발간논문

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For the purpose of Fe removal in the aluminum and silumin melt containing Fe, multicomponent intermetallic compounds which were formed and precipitated were produced by the absorption filtration experiment. Four types of aluminum sample were made by use of 99.99wt.% aluminum, 12.5-50wt.%Fe ferro-aluminum, 10-20wt.% Mn-Al alloy, 25wt.%Si-Al alloy and 99.99wt.% zinc ball. They were Al-1-5wt.%Fe, Al-3wt.%Fe-2-6wt.%Mn, Al-3wt.%Fe-5wt.%Mn-1.5-7.5wt.%Zn, Al-0.6-4wt.%Fe-12.5wt%Si-1.3-4wt.%Mn. In the heating absorption filtration tower at 670℃ which is cylindrical graphite tube filled with alumina ball or cokes chip, the aluminum or silumin sample melts were made by the absorption filtration experiment. And the results are as follows. 1. Filtered Aluminum alloy having initial Fe concentration under 1.6wt.%Fe had no filtration effect. but avove that had the iron concentration about 1.6t.% that is hypoeutectic region. 2. Filtration of aluminum alloy sample containing both Fe and Mn showed the iron concentration under 0.4wt.%, when the Mn/Fe ration was 4/3. 3. Filtration of aluminum alloy sample containing Fe, Mn and Zn was same as Al-Fe-Mn system. The remaining amount of Mn was also the same. 4. The filtration efficiency of aluminum alloy sample containing only Fe was under 60%. This was probably contributed from the small size of formed intermetallic compound. The filtration efficiency of sample having Fe and Mn was between 70 and 80%. The Zn addition did not have an effect on the filtering efficiency of Fe. 5. The filtration effect of Silumin sample containing Fe was larger than the other cases. Using the alumina ball filter tower, the filtered mass showed. 0.29-0.34wt.%Fe, 0.17-0.33wt.%Mn, and using the cake chip filter tower, showed 0.27-0.35wt.%Fe. 0.17-0.33wt.%Mn.

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Corrosion causes a severe problem in molten carbonate fuel cell(MCFC) at the cell operating temperature of 650℃. To solve the corrosion problem, aluminum was coated by pack cementation on 316L stainless steel which is used for cell housing of MCFC. The coating was done in Ar atmosphere at 900℃ and 1100℃ for 2hrs using a pack composed of aluminum(30wt.%), activator(NH₄Cl:5wt.%) and inert filler(Al₂O₃:balance, 65wt.%) powders. The microstructure of aluminized specimen was examined by scanning electron microscope and phases formed on the specimen were analysed using XRD and EPMA. The non-coated and aluminized specimens were tested in molten carbonate(62㏖%Li₂CO₃-38㏖%K₂CO₃) and their corrosion resistances were evaluated.

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Etching characteristics of Ni₃Al grams was found to depend heavily upon their crystallographic orientation. A selected area electron channeling pattern (SACP) study in the scanning electron microscope has shown that upon etching, grains oriented near <001> appear light, while those oriented near <111> appear dark with a gradual change in gray level for grains of intermediate orientations. The secondary electron images takers from the etched surface have shown that the <111> grains contain many fine pyramidal protrusions, while the <001> grains appear smooth with no such protrusions. The SACP technique has established that the 3 faces of the protruding pyramid consist of {001} planes.

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High temperature oxidation behavior of 19Cr-Ti ferritic stainless steel, which is used for stud pin as a glass sealing material for TV cathode ray tube, has been studied by using thermogravimetric analysis in wet (75%H₂-25%N₂) gas mixture and air, respectively. The oxide film formed on the metal surface by oxidation treatment was investigated by means of SEM, EDS and EPMA. Oxidation rate contants in the wet gas mixture change linearly in the range of 1000℃ to 1200℃, and the activation energy for oxidation was 35.3㎉/mole. The composition of oxide films obtained in both atmosphere was similar but weight gain of oxide obtained in air was higher than that in the vet gas mixture. Around l㎛ Fe metal particles were found on the surface of the oxide film of 19Cr-Ti stainless steel oxidized at 1100℃ in the wet gas mixture. From this observation, the characteristics of scale formation at high temperature can be explained as follows. As temperature goes up, initially both Fe & Cr oxides form on the metal surface but above 950℃ Fe oxide reduction occurs despite Cr oxide prolongs its growth. (Received April 23, 1996)

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The ferrite powders having the composition of Mn Zn_0 Fe₂O₄ were synthesized by hydrothermal process. FeSO₄, MnSO₄and ZnSO₄ were used as divalent precusurs, and Fe₂(SO₄)₃, MnSO₄ and ZnSO₄were used as trivalent salt. MnZn-ferrite powders synthesized at 250℃, for 1hr and at pH=12 had the saturation magnetization of 92emu/g and 98emu/g and square shape and irregular shape for Fe^(2-) and Fe^(3-) respectively. The specific permeability(μ) of sintered toroidal pellets was about 30,000∼40,000 The sintered body which is sintered at 1350℃, for 3hr was nearly closed to theoretical density.

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The main objective of this study is to establish vacuum compo-casting fabrication processes for A356 Al composites reinforced with 15 volume percent SiC particulates. In order to cast the Al-SiC_p composite ingots. a vacuum compo-caster was set up, and casting and stirring variables were optimized. Using the stirring temperature of 610℃ under vacuum of 10^(-2) torr, good quality Al-SiC_p composite ingots having relatively homogeneous microstructure and sound Al/SiC interfacial bonding were obtained, although they contained small amount of micro-pores. The microstructures and mechanical properties of the composites were found to be comparable with those of the conventional composites processed by Duralcan. To process the better composite ingots, elimination of micro-pores, uniform distribution of reinforcements, and optimization of processing variables are suggested.

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Cu/ZSM-5 zeolite catalyst was produced by mechanical alloying and their microstructures together with catalytic reaction mechanism for NO removal were investigated by means of X-ray diffraction, electron microscopy, energy dispersive X-ray spectrometry, and in situ Fourier transform infrared spectroscopy. The results were compared with those from copper ion-exchanged ZSM-5 zeolite catalyst. During mechanical alloying, Copper remains in crystalline and a part of ZSM-5 zeolite transformed to amorphous phase. In the copper ion-exchanged ZSM-5 catalyst, however, copper was found to be noncrystalline, while the ZSM-5 zeolite was crystalline. Cu/ZSM-5 zeolite catalyst produced by mechanical alloying showed a high efficiency in reduction of NO at 250℃. This indicates that at temperatures lower than 300℃ the mechanically alloyed Cu/ZSM-5 catalyst is more effective than Copper ion-exchanged ZSM-5 catalyst whose high efficiency for NO deduction was achieved at 360℃.

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The mechanical properties and electrical conductivity of mechanically alloyed Cu alloys containing either Fe or Cr were investigated. The mechanical alloying process by rod milling was also compared with that by conventional ball milling. Rod milling needed less milling time to reach a steady state in mechanical alloying than ball milling. The grain size of the extruded bar after rod milling was as small as 200 ㎚. The Cu alloys produced by rod milling showed higher thermal stability and higher electrical conductivity than those produced by ball milling. The addition of either Fe or Cr as small as 1vol.% into Cu resulted in high tensile strength over 600MPa and the electrical conductivity of % IACS 68% and 74.5%, respectively.

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