• 한국응용과학기술학회지
• /
• 제22권4호
• /
• pp.306-314
• /
• 2005

In this study, spherical $pre-BaTiO_3$ particles are prepared by gelation and aging process in autoclave without catalysts. The (Ba-Ti) gel used as a starting material was prepared by aging mixtures of titanyl acylate with barium acetate aqueous solution([glacial acetic acid (AcOH)]/[titanium isopropoxide (TIP)] 4, [barium acetate]/[TIP] 1) at $45^{\circ}C$ for 48hrs. XRD and SEM results for the (Ba-Ti) gel sample at aging process showed that the gel was formed via aggregation of the fine particles. It seems to be the primary particles of bulk (Ba-Ti) gel amorphous, but the spatial arrangement of barium and titanium in the (Ba-Ti) gel is similar to that in crystalline $BaTiO_3$ particles. From XRD and FT-IR. spectroscopy analysis it was found that the crystal structure of the prepared particles continuously transformed from amorphous to tetragonal as the calcination temperature increased, and crystallized spherical cubic and tetragonal $BaTiO_3$ powder obtained at the very low calcination temperature between $500^{\circ}C$ and $900^{\circ}C$ after 1hrs of heat treatment respectively. According to BET analysis result, final particle have pore structure of ink bottle shape which is produced by aggregation of fine spherical particles with surface area of $280m^2/g$ and average pore size of 130nm.

• 공업화학
• /
• 제18권6호
• /
• pp.568-574
• /
• 2007

투명결정화 유리의 전구체로서 균열이 없는 $Li_2O1{\cdot}7Al_2O_3{\cdot}8.6SiO_2$ 조성인 다공성 괴상 겔을 formamide를 첨가한 알콕시드 용액으로부터 sol-gel방법으로 합성하였다. 겔 합성에서 겔화 활성화 에너지, 비표면적, 습윤겔의 완전 탈수에 필요한 온도, 기공의 부피 및 기공크기와 분포를 측정하였고, 겔의 결정화온도를 검토하고자 시차열분석을 실시하였다. 겔화의 활성화에너지는 가수분해에 필요한 물의 첨가량에 따라 13~14 kcal/mol 범위를 나타내고, 물의 첨가량이 가수분해시 필요한 이론량의 3배 이상일 경우, $70{\sim}75^{\circ}C$, 건조속도 0.1~0.3 %/h에서는 겔의 균열을 방지할 수 있어 안정한 괴상 겔을 제조할 수 있었다. $180^{\circ}C$에서 건조한 겔체는 비표면적, 기공부피 및 기공크기분포는 $239.40m^2/g$, 0.001~0.03 mL/g 그리고 1~122 nm 반지름의 미세구조로 된 투명 겔체로서 다공질 물질임이 확인되었고, 건조겔의 시차열분석 결과 $800^{\circ}C$ 부근에서 1차 발열피크, $980^{\circ}C$ 부근에서가 2차 발열피크가 확인되어 결정화가 일어남을 알 수 있었다.

• 전기화학회지
• /
• 제10권4호
• /
• pp.252-256
• /
• 2007

A series of spherical porous carbons were prepared via resorcinol-formaldehyde (RF) sol-gel polymerization in the presence of cationic surfactant (CTAB, cetyltrimethylammonium bromide), wherein the carbon sphere size was controlled by varying the CTAB introduction time after a pre-determined period of addition reaction (termed as "pre-curing"). The sphere size gradually decreases with an increase in the pre-curing time within the range of 30-150 nm. The carbons possess two types of pores; one inside carbon spheres (intra-particle pores) and the other at the interstitial sites made by carbon spheres (inter-particle pores). Of the two, the surface exposed on the former was dominant to determine the electric double-layer capacitor (EDLC) performance of porous carbons. As the intra-particle pores were generated inside RF gel spheres by gasification, the pore diameter was similar for all these carbons, thereby the pore length turned out to be a decisive factor controlling the EDLC performance. The charge-discharge voltage profiles and complex capacitance analysis consistently illustrate that the smaller-sized RF carbons deliver a better rate capability, which must be the direct result of facilitated ion penetration into shorter pores.

• 한국세라믹학회지
• /
• 제40권12호
• /
• pp.1213-1219
• /
• 2003

비정질알루미나에 기공형성제를 첨가하여 성형하고 수열반응, 열처리 및 수세를 통해 pellet 형태의 다공성 세라믹 담체를 제조하였다. 기공형성제는 64, 222, 405 $\mu\textrm{m}$의 평균 입경을 가지는 활성탄, 폴리머와 무기염의 변화를 두었으며, 20$0^{\circ}C$에서 24시간동안 수열반응 한 다음 $650^{\circ}C$에서 5시간동안 열처리 및 8$0^{\circ}C$에서 48시간 동안 수세하고, 결정의 생성 및 변화, 기공률, 기공의 분포 및 압축 강도를 측정하였다. 수열반응 이후 활성탄이 첨가된 시편은 boehmite로의 상전이가 이루어졌으나, 기공형성제로 폴리머 및 무기염이 첨가된 시편은 수열 반응 시 비정질알루미나의 aquohydroxy complex gel의 형성을 방해하여 boehmite 결정성장 억제를 가져왔다 활성탄을 기공형성제로 첨가하여 제조한 시편의 경우, 70% 이상의 기공률과 40kgf/$\textrm{cm}^2$ 이상의 강도를 갖는 ${\gamma}$-알루미나의 담체를 제조할 수 있었다.

