발간논문

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Fabrications of TiS₂ cathode films for Li solid batteries were executed with LPCVD method using TiCl₄ and H₂S as source gases to improve TiS₂ films having (110) crystallographic orientation in which the c-axises were parallel to the substrate plane. A (110) preferentially oriented TiS₂ thin films were obtained at 600℃ and total gas flow rate of about 400sccm. Improvement of surface roughness was obtained at the condition of 550℃ and 20mole ratio of H₂S/TiCl₄. Surface roughness, namely H_(max) of TiS₂ film obtained at 550℃ and of 20 mole ratio condition was about 0.67 ㎛. Micro hardness value was closely related to the surface morphology of TiS₂ film owing to surfacial crystallographic weaving. During discharging process from OCV to 1V at a 50 μA/㎠ current density with a battery system composed of TiS₂ cathode layer and LiClO₄-PC-DME electrolyte, the magnitude of discharge capacity was obtained about 100μAh/㎠

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After performing boronizing treatment on the flame sprayed stainless steel coatings formed on SM45C substrate, mechanical properties and corrosion resistance were investigated. The mechanical properties were measured by microhardness test, abrasion test and bond strength test. the corrosion resistance was examined by potentiodynamic polarization method in 2M H₂SO₄, 2M HCl, 2M H₃PO₄ and 2M HNO₃ solutions. The thickness of boride layers formed on stainless steel coatings increased with boronizing temperature and time. but fairly this layers formed on stainless steel coatings compared with low alloy steels. The microhardness of boronized stainless steel coatings was about 7 times higher than that of as-sprayed stainless steel coatings because of the formation of boride such as FeB and Fe₂B. The wear resistance was also improved about 5 times by boronizing treatment. The corrosion resistance of boronized stainless steel coatings was superior to that of as-sprayed stainless steel coatings in acid solutions as 2M HCl, 2M H₂SO₄ and 2M H₃PO₄. The bond strength between the substrate and stainless steel coatings was increased about two times by boronizing treatment.

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SiC coated WC powders were obtained by a single step carburization of SiO₂ coated W powder. The sinterability of the single step carburized (W-Si)C powders were investigated and compared with the dual step carburized powders which were obtained by carburizing of the powder of SiO₂ powders coated on precarburized WC powders. Silica was coated on the surface of W powder, and the powder was carburized at 1450℃, in H₂ atmosphere. As the amount of coated silica increased from 0.6wt% to 1.2wt%, SiC coated layer thickness increased from 20A˚ to 80A˚. After carburization, the specific surface area decreased. Particle size of the cariburized powder was increased with the coated amount of silica. WC-SiC powder was milled with 10wt% Ni powder, and it was sintered at 1450℃ in vacuum atmosphere after pre-sintering. The sinterability of the single step carburized powders was found to be the same as that of the dual step carburized powders. The exposure time of the carburized powders in the air atmosphere did not affect the sinterability within a week.

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Aluminum matrix composites reinforced with stainless steel chips by hot pressing at 773K, 823K and 873K for 10 min, 30 min and 60 min, respectively, and under 100 MPa and 150 MPa of hot pressing pressure. The maximum tensile strength at room temperature was obtained in composite fabricated at 823K for 10 min under 150 MPa of hot pressing pressure. Due to a reaction between the stainless steel chips and the aluminum matrix at the chips/matrix interface FeAl₃-type intermetallic compounds were formed during the farbrication of the composites by hot pressing. The exess amount of the compounds significantly reduced the strength of the composites since the intermetallic compound of the chips/matrix interface is extremely brittle.

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The experimental results from the fabrication of AC4C/Ni-coated Al₂O₃ composites by oxide dispersion strengthening are summerized as follows; 1) Optimum condition obtained in Ni-Al₂O₃ composites powder preparation was molar ratio of NH₃/Ni^(++) 1.5 : 1, reduction temperature 130℃, stirring speed 600rpm, hydrogen partial pressure 350 psi and reduction time 60 mins. 2) Ni coating to Al₂O₃ surface improved wettability by decreasing surface tension of the matrix and particles. 3) The tensile strength, hardness and wear resistance increased with increasing the volume fraction and decreasing the particle size. In case of the tensile strength at 12vol.% was about 25% higher than that of matrix alloy(Al-2Cu-2Mg).

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