesia is reduced by aluminum to form magnesium and spinel at first, and then the excess aluminum reacts with spinel slowly. The temperature at which the reaction starts increases with an increasing heating rate. The reaction rate is also affected by pellet-forming conditions. A kinetic model is proposed to explain the experimental results. The activation energy of the reduction of magnesia by aluminum is 151.2 kJ/mol. Good agreement between calculated and experimental results is obtained.     

Study of flow instability in off design operation of a multistage centrifugal pump

In recent years, attempts have been made to make multistage centrifugal pumps smaller in size and more efficient. However, such designs are known to cause positive-slope phenomena in the Q-H curve, especially under low-flow conditions. These phenomena, which have thus far been studied experimentally and numerically, stem from flow instability in the pump. However, their mechanisms have not yet been clarified because it depends on various parameters. In this study, we focused on diffuser rotating stall, observed in positive Q-H characteristics. This study elucidates the mechanism of positive-slope generation through experimental results and two-dimensional numerical analysis.     

Thermal conductivity reduction of crystalline silicon by high-pressure torsion

We report a dramatic and irreversible reduction in the lattice thermal conductivity of bulk crystalline silicon when subjected to intense plastic strain under a pressure of 24 GPa using high-pressure torsion (HPT). Thermal conductivity of the HPT-processed samples were measured using picosecond time domain thermoreflectance. Thermal conductivity measurements show that the HPT-processed samples have a lattice thermal conductivity reduction by a factor of approximately 20 (from intrinsic single crystalline value of 142 Wm⁻¹ K⁻¹ to approximately 7.6 Wm⁻¹ K⁻¹). Thermal conductivity reduction in HPT-processed silicon is attributed to the formation of nanograin boundaries and metastable Si-III/XII phases which act as phonon scattering sites, and because of a large density of lattice defects introduced by HPT processing. Annealing the samples at 873 K increases the thermal conductivity due to the reduction in the density of secondary phases and lattice defects.     

Metal salts requisite for the production of eicosapentaenoic acid by a marine bacterium isolated from mackerel intestines

Metal salts important for the growth and 5,8,11,14,17- ciseicosapentaenoic acid EPA) production of a bacterium isolated from Pacific mackerel intestines were investigated at 25°C in culture media containing 1.0% peptone and 0.50% yeast extract, and the composition of an optimum culture medium was determined. This bacterium could grow in the media in which sodium chloride was the sole added inorganic component. By raising the concentration of sodium chloride from 1.2 to 2.4%, the yield of bacterial cells increased and the yield of EPA reached a maximum at 2.0% NaCl concentration. In contrast to calcium chloride, potassium chloride and magnesium chloride as second metal salts promoted the growth of this bacterium at relatively low concentrations without inhibiting the accumulation of EPA. The yield of EPA reached its maximum value of 51.9 mg/L of culture broth at 8 hr at 2.0% NaCl, 0.15% KCl and 0.16% MgCl₂ concentrations. This yield of EPA was 20% greater than that obtained with Jamarin S artificial sea water. *To whom correspondence should be addressed at Department of Chemical Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152, Japan. ¹Sagami Chemical Research Center, 4-4-1 Nishi-ohnuma, Sagamihara, Kanagawa 229, Japan.     

Phase transition at a temperature immediately below the melting point of poly(vinylidene fluoride) from I: A proposition for the ferroelectric Curie point

A phase transition at a temperature immediately below the melting point of poly(vinylidene fluoride) form I has been found by means of differential scanning calorimetry (d.s.c.) and infra-red (i.r.) vibrational spectroscopy. An endothermic d.s.c. shoulder has been observed at a temperature about 10°C below the melting point, in the vicinity of which the i.r. crystalline trans bands decrease in intensity steeply and the crystalline gauche bands increase in intensity, indicating the conformational change from all-trans to T₃GT₃G type. These observations have been found to be detectable more clearly for samples subjected to the poling treatment under a d.c. high voltage. The transition shows the characteristic behaviour essentially identical to those observed for ferroelectric copolymers of vinylidene fluoride and trifluoroethylene, except for the irreversibility of the structural change, suggesting that the phase transformation revealed here may be a ferroelectric-to-paraelectric phase transition of polar form I crystal and the the Curie point may be about 172°C. It is consistent with Micheron's measurement of the temperature dependence of the dielectric constant. Other structural changes in the form I sample occurring in the temperature range from 20° to 170°C have also been discussed based on the i.r. spectral measurements.     

