BT-BNT계에서 (Bi_0.5Na_0.5)TiO₃ 첨가에 따른 효과

이미재,백종후,김세기,김빛남,이우영,이경희,Lee, Mi-Jai,Paik, Jong-Hoo,Kim, Sei-Ki,Kim, Bit-Nam,Lee, Woo-Yong,Lee, Kyung-Hee 한국전기전자재료학회 2009 전기전자재료학회논문지 Vol.22 No.1

Lead free positive temperature coefficient of resistivity (PTCR) ceramics based on $BaTiO_3-(Bi_{0.5}Na_{0.5})TiO_3$ solid solution were prepared by a conventional solid state reaction method. The phase structure was showed single phase with perovskite structure regardless calcinations temperature and $Ba_{1-x}(Bi_{0.5}Na_{0.5})_xTiO_3$ structure was transformed from tetragonal to orthorhombic phase at $x{\geq}0.15$ mole. The XRD peaks with $45^{\circ}{\sim}46^{\circ}$ shifted in right the influence of crystal structure change and the intensity of peak was decreased with additive $(Bi_{0.5}Na_{0.5})TiO_3$. The curie temperature risen with additive $(Bi_{0.5}Na_{0.5})TiO_3$ but disappeared for $(Bi_{0.5}Na_{0.5})TiO_3$ addition more than 0.15 mole in TMA. In relative permittivity, the curie temperature by the transform of ferroelectric phase risen with additive $(Bi_{0.5}Na_{0.5})TiO_3$ but decreased in relative permittivity. Also, the peak of new curie temperature showed the sample containing $0.025{\sim}0.045$ mole of $(Bi_{0.5}Na_{0.5})TiO_3$ near $70^{\circ}C$ caused by phase transform from ferroelectric to ferroelectric and the peak of new curie temperature disappeared at 0.045 mole of $(Bi_{0.5}Na_{0.5})TiO_3$. In our study, it was found that the PTCR in $BaTiO_3-(Bi_{0.5}Na_{0.5})TiO_3$ system was possible for $0{\sim}0.025$ mole of $(Bi_{0.5}Na_{0.5})TiO_3$ and the maximum curie temperature by phase transition showed about at $145^{\circ}C$.

초소형 회로보호용 적층 PTC 써미스터의 출발원료 및 Sr 첨가에 따른 전기적 특성

이미재,김빛남,황종희,김진호,박성철,송준백,Lee, Mi-Jai,Kim, Bit-Nan,Hwang, Jong-Hee,Kim, Jin-Ho,Park, Seong-Chul,Song, Jun-Baek 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.6

We investigated the electrical properties the starting material and sintering condition on the laminated PTC thermistor for micro circuit protection. The influences of $BaTiO_3$ powder with the 0.3 and 0.45 ${\mu}m$ size and the electrical characteristics (Ba,Sr)$TiO_3$ sintered at 1350~1400$^{\circ}C$ for 2 h in a reducing atmosphere (1% $H_2/N_2$). The sintered (Ba,Sr)$TiO_3$ was increased pore and the grain size was decreased according to increasing Sr additions. In relative permittivity, the phase transition temperature of (Ba,Sr)$TiO_3$ was decreased for 2.5$^{\circ}C$ according to increasing 0.01 mole Sr additions, and the phase transition dose not appeared about 0.3 mole Sr addition. The (Ba,Sr)$TiO_3$ was show the low resistance from 0.01 mole to 0.05 mole by Sr addition, regardless of sintering temperature. The (Ba,Sr)$TiO_3$ was show $10^2$ jump order at 0.1 and 0.2 mole Sr addition, and PTCR of the sintered $(Ba_{0.7}Sr_{0.3})TiO_3$ does not appeared about 0.3 mole Sr addition, regardless of the sintering temperature and starting material size.

Modified Oxalate Method 의해 합성한 SOFC용(La_0.6Sr_0.4)(Co_0.2Fe_0.8)O₃ Cathode의 pH 변화에 따른 특성

이미재,최병현,김세기,박상선,이경희,Lee, Mi-Jai,Choi, Byung-Hyun,Kim, Sei-Ki,Park, Sang-Sun,Lee, Kyung-Hee 한국전기화학회 2007 한국전기화학회지 Vol.10 No.4

