• Korean Journal of Materials Research
• /
• v.10 no.3
• /
• pp.233-240
• /
• 2000

In order to fabricate dense cordierite ceramics without sintering aid, thermal behavior of Mg-Al-Si compounds during sintering was investigated. The dispersibility of cordierite suspension in aqueous media was measured by ESA(electrokinetic sonic amplitude). To prevent aggregation and insufficient dispersion of the cordierite sol, the pH of the suspension was controlled to 1.03 and 8.30 by adding $2N\;HNO_3$ and $2N\;NH_4OH$, respectively. Magnesium-aluminum-silicate complex gel coexisted in the specimen which has been gelled at $150^{\circ}C$ fir 12 hours, however several metastable phase such as ${\mu}-cordierite(Mg_2Al_4Si_5O_{18}),\;spine(MgAl_2O_4)\;and\;mullite(Al_6Si_2O_{13})$ existed below $1300^{\circ}C$ Nucleation rates of the two suspension were similar, but densification of the gel was sensitive to the pH of the sol. Densification of the sol with the pH of 8.3 was more pronounced than that of the sol with pH of 1.63.

• The Korean Journal of Ceramics
• /
• v.5 no.1
• /
• pp.50-54
• /
• 1999

$(Pb_xLa_{1-x}) (Zr_yTi_{1-y})O_3$ (PLZT) thin films with electrooptic effect are promising for the optical application such as display or light shutter. However, it is difficult to use inexpensive and transparent glass substrates because the conventional process for preparation of PLZT requires temperatures above $600^{\circ}C$. In order to deposit a perovskite PLZT thin films at low processing temperatures through alkoxide route, we have offered several seeding processes which reduce the activation energy for crystallization. In this study, we optimized the stacking structure of multilayered PLZT for obtaining single phase perovskite at lower temperatures. As a result, ferroelectric PLZT thin films with different compositions were successfully prepared at a temperature as low at $500^{\circ}C$.

• Journal of information and communication convergence engineering
• /
• v.1 no.2
• /
• pp.63-66
• /
• 2003

High $T_c$ superconducting lines will be applied as key materials in the areas of power transmission line; magnetic levitation of vehicle; magnetic separation; magnetic energy storage and marine propulsion. A combination method of electrophoresis deposition and zone-melting for preparation of YBaCuO tape is proposed. The submicron particle powder of YBaCuO made by sol-gel method is used in the electrophoresis process. A 40∼50 ${\mu}\textrm{m}$ thickness of YBaCuO film on Ag plate could be deposited in about three minutes. After deposition the film is rolled and heat treated in order to increase the density and the adhesion of the film to the Ag plate. Silver(Ag) and lead oxide(PbO) were added in the YBaCuO powder in order to reduce its melting point. The YBaCuO coating with controlled Ag and PbO contents was preliminarily zone-melted at about $945^{\circ}C$.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.23 no.1
• /
• pp.156-163
• /
• 1994

To investigate the optimum conditions of seaweed Mooks prepared with sea mustard (Indaria pinnatifida) and sea tangel(Laminaria japonica), pH, viscosity , yield and jelly strength were studied on the sol and /or gel (Mook ) made from homogenized seaweeds. Solubilization conditions of homogenized seaweeds were heating at $65^{\circ}C$ for one hour after mixing homogenized seaweed with 1 % $K_2$HPO$_4$ by 1 ; 1 (v/v) . Gelation conditions were 24 hrs by natural permeation of Ca++ into the sol in three times (v/v) of 1 % CaCl$_2$ solution to solubilized seaweed passed through 60 mesh of sieve. There are generally no relationship between viscosity of solubilized seaweed and jelly strength of Mook produced by gelation of the sol in CaCl$_2$ solution . Jelly strength of sea mustard Mook was more than 500g/$\textrm{cm}^2$ , yield was 87.5% of the solubilized and filtrated seaweed . Jelly strength and specific gravity of sea tangle Mook were higher those of sea mustard Mook, while its yield was lower than that of sea mustard Mook.

• Analytical Science and Technology
• /
• v.6 no.2
• /
• pp.225-229
• /
• 1993

ATZ was prepared by adding an alumina sol equivalent to 2wt% as $Al_2O_3$ to an aqueous slurry of alumina (AKP-30) and zirconia (TZ-2Y or TZ-0Y) in the range of 10-30ATZ, followed by gelation, calcination, and sintereing between $1450^{\circ}C{\sim}1550^{\circ}C$ for 2h. They showed excellent microstructure with alumina grains of <$0.5{\mu}m$ and>99% of the theoretical density. Fracture toughness of ${\sim}8MPa{\cdot}m^{1/2}$ was observed around 20ATZ which was higher than $6MPa{\cdot}m^{1/2}$ obtainable by ball-milling.

