발간논문

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This study is to find out the mechanism by which reaction products form when the bismuth trioxide and molybdenum trioxide is sufficiently mixed with a mole ratio of 1 to 1 and then heated at various temperatures selected from the differential thermal analyses. The results obtained from the experiment that these reaction products have been alkalileached are summarised as follows ; 1. The reaction products of the mixture of Bi₂O₃and M_0O₃(mole ratio=1 : 1) for 500℃ are Bi₂M_0O_6, Bi₄M_0O_9 and αBi₂O₃, whereas at above 670℃ the product obtained is identified to be Bi₄M_0O_9 by the reaction B₂M_0O_6 +α-Bi₂O₃→Bi₄M_0O_9. 2. At a temperature of 900℃ which is above the melting point of Bi₂O₃there is no change in weight. In the temperature range of 820℃ to 1000℃ below the boiling point of M_0O₃, however, it is shown to be a decrease in weight by 80%. 3. The melting point of Bi₄M_0O_9 is found to be 950℃ the change in weight of Bi₄M_0O_9 formed by mixing M_0O₃and Bi₂ O₃is not shown because of the formation of the compound Bi₄M_0O_9. 4. The chemical reaction analysis has shown that one of the reasons why the leaching rate of roasted ores of M_0S₂containing Bi is lowered can be explained by the fact that Bi₂M_0O_6 and Bi₄M_0O_9 are not soluble in a solution of NaOH under the condition of atmospheric pressure.

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Hardness distributions in Ag-CdO layers obtained by the internal oxidation have been studied laying emphasis on the effects of impurity elements added. The hardness of specimens including 0.1% aluminum or beryllium was larger than that of specimens without the elements, whereas the hardness of specimens with 0.1% antimony or copper was about the same as that of specimens without them. The specimens oxidized at lower temperatures were harder than those oxidized at higher temperatures. The hardness of specimens decreased with increasing depth from the surface. These phenomena were discussed based on the particle size distribution and particle shape.

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A study on the direct reduction of Cuprous Sulfide by Hydrogen gas in the presence of CaO was investigated in the temperature range of the 500℃ to 1,000℃. Under the constant velocity of hydrogen gas, experiments were carried out isothermally and Sulfur Elimination Percent was determined by quantitative sulfur analysis. The effects of reaction temperature, time, and ratio of CaO/Cu₂S were studied. In all cases reduction reactions were carried rapidly in the initial stage and after that reaction rates were decreased gradually. The effects of additives-Na₂O₃ and NaF-were explained by the rapid increasing of the initial reaction rates but the mechanism of that will be studied more. The activation energy of reduction process of the system was found to be 4.44Kcal/mole and the rate constant could be expressed by the following equation K=80.31 exp (-4440/RT).

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The general mechanical properties, the influence of heat treatment condition and the initial microstructure on machinability of Ni-Cr-Mo steel has been studied. The results from the study were as follows 1. The influence of an initial microstructure on hardenability was pronounced. The critical diameter of a hardenability increased as the initial microstructure changed from the spheroidized, patented and to normalized. 2. The influence of an initial microstructure on the mechanical properties increased as the quenching temperature increased. 3. The machinability increases as the quenching temperature increased and the tempering temperature decreased. 4. When the quenching temperature was high, the machinability increased as the initial microstructure changed in a sequence from the normalized, spheroidized and to patented one. 5. However, when the quenching temperature was low, the sequence of improving machinability was the same as when quenching temperature was high.

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Sintering studies of the mixture of a coarse 60wt% Sm-Co additive (about 200㎛ size) and a fine SmCo_5 powder (about 5㎛ size) and the mixture of a coarse SmCo_5 powder and a fine additive were made to understand the role of the liquid additive during sintering of the SmCo_5 permanent magnets. The density change of the fine powder mixtures was also studied, varying their total Sm content and sintering time, to understand the sintering of a Sm-rich phase powder of the SmCo_5 homogeneity region. The results showed that the mixture of the SmCo_5 powder and the 60wt% Sm-Co additive was sintered through three stages; 1) Upon melting of the Sm-Co additive, the liquid phase immediately permeated through the SmCo_5 powder during the first stage. 2) As the liquid phase was brought to contact with the SmCo_5 powder, new phases, SmCo₃ and Sm₂Co_7 were formed by interphase reaction and interdiffusion of Sm and Co atoms between the liquid phase and the SmCo_5 powder. On continued sintering, the liquid phase, the SmCo₃ and the Sm₂Co_7 phase disappeared successively in the order of listing, while an equilibrium phase of the powder mixture, that is, a Sm-rich phase of the SmCo_5 homogeneity region was formed during the second stage. 3) During the last stage, solid state sintering of the Sm-rich phase of the SmCo_5 homogeneity region occurred by diffusion of Co-vacancies that were believed to exist in the Sm-rich phase. The experimentally observed relationship between density change of sintered magnets and sintering time was discussed in relation to the theories and experimental results reported previously.

