• Bulletin of the Korean Chemical Society
• /
• v.17 no.7
• /
• pp.621-625
• /
• 1996

A variety of metal oxides were coated by sol-gel process from their metal alkoxides on the ribbons of Co-based and Fe-based amorphous alloys, and the effects of surface oxide coating on the magnetic properties of the alloy are investigated. The core loss is found to be reduced significantly by the oxide coating, the loss reduction becoming more prominent at higher frequencies. The shape of the hystersis loop is also dependent upon the kind of the coated metal oxide. The coatings of MgO, SiO2, MgO·SiO2 and MgO·Al2O3 induce tensile stress into the Fe-based ribbon whereas those of BaO, Al2O3, CaO·Al2O3, SrO·Al2O3 and BaO·Al2O3 induce compressive stress. These results may be explained by the modification of domain structures via magnetoelastic interactions with the shrinkage stress induced by the sol-gel coating.

• Bulletin of the Korean Chemical Society
• /
• v.28 no.12
• /
• pp.2288-2292
• /
• 2007

The catalytic activities of nickel-based catalysts were estimated for oxidizing acetaldehyde of VOCs exhausted from industrial facilities. The catalysts were prepared by sol-gel methods of SiO2 and SiO2-TiO2 as a xerogel followed by impregnating Al2O3 powder with the nickel nitrate precursor. The crystalline structure and catalytic properties for the catalysts were investigated by use of BET surface area, X-ray diffraction (XRD), Xray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) techniques. These results show that nickel oxide is transformed to NiAl2O4 spinel structure at the calcination temperature of 400 °C in response to the steps with after- and co-impregnation of Al2O3 powder in sol-gel process. The NiAl2O4 could suppress the oxidation reaction of acetaldehyde by catalysts. The NiO is better dispersed on SiO2-TiO2/Al2O3 support than SiO2/Al2O3 and SiO2-TiO2-Al2O3 supports. From the testing results of catalytic activities for oxidation of acetaldehyde, Catalysts showed a big difference in conversion efficiencies with the way of the preparation of catalysts and the loading weight of nickel. The catalyst of 8 wt.% Ni/TiO2-SiO2/Al2O3 showed the best conversion efficiency on acetaldehyde oxidation with 100% conversion efficiency at 350 °C.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.7 no.5
• /
• pp.801-804
• /
• 2006

[ $GdAlO_3(GAO)$ ] buffer layer for $YBa_2Cu_3O_{7-{\delta}}(YBCO)$ coated superconductor wire was fabricated by sol-gel processing. Precursor solution was prepared by dissolving 1:1 stoichiometric quantaties of gadolinium nitrate hexahydrate and aluminum nitrate nonahydrate in methanol. The solution was spin-coated on $SrTiO_3(STO)$(100) single crystal substrates and heated at $1000^{\circ}C$ for 2h in wet $N_2-5%\; H_2$, atmosphere. A SEM(scanning electron microscopy) observation of the surface morphology of the GAO layer has shown that it has a faceted morphology indicating epitaxy. It was shown from x-ray diffraction(XRB) that GAO buffer layer was highly c-axis oriented epitaxial thin film with both good out-of-plane($FWHM=0.29^{\circ}$ for the (002) reflection) and in-plane ($FWHM=1.10^{\circ}$ for the {112} reflection) alignment.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2003.11a
• /
• pp.137-137
• /
• 2003

Optical amplificator have been used to compensate the losses in the optical signal transmission and processing. Today, there has been increasing demand for the very low cost optical amplifier. Sol-gel offers considerable potential both low cost manufacture, and for great flexibility in materials composition and structure. In addition, the sol-gel process is a very attractive method for producing porous materials with controlled structure. In this work, we present the potoluminescence properties of Er doped A1$_2$O$_3$/SiO$_2$ films. Erbium doped alumina nano sol was prepared by Al(NO$_3$)$_3$.9$H_2O$ and Er(NO$_3$)$_3$.5$H_2O$ through hydrolysis and peptization, and then GPS (3-Glycidoxypropyltrimethoxysilane) was added into Er doped alumina nano sol for organic- inorganic hybridization. Er doped A1$_2$O$_3$/SiO$_2$ film was obtained by spin coating, dip coating and thermal treatment from 30$0^{\circ}C$~120$0^{\circ}C$, and there were crack-free after thermal treatment. The thickness of film was measured SEM, and the porosity of film was characterized by BET and TGA. The crystal phase of Er doped A1$_2$O$_3$/SiO$_2$ were determined by XRD. Finally, the photoluminescence properties of Er doped A1$_2$O$_3$/SiO$_2$ films will be discuss with the consideration of porosity and crystallity.