Modified oxalate method에 의해 합성한 중온형 Solid Oxide Fuel Cell 용 LSCF cathoded의 pH 변화에 따른 분말특성 및 여러 종류의 전해질에 따른 전극특성에 대해 연구하였다. LSCF를 합성하기 위한 출발물질로는 La, Sr, Co 및 Fe의 염화물과 oxalic acid, ethanol 및 $NH_4OH$를 사용하여, $80^{\circ}C$ 에서 pH 2, 6, 7, 8, 9 및 10에서 합성하였다. 합성한 LSCF 분말은 pH $2{\sim}9$까지는 단일상의 LSCF 결정상을 생성하였다. 그러나, PH 10에서는 LSCF결정상 외에 이차상인 $La_2O_3$ 결정상이 나타났으며, 또한 $800^{\circ}C$에서 4시간 하소한 경우 50 nm정도의 작은 크기를 나타내었다. 합성한 LSCF cathode 분말의 전기전도도는 pH 7에서 합성한 LSCF 분말의 경우 $600^{\circ}C$부터 $900^{\circ}C$까지 측정하였을 때 약 950 S/cm의 높은 값을 나타내었다. 또한 분극저항의 경우 같은 합성 조건에서 합성한 LSCF 분말이라도 하소조건에 따라 다른 결과를 나타내었는데, $800^{\circ}C$에서 하소한 분말의 경우 $1200^{\circ}C$에서 하소한 분말 보다 낮은 분극저항을 나타내었다. 특히 $800^{\circ}C$에서 4시간 하소하여 합성한 LSCF 분말은 $600^{\circ}C$에서 Scandia Stabilized Zirconia (ScSZ), yttria (8mol.%)-stabilized zirconia(8Y-YSZ) 및 Gadolinium Doped Ceria(GDC) 전해질을 사용하였을 때, 전극면적이 $0.5\;cm^2$일 때 각각 2.52, 1.54 및 $2.58\;{\Omega}$을 나타내었다. The LSCF cathode far Solid Oxide Fuel Cell was investigated to develop high performance unit cell at intermediate temperature by modified oxalate method with different electrolytes and different pH. The LSCF powders employed La, Sr, Co and Fe oxides, oxalic acid, ethanol and $NH_4OH$ solution were synthesized with pH controlled as 2, 6, 7, 8, 9 and 10 at $80^{\circ}C$ Single crystalline phase was obtained from pH $2{\sim}9$. on the other hand, $La_2O_3$ appeared from pH 10. Very fine powder with particle size of 50 nm was obtained at calcination temperature of $800^{\circ}C$ for 4 hours. LSCF cathode synthesized at pH 7 showed the highest electric conductivity in the temperature range of $600^{\circ}C$ to $900^{\circ}C$ its value was 950 S/cm at $900^{\circ}C$ Under same synthesis conditions, polarization resistance of each LSCF cathode was changed with different calcination temperatures. As-prepared powder presented 2.52, 1.54 and $2.58\;{\Omega}$ at $600^{\circ}C$ with ScSZ, 8Y-YSZ and GDC as its electrolyte respectively after calcination at $800^{\circ}C$ for 4 hours.

고순도.미립 $TiO_2$분말 제조에 관한 연구 -고순도화 연구(I)-

이미재,지미정,김환,이철태,최병현,Lee, Mi-Jai,Jee, Mi-Jung,Kim, Hwan,Lee, Chul-Tae,Choi, Byung-Hyun 한국세라믹학회 2000 한국세라믹학회지 Vol.37 No.10

고기능성 전자재료용 TiO$_2$분말 및 박막제조에 사용되는 중간생성물인 TiCl$_4$는 99% 이상의 고순도가 요구된다. 고순도.미립의 TiO$_2$분말 및 TiCl$_4$는 황산법으로 제조한 저순도 TiO$_2$원료를 사용하여 염소화법으로 Ti-염화물 및 염화불순물로 제조한 후, 대부분의 염화불순물들은 3단계 과정을 거쳐 고순화 하였다. 대부분의 염화불순물은 분리.응축 및 분별증류로, VOCl$_3$는 mineral oil을 첨가하여 비등점을 변화시켜, 그리고 미량의 염화불순물은 열가수분해하여 침전시킨 후 유기용제 처리하여 제거하였다. 유기용제 처리는 TiO$_2$분말의 고순도화에 도움이 되었으며, 입자간의 응집을 적게 하여 TiO$_2$입자크기도 작아졌다. 또한 anatase에서 rutile 결정구조로의 전이온도도 낮아지는 부수적인 효과를 보였다.