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In order to investigate the effects of graphite content and graphite particle size on structure and mechanical properties of graphite dispersed tin bronze castings, macro and micro structure have been observed, and mechanical test and wear test were also carried out. The Specimens were prepared by dispersing graphite into the molten metal through the Vortex process. From this experiment, the results were summarized as follows, 1) Graphite in tin bronze castings could be distributed uniformly by Vortex process, and the inter particle distance of graphite were quite similar. 2) Mechanical strength of the alloy decreased as the graphite content and particle size increased. 3) Wear resistance increased as the graphite content and graphite particle size increased. 4) The affect of graphite addition became remarkable as the load and sliding length increased.

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The effect of austenitizing temperature and tempering condition on the plane strain fracture toughness K_(Ic) and tensile properties was studied for AISI 4340 and 4130 steels in the austenitized temperature range between 870℃∼1200℃. In the as-quenched condition, plane strain fracture toughness measurements exhibited approximately 70% increase in K_(Ic) values without significant loss in strength for specimens austenitized at 1200℃ compared to those austenitized at 870℃. The specimens tempered at various temperatures after austenitizing at 1200℃ showed, in general, higher K_(Ic) values than those tempered at the same temperatures when austenitized at 870℃. However, the former showed a severe decrease in K_(Ic) values because of temper embrittlement compared to toe latter when they were tempered at 300℃. Under constant austenitizing temperature, specimen with the smaller grain size showed a higher value of toughness, on the other hand, when austenitizing temperature was increased, specimens with the same austenite grain size, the toughness value was significantly increased. These results were also discussed in terms of impurity segregation to prior austenite grain boundary in connection with fracture surface topography. It was concluded that enhancement in K_(Ic) values by high temperature austenitization was attributed to a reduction in the impurity segregation at the grain boundary as compared to conventional austenitizing treatments.

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The leaching of galena with ferric chloride was investigated as a function of the particle size of the galena, stirring speed, ferric chloride concentration, the persence of sodium chloride and calcium chloride, and the reaction temperature. Also, leaching kinetics was discussed with the experimental data obtained in this investigation. It was found that more than 98 percent of the lead was extracted from the galena which was treated with ferric chloride solution of 3 to 1 mole ratio of FeCl₃/PbS at 100℃. At 50℃, more than 99 percent of the lead was obtained from the galena leached with the solution contained with 3 to 1 mole ratio of FeCl₃/PbS and 3 mole NaCl. While, at room temperature, over 99 percent of the lead was extracted from the galena leached with the solution mixed with 3 to 1 mole ratio of FeCl₃/PbS, 3 mole NaCl and 2 mole of CaCl₂. The rate equation for the leaching of galena was shown to be in a good agreement with 1- (2/3)R-(1-R)^⅔=K`t.

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Interdiffusion coefficients of manganese D～_(Mn) were investigated as the functions of solute atoms of manganese and impurity atoms of aluminum in FCC-γ phase of Cu-Mn-Al ternary alloy at 800℃ by using the vapor-solid couple method. Diffusivity of manganese are gradually increased by the addition of manganese, but decreased by the addition of aluminum. D～_(Mn) in Cu-Mn binary alloy is 0.50×10^(-9) ㎠/sec at 10a/o Mn, 0.93×10 D～_(Mn) ㎠/sec at 20a/o Mn, but it is decreased by the addition of 0.5a/o Al to 0.43×10^(-9) ㎠/sec at 10a/o Mn, 0.82×10^(-9) ㎠/sec at 20a/o Mn.

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The effect of ultrasonics on the mechanism and mechanical properties of liquid and electro-boronizing has been investigated. Surface hardness and wear resistance were increased by ultrasonics in electro-boronizing and liquid boronizing, the effect of ultrasonic was more effective at lower temperature. The depth of boride layer was increased by ultrasonics, especially, in the case of electro-boronizing, it was found that the case with treating temperature 850℃ and current density 0.5A/㎠ was effective. The increased rate of boronizing is supposed by the following facts; promotion of mixing of salts, activation of surface, acceleration of chemical reaction by degassing effect.

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