• Journal of the Korean Ceramic Society
• /
• v.28 no.7
• /
• pp.503-508
• /
• 1991

High pure and fine mullite powders were synthesized from Al-secbutoxide[Al(OC4H9)3] and TEOS[Si(OC2H5)4] (SiO2/Al2O3=2/3 mole). Sol-Gel process by partial hydrolysis technique, as it were, first, TEOS was partially hydrolysized and then mixed with Al-secbutoxide for complete hydrolysis was used. The mullite precursor was synthesized within 30 hrs, which was reduced about a half of synthetic time in comparison with the other's study. Al-Si spinel was formed at 980℃ and mullite crystal was formed at 1200℃. Mullite powders synthesized in this study was spherical type like those of the other studies and particle sizes were very fine. Also mullite powders calcined at 1,600℃ had a stoichiometric composition (3Al2O3·2SiO2) and lattice constants were coincided with known theoretical values.

• Korean Chemical Engineering Research
• /
• v.52 no.2
• /
• pp.209-213
• /
• 2014

A graft copolymer of poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g-POEM) was synthesized via atom transfer radical polymerization (ATRP) and used as a structure-directing agent to prepare $Al@Fe_2O_3$ core-shell nanocomposites through a sol-gel process. The amphiphilic property of PVC-g-POEM allows for good dispersion of Al particles and leads to specific interaction with iron ethoxide, a precursor of $Fe_2O_3$. Secondary bonding interaction in the sol-gel composites was characterized by Fourier transform-infrared (FT-IR) spectroscopy. The well-organized morphology of $Al@Fe_2O_3$ core-shell nanocomposites was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) were used to analyze the elemental composition and crystallization structure of the composites.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.18 no.1
• /
• pp.50-55
• /
• 2008

AI-doped ZnO(AZO) thin films have been fabricated on glass substrate by sol-gel method, and the effect of Al precursors and post-annealing temperature on the characteristics of AZO thin films was investigated. The sol was prepared with zinc acetate, EtOH, MEA and Al precursors. In order to dope Al in ZnO, two types of aluminum nitrate and aluminum chloride were used as Al precursor. Zinc concentration was 0.5 mol/l and the content of Al precursor was 1 at% of Zn in the sol. The sol was spin-coated on glass substrate, and the coated films were annealed at 550ue for 2 hand were post-annealed at temperature ranges of $300{\sim}500^{\circ}C$ for 2 h in reducing atmosphere ($N_2/H_2$= 9/1). Structural, electrical and optical propertis of the fabricated AZO thin films were analyzed by XRD, FE-SEM, AFM, hall effect measurement system and UV-visible spectroscopy. Optical and electrical properties of AZO thin films prepared with aluminum nitrate as Al precursor were better than those of films prepared with aluminum chloride. The electrical resistivity and the optical transmittance of films decreased with increasing post-annealing temperatures. The minimum electrical resistivity of $2{\times}10^{-3}$ and the maximum optical transmittance of 91% were obtained for the AZO thin films post-annealed at $550^{\circ}C\;and\;300^{\circ}C$, respectively.

