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황산용액중의 납의 산화반응에 대한 전기화학적 등가회로해석
김기원 국립경상대학교 공과대학 부설 첨단소재연구소 1991 尖端素材 Vol.1 No.-
In order to verify that the oxidation mechanism of lead in sulfuric acid solution at low overpotential region is a series two step process of dissolution-crystallization, electrochemical equivalent circuit analysis was done for the reaction at equilibrium potential with data obtained by A.C. Impedance measurements. From the results of analysis, it was considered to be reasonable that the oxidation mechanism of lead at low overpotential region was a dissolution-crystallization process.
Jung, Yun-Chul,Ohmori, Yasuya,Nakai, Kiyomichi,Hirosawa, Satoshi,Kanekiyo, Hirokazu 경상대학교 첨단소재연구소 2001 NANO 기술 심포지엄 Vol.2001 No.1
The effect of Cr addition on the crystallization processes and the magnetic properties of Nd4.5Fe77-xB18.5(x = 1 to 20at%) amorphous ribbons have been investigated by means of DTA, XRD and HRTEM. The crystallization sequences of the amorphous ribbons with 0 to 5% Cr can be expressed as: Am (amorphous)→Fe3B+[Am]→Nd2Fe23B3+[Am+Fe3B]→Nd2Fe14B+[Am+Fe3B+Nd2Fe23B3]→〈-Fe+[Fe3B+Nd2Fe23B3+Nd2Fe14B3+Nd2Fe14B]→[Fe3B+Nd2Fe14B+〈-Fe]→ NdFe4B4+[Fe3B+Nd2Fe23B+〈-Fe]. In the ribbons with Cr above 10%, the Cr1.65Fe0.35B0.96 and the (Cr, Fe)2B phases were formed instead of Nd2Fe23B3 and NdFe4B4, respectively. By the Addition of Cr, the crystallization temperature and the incubation time for the first crystallization increased and the formation of Nd2Fe23B3 was suppressed. With increasing the amounts of Cr content, the coercive force increased. However, the crystallization temperature and the incubation time for the first crystallization decreased in the 1% Cr ribbon.
Al₂O₃의 미세구조와 기계적성질에 미치는 Mo 첨가의 영향
정원도,배원태 국립경상대학교 공과대학 부설 첨단소재연구소 1991 尖端素材 Vol.1 No.-
The effects of Mo addition on the microstructure and mechanical properties of Al₂O₃ were studied, Mo powders with average sizes of 6, 1.6, and 0.6 ㎛ were dispersed in Al₂O₃. Mo particles suppressed the grain growth of Al₂O₃. With the increase of Mo amount, the relative densities of Al₂O₃/Mo composites decreased. Regardless of the particle size of Mo, the bending strength and the fracture toughness were maximized when 2.5 and 5 vol% of Mo were added respectively. When the 0.6 ㎛ Mo was used, the relative density, the bending strength, and the fracture toughness were higher than others. Comminution of 0.6 ㎛ Mo was not effective in increasing the bending strength and fracture toughness. The toughening mechani는 of Al₂O₃/Mo composite are thought to be the crack deflection and microcracking.
조직이 불균질화된 Al₂O₃-Zr₂O 복합체의 열-기계적 성질
김의훈,황규홍 국립경상대학교 공과대학 부설 첨단소재연구소 1991 尖端素材 Vol.1 No.-
The thermo-mechanical properties of Al₂O₃-ZrO₂ ceramics having dual microstructure were studied. The Al₂O₃-ZrO₂composites having dual microstructure were fabricated by dry mixing the sieve-granulated Al₂O₃vol.% (t)ZrO₂ granule and 15 to 30 vol.% Al₂O₃-20 vol.% (m) ZrO₂granule, followed by isostatic pressing and sintering at 1600℃ for 1 hr. So Al₂O₃-20 vol.% (t)ZrO₂part was become to matrix region and Al₂O₃-20 vol.% (m)ZrO₂part was become to dispersed region as irregular sieve-shaked granule shape. When weak granule was used for dispersed region, initial strength was slightly decreased than the matrix composite, but retained strength after thermal shock was increased. And if weak granule have been used for dispersed region smaller than that for matrix region, critical temperature and strength was slightly increased due to the different existing shape of dispersed region in the duplex composites. But strong granule made by high temperature calicination was used for dispersed region, thermal shock behavior showed stable crack growth because the dispersed region had lower density than matrix.
