• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.31.1-31.1
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• 2009

In an approach to acclimate ourselves torecent ecological consciousness trend, a lead-free piezoelectric material, bismuth sodium titanate (abbreviated as BNT) based bismuth sodium barium titanate (abbreviated as BNT-BT), was considered as an environment-friendly alternative for a lead based piezoelectric system. Ceramic specimens of0.94[(BixNa0.5)TiO3]-0.06[BaTiO3] (x = 0.500~0.515) compositions were prepared by a modified mixed oxide method. To increase the chemical homogeneity andre action activity, high energy mechanical milling machine and pre-milled nanosized powder has been used. In this method (BixNa0.5)TiO3 (x=0.500~0.515) andBaTiO3 were prepared separately from pre-milled constituent materials at low calcination temperature and then separately prepared BNTX (X=1, 2, 3 and 4) and BT were mixed by high energy mechanical milling machine. Without further calcination step the mixed powders were pressed into disk shape and sintered at $1110^{\circ}C$. Microstructures, phase structures and electrical properties of the ceramic specimens were systematically investigated. Highly dense ceramic specimens with homogenous grains were prepared in spite of relatively low sintering temperature. Phase structures were not significantly influenced by the excess amount Bi. Large variation on the piezoelectric and dielectric properties was detected at relative high excess Bi amounts. When $x{\leq}0.505$, the specimens exhibit insignificant variation in piezoelectric and dielectric constant though depolarization temperature is found to be decreased. Considerable amount of decrease in piezoelectric and dielectric properties are observed with higher excess of Bi amounts ($x{\geq}0.505$). This research indicates the advantages of high energy mechanical milling and importance of proper maintenance of Bi stoichiometry.

• 한국세라믹학회지
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• 제50권2호
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• pp.108-115
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• 2013

Oxide coatings were prepared on Al-1050 substrates by an environment-friendly plasma electrolytic oxidation (PEO) process using an electrolytic solution of $Na_2SiO_3$ (8 g/L) and NaOH (3 g/L). The effects of three different duty cycles (20%, 40%, and 60%) and frequencies (50 Hz, 200 Hz, and 800 Hz) on the structure and micro-hardness of the oxide coatings were investigated. XRD analysis revealed that the oxides were mainly composed of ${\alpha}-Al_2O_3$, ${\gamma}-Al_2O_3$, and mullite. The proportion of each crystalline phase depended on various electrical parameters, such as duty cycle and frequency. SEM images indicated that the oxide coatings formed at a 60% duty cycle exhibited relatively coarser surfaces with larger pore sizes and sintering particles. However, the oxides prepared at a 20% duty cycle showed relatively smooth surfaces. The PEO treatment also resulted in a strong adhesion between the oxide coating and the substrate. The oxide coatings were found to improve the micro-hardness with the increase of duty cycle. The structural and physical properties of the oxide coatings were affected by the duty cycles.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 하계학술대회 논문집
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• pp.194-197
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• 1991

In this study, $(Pb_{0.99}La_{0.01})[(Sb_{1/2}Sn_{1/2})_{0.10}Ti_{0.25}Zr_{0.65}]O_3$, added $MnO_2$ (0-0.30[mol%]) ceramics were fabricated by the mixed oxide method. The sintering temperature and time were $1250[^{\circ}C]$, 2[hr], respectively. In the $(Pb_{0.99}La_{0.01})[(Sb_{1/2}Sn_{1/2})_{0.10}Ti_{0.25}Zr_{0.65}]O_3$ added $MnO_2$ (0.24[mol%]) specimens, relative dielectric constant and dielectric loss were minimum values 3.52, 0.003, respectively, and Curie temperature were highest values $256[^{\circ}C]$. Pyroelectric coefficient and voltage responsivity of the $(Pb_{0.99}La_{0.01})[(Sb_{1/2}Sn_{1/2})_{0.10}Ti_{0.25}Zr_{0.65}]O_3$, and added $MnO_2$ (0.24[mol%]) specimen were good values, $6.73{\times}10^{-8}[C/cm^2K],\;125[v/W]$, respectively. Figure of merit of pyroelectric current, voltage and detectivity of the specimen, $(Pb_{0.99}La_{0.01})[(Sb_{1/2}Sn_{1/2})_{0.10}Ti_{0.25}Zr_{0.65}]O_3$ added $MnO_2$ (0.24[mol%]) were good values $2.714{\times}10^{-8}[Ccm/J],\;7.706{\times}10^{-11}[Ccm/J],\;2.640{\times}10^{-8}[Ccm/J]$, respectively. Voltage responsivity of the $(Pb_{0.99}La_{0.01})[(Sb_{1/2}Sn_{1/2})_{0.10}Ti_{0.25}Zr_{0.65}]O_3$ added $MnO_2$ (0.24[mol%]) specimens were decreased with increasing the chopper frequency.

