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      • 상수도 강관용 세라믹 코팅의 특성 분석

        李豊憲,李揆鎭 홍익대학교 산업기술연구소 2002 産業技術 Vol.12 No.-

        A ceramic coating of glass was deposited on a water supply steel pipe sample and its microstructure and chemical resistance were evaluated. Glass enamel coating was found to be relatively uniform over the substrate surface. However, a number of pin holes were observed due to the evolution of gases formed from the steel substrate. Iron oxide was present along with glass in the coating, as a result of oxidation of the substrate exposed by pin holes. The chemical resistance tests showed that the coating has less chemical resistance than industrial coating reported in the literature. This resulted from the chemical composition of the enamel glaze used in this study.

      • 흑연질 브러쉬 제조에 있어서 흑연화 조건에 관한 연구

        李豊憲 홍익대학교 산업기술연구소 1998 産業技術 Vol.8 No.-

        Samples for graphitization were prepared using 33% coal tar pith as a binder and forming pressure at 15㎏/㎤. The bulk density was found to be 1.45g/㎤ before sintering and 1.51g/㎤ after sintering, respectively as-sintered sample had 1.45g/㎤ of bulk density, 25% of porosity and 384 ㎏/㎠ of hending strength. After the impregnation process was repeated several times. however, the samples exhibited optimum physical properties having 1.76g/㎤ of bulk density and 3.8% of porosity. The results of graphitization at 1800-2300℃ showed that the degree of graphitization could be optimized up to 65% and specific resistivity was 6.3×10 exp (3) Ω·cm at 2300℃.

      • 전동차용 흑연질 브러쉬 제조에 있어서 함침, 흑연화 조건에 관한 연구

        李豊憲 홍익대학교 산업기술연구소 1997 産業技術 Vol.7 No.-

        We have taken specimens with coal tar pitch 33% as binder and formation pressure 15㎏/㎠. The result of the volume density of these specimens were shown 1.45㎏/㎤ before sintering and 1.51g/㎤ after sintering at 1300℃. At first these sample were presented volume density 1.45g/㎤. porosity 25%, bending strength 384 ㎏/㎠. After several time impregration process using pitch, however, these specimens were shown optimum physical properties with increasing of volume density 1.76g/㎤, porosity 3.8%.

      • 경량골재 형성에 미치는 폐 FRP의 열분해 특성

        李豊憲,李揆鎭 홍익대학교 산업기술연구소 2003 産業技術 Vol.13 No.-

        In order to utilize waste FRP as lightweight aggregates, waste FRP was thermally decomposed in N2 and air atmospheres. Thermal analysis and ball milling of the decomposed FRP were carried out and the results were evaluated with respect to forming and foam structure of the aggregate. The decomposed FRP containing char and glass fiber was found to be milled with ease and formed into aggregate. Decomposition of FRP in N2 atmosphere resulted in a large amount of char, which remained during firing due to glassy phase formed. However, decomposition in air reduced the amount of char and resulted in foam structure with isolated pores and low density. The results of thermal analysis indicate that porous lightweight aggregates can be fabricated by controlling the amount of char and adding a foam agent.

      • ZnCr_2O_4의 습도감지 특성에 미치는 MgO및 PbO의 치환효과

        李豊憲 홍익대학교 산업기술연구소 1994 産業技術 Vol.4 No.-

        Through ZnO substitution in spinel type ZnCro_2O_4 with MgO or PbO were synthesized by the method of coprecipitation. Its crystal structure was confirmed with x-ray diffraction analysis and scanning electron micrograph. The humidity sensing characterostics and its mechanism were studied by measuring the electical resistance in the various concentration of moisture. These syntesized compounds were found to be spine type cubic structure. The Humidity sensing ability was improved by substitution of MgP or PbO.

      • ZnCr_2O_4 소결체의 가스감지 특성에 관한 연구

        李豊憲 홍익대학교 산업기술연구소 1995 産業技術 Vol.5 No.-

        Through ZnO Substitution in spinel type ZnCr_2O_4 with CoO NiO CuO were synthesized by method of coprecipitation. Its crystal structure was confirmed with x-ray diffraction analysis asnd scanning electron micrograph and its thermochemical properties were inspected by TG-DTA analysis. The gas sensing characteristics and its mechanism were studied by measuring the electerical resistance in the various concentration of propane. These synthesized compounds were found to be spinel type cubic structure. The substiation fo CoO NiO and CuO shoued excellent gas sensitivity. The response in propane environment reached the maximum value at avout 2000ppm of each gas content. The gas sensitivity reached a maximim peak at the operating temperature of 400℃ and this was the temperature at which the exothermic peak appeared on DTA curve. Theresponse properties of these compounds to propane showed the characteristics of p-type semiconductor.