플렉서블 Li/MnO₂ 일차전지의 제조공정에 따른 전기적 특성

이미재,채유진,김진호,황종희,박상선,Lee, Mi-Jai,Chae, Yoo-Jin,Kim, Jin-Ho,Hwang, Jong-Hee,Park, Sang-Sun 한국재료학회 2012 한국재료학회지 Vol.22 No.12

Manganese dioxide ($MnO_2$) is one of the most important cathode materials used in both aqueous and non-aqueous batteries. The $MnO_2$ polymorph that is used for lithium primary batteries is synthesized either by electrolytic (EMD-$MnO_2$) or chemical methods (CMD-$MnO_2$). Commonly, electrolytic manganese dioxide (EMD) is used as a cathode mixture material for dry-cell batteries, such as a alkaline batteries, zinc-carbon batteries, rechargeable alkaline batteries, etc. The characteristics of lithium/manganese-dioxide primary cells fabricated with EMD-$MnO_2$ powders as cathode were compared as a function of the parameters of a manufacturing process. The flexible primary cells were prepared with EMD-$MnO_2$, active carbon, and poly vinylidene fluoride (PVDF) binder (10 wt.%) coated on an Al foil substrate. A cathode sheet with micro-porous showed a higher discharge capacity than a cathode sheet compacted by a press process. As the amount of EMD-$MnO_2$ increased, the electrical conductivity decreased and the electrical capacity increased. The cell subjected to heat-treatment at $200^{\circ}C$ for 1 hr showed a high discharge capacity. The flexible primary cell made using the optimum conditions showed a capacity and an average voltage of 220 mAh/g and 2.8 V, respectively, at $437.5{\mu}A$.

전사법을 이용하여 제조한 SOFC 단전지의 특성 분석

이미재,김빛남,임태영,김세기,최병현,Lee, Mi-Jai,Kim, Bit-Nan,Lim, Tae-Young,Kim, Sei-Ki,Choi, Byung-Hyun 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.6

The properties of manufactured SOFC unit cell using decalcomania method were investigated. The decalcomania method that used in ceramics, dish, vessel and etc. was the very simple process. The SOFC unit cell manufacturer using decalcomania method is very simple process. Especially, the decalcomania method was the most suitable manufacturing method for the segmented type SOFC. The cathode, prevent diffusion layer (PDL), anode functional layer (AFL) and electrolyte were manufactured using decalcomania method on porous anode support. The sintered electrolyte at 1450$^{\circ}C$ for 2 h using decalcomania method was very dense, and the thickness was about 10 ${\mu}m$. The cathode, the PDL and the AFL were manufactured using decalcomania method and was sintered at 1250$^{\circ}C$ for 2 h, and the sintered electrodes were the porous. As a result, with humidified hydrogen used as fuel, the cell with an 15 ${\mu}m$-thick AFL exhibited maximum power densities of 0.246, 0.364, 0.504W/$cm^2$ at 700, 750, 800$^{\circ}C$, respectively.

적층 SMD형 PTC 써미스터의 열처리 조건에 따른 PTCR 특성 변화

이미재,장재원,임태영,박성철,송준백,한정화,Lee, Mi-Jai,Jang, Jae-Woon,Lim, Tae-Young,Park, Seong-Chul,Song, Jun-Baek,Han, Cheong-Hwa 한국세라믹학회 2012 한국세라믹학회지 Vol.49 No.5

Electrical properties of the laminated SMD-type PTC thermistor for microcircuit protection were investigated as a function of calcination and sintering temperature. $BaTiO_3$ with $Y_2O_3$ and $MnO_2$ were calcined at 1000 to $1150^{\circ}C$ for 2h and the laminated SMD-type PTC thermistor was sintered at 1350 to $1400^{\circ}C$ for 2h in a reduced atmosphere (1% $H_2/N_2$). Sintered density of the sample was dependent on the calcination and sintering temperature. Electrical properties of the sintered samples were strongly dependent on the densities of samples. For the samples with density below 4.6 g/$cm^3$, the insulator characteristics were observed, while PTC jump characteristics (R150/R30) were disappeared for the sample with density above 5.05 g/$m^3$. Optimal PTC characteristics were obtained for the sintered samples with density of 5.05 g/$m^3$. The laminated SMD-type PTC thermistor prepared by calcination at $1100^{\circ}C$ for 2h and sintering at $1270^{\circ}C$ for 2h showed the room temperature resistivity of $11{\Omega}{\cdot}cm$ and PTC jump characteristics of $10^2$ order.

된소리 현상의 새 분석

이미재,Lee Mi-Jae 대한음성학회 1993 말소리 Vol.25 No.-

This paper deals with the nature and function of intensification in Korean in a wider scope of context which was not paid proper attention. Unobserved new areas of intensification are paid more attention like sound split of polysemy e.g. [s'eda], [kyongk'i] by n of intensification and north Korean application of intensification on [wonsu] and intensification of borrowed English. The recent phenomenon of 'gwua' intensification is experimented on two groups of people, young students and old people beyond 65 years old by means of sociolinguistic analysis. The result shows that its intensification is a form of student violent power and a mark of extreme solidarity among activist students. In conclusion, the nature of so called saisiot[t] e.g. intensification is voiceless tensed pause and its functions are the polarization of the original meaning of the word, sound split of polysemy and attachment of social values by intensification.