• 한국결정성장학회지
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• 제7권2호
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• pp.284-291
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• 1997

V-Ti(V-rich) 수소저장합금을 기초(base)로 하여 2가지 타입(type)의 전극을 제조하였다. 첫째로 V-Ti 합금에 Ni 분말을 혼합하여 성형한 후 급속가열방법으로 소결하여 전극을 제조하였다. 둘째로 Ni을 V-Ti 합금과 합금화한 V-Ti-Ni 3원계 수소저장합금에 Ni, PTFE 분말을 혼합하여 냉간압축으로 성형하여 전극을 제조하였다. 이와같이 제조된 전극으로 싸이클에따른 충/방전 실험을 한 결과, 모든 전극에 있어 10싸이클 이내에 퇴화(degradation)가 일어났다. 충방전 실험후 전해질내의 조성분석결과 Ti에 비해 V이 많이 전해질 내에 용해되었으며 합금원소의 용해에 의한 표면 형상의 변화가 관찰되었고, 전극표면에 매우 passive 한 Ti-oxide($TiO_2$)가 형성되었다. Ti-oxide($TiO_2$)는 전기전도도가 매우 낮고, 수소에대한 확산계수(diffusivity)도 낮기때문에 전극표면에 형성된 $TiO_2$층은 충/방전 싸이클동안 방전용량을 크게 감소시키는 것으로 나타났다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 D
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• pp.1303-1305
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• 1998

In order to reduce or avoid oxidation problem at operation the interconnects in SOFCs have so far mostly been made of ceramic material. It has high chemical stability both under cathode and anode condition, relatively thermal expansion coefficient that matchs that of electrolyte material YSZ. But this material shown rather weak in the low oxygen atmosphere and thermal shock, and it has lower mechanical strength than alloys. To avoid these problems one may consider to use metals or alloys as materials for interconnects. Metallic interconnects are advantageous because of their high thermal and electronic conductivities. But it has some problems, Those are high thermal expansion and oxidation at high temperature in air. To solve these problems in the interconnection material in this study, $LaCrO_3$-dispersed Cr alloys for metallic interconnector of SOFC have been investigated as a fuction of $LaCrO_3$ content in the range of 5 to 25 vol.%. The Cr alloy were prepared by mixing Cr and $LaCrO_3$ powders in high-energy ball mill for 48h and by sintering under Ar atmosphere with 5vol.% $H_2$ for 10h at $1500^{\circ}C$. The alloys had a relative density of 95% and above. The Cr alloys in composed of two kind of small $LaCrO_3$ and large Cr particles. As the $LaCrO_3$ content increased, the Cr particle size decreased but the $LaCrO_3$ particle size remained contant. Also the oxidation tests show that the $LaCrO_3$-dispersed Cr is very resistant to oxidation in air. These results means that $LaCrO_3$-dispersed Cr is a useful material for metallic interconnect of planar SOFC.

• 한국기계가공학회지
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• 제14권4호
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• pp.62-72
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• 2015

Interest in three-dimensional (3D) printing processes has grown significantly, and several types have been developed. These 3D printing processes are classified as Selective Laser Sintering (SLS), Stereo-Lithography Apparatus (SLA), and Fused Deposition Modeling (FDM). SLS can be applied to many materials, but because it uses a laser-based material removal process, it is expensive. SLA enables fast and precise manufacturing, but available materials are limited. FDM printing's benefits are its reasonable price and easy accessibility. However, metal printing using FDM can involve technical problems, such as suitable component supply or the thermal expansion of the heating part. Thus, FDM printing primarily uses materials with low melting points, such as acrylonitrile butadiene styrene (ABS) or polylactic acid (PLA) resin. In this study, an FDM process for enabling metal printing is suggested. Particularly, the nozzle and heatsink for this process are focused for stable printing. To design the nozzle and heatsink, multi-physical phenomena, including thermal expansion and heat transfer, had to be considered. Therefore, COMSOL Multiphysics, an FEM analysis program, was used to analyze the maximum temperature, thermal expansion, and principal stress. Finally, its performance was confirmed through an experiment.