염화물수용액중에서 니켈및 아연의 니켈금속표면에서의 전해환원 분극곡선
김기원 국립경상대학교 공과대학 부설 첨단소재연구소 1992 尖端素材 Vol.2 No.-
Cathodic polarization curves of nickel and zinc on nickel electrode in aqueous chloride solution were obtained using potentiodynamic polarization methode. The cathodic current density considered due to metallic nickel formation was extremely small in week acid solution, but in strong acid solution, it greatly increased. And, it was independent on nickel ion concentration. Equilibrium potentials of nickel electrode were also highly dependent on hydrogen ion concentration of chloride solution. From these result, it could be expressed that reduction of nickel oxide layer existing on nickel surface to metallic nickel preceded direct deposition of nickel from aqueous ionic state in chloride solution.
안효준 국립경상대학교 공과대학 부설 첨단소재연구소 1993 尖端素材 Vol.3 No.-
In order to study the phase changes of ErFe₂by hydrogenation reaction, static and cyclic hydrogenation were performed. During the static isothermal hydrogenation, an amorphous hydride phase is observed at about 200℃, and phase decomposition of stable hydride, ErH₂and Fe at 350℃. Hydrogen absorption-desorption cycling results in a decrease in the reversible hydrogen content with increasing number of cycles. As a result of degradation, amorphous of mixed ErH₂and Fe phases are formed. The heat of hydrogenation and repetitive strain induce a phase decompositiobn. Amorphous hydride phase formation as wel as binary stable hydride is one of the possible degradation mechanism of the metal hydride during cyclic operation.
황규홍,박정환,윤태경,김의훈 국립경상대학교 공과대학 부설 첨단소재연구소 1993 尖端素材 Vol.3 No.-
The reaction-sintered alumina ceramics were fabricated using the oxidation of Al, and their properties were measured. Alumina ceramics of low dimensional changes were prepared from the Al₂O₃/Al powder mixtures using the volume expansion due to the oxidation of Al. Intensive milling process such as attrition milling was beneficial for homogeneous oxidation of Al. After isopressing at 50 to 400 MPa the specimens were oxidated at 800∼1200℃ for 8 hrs. During this process fine alumina grain was formed at the surface of Al and volume expansion was occured. Sintering was carried out at 1450 to 1600℃ for 3 hrs. The sintered density of 97% theoretical was achieved, but low contents of Al leads to relatively high shrinkage of about 8%. On the other hand Al₂O₃/AlMg powder compacts were easily densified at the relatively low sintering temperature of 1450℃. But relatively high shrinkage was obtained due to the spinel formation. So SiC was added to compensate the large shrinkage because the volume of SiC was much increased during the oxidation that near net shape product could be fabricated. But in the contrary to the Al₂O₃/Al composites, the sintered body of Al₂O₃/Al-Mg/SiC was consisted of alumina and spinel phases. And mullite was formed at the higher SiC contents.
곽주섭,강은태 국립경상대학교 공과대학 부설 첨단소재연구소 1992 尖端素材 Vol.2 No.-
The reactions between water and mixed alkali glasses have been studied in the several temperatures and times ranging from a few to several houndred minutes. The effects of composition, SA/V ratios, and temperatures on the chemical durability were examined and the magnitude of the mixed-alkali effect was shown to be related to both the corrosion kinetics and the dominant mechanism of corrosion. If SA/V and temperature are higher, the mixed-alkali effect become large. Fro pH≥9, this effect also clearly appears. Because the leaching tendency of alkali and SiO₂are similar, the corrosion mechanism can be explained by ion-exchange and congruent leaching for SiO₂-rich nrotective laver.