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The effects of evaporation rate and pressure of helium gas on the size of ultrafine tin oxide powder were studied in a gas condensation method. The velocity and size of convection current of helium gas were regulated by varying gas pressure in the chamber and temperature of an evaporation source. As the convection current became slow in velocity and reduced in size, the average size of the synthesized tin oxide powder increased. The respective effects of evaporation rate and gas pressure were analyzed by computer simulation of convection currents at a steady state condition, based on the experimental results. Oxygen gas flown into a condensation chamber filled with constant helium gas provided a proper condition for synthesis of ultrafine tin oxide powder having a narrow size distribution.

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A new MA processing method has been suggested using a pulverizer. Even in the pulverizer. the real atomic alloying process could happen and the five MA stages were also observed. Because of high efficiency of energy input to specimen, however, the period of each stage was shortened. The energy input to specimen during pulverizing process has been estimated quantitatively, and the necessary condition for vitrification of the Ni_(50)Ti_(50) system was expressed with energetic terms. As pulverization proceeded, the N_(50)Ti_(50) powders transformed to metallic glass followed by intemetallic crystals. Though the crystallization behavior could be rationalized by thermal effect during pulverizing, the exact mechanism needs further elaborate works.

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This study was focused to examine fabrication process of TiB₂ particle reinforced TiAl based intermetallic composites by reactive synthesis. The mixed powders were canned, hot-pressed under vacuum and then hot-extruded at 420℃ under extrusion ratio of 15:1. Subsequently. reactive synthesis was carried out at 700℃ under vacuum Thermal analysis has been perfomed to investigate the ignition temperature and combustion temperature for Ti-Al system and Ti-Al-B system. The combustion temperature of Ti-Al-B powder mixture was found to be higher than that of Ti-Al powder mixture. The Ti-Al-B powder mixture was reacted exothermically to form the material consisting of TiAl and TiB₂. The tensile strength of the TiB₂/TiAl composites was proved to be higher than that of the matrix. Swelling phenomenon, resulting from formation of a large amount of pores was observed at all reactive synthesis conditions.

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Intermetallic compound TiAl has good mechanical properties at high temperatures but it is brittle at room temperature. On the other hand the Ti-10V-2Al-3Fe alloy(Ti-10-2-3), one of β-Ti alloys, has high strength and toughness at room temperature. The purpose of this work was to manufacture composite materials having only merits of both TiAl and Ti-10-2-3, and to investigate the mechanical properties of the composite materials at high temperatures. TiAl and Ti-10-2-3 powders were prepared by mechanical alloying. The mixed powders of TiAl and Ti-10-2-3 were consolidated by pseudo-HIP. The high density could not be obtained in composite materials by this method as TiAl particles constrained the flow of Ti-10-2-3 particles during consolidation. The reaction layer(Ti₃Al) about 5 ㎛ thick was formed between TiAl and Ti-10-2-3, and the interface between the layer and TiAl, and/or between the layer and Ti-10-2-3 was the path of crack propagation. The UTS of TiAl/Ti-10-2-3(40:60 vol. ratio) composite material was found to be higher than that of typical Ti-6V-4Al alloy at 815℃, while it was lower at 600℃.

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With a view to studying the possibility of separating uranium from aqueous solution by coprecipitation, the carrier properties of ferric and titanium hydroxides were examined. The results obtained were as follows. The values of pH at which uranium started to coprecipitate with the carriers were 3.0 for Ti(OH)₄, 4.0 for Fe(OH)₃ and optimum pH values to obtain maximum recovery of uranium were 6.0∼10.0 for Ti(OH)₄, 6.0∼8.0 for Fe(OH)₄, respectively. It was found that the HCO₃ ion had a negative effect on uranium adsorption when its concentration was higher than 5.0mM. And the relation between equilibrated uranium adsorption and the concentration of uranium in the aqueous solution followed Freundlich`s isotherm formula in the region of low concentration. The uranium in the aqueous solution which was not adsorbed was determined by Arsenazo III method.