• 센서학회지
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• 제4권2호
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• pp.37-44
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• 1995

공침법을 이용하여 Ca 및 Pt 가 첨가된 $SnO_{2}$ 미세 분말을 제조하였다. 제조한 미세분말에 대해 TEM, XRD 및 BET 분석으로 결정크기 및 비표면적을 분석하였으며, 제조한 원료분말을 이용하여 스크린 인쇄법으로 후막형 가스 감지 소자를 제작하고, 그 특성과 탄화수소계가스에 대한 감지 특성을 조사하였다. 첨가된 Ca 및 Pt에 의해 하소와 소성의 열처리 과정 중에 $SnO_{2}$ 결정 성장이 억제되었으며, 탄화수소계가스에 대한 응답특성의 향상을 가져왔다. 한편, 소자의 전극으로써 Au 와 Pt를 사용하여 비교 분석하였는데, Au를 전극으로 사용할 경우에 Pt에 비해 가스 감응 특성 면에서 큰 저하를 가져왔다. 이는 Pt 전극도 $CH_{4}$의 산화에 기여했기 때문이다. Ca 및 Pt를 각각 0.1, 1 wt% 첨가한 $SnO_{2}$ 후막소자의 경우 2000 ppm의 $CH_{4}$에 대해 약 83%의 감도를 보였다.

• The Korean Journal of Ceramics
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• 제4권3호
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• pp.249-253
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• 1998

The influence of PbO additive on dielectric properties and sintering behavior of $(Pb_{0.46}Ca_{0.55})$ {$(Fe__1/2}Nb_{1/2}){0.9}Sn_{{0.1}$}$O_3$ ceramics has been investigated. The incorporation of a limited excess PbO ($\leq$2.0 wt. %) in the starting materials is quite beneficial for densification in the temperature range of 1150~$1175^{\circ}C$ in air. At a small doping level (0.8 wt. %) the ceramics prepared from powders calcined at $900^{\circ}C$ showed the best dielectric properties. The dielectric constants ($\varepsilon_r$) and Q.f were found to be 85.8~85.6 and 8530~8600 GHz, respectively. The temperature coefficient of resonant frequency ($\tau_f$) varied in the range of -2~4 $ppm/^{\circ}C$. Examination of the microstructure as well as analysis of the second phases in these materials revealed the presence of the pyrochlore-type phase which is detrimental to the dielectrics.

• 한국세라믹학회지
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• 제40권12호
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• pp.1177-1182
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• 2003

BaTiO$_3$ 분말에 흑연 분말을 첨가하여 BaTiO$_3$계 가스센서용 다공성 감지물을 제조하였으며, 이 감지물의 결정구조와 미세구조를 연구하였다. 이 감지물 소성체는 정방정 perovskite 결정구조를 가지고 있었다 흑연 분말의 첨가량이 증가함에 따라 소성체의 기공도가 증가하였다. 이것은 소성 시 흑연 분말과 산소가 발열반응하여 CO 및 $CO_2$ 가스를 생성하고, 이 가스가 휘발하였기 때문이라고 생각된다. 제조한 BaTiO$_3$계 소성체는 대기에서 측정한 저항과 CO 가스에서 측정한 저항이 고온( >∼20$0^{\circ}C$)에서 큰 차이를 나타내고 있으며 온도가 증가함에 따라 차이가 커짐을 관찰하였다. 소성체 기공도의 증가에 따른 반응 site의 증가로 인하여 소성체의 표면흡착기인 $O_2$$^{-}$와 CO 가스의 반응과, 소성체에 있는 $O^{-}$와 CO 가스의 반응이 활발하기 때문에 CO 가스의 민감도가 크게 증가하였다. 본 연구에서 제조된 다공성 BaTiO$_3$계 세라믹스는 CO 가스센서의 감지물 재료로써 유망하다고 생각된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.352.1-352.1
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• 2014

Indium Tin Oxide (ITO) films are the most extensively studied and commonly used as ones of TCO films. The ITO films having a high electric conductivity and high transparency are easily fabricated on glass substrate at a substrate temperature over $250^{\circ}C$. However, glass substrates are somewhat heavy and brittle, whereas plastic substrates are lightweight, unbreakable, and so on. For these reasons, it has been recently suggested to use plastic substrates for flexible display application instead of glass. Many reaearchers have tried to produce high quality thin films at rood temperatures by using several methods. Therefore, amorphous ITO films excluding thermal process exhibit a decrease in electrical conductivity and optical transparency with time and a very poor chemical stability. However the amorphous Indium Gallium Zinc Oxide (IGZO) offers several advantages. For typical instance, unlike either crystalline or amorphous ITO, same and higher than a-IGZO resistivity is found when no reactive oxygen is added to the sputter chamber, this greatly simplifies the deposition. We reported on the characteristics of a-IGZO thin films were fabricated by RF-magnetron sputtering method on the PEN substrate at room temperature using 3inch sputtering targets different rate of Zn. The homogeneous and stable targets were prepared by calcine and sintering process. Furthermore, two types of IGZO TFT design, a- IGZO source/drain material in TFT and the other a- ITO source/drain material, have been fabricated for comparison with each other. The experimental results reveal that the a- IGZO source/drain electrode in IGZO TFT is shown to be superior TFT performances, compared with a- ITO source/drain electrode in IGZO TFT.