      • Thermodynamic Analysis on the Phase Diagram of NiO-MgO System

        李豊憲 홍익대학교 산업기술연구소 1996 産業技術 Vol.6 No.-

        깁스 자유에너지의 표현을 사용한 열역학적 모델링으로부 MgO-NiO 계 상태도가 분석되었다. 액체 용액에 대하여 규칙용액이 그리고 고체 용액에 대하여 이상용액이 가정되었으며, 이는 두 용액에 대하여 이상용액을 가정한 결과보다 휠씬더 실험치에 접근하였다.

      • 수소로 환원한 Mn_xFe_3-xO_4를 이용한 이산화탄소의 분해

        李豊憲 홍익대학교 산업기술연구소 2001 産業技術 Vol.11 No.-

        Decompose carbondioxide, Mn_xFe_3-xO_4 was synthesized with FeSO_4·7H_2O, MnSO_4·H_2O and NaOH by coprecipitation. Synthesized catalyst was prepared by hydrogen reduction for 2hr at 350℃. The crystal structure of the synthesized catalyst was indentified spinel structure by X-ray powder diffractions. With the increse of Mn the decomposition rate of carbon dioxide was decreased.

      • YSZ에 코팅된 NiO 나노입자의 결정성장 거동

        李豊憲 弘益大學校 産業技術硏究所 2005 産業技術 Vol.15 No.-

        Powders of Ni hydroxide-coated YSZ and Ni precipitate were prepared and crystal growth of NiO in the powders was investigated. The crystallization of NiO from Ni hydroxide was retarded on YSZ surfaces and occurred at higher temperature than that on Ni precipitate powder. NiO crystallite on the Ni precipitate powder grew rapidly without any constraint as the calcination temperature increased, resulting in ~100 ㎚ size at 800℃. However, growth of NiO crystallite on the YSZ surface was significantly retarded and resulted only in ~30 ㎚ size at 800℃.

      • SCOPUSKCI등재

        Y<sub>2</sub>O<sub>3</sub>가 도핑된 SrZrO<sub>3</sub>-금속전극계의 전기전도 특성

        백현덕,이풍헌,Baek, Hyun-Deok,Lee, Poong-Hun 한국세라믹학회 2002 한국세라믹학회지 Vol.39 No.4

        Electrical conduction in $SrZr_{1-x}Y_xO_{3-\delta}$((x=0.05, 0.10)-metal electrode system was investigated by impedance spectroscopy and two-probe d.c. conductivity measurement. Electrode conductivity in anodic direction varies with $P_W^{1/2}$( and that in cathodic direction with $P_{O2}^{1/4}$ in oxidizing atmosphere. In hydrogen atmosphere, the addition of water vapor increased the electrode conductivity both in anodic and cathodic direction. Increasing dopant concentration from 5 to 10% showed a more than four times increase in anodic conduction as well as bulk conduction of the solid electrolyte. This observation implies that unfilled oxygen vacancy concentration increases rapidly as the dopant content increases in humid atmosphere. The activation energy of cathodic conduction in Pt and Ag electrode was nearly same below $800^{\circ}C$ which means the rate of cathodic reaction is determined by the reaction in the electrolyte surface rather than on the metal electrodes. $SrZr_{1-x}Y_xO_{3-\delta}$(x=0.05, 0.10)-금속전극 계에서 임피던스법과 d.c.법으로 전기전도도를 측정함으로써 고체전해질 및 전극전도도를 고찰하였다. 고체전해질과 anode를 통한 전기전도도는 $P_W^{1/2}$(PW는 수증기분압)에 의존하여 증가함을 보였다. Cathode 전도도는 $P_{O2}^{1/4}$에 비례함을 보였으며, 수증기분압 증가와 함께 감소하여 고체전해질내의 전자 결함의 농도와 함께 증가하는 것을 알 수 있었다. 수소분위기에서는 수증기의 첨가가 anode와 cathode 두 방향의 전극반응 속도 모두를 촉진하였다. 도펀트 첨가량이 5%에서 10%로 증가될 때 anode와 고체전해질의 전기전도도가 3배 이상 크게 증가하여 유효 산소이온공공의 농도가 급격히 증가함을 알 수 있었다. Pt와 Ag전극을 통한 cathode 전도도의 활성화에너지가 거의 같은 값을 나타냈으며 이는 cathode반응의 속도가 금속전극이 아니라 고체전해질표면에서 일어나는 반응에 의하여 결정되는 것으로 해석되었다.

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