• Journal of the Korean Ceramic Society
• /
• v.28 no.5
• /
• pp.365-372
• /
• 1991

LAS (lithium aluminosilicate) sol was synthesized using the hydrolysis-condensation reaction of TEOS, chelated Al(OBus)3 and Li-salt with H2O in alcohol (EtOH+2-Propanol) medium. Effects of important reaction parameters on the properties of sol and gel-derived LAS were examined. The crystallization of the sol-gel derived LAS with ${\beta}$-spodumene composition began at ∼600$^{\circ}C$, and a series of polymorphic transformations occurred as temperature was increased to 1100$^{\circ}C$: amorphous LAS\longrightarrowhexagonal LiAl(SiO3)2\longrightarrow${\beta}$-spodumene. Lowering Li content in the gel enhanced densification and retarded the crystallization significantly. Optimum reaction conditions of LAS sol formation for thin coating applications were derived from rheological measurements, and these can be summarized as: H2O/total alkoxides molar ratio=4, pH=∼2.5, and aging time of ∼250h.

• Korean Journal of Materials Research
• /
• v.24 no.5
• /
• pp.259-265
• /
• 2014

$ZrO_2$ films were coated on aluminum etching foil by the sol-gel method to apply $ZrO_2$ as a dielectric material in an aluminum(Al) electrolytic capacitor. $ZrO_2$ films annealed above $450^{\circ}C$ appeared to have a tetragonal structure. The withdrawal speed during dip-coating, and the annealing temperature, influenced crack-growth in the films. The $ZrO_2$ films annealed at $500^{\circ}C$ exhibited a dielectric constant of 33 at 1 kHz. Also, uniform $ZrO_2$ tunnels formed in Al etch-pits $1{\mu}m$ in diameter. However, $ZrO_2$ film of 100-200 nm thickness showed the withstanding voltage of 15 V, which was unsuitable for a high-voltage capacitor. In order to improve the withstanding voltage, $ZrO_2$-coated Al etching foils were anodized at 300 V. After being anodized, the $Al_2O_3$ film grew in the directions of both the Al-metal matrix and the $ZrO_2$ film, and the $ZrO_2$-coated Al foil showed a withstanding voltage of 300 V. However, the capacitance of the $ZrO_2$-coated Al foil exhibited only a small increase because the thickness of the $Al_2O_3$ film was 4-5 times thicker than that of $ZrO_2$ film.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.431.1-431.1
• /
• 2014

최근, 높은 캐리어 이동도와 유연성, 투명성의 우수한 전기적 기계적 특성을 갖는 그래핀에 관한 연구가 활발해지고 있으며 이를 기반으로 한 그래핀 field effect transistor (FET) 센서 응용 또한 관심이 커지고 있다. 작은 소자 크기, 견고한 구조, 빠른 응답속도와 CMOS 공정과의 호환성이 좋은 FET 기반의 센서의 감지 특성은 주로 전해질과 직접 접촉하는 게이트 절연체의 고유 특성에 의해 결정된다. 이러한 게이트 절연체는 일반적으로 스퍼터링, atomic layer deposition (ALD), plasma enhanced chemical vapor deposition (PECVD) 등의 진공 방법에 의해 형성되며, 이 공정 기술은 고가의 장비, 긴 공정 시간과 높은 제조비용이 요구된다. 더욱이, 위의 방식들은 소자 제작 동안에 플라즈마 발생 또는 열처리를 필요로 하게 되며 이는 그래핀 기반의 소자의 제작에 있어 큰 손상을 발생시키게 된다. 이러한 이유로 인해, 그래핀 FET 센서의 게이트 절연체의 형성에 있어 진공 증착 기술은 적절하지 않다. 본 연구에서는, 진공 증착 기술의 문제점을 극복하기 위해 sol-gel 방식을 통한 Al2O3 게이트 절연체를 갖는 그래핀 FET 센서를 제작하였다. Sol-gel 방식은 적은 비용, 공정의 단순화, 높은 처리량 뿐 아니라 소자의 대면적화 제작에 유리하다는 장점을 가지며, 또한 게이트 절연체를 증착함에 있어서 플라즈마가 발생하지 않기 때문에 그래핀 FET 제작에 쉽게 적용될 수 있다. 특히, 게이트 절연체 중 Al2O3은 우수한 화학적 안정성과 감지 특성으로 인해 본 실험에 사용하였다. 결론적으로, sol-gel 방식을 통한 Al2O3 게이트 절연체를 갖는 그래핀 FET 센서는 우수한 전기적 특성과 감지 특성 측면에서 매우 전망적이다.