• Progress in Superconductivity
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• 제14권1호
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• pp.39-44
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• 2012

The fabrications condition and superconducting properties of top-seeded melt growth (TSMG) processed $GdBa_2Cu_3O_{7-y}$ (Gd123) bulk superconductors were studied. Processing parameters (a maximum temperature ($T_{max}$), a temperature for crystal growth ($T_G$) and a cooling rate ($R_G$) through a peritectic temperature ($T_P$) for the fabrication of single grain Gd123 superconductors were optimized. The magnetic levitation forces, trapped magnetic fields, superconducting transition temperature ($T_c$) and critical current density ($J_c$) of the Gd123 bulks superconductors were estimated. Single grain Gd123 bulk superconductors were successfully fabricated at the optimized processing condition. The $T_c$ of a TSMG processed Gd123 sample was 92.5 K and the $J_c$ at 77 K and 0 T was approximately $50kA/cm^2$. The trapped magnetic field contour and magnetic levitation forces were dependent on the top surface morphology of TSMG processed Gd123 samples. The single grain Gd123 samples, field-cooled at 77 K using a Nd-B-Fe permanent magnet with 5.27 kG and 30 mm dia., showed the trapped magnetic field contour of a single grain with a maximum of 4 kG at the sample center. The maximum magnetic levitation forces of the single grain Gd123 sample, field-cooled or zero field-cooled, were 40 N and 107 N, respectively.

• 한국결정성장학회지
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• 제12권2호
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• pp.91-95
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• 2002

Titannium tetra-isoporpoxide의 가수분해 반응을 이용하여 nanosize의 $TiO_2$powder를 합성하고, 가수분해 반응에 있어서 촉매로 사용되는 HCI과 $NH_4$OH의 첨가량에 따른 반응양상과 생성된 $TiO_2$분말의 특성의 변화를 조사하였다. 염기성 촉매인 $NH_4$OH,를 사용하였을 경우에 균질한 형상의 powder 형태의 $TiO_2$를 합성할 수 있었으며, 산성 촉매인 HCI을 사 용하여 p보가 5.04 이하일 경우에는 괴상이나 과립의 형태로 생성되었다. 사용한 촉매의 종류와 양에 따라 저온의 결정상인 anatase의 생성속도와 보다 안정한 rutile상으로의 상전이 속도가 영향을 받았다.

• 접착 및 계면
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• 제21권3호
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• pp.113-122
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• 2020

중간 세공체(mesoporous) 물질은 높은 표면적과 조절 가능한 기공 크기를 가진 규칙적인 다공성 구조로 최근 다양한 응용분야를 가진 매력적인 재료로 알려져 있다. 중간 세공체 물질 중 특히 유/무기 하이브리드형 실리카 나노세공체(Periodic Mesoporous Organosilica; PMO)는 세공의 크기가 확대되고 골격에 유기물을 도입함으로써 더욱 다양한 응용분야를 확보할 수 있는 새로운 재료로 큰 주목을 받고 있다. 골격 구조에 유기 그룹을 도입하게 되면 표면 물성과 재료 전체 물성의 제어가 가능하게 된다. 본 총설은 PMO의 합성, 기능성, 모폴로지는 물론이고 촉매나 환경분야 응용 등을 포함한 내용을 개괄적으로 고찰하였으므로, PMO의 주요 기능과 응용성에 대한 이해를 높이는데 기여할 것이다.

• 한국분말재료학회지
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• 제29권6호
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• pp.485-491
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• 2022

Lithium lanthanum titanium oxide (LLTO) is a promising ceramic electrolyte because of its high ionic conductivity at room temperature, low electrical conductivity, and outstanding physical properties. Several routes for the synthesis of bulk LLTO are known, in particular, solid-state synthesis and sol-gel method. However, the extremely low ionic conductivity of LLTO at grain boundaries is one of the major problems for practical applications. To diminish the grain boundary effect, the structure of LLTO is tuned to nanoscale morphology with structures of different dimensionalities (0D spheres, and 1D tubes and wires); this strategy has great potential to enhance the ion conduction by intensifying Li diffusion and minimizing the grain boundary resistance. Therefore, in this work, 0D spherical LLTO is synthesized using ultrasonic spray pyrolysis (USP). The USP method primarily yields spherical particles from the droplets generated by ultrasonic waves passed through several heating zones. LLTO is synthesized using USP, and the effects of each precursor and their mechanisms as well as synthesis parameters are analyzed and discussed to optimize the synthesis. The phase structure of the obtained materials is analyzed using X-ray diffraction, and their morphology and particle size are analyzed using field-emission scanning electron microscopy.