• 대한화학회지
• /
• 제16권6호
• /
• pp.341-348
• /
• 1972

질소의 흡착 등온곡선을 이용하여 흡착체의 동공부피 분포를 계산하는 과정에서 표면장력의 곡률 의존도 고려 효과를 조사하였다. 즉, 장세헌 등에 의한 표면장력의 곡률 의존도식과 캘빈 식으로부터 주어진 압력에서의 캘빈반경을 구하고, 이것으로부터 흡착체의 동공부피 분포를 계산하였다. 이와 같이하여 얻은 계산 결과를 표면장력의 곡률 의존도를 고려하지 아니한 종래방법에 의한 계산 결과와 비교하였다. 일반적으로 곡률 의존도를 고려해주면 동공부피 분포 곡선의 극대부분이 큰 동공 쪽으로 이동한다. 또한 모세관 응축이 일어나는 상대압력이 종래까지 생각했던 것보다 훨씬 낮아지고 있다. 이러한 효과들은 흡착체의 동공들이 미세해 질수록 더욱 현저하게 일어난다.

• Bulletin of the Korean Chemical Society
• /
• 제27권3호
• /
• pp.399-402
• /
• 2006

Porous organic-inorganic hybrids have been prepared from tetraethylorthosilicate (TEOS) and organosilane precursors by sol-gel method. Two organosilanes, 3-(2,4-dinitrophenylamino)propyltriethoxysilane (DNPTES) and N-[[(2-nitrophenyl)methoxy]carbonyl]-3-triethoxysilylpropylamine (NPTES) were used to incorporate electron-accepting (di)nitrophenyl groups into the hybrids. The hybrids were characterized by FT-IR spectroscopy and elemental analysis, and their pore characteristics were studied by nitrogen sorption porosimetry. Surface area of the hybrids ranged from 563 to 770 $m^2$/g, pore volume, 0.23-0.30 $cm^3$/g, and porosity, 35-41%. It was demonstrated by UV-vis spectroscopy that aniline, ethylenediamine, and 1-aminonaphthalene could be removed from their hexane solutions in the presence of the hybrid powders. The removal of amines is attributable to donor-acceptor interaction between the electron-donating amines and electron-accepting (di)nitrophenyl moiety.

• 한국세라믹학회지
• /
• 제34권9호
• /
• pp.986-992
• /
• 1997

Cordierite ceramic was prepared by sol-gel method. It was analyzed by Infrared spectroscopy and X-ray diffraction patterns that the ceramic was chemically mixed in molecular level and transformed to $\alpha$-cordierite at 125$0^{\circ}C$. Water vapour treatments for aging and drying process were conducted to get porous cordierite with thermally stable pore structure. It resulted in 220-410 $m^2$/g BET surface area and mesoporous structure with mean pore diameter, 40$\AA$. Compared to naturally dried ceramic, the ceramic showed superior thermal stability of surface area up to $700^{\circ}C$. Surfaces of porous cordierite ceramics were observed by SEM.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
• /
• pp.472-473
• /
• 2006

Maghemite and hematite nanospheres were synthesized by using the Sol-gel technique. The structural properties of these nanosphere powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), and pore size distribution. Hematite phase shows crystalline structures. The mean particle size that resulted from BET and XRD analyses were 4.9 nm and 2 nm. It can be seen from transmission electron microscopy that the size of the particles are very small which is in good agreement with the FESEM and the X-ray diffraction. The BET and pore size method were employed for specific surface area determination.

• Korean Membrane Journal
• /
• 제10권1호
• /
• pp.13-19
• /
• 2008

Water softening is a very promising field for membranes and especially ultra low pressure membranes. Nanofiltration membranes based on pore-filling technology was prepared by using a new technique: the in-situ cross-linking. This route involves introducing a pre-formed polymer into the pores of a host membrane and then locking the polymer in the pores by in-situ cross-linking with an appropriate reagent. By this way, it is possible to make robust and competitive, pore-filled, anion-exchange membranes with excellent control over the properties of the incorporated gel without affecting the host membrane. In this paper, the possibilities of tuning such membranes for ultra low pressure water softening was examined by altering pore-filling chemistry (by changing cross-linking and aminating reagents). The results showed that tuning the chemistry of the pore-filling has important effects. In particularly, it had been shown that the correct selection of cross-linking reagent was not only essential to get pore-filled membranes but it could control their properties. Moreover, the aminating reagent could improve membrane performance. It was found that an increase in hydrophobicity could improve the Darcy permeability.

• 한국세라믹학회지
• /
• 제44권12호
• /
• pp.727-732
• /
• 2007

In order to fabricate a highly performing cathode for low-temperature type solid oxide fuel cells working at below $700^{\circ}C$, electrode microstructure control and electrode polarization measurement were performed with an electronic conductor, $La_{0.8}Sr_{0.2}MnO_3$ (LSM) and a mixed conductor, $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_3$(LSCF). For both cathode materials, when $Sm_{0.2}Ce_{0.8}O_2$ (SDC) buffer layer was formed between the cathode and yttria-stabilized zirconia (YSZ) electrolyte, interfacial reaction products were effectively prevented at the high temperature of cathode sintering and the electrode polarization was also reduced. Moreover, cathode polarization was greatly reduced by applying the SDC sol-gel coating on the cathode pore surface, which can increase triple phase boundary from the electrolyte interface to the electrode surface. For the LSCF cathode with the SDC buffer layer and modified by the SDC sol-gel coating on the cathode pore surface, the cathode resistance was as low as 0.11 ${\Omega}{\cdot}cm^2$ measured at $700^{\circ}C$ in air atmosphere.