A comparative study of anisotropic creep theories

Quantitative comparisons are drawn between the predictions of three kinds of multiaxial anisotropic creep constitutive equations (the author's model, the Murakami-Ohno model and the Mróz-Trampczynski-Hayhurst model) with special consideration of repeated stress changes. Numerical simulations of these anisotropic creep models are performed regarding the creep behavior observed for type 304 stainless steel at 650 °C under repeated multiaxial nonproportional loading conditions. From these results, it is shown that these creep models can reproduce fairly well the observed anisotropic creep behavior and that the predictive capabilities are almost comparable with each other. The similarities and differences between them are also discussed within the context of the structure of the theories and the procedure to determine the material constants involved.     

Improvement of desulfurization efficiency of molten iron with magnesium vapor produced <Emphasis Type="Italic">In situ</Emphasis> by aluminothermic reduction of magnesium oxide

Based on the desulfurization process of molten iron with magnesium vapor produced in situ by the aluminothermic reduction of magnesium oxide, methods for improving the desulfurization efficiency of magnesium (η _S,Mg) have been studied. By use of the mixed-control model of gas- and liquid-phase mass transfer developed in a previous article, it is shown that η _S,Mg can be improved by reducing the bubble size, increasing the lance immersion depth, dividing MgO-Al pellet charging into several portions, and lowering the operating temperature. A new method for improving η _S,Mg, by adjusting the initial magnesium molar ratio in the bubble (N _Mg,0) through a change in the Ar carrier gas flow rate, is proposed. The optimum initial magnesium molar ratio in the bubble (N _Mg,opt) for obtaining the maximum η _S,Mg value exists, and its value changes with the sulfur concentration in the molten iron. Under the condition of N _Mg,0=N _Mg,opt, reducing the bubble diameter improves η _S,Mg and decreases the Ar carrier gas flow rate that is needed to adjust N _Mg,0 to N _Mg,opt. The aluminum consumption is decreased by the use of the 4MgO-2Al pellet instead of the 3MgO-2Al pellet and is further decreased by lowering the temperature from 1673 to 1623 K. Experimental examinations of the influences of lance immersion depth, pellet charging method, and carrier gas flow-rate pattern have been conducted. Reasonable agreement between the calculated and the experimental results indicates the validity of the present optimization method.     

New Directions in the Study of General Social Attitudes: Trend and Cross-National Perspectives

The importance of trend and cross-national studies on general social attitudes has become widely recognized. However, very little published trend and cross-national data or studies on general social attitudes, which persistently use identical survey systems, have been identified. Up to now, despite some methodological limitations, the studies published in recent years have provided an encouraging base for the future of trend and cross-national studies of general social attitudes. Cooperation will be essential for future studies as they apply various improved methodologies not only to existing trend and cross-national data but also to new survey data collection procedures. Like the development of cohort analysis for trend studies of general social attitudes, as well as the development of correspondence analysis for cross-national studies of general social attitudes, combinations of both cohort and correspondence analyses have been proposed.

Finally, it is suggested that for both trend and cross-national studies of general social attitudes, it is better not only to develop the hard-mode approach but also to develop the soft-mode approach by fully utilizing the hard-mode approach. Conducting this type of research in the context of trend and cross-national analyses will enable empirical analyses to verify existing sociological theories as well as contribute to the establishment of new or modified theories.