• Korean Journal of Materials Research
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• v.12 no.11
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• pp.845-849
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• 2002

Alloys of $Fe_3$Al, $Fe_3$Al-6Cr, $Fe_3$Al-4Cr-1Mo, $Ni_3$Al, and $Ni_3$Al-2.8Cr were oxidized at $1000^{\circ}C$ in air, and the oxide scales formed were studied using XRD. SEM, EPMA, and TEM. The oxide scales that formed on $Fe_3$Al-based alloys consisted primarily of $\alpha$-$Al_2$$O_3$ containing a small amount of dissolved Fe and Cr ions, whereas those that formed on $Ni_3$Al-based alloys consisted primarily of $\alpha$-$Al_2$$O_3$, together with a small amount of $NiAl_2$$O_4$, NiO and dissolved Cr ions. For the entire alloys tested, nonadherent oxide scales formed, and voids were inevitably existed at the scale-matrix interface.

• Korean Journal of Materials Research
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• v.12 no.11
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• pp.856-859
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• 2002

To investigate effects of heat treatments including grain size control in substrate aluminum on nanopore arrays in anodic alumina template, aluminum was heat treated at $500^{\circ}C$ for 1h. The heat treated aluminum was anodized by two successive anodization processes in oxalic solution and the nanopore arrays in anodic alumina layer were studied using TEM and FE-SEM. The highly ordered porous alumina templates with 110 nm interpore distance and 40 nm pore diameter have been observed and the pore array of the anodic alumina has a uniform and closely-packed honeycomb structure. In the case of alumina template obtained from heat treated aluminum substrate, the well- ordered nanopore region in anodic alumina increased and became more homogeneous compared with that from non-heattreated one.

• Korean Journal of Materials Research
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• v.15 no.4
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• pp.240-245
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• 2005

An oxygen free copper was severely deformed by accumulative roll-bonding (ARB) process for improvement of its mechanical properties. Two copper sheets 1 m thick, 30 mm wide and 300 m long are first degreased and wire-brushed for sound bonding. The sheets are then stacked to each other, and roll-bonded by about $50\%$ reduction rolling without lubrication at ambient temperature. The bonded sheet is then cut to the two pieces of same dimensions and the same procedure was repeated to the sheets up to eight cycles $(\varepsilon-6.4)$. TEM observation revealed that ultrafine grains were developed after the third cycle, and their size was slightly increased at higher cycles. Tensile strength of the copper increased with the strain at low strain levels, but it hardly increased from 3 cycles $(\varepsilon>2.4)$ due to occurrence of dynamic recovery, even if the imposed strain increased.

• Korean Journal of Materials Research
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• v.3 no.6
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• pp.678-683
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• 1993

Atomic arral1gement of ordered phase in $GaAs_{0.5}Sb_{0.5}$ epilayer was studied by observation of selected area diffraction patterns and high resolution images. The epilayer was grown on untilted (001) GaAs substrate at $580^{\circ}C$ by molecular beam epitaxy(MBE). A 1/2(111) type long-range ordered phase is formed in the epilayer. Atomic arrangement of the ordered phase is described as an alternative stacking of As-rich and Sb-rich {111} planes in group V sublattice. Space group of the ordred structure belongs to R3m, and unit cell of the ordered structure is rhombohedral.

• Korean Journal of Materials Research
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• v.6 no.3
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• pp.309-317
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• 1996

세가지 다른 방법을 이용하여 형성시킨 비정질 실리콘(SiH4 a-Si, Si2H6 a-Si, Si+ implanted SiH4 a-Si)들에 대한 저온 결정화 기구의 차이를 고전적 이론인 Avrami 식(X=1-exptn, X=결정화 분율, t=열처리 시간, n=지수)을 이용하여 검토하였다. Silane으로 형성된 비정질 실리콘의 결정화 과정에서는 Avrami 식에서의 n의 값이 2.0을 나타내고 있어, 결정성장이 이차원적으로 이루어지면서 핵생성률이 시간에 따라 감소하고 있음을 알 수가 있었다. Si+ 이온 주입에 의하여 형성된 비정질 실리콘의 결정화에서는 3.0의 지수 값이 얻어지고 있어, 정상상태의 핵생성과 함께 2차원적인 결정 성장이 이루어지고 있었다. Disilane으로 형성된 비정질 실리콘에 대한 결정화에서는 2.8의 지수값이 얻어져, 정상상태의 핵 생성이 우세하게 일어나는 2차원적인 결정성장이 일어나고 있음을 알 수 있었다. 또한 TEM을 이용하여 시간에 따라 변하는 핵생성률을 조사하여, Avrami 식의 적용이 타당성 있음을 증명하였다. 마지막으로, 최종 입자의 크기가 열처리 온도에 크게 영향을 받고 있지 않음을 확인하였다.

