발간논문

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The direct reduction of zinc sulphide by hydrogen gas in presence of calcium oxide was investigated in the temperature range of 600-900℃. The reaction kinetics were determined by the thermo-gravimetric analysis technique with silica spring. The effects of temperature, additives, hydrogen flow rate and sample porosity were studied. The rates of reaction increased as temperature raising and more considerably increased markedly when calcium oxide was added as a sulphur scavenging agent. The effects of additives, Na₂CO₃and NaF on reaction rate were explained by the increase of initial reaction rates but their mechanism will be studied more extensively. Under these experimental conditions the rates of reaction were controlled by chemical reaction. It was discovered that the apparent activation energy of ZnS with 2CaO was about 26.3 ㎉.

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In order to recover cobalt from the waste WC-Co alloys, the oxidation & acid leaching process has been studied. In the oxidation under air at various temperatures, the maximum oxidation was achieved at 900℃. For given composition of alloy, the rate of oxidation was more or less constant with the extent of reaction time but the higher the cobalt content of alloys, the faster the oxidation rate was observed. After a complete oxidation, the hardmetals were easily crushed into powder form, followed by leaching of cobalt by HC1. The rate of leaching was increased with increasing reaction temperature and also the concentration of HC1.

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Weldability of the SM58Q, Quenched and Tempered HT60 Steel, was investigated by employing the SH-CCT diagram and the cold cracking tests such as Controlled Thermal Severity(CTS) and Slit type restraint cracking test. An investigation was also carried out whether the localization of the electrode for SM58Q steel is possible. Results can be summarized as follows; 1. Weldability of domestic SM58Q steel was proved to be fairly good. 2. Though specimens were welded at ambient temperature, no cracking occurred in the CTS test with an energy input of 2KJ/㎜. It is, however, necessary to preheat them up to 150℃ in order to prevent root cracking in case of Slit type restraint cracking test. 3. As for mechanical properties, microstructures and hydrogen contents, there is no difference between domestic and imported electrodes in itself. Therefore it is possible that the electrodes for SM58Q steel would be localized.

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The spot-weldability of such products as galvanized steel, galvannealed steel and galvalume steel was investigated. In this study, both tension-shear force and nugget diameter were used to determine the optimum welding range so as to enhance the applicability of the data in practical field. The results are summarized as follows; 1) Over the range of 7.3% to 11.5%, the Fe content in alloy layer of galvannealed steel improves the spot-weldability almost proportionally. 2) The spot-weldability of 0.64 mmt coated steels can set galvannealed-, galvanized- and galvalume steel in array, but last two steels show similar result. 3) It is considered that ductile/brittle fracture of weld nugget has mainly nothing to do with fracture appearance such as button- or interface- fracture when the Ceq. of specimen is 0.1 or so.

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A kinetic model which describes mass transfer involved in the reaction between a porous solid and a fluid is proposed. The pores are assumed to be spherical and distributed uniformly within the solid particle. The model takes into consideration of rate constant, intraparticle diffusion and specific surface area of the solid which increases as the reaction progresses. From the solution of the differential mass balance for the fluid species, incorporated with the formulation of the specific surface area of the solid, by the finite difference method, conversion of solid versus time is obtained.

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