• 한국세라믹학회지
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• 제51권5호
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• pp.442-446
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• 2014

Influences of Co and inhibitors from nano-sized WC materials were observed in the sintering process. VC and $Cr_3C_2$ were used as inhibitors. The crystal structure and surface images of sintered nano-sized WC materials, as functions of Co and inhibitors, were evaluated by XRD and FE-SEM analyses. The relative densities of sintered nano-sized WC materials did not change even with increased quantity of Co and increased temperature. The density of sintered nano-sized WC materials with inhibitors was lower than that of sintered nano-sized WC materials without inhibitors. No difference in hardness due to change of inhibitors was found.

• Steel and Composite Structures
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• 재36권6호
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• pp.631-642
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• 2020

This paper studies nonlinear stability behavior of a nanocrystalline silicon curved nanoshell considering strain gradient size-dependency. Nanocrystallines are composite materials with an interface phase and randomly distributed nano-size grains and pores. Imperfectness of the curved nanoshell has been defined based on an initial deflection. The formulation of nanocrystalline nanoshell has been established by thin shell theory and an analytical approach has been used in order to solve the buckling problem. For accurately describing the size effects related to nano-grains or nano-pores, their surface energies have been included. Nonlinear stability curves of the nanoshell are affected by the size of nano-grain, curvature radius and nano-pore volume fraction. It is found that increasing the nano-pore volume fraction results in lower buckling loads.

• 산업기술연구
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• 제25권B호
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• pp.127-133
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• 2005

Manufacturing methods of Nano particles can be distinguished by top-down technology as physical method and bottom-up technology as chemical synthetic method. Top-down technology is a kind of method for making microstructure as like carving after forming a macroscopic structure in advance and its typical methods are ball milling, gas condensation method and so on. Nano Particles synthesized by bottom-up method have got to do dispersing process for using them as actual nano particles because their viscosity are very strong and so easy to shape cohesive substances. Therefore, this study is about a particle separating device which separates a certain constant size of grains processed already in mill and mixer because we mostly use media agitating mill as a device of milling and dispersing and we necessarily use very slight balls as media for manufacturing nano particles in the machine. The centrifugal device has been designed for passing and separating below a certain type of grain size after final process of particles in the mill.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.251-252
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• 2012

Recently, the growing interest in organic microelectronic devices including OLEDs has led to an increasing amount of research into their many potential applications in the area of flexible electronic devices based on plastic substrates. However, these organic devices require a gas barrier coating to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency OLEDs require an extremely low Water Vapor Transition Rate (WVTR) of $1{\times}10^{-6}g/m^2$/day. The Key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required ($1{\times}10^{-6}g/m^2$/day) is the suppression of defect sites and gas diffusion pathways between grain boundaries. In this study, we developed an $Al_2O_3$ nano-crystal structure single gas barrier layer using a Neutral Beam Assisted Sputtering (NBAS) process. The NBAS system is based on the conventional RF magnetron sputtering and neutral beam source. The neutral beam source consists of an electron cyclotron Resonance (ECR) plasma source and metal reflector. The Ar+ ions in the ECR plasma are accelerated in the plasma sheath between the plasma and reflector, which are then neutralized by Auger neutralization. The neutral beam energies were possible to estimate indirectly through previous experiments and binary collision model. The accelerating potential is the sum of the plasma potential and reflector bias. In previous experiments, while adjusting the reflector bias, changes in the plasma density and the plasma potential were not observed. The neutral beam energy is controlled by the metal reflector bias. The NBAS process can continuously change crystalline structures from an amorphous phase to nano-crystal phase of various grain sizes within a single inorganic thin film. These NBAS process effects can lead to the formation of a nano-crystal structure barrier layer which effectively limits gas diffusion through the pathways between grain boundaries. Our results verify the nano-crystal structure of the NBAS processed $Al_2O_3$ single gas barrier layer through dielectric constant measurement, break down field measurement, and TEM analysis. Finally, the WVTR of $Al_2O_3$ nano-crystal structure single gas barrier layer was measured to be under $5{\times}10^{-6}g/m^2$/day therefore we can confirm that NBAS processed $Al_2O_3$ nano-crystal structure single gas barrier layer is suitable for OLED application.

• 한국세라믹학회지
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• 제41권1호
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• pp.86-91
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• 2004

기계 화학법에 의해서 70-300nm 수준의 입도 분포를 갖는 $LiCoO_2$ 양극 분말을 제작하였다. $K_2SO_4$에 의하여 코팅 된 Li-Co 전구체는 약 $800^{\circ}C$에서 고온상 $LiCoO_2$로 결정화 되었으며, 이때 이 온도까지는 열분해 또는 서로 반응을 하지 않는 $K_2SO_4$의 영향에 의하여 분말의 입성장이 억제되어 나노 크기에 접근하는 입자를 얻을 수 있었고, 상대적으로 큰 표면 에너지에 기인하여 입자의 모양이 구형에 가깝게 형성되어 졌다. 합성돤 분말은 상용화 분말과 동일한 결정특성을 보였으나 , 투과전자현미경의 회절패턴 분석결과, 층상 뿐 아니라 부분적으로 정방정의 $LiCoO_2$ 상을 갖는 것으로 나타났다. 이러한 정방정은 주로 입자 표면에 존재하게 되어 Li의 확산을 용이하지 않게 하므로, 합성된 $LiCoO_2$ 분말은 그 크기가 나노에 접근함에도 불구하고 전체 용량 및 rate 용량이 상용화 분할보다 더 낮은 값을 보였다. 이상의 결과로부터 뛰어난 고출력 및 고성능의 전지 제작을 위하여 분말의 크기를 미세화하는 작업은 물론 입자 표면의 결정상이 잘 조절된 분말을 사용하는 것이 바람직함을 알 수 있다.

