For high-density audio/video recording-use iron-based fine acicular parti-cles, prepared from almost the same dimensional goethite industrially, the relation between the powder characteristics and the reversal properties of the magnetiza-tion was theoretically and experimentally investigated.
First, it was shown that the particles studied here are of the so-called skeleton type: In the case of the particles of α-Fe, they consist of the crystal grains of order of 100 or 300Å, belonging to the BCC. phase crystallographically. Next, it was proposed to represent this type of the particle morphology and the reversal of the magnetization by a modification of Jacobs and Bean's “chain-of-spheres” fanning model. In this morphological model-scheme for the reversal of the magnetization, it was found that the dipole conformation plays a very important role and the most physically available one is strongly dependent on the particle morphology. It was also found that the local aggregate structure of the particles affects the re-versal of the magnetization: Usually, the aggregates such as so-called “multiple” or “bundle” lead to the extremely large lowering of the coercivity.
Finally, the interparticle-interaction effect on the reversal of the magnetization was also investigated under a hypothesis that assumes a formation of an infinite regular space-lattice of the particles. Comparison with experiments was also tried.

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Magnetocaloric energy conversion using magnetic fluid has been studied by some researchers. The development of high temperature sensitivity and high ther mal conductivity of magnetic fluid is needed for efficient heat transfer. In this experiment, especially the highly temperature sensitive ultrafine ferrites at temper atures of 223 to 373 K were investigated. Mixed zinc ferrites of lOnm containing calcium ion were prepared by coprecipitation. They showed larger magnetizationand larger magnetization change per temperature than mixed zinc ferrites containing no calcium. Ni-Ca-Zn or Co-Ca-Zn ferrites gave approximately 2×10^-3T/K at 273K by applying 3.2×10⁵A/m of magnetic field. Higher temperature sensitive, kerosene or water based magnetic fluid was prepared by dispersing these ferrites than the conventional magnetic fluid.

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An alternating copolymer of maleic acid and m, p-methylstyrene was prepared and the pH-induced conformational transition in aqueous salts has been investigated by pH-titration, viscometric and optical measurements. The relationbetween the intrinsic viscosity and the degree of neutralization of the primary carboxyl group shows a transition from a compact form to an extended coil one. The values of ΔG_t⁰, which is the standard free energy change of the transition, were calculated from the modified pH-titration curves in the range of NaCl concentration between 0.01M and 0.27M. Also, the transition curves were calculated from the pH data in terms of the coil fraction in the molecule. All results were compared with those for maleic acid-styrene copolymer and maleic acid-amethylstyrene copolymer studied previously, and the influence of methyl groups on the transition was discussed.

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In order to obtain a reasonable bubble column to separate surface active metal chelates, liquid mixing characteristics of DBS solution in a 6-stage counter current bubble column have been investigated. From the delta-response analysis by measuring the electrical conductivity at each stage, it proved that back flow modelthrough perforated plates was applicable to the system with good approximation.
Back flow ratio took a clear muximum value at a certain gas velocity in DBS solution rather than in pure water, depending on gas velocity, liquid velocity and dimensions of perforated plates such as diameter of the hole and open area ratio. The autnors introduced a conceptual mechanism that the back flow resulted from the viscous shear force at gas-liquid interface similar to a counter current wetted wall colum, and obtained simple relations of (r_G/r_o) ² with Reynolds number, Galilei number and open area ratio.

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This study is undertaken to investigate the alumina particle which was activatedby typical fine crushing and effect of crushing method. The crushing experimentsare carried out by vibration ball milling, centrifugal fluidized milling and flow milling. The products taken from the typical fine crushing are used for the measurements of mechanochemical, powder, and sintering characteristics. From measured data of these characteristics, good knowledge about the interaction was obtained.

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Thermal and reaction characteristics were studied of the sulfuric acid digestion of ilmenite are (FeTiO₃) in a small batch stirred-tank reactor. With a treatment of relatively large are particles first, the digestion process was found to becharacterized through the fracture of particles owing to the growth of iron sulphate crystals in an ore. Then, by processing small particles in a 70vol% sulfuric acid solution with the initial temperature range from 120 to 160°C, the sequential changes were observed in the extent of conversion for titaniuand iron, with temperature. Simulation for the thermal and reaction features along the course proved to besuccessful with a volume reaction model in which the are particles were grouped into three for titanium and two for iron due to difference in reactivity.

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A ZnO-Bi₂O₃ two-layer composite film formed by rf sputtering was studied as a model of a single grain boundary in a ZnO varistor. The current-voltage (I-V) characteristics, capacitance-voltage (C-V) characteristics and thermallystimulated currents (TSC) were measured. The ZnO-Bi₂0₃ two-layer films showed highly non-linear conduction. A negative charge and associated potential barrier at the ZnO-Bi₂O₃ interface controlled the conduction. The breakdown voltage was also affected by the thickness of the Bi₂O₃ layer. This and TSC experiments showed that space charge was responsible for the thickness dependence. This system can be used as a thin-film varistor and a humidity sensor because of its high non-linearity coefficient (60-100), and high sensitivity and fast response to humidity.

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The world supply of raw materials for the production of magnesium is unlimited. Sir Humphrey Davy was the first experimenter to produce magnesium. In 1808 he reported the production of metal from amalgams formed by the reduction of magnesium oxide. but, mass production of magnesium started in the early thirties after the world war I. by using silicothermic, carbothermic and electrolytic production methods. in case of electrolytic method, the biggest problem was how to make magnesium anhydride

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