발간논문

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In the present study, fatigue strength of corroded nickel was examined after irradiation in a TRIGA-II reactor. Before the fatigue test, the samples which has been placed in distilled water were irradiated with the total neutron dosage of 4.6×10^(18) nvt (1.6×10^(18) nvt of fast neutrons and 3.0×10^(18) nvt of thermal neutrons) for ten months. The experimental result showed that the irradiated samples decrease about 10% in fatigue strength as compared to the control samples. This may be due to the formation of fatigue cracks at the grain boundaries caused by intergranular corrosion.

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The interaction of sodium sulfate with molybdenum trioxide was studied by differential thermal analysis. It was inferred from this study that sodium sulfate and molybdenum trioxide should react at elevated temperature to yield sulfur trioxide and sodium polymolybdate. The same incipient compound and/or mixture seemed to be formed first at around 660℃ regardless of Na₂SO₄, to MoO₃ratio of mixture during the reaction. When Na₂SO₄to MoO₃molecular ratio of mixture was lower than 1:3, the evaporation of molybdenum trioxide was not observed even at 1000℃.

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The initial oxidation rate on electropolished cadmium surfaces was studied at the temperature range of 100 to 195℃ and the initial oxygen pressure range of (7∼8)×10^(-1)㎜ Hg by using manometric method in a constant volume of reaction cell. The reproducibility of oxidation rate is greatly affected by the surface preparation. Some of these effects were shown. Two stages of logarithmic initial oxidati on rate were observed in the temperature range of 100 to 180℃. No longer the log-arithmic rate above about 195℃ was observed. The density of sites for trapped electrons in the constant density space-charge layer and the density of available sites for trapped charge in the diffuse layer were calculated by using Uhlig`s concept for space-charge effects, showing 1.53×10^(18) and 1.17×10^(18) per cubic centimeter at 180℃, respectively. The empirical and calculated values of oxide thicknesses at which the second stage oxidation begins for electropolished surfaces was revealed much thinner than those of mechanically polished surfaces in other metals, and these values were 6.3 and 11.86Å at 180℃ respectively. Some of initial oxidation characteristics on an evaporated clean cadmium film were shown in comparing with that of the electropolished surface.

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This paper describes the analog application for the study of metalworking parameters, such as friction, redundant deformation, material flow direction and tool geometry. Also the various metalworking processes adaptable to the analog technique have been reviewed. Since the exact theoretical analysis of practical forming operation is most difficult, along with analog applications for the process parameter study, this paper describes analytically how the forming load can be estimated by the analog technique. The equations for the application of the strain rate dependent materials and the strain hardening materials mere obtained. A powerful tool in metalforming research and development is the use of analog technique by which the study of various metalworking processes and their porameters possible with reasonable expenditure. Also it appears that the forming loads for steady state processes can be determined from the analog technique. The analog study provides a means of determining the average strain rate for strain rate dependent materials and the average strain for strain hardening materials.

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An optimum process for the production of technical grade zirconia was studied by employing the method of caustic fritting of zircon. The optimum conditions for the production of caustic zircon frit was as follows; 1.4 of caustic to zircon sand weight ratio, 650-700 deg. C. of reaction temperatures and 10-60 minutes of reaction times. The frit was leached by water and the 6∼7% of sodium content remained after leaching was eliminated by digesting it with dilute HCl solution in an autoclave. The digested product was structually amorphous but when roasted at 700 deg. C. for one hour, it became cubic zirconia. The composition of the final product was 1.07% of SiO₂, trace of sodium, 0.37% of Al₂O₃, 0.24% of Fe₂O₃, 0.36% of TiO₂, and 97.96% of ZrO₂.

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The aim of these experiments is to get a high recovery of antimony from precipitation process with Choong Nam district Stibnite. This experiment is done in the electric furnace concerned operation temperature, recovery, rate of mixture with Stibnite flotation concentrates, added iron scrap, Na₂CO₃, and Na₂SO₄. As a result of this experiment, antimony can be obtained with high recovery at 870℃∼900℃ by adding Na₂CO₃30% and Na₂SO₄25%.

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