• 한국광물학회지
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• 제1권2호
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• pp.117-130
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• 1988

감포지역(甘浦地域)에서 산출(産出)되는 성질(性質)이 다른 시료(試料)들을 전자현미경(電子顯微鏡)에 의하여 그 형태적(形態的) 특징(特徵)을 관찰한 결과 몬모릴로나이트는 화산성물질(火山性物質) 즉 응회암기원(凝灰岩起源)임을 지시(指示)한다. 주사전자현미경(走査電子顯微鏡)에 의한 몬모릴로나이트의 형태적특징(形態的特徵)은 결정성장(結晶成長)에 필요한 가용공간(可用空間)의 유무(有無)에 따라 크게 영향을 받는 것으로 보이며, 가용공간(可用空間)이 충분한 경우엔 전형적(典型的)인 honeycomb 구조를 이루며 그와 반대인 경우에는 조밀하게 패킹된 판상(板狀)의 집합체(集合體)로 산출(産出)되는 경향을 보인다. 투과전자현미경(透過電子顯微鏡)으로 관찰된 결정형(結晶型)의 종류는 동일(同一)한 시료내에서 여러 가지가 관찰되나 불규칙한 엽상(葉狀)의 집합체(集合體)가 가장 우세하게 산출(産出)되며 판상(板狀)의 결정형(結晶型)이 흔히 관찰된다. 일반적으로 본 연구지역 중 죽전리(竹田里)의 효동리화산암류(孝洞里火山岩類)에서 산출되는 시료들보다 용동리(龍洞里)의 용동리응회암내(龍洞里凝灰岩內)에 배태(胚胎)된 시료에서 상대적(相對的)으로 판상(板狀)의 결정형이 우세하다.

• Korean Chemical Engineering Research
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• 제46권1호
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• pp.137-141
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• 2008

일반적인 균일계 촉매의 담지 방식 대신 스티렌을 이용하여 촉매를 embedding 시키는 간단한 방법으로 균일계 촉매를 불균일화하여 에틸렌과 알파올레핀의 공중합을 실험하였다. 미량의 스티렌을 $rac-Et[Ind]_2ZrCl_2$ 촉매를 이용하여 중합시켜 embedded $rac-Et[Ind]_2ZrCl_2$ 촉매(이하 embedded 촉매)를 제조하였으며 이를 이용하여 embedding 시키지 않은 homogeneous $rac-Et[Ind]_2ZrCl_2$ 촉매(이하 homogeneous 촉매)를 사용하여 중합한 결과와 비교해 보았다. Embedded 촉매시스템을 사용하여 중합하는 경우, 공단량체의 종류에 상관없이 모든 공단량체 농도에서 촉매의 공중합 활성이 homogeneous 촉매보다 우수하였으며 embedding 과정이 균일계 메탈로센 촉매 활성점의 특성에 영향을 미치지 않았다. 또한 각 촉매시스템으로부터 생성된 고분자의 $T_m$과 NMR 분석 결과로 볼 때, embedded 촉매의 공단량체 삽입 능력은 homogeneous 촉매와 비슷하거나 조금 나은 수준의 결과를 보였으며, embedded 촉매로 중합한 공중합체는 겉보기밀도와 morphology가 우수하여, 스티렌을 이용한 촉매 embedding 방법이 담지 촉매를 이용하여 중합하는 효과를 보일 수 있음을 관찰할 수 있었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1523-1525
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• 2003