• Bulletin of the Korean Chemical Society
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• 제33권6호
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• pp.1962-1966
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• 2012

Boehmite sols have been prepared by crystallization of amorphous aluminum hydroxide gel obtained by hydrolysis and peptization of aluminum using acetic acid. The size of the boehmite crystallites could be controlled by Al molar concentration in amorphous gel by means of controlling grain growth at nucleation stage. The size of boehmite increases as a function of Al molar concentration. With increasing boehmite crystallite size, the $d_{(020)}$ spacing and the specific surface area decreases, whereas the pore volume increases along with pore size. Especially, the pore size of the boehmite sol particles is comparable to the crystallite size along the b axis, suggesting that the fibril thickness along the b axis among the crystallite dimensions of the boehmite contributes to the pore size. Therefore, the physical properties of boehmite sols can be determined by the crystallite size controlled as a function of initial Al concentration.

• 열처리공학회지
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• 제23권5호
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• pp.239-244
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• 2010

Influence of Zr addition on grain stability at elevated temperatures has been investigated for extruded pure Mg and Mg-0.25%Zr alloy. The grain size of pure Mg increases rapidly with increasing annealing temperature when isochronally annealed for 60 min from 573 to 773 K, whereas the grains are stable up to 723 K for the Zr-containing alloy. The activation energies for grain growth ($E_g$) at this temperature range were determined as 75.3 and 105.9 kJ/mole for the pure Mg and Mg-0.25%Zr alloy, respectively. TEM observations on the annealed Mg-Zr samples revealed that higher thermal stability and higher activation energy for grain growth resulting from Zr addition in Mg may well be associated with the restriction of grain growth by nano-sized Zr particles distributed in the microstructure.

• 한국진공학회지
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• 제16권6호
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• pp.453-457
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• 2007

상온에서 RF magnetron sputtering 을 이용하여 10nm에서 50nm 의 두께를 가지는 ZnO와 GZO 를 유리 기판위에 증착하여 두 물질 간의 구조적 특성과 광학적 특성을 평가하였다. 구조적인 특성은 투과전자현미경 (TEM) 과 주사전자현미경 (SEM)을 통해 이루어졌다. 광학적 특성 평가는 spectrophotometer를 이용하여 UV-VIS-NIR 영역에 관한 투과도를 측정하였다. ZnO의 결정크기가 GZO보다 상대적으로 더 크게나왔으며 이는 결정 경계면에서 발생하는 광산란을 줄임으로서 투과도의 향상을 가져왔다. 투과 전 영역에서 ZnO의 투과도가 더 높게 나왔으며, 특히 50nm 박막의 경우 ZnO의 투과도가 GZO 보다 20% 이상 더 뛰어난 것을 확인 할 수 있었다.

• 한국진공학회지
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• 제17권1호
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• pp.23-27
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• 2008

본 연구에서는 상온에서 RF 마그네트론 스퍼터링 법으로 유리 기판위에 증착된 Ga 도핑 된 다결정 ZnO 박막의 특성을 개선하기 위하여 적정 열처리 조건을 분석하였다. 먼저 박막 성장 후 박막의 특성을 분석하였고 각각 $400{\sim}600^{\circ}C$에서 30분, 60분간 질소 분위기에서 열처리를 한 후 구조적, 광학적 특성을 평가하였다. XRD와 FE-SEM을 사용하여 열처리온도 변화에 따른 결정입자의 크기의 변화를 관찰하였다. 그 결과 성장된 결정의 크기의 증가와 박막의 결정성이 향상되었음을 확인할 수 있었으며 그로 인해 박막 특성을 중시하는 투명 전도막의 투과도의 향상 또한 확인할 수 있었다. 결론적으로, 본 실험을 통하여 ZnO 성장 후 적절한 열처리를 수행함으로서 GZO 박막을 사용하여 제작된 소자의 특성을 개선할 수 있으리라 판단된다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.183-184
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• 2005

In this study, our varistors based on M.Matsuoke's composition were fabricated with ZnO nano-powder whose sizes were 50nm and 100nm. Electrical properties of ZnO nano-powder varistors were obtained by capacitance-voltage and frequency-real impedance. nano-powder varistors are indicated the change of the interface defects density $N_t$ at the grain boundaries and the donor concentration $N_d$ in the ZnO grains. Frequency analysis was accomplished to understand the equivalent circuit.