발간논문

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The eutectic structure of gray iron is determined by the manner in which solidification takes place through the eutectic temperature and by the status of iron melts which depends not only on the composition, metallographic structure of cast irons but their melting conditions. The main purpose of the present investigation was to study the effects of metallographic structures and the melting conditions of cast iron on solidification at a given composition and results obtained are as follows : 1) The higher temperature and the longer holding time were applied in melting of iron, the lower eutectic temperature were observed. 2) The white iron remelted at high temperature gave rise to the more degree of supercooling, compared with the gray iron with the same composition and in the same cooling rate. 3) Differences in melting of the flake graphite in gray iron and of the temper-carbon decomposed from white iron have been discussed.

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In order to study the effect of pressure during the solidification on the structure and tensile strength, Zn-22% Al alloy was subjected to pressure as high as 250∼1000 ㎏/㎠ during solidification, and poured into cylindrical steel mould from crucible electric furnace. The application of pressure during solidification has been shown to induce a number of important modification to the gravity cast structure. Chief among these were as follows. 1. Suppression of piping 2. Elimination of pores. 3. Columnar crystal change to equiaxed crystal by increasing the applied pressure. 4. Refining of grain size and markedly improving of tensile strength

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The diffusivity of carbon in austenite containing 3%-Ni, 0.8%-Cr and 0.45%-Mo has been determined using diffusion couples for the temperature range 1,000℃ to 1,200℃. The diffusion coefficient of carbon increases approximately 50% as the carbon concentration is increased from 0.1 to 0.5 Wt. percent. The rate of diffusion of carbon is not appreciably affected by the presence of alloying elements at about 1,000℃ but slightly accelerated at higher temperature and slightly retarded at lower temperature. This retardation can explain only a amall part of the effect of these alloying elements on hardenability of Ni-Cr-Mo steel. The diffusion equation is D=D_o exp(-36.6 ㎉/RT), where D_o varies from 0.53 to 0.74 between 0.1 and 0.5 weight percent carbon.

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The aging effect of Fe-Cr-Ni alloys at about 500℃ has been investigated by using the Mo¨ssbauer effect and the magnetic measurements. From the comparison between the Mo¨ssbauer patterns of the quenched and the aged specimens, it has been revealed that the anomalous behaviour of some physical properties associated with aging of the specimens is possibly due to the simultaneous precipitation of Fe-rich and Cr-rich phases.

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The reaction between wolframate ion, WO₄^=, H^+ and mannitol has been studied at 25℃. The reaction was found to be: 2H^+＋2WO₄^=＋C_6H_(14)O_6=W₂O_7·C_6H_(14)O_6^=＋H₂O with the equilibrium constant. logk=20.24±0.04. Acidimetric determination of wolframate in the presence of mannitol has been studied potentiometrically. Mixed indicator made of bromcresol green: methyl red=3:2 was found to be best indicator for this titration. Effect of mannitol concentration and influences of molybdate, silicate, and carbonate have been studied. Analytical procedure was described for the determination of wolframate in pregnant solution obtained by pressure leaching of Scheelite.

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The electrorefining of crude lead was studied in a lead perchlorate-perchloric acid electrolyte. Curves of cathodic and anodic polarization of lead showed that with increasing in lead concentration the polarization of both electrodes decreased considerably. Even at high current density of 3A/d㎡ Ag, Cu, Bi and Sb were removed from lead as slime. In the presence of small amount of gelatine smooth and uniform thick cathode deposits were obtained. Current efficiency was 99.5∼99.9%.

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