• 공업화학
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• 제22권4호
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• pp.358-366
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• 2011

선상의 액정 dimer 동족체인 ${\alpha},{\omega}$-(4-사이아노아조벤젠-4'-옥시)알케인(CATWETn, n = 2~10, 유연격자 중의 메틸렌 단위들의 수)을 합성함과 동시에 이들의 열방성 액정 거동을 검토하였다. n이 3, 6인 dimer들은 단방성 네마틱 상을 형성하는 반면 다른 유도체들은 양방성 네마틱 상을 형성하였다. Dimer들의 네마틱액체 전이온도와 상 전이시의 엔트로피 변화는 n의 함수로서 커다란 홀수-짝수 효과를 나타냈다. 이러한 상 전이 거동은 유연격자의 홀수-짝수의 변화에 의한 유연격자의 평균적인 형태변화의 견지에서 합리적으로 설명된다. CATWETn이 나타내는 네마틱 상의 열적 안정성과 질서도 그리고 홀수-짝수 효과는 메톡시, 니트로 그리고 펜틸기로 치환된 dimer에 대해 보고된 결과와 유사한 경향을 나타내는 반면 monomesogenic 화합물인 1-{4-(4'-사이아노페닐아조)펜옥시}알킬브롬 그리고 곁사슬형 액정 고분자인 폴리[1-{4-(4'-사이아노페닐아조)펜옥시알킬옥시}에틸렌]에 대해 보고된 결과와 현저히 달랐다. 이들의 결과를 Imirie에 의한 'virtural trimer model'의 견지에서 검토하였다.

• 정보저장시스템학회논문집
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• 제3권3호
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• pp.118-122
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• 2007

Phase-change wet-etching technology using GeSbTe phase-change films is developed. Selective etching between an amorphous and a crystalline phase can be carried out with an alkaline etchant of NaOH. Etching selectivity is dependent not only on the concentration of the alkaline etchant but also on the film structure. Specifically, metal films for heat control cause marked effects on the etching properties of GeSbTe film. Surviving amorphous pits can be obtained with Al metal layer, however etched amorphous pits are seen with Ag metal layer. An opposite selective etching behavior can be observed between samples with two different metal layers.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.77-80
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• 2006

Structural phase transformations of silicon during nanoindentation were investigated in detail at the atomic level. The molecular dynamics simulations of nanoindentation on the (100), (110) and (111) surface of single crystalline silicon were simulated, and this supported the theoretical prediction of the anisotropic behavior of structural phase transformations. Simulations showed that microscopic aspects of phase transformation varied according to the crystallographic orientation of the contact surface and were directly linked to the slip system.

• 대한기계학회논문집B
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• 제33권3호
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• pp.186-193
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• 2009

In this article, the effect of silica addition on the phase transformation characteristics of $TiO_2$ nanoparticles synthesized by using an $O_2$-enriched coflow, hydrogen, diffusion flame was investigated. TTIP(titanium tetra-isopropoxide) and TEOS(tetraethyl-orthosilicate) were used as precursors for $TiO_2$ and $SiO_2$ nanoparticles, respectively. Based on the results from TEM and XRD analysis, it is believed that the silica addition on the flame synthesis of $TiO_2$ nanoparticles reduces the particle size distribution and raises the temperature of the phase transition from anatase to rutile. But the reduced sizes of the synthesized particles due to the silica addition made the sintering and phase transformation of particles more easily.

• 한국재료학회지
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• 제30권7호
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• pp.359-368
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• 2020

This study is aimed at improving the plasma resistance of Al₂O₃ ceramics on which plasma resistant YAS(Y₂O₃-Al₂O₃-SiO₂) frit is melt-coated using a simple heat-treatment process. For this purpose, the results of phase analysis and microstructural observations of the prepared YAS frits and the coating layers on the Al₂O₃ ceramics according to the batch compositions are compared and discussed with regard to the results of plasma resistance test. The prepared YAS frits consist of crystalline or amorphous or co-existing crystalline and amorphous phases according to the batch compositions, depending on the role and content of each raw material. The prepared YAS frit is melt-coated on the densely sintered Al₂O₃ ceramics, resulting in a dense coating layer with a thickness of at least ~ 80 ㎛. The YAS coating layer consists of crystalline YAG(Y₃Al₅O₁₂), Y₂Si₂O₇, and Al₂O₃ phases, and YAS glass phase. Plasma resistance of YAS coated Al₂O₃ ceramics is strongly dependent on the content of the YAG(Y₃Al₅O₁₂) and Y₂Si₂O₇ crystalline phases in the coating layer, especially on the content of the YAG phase. Comparing the weight loss of YAS coating ceramics with values obtained for commercial Y₂O₃, Al₂O₃, and quartz ceramics, the plasma resistance of the YAS coating ceramics is 6 times higher than that of quartz, 2 times higher than that of Al₂O₃, and 50 % of the resistance of Y₂O₃.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 1997년도 춘계연구발표회 논문개요집
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• pp.102-103
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• 1997