Sr과 Mg 첨가량 및 소결조건에 따른 LSGM계 전해질의 특성 변화

이미재,박상선,최병현,Lee, Mi-Jai,Park, Sang-Sun,Choi, Byung-Hyun 한국세라믹학회 2002 한국세라믹학회지 Vol.39 No.4

The variations of the properties of Sr and Mg added $LaGaO_3$ system electrolyte with the amount of the additive and the sintering condition were studied. Main phase was (La$_{1-x}Sr_x)(Ga_{1-y}Mg_y)O_{3-\delta}$ phase for each compositions and the single phases $(La_{0.85}Sr_{0.15})(Ga_{0.85}Mg_{0.15})O_{3-\delta},(La_{0.85}Sr_{0.15})(Ga_{0.8}Mg_{0.2})O_{3-\delta}$ and $(La_{0.8}Sr_{0.2})(Ga_{0.8}Mg_{0.2})O{3-\delta}$ were obtained with the decrease in the sintering temperature and Mg addition. Thermal expansion coefficient of the $(La_{0.8}Sr_{0.2})(Ga_{0.8}Mg_{0.2})O_{3-\delta}$ decreased with the increase in the sintering temperature. Electric conductivity of electrolyte sintered at $1500^{circ}C$ for 1h was 0.14 S/cm at $800^{circ}C$ with 1 mA. 고체산화물 연료전지의 전해질로서 $LaGaO_3$계를 선정하여 La 대신 Sr을, Ga 대신에 Mg를 치환하여 첨가할 때 첨가량 및 소결 조건에 따라 전해질을 제조하고, 그 특성을 조사하였다. Sr과 Mg가 0.15와 0.20 mole 첨가되었을 때 Sr과 Mg가 La와Ga 자리에 동시 고용되어 (La$_{1-x}Sr_x)(Ga_{1-y}Mg_y)O_{3-\delta}$ 단일상이 나타났고, 일부 조성에서는 $LaSrGa_3O_7$ 상과 $LaSrGaO_4$ 상이 2차상으로 나타났다. $LaSrGa_3O_7$ 상은 Sr과 Mg 첨가에 의한 상이며, $LaSrGaO_4$ 상은 액상형성에 의한 것으로 나타났으며, 또한 $LaSrGaO_4$ 상은 소결온도와 Mg 첨가량이 감소함에 따라 얻어졌다. $(La_{0.8}Sr_{0.2})(Ga_{0.8}Mg_{0.2})O_{3-\delta}$ 상의 경우 소결온도를 증가함에 따라 열팽창계수는 감소하였으며, $1500^{circ}C$에서 1시간 소결한 소결체의 전기전도도는 $800^{circ}C$, 1mA에서 0.14S/cm를 나타내었다.

Na 및 K 치환에 따른 BaTiO₃의 Positive Temperature Coefficient Resistor 특성

이미재,임태영,김세기,황종희,김진호,서원선,Lee, Mi-Jai,Lim, Tae-Young,Kim, Sei-Ki,Hwang, Jong-Hee,Kim, Jin-Ho,Seo, Won-Seon 한국재료학회 2010 한국재료학회지 Vol.20 No.12

The influences of Na and K content on the crystal phase, the microstructure and the electrical property of $BaTiO_3$-based thermistors was found to show typical PTC effects. The crystal phase of powder calcined at $1000^{\circ}C$ for 4hrs showed a single phase with $BaTiO_3$, and the crystal structure was transformed from tetragonal to cubic phase according to added amounts of Na and K. In XRD results at $43^{\circ}\sim47^{\circ}$, the $(Ba_{0.858}Na_{0.071}K_{0.071})(Ti_{0.9985}Nb_{0.0015})O_{3-\delta}$ showed (002) and (200) peaks but the $(Ba_{0.762}Na_{0.119}K_{0.119})(Ti_{0.9975}Nb_{0.0025})O_{3-\delta}$ showed (002), (020) and (200) peaks. In sintered bodies, those calcined at $600^{\circ}C$ rather than at $1000^{\circ}C$ were dense, and for certain amounts of Na and K showed rapid decreases in grain size. In relative permittivity, the curie temperature due to the transformation of ferroelectric phase rose with added Na and K but decreased in terms of relative permittivity. In the result of the R-T curve, the sintered bodies have curie temperatures of about $140^{\circ}C$ and the resistivity of sintered bodies have scores of $\Omega{\cdot}cm$; the jump order of sintered bodies was shown to be more than $10^4$ in powder calcined at $1000^{\circ}C$.