발간논문

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Then Hypo-eutectoid carbon steel, containing 0.3% of carbon, was treated by repeated thermal cycling after hot work-quenching. The results of simple repeated thermal cycling treatment and that of repeated thermal cycling treatment after hot work-quenching were compared and discussed mainly in point of the spheroidization rate (sph) of pearlite and number of fine spherical cementite (NO/100u²) deposited in ferrite particles. Consequently the shape of pearlite, the cooling velocity and the effect of working degree and steady heating were examined, and also the mechanical properties were surveyed. The results are as follows (1) Repeated thermal cycling treatment after hot work-quenching accelerated the spherical tendency than steady heating treatment after hot work-quenching and the effect of hot work-quenching on the repeated thermal cycling. (2) The thermal peak of the simple thermal cycling treatment was 200 cycles and the cycles less than this peak deserves the nucleation process and that more than this peak comes under the growth process of nucleus. The thermal peak of thermal cycling treatment after hot work-quenching, however, was 100 cycles and both treatment showed that the nucleation takes place, until 300 cycles, even it is a very small amount. (3) When the repeated thermal cycling treated after hot work-quenching spheroidization rate was promoted in proportion to the increase of working degree at high temperature, the number of cycles, and the cooling velocity. (4) In the case of repeated thermal cycling treatment the structure of sample accelerated the spherical tendency in order of coarse pearlite-fine pearlite-martensite. (5) On the whole, it could be understood that the toughness was increased in contrast with decrease of tensile strength and hardness of the material, according to the number of cycling in the case of repeated thermal cycling. Tensile strength and hardness in the case of repeated thermal cycling treatment after hot work-quenching were decreased than those of simple repeated thermal cycling treatment. Consequently, it is anticipated that the toughness would be increased.

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A study has been made to investigate the roasting mechanism of synthetic chalcopyrite, with varing the temperature, the reaction atmosphere(partial pressures of O₂ and SO₂), and the size of particles. The composition of the chalcopyrite prepared at our laboratory was confirmed to be CuFeS_(1.8) by means of X-Ray diffraction technique. Under the condition of the flow rate of air, 150cc/min and the rate of temperature increment 3 cc/min the following is postulated as possible successive decomposition steps commensurate with the observed D. T. A peaks and the X-Ray Analysis of end products. Effects of the flow rate of air and the partial pressure of oxygen upon D. T. A. peak were not significant, while results were also indicated that in the presence of small amount of SO₂ a new phase Fe₂(SO₄)₃ was formed, which signified by a unique D. T. A. peak(about 500℃).

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Decomposition reaction of the dehydrated cupric sulphate was carried out at relatively elevated temperatures because of the formation of basic cupric sulphate, but it was found that under the Cu-O-S-C system anhydrous cupric sulphate could be roasted without formation of basic cupric sulphate. As the result of roasting anhydrous cupric sulphate mix charcoal carbon, mast reaction was carried out at the satisfactory reaction rate at between temperature 500℃ and 600℃ and cuprous oxide, which is high in desulphurizing as the roasted, was formed. The energy required for roasting anhydrous cupric sulphate was 323㎉/㎏ Cu₂SO₄; 720㎉/㎏ Cu₂O.

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Four kinds of alloy, Fe-18%Mn-14%Cr-2%Co, Fe-18%Mn-14%Cr-4%Co, Fe-17%Mn-14%Cr-4%Ni and Fe-17%Mn-14%Cr-2%Co-B. were prepared in air by means of a high frequency induction furnace. Then the mechanical and corrosive Properties of these alloys were studied, being compared with those of 18-8 stainless steel. It is concluded that the mechanical properties and corrosion resistance of the cobalt alloy increase with cobalt is replaced by boron, the two properties of the alloy can also be improved greatly as those of the alloy having cobalt.

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To obtain a better understanding of quartz and orthoclase activation, zeta potentials of the minerals were studied in the presence of metallic ions such as Mg^(++), Cu^(++), Zn^(++) and Al^(+++). A microelectrophoresis technique has been used to measure the zeta potential, and the results have been correlated with the hydrolysis of the metallic ions in the solution. The experimental results have led to the following conclusions. 1. Zeta potentials of orthoclase in the presence of the metallic ions show a similar behavior to those of quartz. 2. Adsorption of the metallic ions renders the zeta potential of quartz and orthoclase positive. The pH range of positive zeta potential varies with the kind of cation. 3. Zero point of charge(ZPC) of the mineral surface in the presence of metallic ions appears at two different pH of solution. One of two pH of ZPC is consistent with the pH at which M^(II)(OH)^+ and M^(III)(OH)^+_2 or M^(III)(OH)^(++) species are predominant. 4. Comparison of the zeta potential data with the hydrolysis for Mg(II), Cu(II), Zn(II) and Al(III) species suggests that Mg^(++), Cu^(++), Zn^(++) and Al^(+++) are only weakly adsorbed at the mineral surface and that M^(II)(OH)^+ and M^(III)(OH)^+_2 or M^(III)(OH)^(++) are the main metallic ionic species adsorbed.

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The electrorefining of the crude lead was carried out by both techniques, the amalgam electrorefining and the conventional electrorefining. The amalgam electrorefining used a cell which consists of two compartments separated by a barrier which was suspended in a shallow pool of liquid lead amalgam to give a gap between the barrier and the cell bottom. The lead anode and the lead anode which surface was amalgamated in HgCl₂ solution were employed for the conventional electrorefining. Pb(ClO₄)₂-HClO₄ solution was used as an electrolyte and gelatin was also used as the additive agent. Even at high current densities the polarization of the liquid lead amalgam was similar to that of the metallic lead, and increased linearly with increasing the current density. The impurity level in the refined lead obtained by the amalgam electrorefinig was less than 10^(-4) percent. The polarization of amalgamated anode was also similar to that of the matallic lead. Refined lead produced by the electrorefining of the crude with amalgamated surface was purer than that of the conventional electrorefining.

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The diffusivity of carbon in austenite steel containing 3 percent nickel, 0.8 percent chronium and 0.3 percent molybdenium has been determined using diffusion couples at the temperatures from 900℃ to 1,100℃. Carbon isotope C^(14) was added to the higher carbon side of the couple. After cast into steel moulds and forged, the specimens were homogenized in the purified argon atmosphere for 24 hrs. at 1400℃ or 1280℃ and then friction welded to make the diffusion couples. After the couples were annealed, the surface counting technique and the microphotography-autoradiograph technique were used to obtain the concentration-penetration curves, and then the diffusion coefficient, D, was computed by the Boltzman-Matano method. The experimental results lead to the following conclusions. 1) The computed diffusivities obtained by the both methods were agreed well within 3 percent error. Therefore the microphotography method can be effectively used to determine the diffusion coefficient. 2) The rate of diffusion of carbon was slightly accelerated at 1100℃ and the diffusion coefficient was proportional to the carbon concentration. 3) The diffusion coefficient could be expressed by D=D_0 exp (-36,000㎈/RT), where D ranged from 0.53 to 0.70 in the carbon concentration ranged from 0.2 to 0.8 percent. These values are in fairly good agreement with those obtained by the chemical analysis technique.

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