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The self-discharge characteristics of nickel-metal hydride (Ni-MH) batteries with anode using Zr_(0. 8)Ti_(0. 2)Cr_(0. 5)Mn_(0. 2)V_(0. 2)NiMm_(0. 05) and ZrV_(0. 8)Ni_(1. 6) alloys have been investigated in a sealed cell or in a modified sealed cell To separately measure the self-discharge characteristics of the anode and the cathode, a modified sealed cell was employed, in which two more electrodes (Pt, counterelectrode; Hg/HgO, reference electrode) were installed. After 7 days of open circuit storage using Zr_(0. 8)Ti_(0. 2)Cr_(0. 5)Mn_(0. 2)V_(0. 2)NiMm_(0. 05) alloy, the capacity loss was 38%, among which 16% of the capacity loss was irreversible. The irreversible capacity loss is attributed to the oxidation and dissolution reactions of hydriding forming elements of the MH electrode. The reversible self-discharge is due to the evolution of hydrogen from the MH electrode. In the case of ZrV_(0. 8)Ni_(1. 6) alloy, the charge retention for both electrodes was measured at latm and 30℃ in air and it was found that the capacity loss of the anode was greater than that of the cathode after open-circuit storage. From X-ray diffraction and thermal desorption spectroscopy. it was found that the self-discharge of the anode might occur by the evolution of hydrogen from the MH electrode due to the difference between the hydrogen partial pressure in the sealed cell and the equilibrium hydrogen pressure of the MH electrode.

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A computer program for a Monte Carlo simulation of grain growth based on the Ising model was developed. The system in the model comprised of a square lattice with each lattice site having an alternative spin of two kinds, either `up` or `down`. Verification of the program confirmed a cluster forming below the critical transition temperature T_0. Starting with a two-dimensional circular grain we studied the grain growth kinetics at a given temperature. A t^(½) time dependence growth rate was found, which was in accord with the classical curvature-driven growth rate theory. Increasing the temperature resulted in a decline of the growth rate at a given Monte Carlo step that appeared as a reduction of the coefficient of the time term. This phenomenon was attributed to abnormal curvature formation at local areas of the grain boundary due to enhanced fluctuation of the lattice sites at high temperature.

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Fe-(20∼25)Cr-(5∼10)Al-xLa alloy ribbons were fabricated by PFC(Planar Flow Casting). Oxidation kinetics of the alloys were investigated. With increasing La content, activation energy for forming the protective Al₂O₃layer on the ribbon surface was increased and Al depletion rate in metal substrate was reduced. With increasing Al content, the oxidation duration time was increased. But activation energy remained constant. Increase in Cr content has no relation for the formation of Cr₂O₃ oxide, but increases the activation energy for forming a protective Al₂O₃layer. Cr₂O₃ oxide formed in Al₂O₃layer at the end of oxidation second stage broke the previous Al₂O₃layer. It is due to the elastic coherency strain energy induced by the volume difference of between Cr₂O₃ and Al₂O₃. The formation of Cr₂O₃ crystal gave rise to breakaway oxidation. The increase of Cr and Al content improves the oxidation resistance

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Reactive element addition, La, to Fe-Cr-Al alloy improves the high temperature oxidation resistance. The object of present study is to examine the role of La. La segregates at grain boundary of metal substrate and is not present in oxide layer during the high temperature oxidation. La addition increases oxidation duration time because Al depletion rate is reduced. Segregation of La decreases the outward diffusion of Al through grain boundary of metal. α-alumina crystal has grown as a columnar grain on metal substrate surface. The oxide/metal interface moved into metal substrate. In case of no La addition, outward diffusion of Al along the metal substrate grain boundary give rise to heterogeneous nucleation and growth of α-alumina crystal on the grain boundary of metal surface. Consequently α-alumina exhibited planar coarse morphology. The major rode of La in Fe-Cr-Al alloy is to suppress the Al diffusion from metal substrate, to change morphology of α-alumina and subsequently to enhance the oxidation resistance.

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The motion of each milling ball during vibratory ball milling of metal powder was simulated by a computer using one-, two-and three-dimensional models of a vibratory ball mill In these models, the consumption of impact energy of the balls by the micro-compaction of metal powder particles during impact was assumed to be equivalent to the energy loss by an imaginary viscosity given to the balls and mill container. As a result of the simulation by using the three models, it was found that the motion of the milling balls is strongly dependent on the ball charge fraction. With an increase in the ball charge, the impact frequency increased, while an avarage of impact velocity normal to each contact surface decreased. The impact velocity or the impact energy obtained by the simulation was related to the microhardness, crystallite size and lattice strain of the powder particles which were mechanically alloyed by vibratory mill.

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