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 somma/kms meeting
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• pp.244-244
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• 2003

• 공업화학
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• 제28권6호
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• pp.679-684
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• 2017

베시클 막을 유연하게 만드는 edge activator를 혼합하여 수화 액정형 베시클을 제조하고 niacinamide를 베시클 안에 포집시켰다. 제조 과정 중 액정 상 형성 및 액정의 열적 상전이 현상을 편광현미경과 시차주사 열량계(DSC)를 통해 살펴보았다. Sodium deoxycholate, lysolecithin, polysorbate 80 등의 edge activator를 첨가하면 수화 액정형 베시클 입자가 수십 나노 사이즈로 줄어들었다. 수화 액정형 베시클을 활용하여 niacinamide를 피부 침투시키면 수용액 상태로 도포했을 때보다 피부 침투된 niacinamide의 양이 크게 증가하는데, 10% sodium deoxycholate를 혼합한 베시클에서는 niacinamide 침투량이 4배 가까이 증가하였다. 이러한 결과로부터 edge activator를 베시클에 혼합하면 베시클의 피부 침투력이 향상됨을 알 수 있었다.

• 한국재료학회지
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• 제21권8호
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• pp.415-418
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• 2011

Tin (IV) dioxide ($SnO_2$) has attracted much attention due to its potential scientific significance and technological applications. $SnO_2$ nanoparticles were prepared under low temperature and pressure conditions via precipitation from a 0.1 M $SnCl_4{\cdot}5H_2O$ solution by slowly adding $NH_4OH$ while rapidly stirring the solution. $SnO_2$ nanoparticles were obtained from the reaction in the temperature range from 130 to $250^{\circ}C$ during 6 h. The microstructure and phase of the synthesized tin oxide particles were studied using XRD and TEM analyses. The average crystalline sizes of the synthesized $SnO_2$ particles were from 5 to 20 nm and they had a narrow distribution. The average crystalline size of the synthesized particles increased as the reaction temperature increased. The crystalline size of the synthesized tin oxide particles decreased with increases in the pH value. The X-ray analysis showed that the synthesized particles were crystalline, and the SAED patterns also indicate that the synthesized $SnO_2$ nanoparticles were crystalline. Furthermore, the morphology of the synthesized $SnO_2$ nanoparticles was as a function of the reaction temperature. The effects of the synthesis parameters, such as the pH condition and reaction temperature, are also discussed.

• 분석과학
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• 제25권1호
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• pp.3-6
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• 2012

내구성 및 내알칼리성이 우수한 다공성 결정화 유리를 제조하기 위하여, zirconium propoxide의 몰농도비가 높은 금속알콕사이드를 출발물질로 하여 $xZrO_2-(1-x)SiO_2$ 구조의 유리전구체를 졸-겔법으로 합성하였다. 본 연구에서는 유리전구체를 500에서 $1,100^{\circ}C$의 범위에서 열처리하여, 열처리 조건이 유리전구체의 결정구조에 미치는 영향을 조사하였다. X-선 회절분석에 의하면, $600^{\circ}C$이상에서 결정피크가 발달하기 시작하였으며, 850$^{\circ}C$이상에 도달하면, 결정성은 확연하게 증가하였다. 그리고 열처리 온도가 증가함에 따라 결정 피크가 발달하며 $2{\theta}$ 값이 $35^{\circ}$, $50^{\circ}$ 및 $60^{\circ}$에서 각각 baddelyite, tetragonal-$ZrO_2$, zircon의 특성피크를 나타냈다.