Due to the rapid development of wireless networking system, researches on the communication devices are mainly focus on microwave frequency devices such as filters, resonators, and phase shifters. Among them, Film bulk acoustic resonator (FBAR) has been paid extensive attentions for their high performance. In this research, ZnO thin films were deposited by RF-magnetron sputtering on Al/$SiO_2$/Si wafer and then crystalline properties and surface morphology were examined. To measure crystalline structure and surface morphology X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) were employed. It was showed that crystalline properties of ZnO thin films were strongly dependant on the deposition conditions. As increasing the deposition temperature and the deposition pressures, the peak intensities of ZnO(002) plane were increased until $300^{\circ}C$, then decreased rapidly. At the sputtering conditions of RF power of 213 W and working pressure of 15 m Torr, ZnO film had excellent c-axis orientation, surface morphology, and adhesion to the substrate. In conclusion we optimized smooth surface with very small grains as well as highly c-axis oriented ZnO film for FBAR applications.

• 한국토양비료학회지
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• 제47권4호
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• pp.242-248
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• 2014

We have five soil series of pan soils in South Korea out of 391 series: Gangreung, Bugog, Yeongog, Jangweon, and Pogog. Productivity decreases in pan soils as pan horizons impede percolation and capillary rise of water and interrupt root extension. This study was performed to investigate pedogenic processes of pan soils mainly located in footslope and river terrace by analyzing physicochemical properties and soil micro-morphology. Korean pan soils belong to Alfisols, Ultisols, or Inceptisols and have udic or aquic soil moisture regime, mesic temperature regime, and mixed mineral substances. Texture of pan horizons selected for the present study was mainly silty clay loam with clay contents ranging from 26.3 to 45.3%. Bulk density of the pan horizons ranged from 1.4 to $2.1Mg\;m^{-3}$ and their soil structure were subangular or angular structure. In terms of micro-morphological structure, Bt horizon of Gangreung series was formed as platy and striated b-fabric structure possibly affected by uplift of coastal terrace following clay sedimentation by flood. Jangweon series showed micro-morphology of massive structure and crystallic b-fabric as macropores between coarse debris established by debris fall in slope were filled with silt-sized particles. The Bt horizons having massive structure and striated b-fabric in Yeongog, Pogog, and Bugog series implies that those horizons experienced horizontal mass flow after clay accumulation.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2002년도 춘계 학술발표강연 및 논문개요집
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• pp.132-132
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• 2002

Diamond is well known as the hardest material in nature. It also has other unique bulk physical and mechanical properties, such as very high thermal conductivity and broad optical transparency, which enable a number of new applications now that large areas of diamond can be fabricated by the new diamond plasma chemical vapor deposition (CVD) technologies. A study on the effects of growth kinetics and properties of diamond films obtained by addition of argon (~7 vol. %) into the methane/hydrogen mixture is carried out using HFCVD system. A negative bias was used as a nucleation enhancement method in addition to the argon dilution. The scanning electron microscopy (SEM) image of surface morphology shows well faceted crystallites with a predominance of angular shapes corresponding to <100> and <110> crystalline surfaces. The nucleation density and growth rate with argon dilution is two orders of magnitude higher than without argon deposition. The Raman spectra show a good quality film whereas XPS spectra show existence of only diamond phase.

• 대한화학회지
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• 제60권5호
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• pp.310-316
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• 2016

Oxidation-reduction cycling (ORC) procedures are widely used for cleaning nanoparticle surfaces when investigating their electrocatalytic activities. In this work, the effect of ORC on the surface structures and electrocatalytic oxygen reduction activity of Au electrodes is analyzed. Different structural changes and variations in electrocatalysis are observed depending on the initial structure of the Au electrodes, such as flat bulk, nanoporous, nanoplate, or dendritic Au. In particular, dendritic Au structures lost their sharp-edge morphology during the ORC process, resulting in a significant decrease in its electrocatalytic oxygen reduction activity. The results shown in this paper provide an insight into the pretreatment of nanoparticle-based electrodes during investigation of their electrocatalytic activities.