발간논문

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Steel wire is characterized by properties of high strength and good ductility. The factors which influence on strength and ductility in steel wire, are chemical composition, heat treatment and cold working. In regard to chemical composition, the steel wire having higher carbon and manganese contents comes to be demanded to get high strength and elasticity. Recently the behaviour of N, H and O in steel wire comes to be attached importance. In regard to heat treatment, patenting is general for steel wire before drawing. Recently direct patenting, batch patenting and fluidized bed patenting are being applied practically to increase productivity, improve quality and reduce manufacturing cost. For steel wire like PC wire, blueing and stabilizing after drawing are applied practically. In regard to cold working, a part of die drawing is gradually shifting to dieless drawing. Namely, rolling is used practically for drawing profile wire and alternate bending continuous drawing is being developed. Recently the ageing of steel wire, that was liable to be passed over before now, is studied and has come to be made clear.

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The reactivity of 15 component minerals of beach sands with sodium hydroxide has been investigated by means of differential thermal analysis in a temperature range up to∼700℃ in two size ranges: 72/300 and -300 mesh fractions. A modified metallic sample holder made of pure silver was employed along with a conventional D. T. A. set-up. The minerals include eleven economic minerals (monazite, zircon, columbite, wolframite, rutile, xenotime, scheelite, apatite, chromite, ilmenite, cassiterite) and four associated gangue minerals(quartz, tourmaline, garnet, hematite). The D. T. A. thermograms showed that all the minerals except cassiterite, ilmenite and hematite reacted within the temperature range considered. Two typical reaction temperatures were observed: one in the temperature range below the m. p. of NaOH(157∼250℃, most of fine minerals) and the other on the melting(300∼350℃). A graphical summary of the test results according to the reaction peaks has been established to visualize the reactivity of the groups of minerals.

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The liquid silicon was oxidized to silicon monoxide by 10-65% CO₂ gas in CO·CO₂gas mixture under a total pressure of about 1 atmosphere at temperatures ranging from 1,450℃ to 1,650℃. The reaction equation was estimated as follows: Si(ℓ)+CO₂=SiO(g)+CO ΔF_α^0=30,840-31.67T The standard free energy change, ΔF_α^0 for the above reaction between the experimental results and calculated data from ΔH^0_(298), ΔS^0_(298) and heat capacity of each component was closely agreed with each other. White and amorphous silicon monoxide powder was obtained by condensation at 900-600℃, but 0.5-1.5% carbon was deposited on silicon monoxide powder by the Boudouard`s reaction, 2CO=CO₂+C, below 600℃.

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The phase transition in α solid solution of the Fe-Cr-Ni system was investigated in the temperature range corresponding to the 475℃ embrittlement, by means of hardness measurements and microstructural changes by potentiostatic etching. The Ni addition in the Fe-Cr binary system affected the miscibility gap to shift to the lower temperatures. Moreover, from the results of electro-chemical measurements, it was confirmed that the α solid solution in alloys aged within this gap would separate into chromium-rich and iron-rich α solid solutions.

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Effects of melting process of 50%Ni-50%Fe alloy on it`s non-metallic inclusion, recrystallization and magnetic properties, especially coercive force were studied. Alloys which were deoxidized by 1% of Mn under the atmosphere of 5mmHg Helium showed good hot workability. and non-metallic inclusions were remarkably reduced by casting in sand mold compared with the alloys casted in metal mold. Non-metallic inclusions increased the coercive force of the alloy and reduced the grain size of the primary recrystallization after 2hr-annealing at 1,000℃. Coercive forces of 4 alloys was lowered, and approached to 0.1 Oe after 8hr-annealing at 1,200℃, regardless the amount of inclusions, supposedly due to the purification effect of dry hydrogen.

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In order to evaluate the reaction kinetics of zinc ferrites reduced by hydrogen, the studies were made on the thermal decomposition of synthetic zinc ferrites in vacuum and on the process of hydrogen reduction at various temperatures and pressures by thermal balance method, so that the parameters of the equation of reducing processes were determined. The results were discussed with the comparison of the rate of zinc and iron oxides. Zinc ferrites were easily decomposed into gaseous zinc and solid magnetite in vacuum at elevated temperatures, then by introduction of hydrogen to the vacuum, the decomposition was followed with the reduction of magnetite into the ferrous oxide, and finally the reaction completed by the formation of metallic iron. The rate of reduction of zinc ferrite at the initial stage may be expressed as follows: 1-(1-Y)^(1/3)=K_0P^(0.92)_(H2) t/ρ·r_0 The activation energies were calculated as 22 ㎉/㏖ for the thermal decomposition, and 17.2 to 17.4 ㎉/㏖ for the hydrogen reduction, respectively.

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Fabrication variables of tantalum solid electrolytic capacitors were studied in relation to their electrical properties. Emphasis was placed on investigating effects of sintering conditions on anodization rates and scintillation voltage, and effects of pyrolysis and aging conditions on electrical properties of tantalum capacitors. The dielectric oxide layer on the surface of sintered porous anode pellets was formed by anodizing in phosphoric acid solution. The solid electrolyte was applied on the dielectric oxide layer by impregnating the anodized pellets with manganese nitrate and then by its pyrolysis. The application of the solid electrolyte and reanodization at a reduced voltage were repeated several times. Vacuum sintering of tantalum pellets at a temperature above 2,000 ℃ was required to achieve the scintillation voltage above 250 volts. The increases in tanδ_f and in frequency dependence of capacitance of the dielectric oxide layer during Pyrolysis and aging process are attributed to increasing diffusion layer of the dielectric oxide layer.

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