• Journal of the Korean Ceramic Society
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• v.37 no.5
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• pp.491-496
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• 2000

Single phae Pb(Mg1/3Nb2/3)O3-based solid solutions, the Mg2+ of which are replaced by 20mol% of Ni2+, Zn2+, Cd2+, and the Pb2+ of which are replaced by 0∼20 mol% of La3+, were synthesized and their ordering structures of B-site cations were investigated by XRD and TEM. The B'-site cations (Mg2+, Ni2+, Zn2+, Cd2+) are disordered while these B'-site cations and the B"-site cations (Nb5+) are nonstoichiometrically 1:1 ordered within the ordered nano-domains dispersed in the Nb5+-rich disordered matrix. The charge imbalance between the B'-rich ordered nano-domains and the B"-rich disordered matrix are compensated by the doping of electron donor such as La3+, which enhances the degree of nonstoichiometric 1:1 ordering. For a given La3+ content, the degree of nonstoichiometric 1:1 ordering increases as the average ionic size difference between the B'-and B"-site cations increases, Ni2+

• Journal of the Korean Ceramic Society
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• v.37 no.5
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• pp.473-478
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• 2000

The TiO2 powder with the values of the large specific surface area more than 150$m^2$/g has been prepared with the homogeneous precipitation process below 5$0^{\circ}C$ and its formation mechanism was investigated using the SEM, TEM and Raman Spectroscopy. With the spontaneous hydrolysis of aqueous TiOCl2 solutions, all the precipitates were fully and homogeneously crystallized with the rutile TiO2 phase simply by heating, which as transformed to the anatase TiO2 phase as increasing the addition of SO42- ions to the aqueous TiOCl2 solution. The precipitates were formed with spherical secondary particles which consisted of acicular, spherical and mixed primary particles corresponding to the rutile, anatase and mixed phases, respectively. It can be thought that the formation and phase determination of crystalline TiO2 powders even at ambient temperature would be related with the existence of the capillary force. This force might be varied depending on the shape change of the primary particles.

• Journal of the Korean Ceramic Society
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• v.46 no.3
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• pp.288-294
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• 2009

The platelet AlO(OH) nano colloids were prepared by hydrothermal reaction of the $\gamma-Al_2O_3$ obtained with dehydration of $\gamma$-AlO(OH) and dilute $CH_3COOH$ solution. In hydrothermal reaction process, reversible reaction was accompanied between $\gamma-Al_2O_3$ and AlO(OH), and hydrothermal reaction temperature, hydrothermal reaction time and $CH_3COOH$ concentration had an effect on the crystal structure, surface chemical property, surface area, pore characteristics and crystal morphology of the AlO(OH) nano colloid particles. In this study, it was investigated to the hydrothermal reaction condition of the AlO(OH) nano colloid for using catalyst support, heat resisting agent, adsorbents, binder, polishing agent and coating agent. The crystal structure, surface area, pore volume and pore size of the platelet AlO(OH) nano colloids were investigated by XRD, TEM, TG/DTA, FT-IR and $N_2$ BET method in liquid nitrogen temperature.

• Korean Journal of Materials Research
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• v.7 no.2
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• pp.93-101
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• 1997

Lead titanate박막을 $Pt/Ti/SiO_{2}/Si(Pt/Ti기판)와\;Pt/Ta/SiO_{2}/SiO_{2}$Si(Pt/Ta 기판) 위에서 전자 사이크로트론 공명플라즈마 화학증착법(ECR PECVD)으로 증착하였다. 증착온도, 산소유입량, MO source유입비등의 증착변수에 따른 lead titanate박막의 조성과 미세구조를 주사전자현미경(SEM), 투과전자현미경(TEM), X선 회절법(XRD)으로 조사하였다. 산소유입량이 적을 경우,Tisource와 Pb source의 산소화의 반응성 차이 때문에 Pb 농도가 부족한 화학양론비가 잘 맞는 박막이 증착되었다. Pt/ti기판은 lead titanate박막증착도중 기판의 Ti층과 Pt층의 확산으로 기판변형이 발생하는 반면, Pt/Ta기판은 기판변형이 일어나지 않았다. Pt/Ta기판에서 페롭스카이트 화학양론비를 갖는 매우 평탄한 lead titanate박막을 증착 하였는데, 산소유입량이 lead titanate박막의 결정성을 크게 지배하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.8
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• pp.660-666
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• 2010

Carbon aerogels are promising materials as electrodes for electrical double layer capacitors (EDLCs). An optimum process is presented for synthesis of nanoporous carbon aerogels via pyrolyzing resorcinol-formaldehyde (RF) organic aerogels, which could be cost-effectively manufactured from RF wet gels. The major reactions between resorcinol and formaldehyde include an addition reaction to form hydroxymethyl derivatives ($-CH_2OH$), and then a condensation reaction of the hydroxymethyl derivatives ($-CH_2-$)- and methylene ether ($-CH_2OCH_2-$) bridged compounds. The textural properties of carbon aerogels obtained were characterized by nitrogen adsorption/desorption analysis and SEM and TEM. The application of the resultant carbon for electrodes of electric double layers capacitor (EDLC) in organic TEABF4/ACN electrolyte indicated that the ESR, as low as 55 $m{\Omega}$, was smaller than for commercially activated carbons. And EDLC with carbon Aerogel electrodes has an excellent stable more than for commercially activated carbons.