• Korean Journal of Materials Research
• /
• v.17 no.3
• /
• pp.147-151
• /
• 2007

Cu-free multi-component sol, of which final oxide composition becomes $Bi_{1.9}Pb{0.35}SrCaO,\;Bi_{1.8}Pb_{0.2}SrCaO\;and\;Bi_{1.5}SrCaO$, respectively, was prepared through sol-gel route and coated on a bare Cu substrate. Starting materials were metal-alkoxides as follows.; [$Bi(OC_{2}H_{5})_{3}\;Pb(O^{1}C_{3}H_{7})_{2},\;Sr(O^{i}C_{3}H_{7})_{2},\;Ca(OC_{2}H_{5})_{2}$] as a reagent grade. Transparent light yellowish sol was obtained in the case of $Bi_{1.9}Pb_{0.35}SrCaO\;and\;Bi_{1.8}Pb_{0.2}SrCaO$ composition and $Bi_{1.5}SrCaO$ composition's sol was light greenish. Each sol was repeatedly dip-coated on Cu substrate four times and pre-heated at $400^{\circ}C$ and finally heat-treated in the range of $740{\sim}900^{\circ}C$. In the results, crystalline phases confirmed by XRD were (2201) orthorhombic and monoclinic phases. However, only $Bi_{1.9}Pb_{0.35}SrCaO_{x}$ composition showed pseudo-superconductive behavior after heat-treatment at $900^{\circ}C$ for 12 seconds and then onset temperature was 77 K, even though it did not exhibit zero resistance below Tc.

• Journal of the Korean Society of Safety
• /
• v.14 no.1
• /
• pp.101-107
• /
• 1999

$TiO_2$ and $xTiO_2-ySiO_2$ system photocatalysts were developed by sol-gel method based on the change of production parameters, and their structure of crystallization and the specific surface area was measured. Considering the efficiency of the ethanol decomposition using the catalyst, the conclusion was made as follows: 1) By means of X-ray analysis of $TiO_2$ powder that is obtained from water and Titanium alkoxide with various molar ratios, it is shown that structure of crystallization is a dominating structure and, on the other hand, the crystallization of rutile also partly exists. The specific surface area is at its maximum value at R=6, which is the molar ratio of water vs. alkoxide, whereas its value goes down as the molar ratio increases. In the reaction of using $TiO_2$ catalyst, the ethanol is decomposed into the extent of 15 ~30% in an hour and three hours are necessitated for 70% decomposition. 2) $TiO_2/SiO_2$ powder is developed from Titanium and Silicon alkoxide by a hetero-condensation process. The increase of SiO$_2$ contents causes the decrease of the degree of crystallization of the gel, whereas the specific surface area preferentially increases. In the decomposition reaction of the ethanol, the decomposition efficiency represents 25~60% in an hour. It is, however, examined that the efficiency inactively increases corresponding to the duration of reaction time. It is shown that more than 90% of ethanol is decomposed when reaction time is about three hours and the efficiency illustrates the maximum value for 60-$TiO_2/4O-SiO_2$ catalyst.

• Korean Journal of Materials Research
• /
• v.3 no.3
• /
• pp.207-214
• /
• 1993

Glass-ceramic monoliths with an ultra-low thermal expansion coefficient have been synthesized by the sol-gel technique using metal alkoxides as starting materials and dimethyl formamide as a drying control chemical additive. The ternary gels: $Li_2O\cdot Al_2O_3\cdot 2, 4 or $6SiO_2$ were obtained by hydrolysis and polycondensation reactions of metal alkoxides of silicon, aluminum and lithium. To produce cylindrical crack-free gel monoliths, excess water was used to the starting solutions and drying rates were controlled precisely to prevent cracking. In conversion process ,${\beta}$-eucryptite, $Li_2O\cdot Al_2O_3\cdot 3SiO_2$ and P-spodumene with ,${\beta}$-quartz solid solution phase were obtained by heating at the range of 750 ~$1000^{\circ}C$. Above $800^{\circ}C$, the ,${\beta}$-spodumene phase increased while ,${\beta}$-eucryptite phase decreased. The thermal expansion coefficient of the crystallized specimens were -15~ $+5{\times}{10^{-7}}/{\circ}C$ over the temperature range from room temperature to $600^{\circ}C$.

• International Journal of Advanced Culture Technology
• /
• v.3 no.1
• /
• pp.21-30
• /
• 2015

Ceramic foams are prepared as positive images corresponding to a plastic foam structure which exhibits high porosities (85-90%). This structure makes the ceramic foams attractive as a catalyst in a dry reforming process, because it could reduce a high pressure drop problem. This problem causes low mass and heat transfers in the process. Furthermore, the reactants would shortly contact to catalyst surface, thus low conversion could occur. Therefore, this research addressed the preparation of dry reforming catalysts using a sol-gel catalyst preparation via a polymeric sponge method. The specific objectives of this work are to investigate the effects of polymer foam structure (such as porosity, pore sizes, and cell characteristics) on a catalyst performance and to observe the influences of catalyst preparation parameters to yield a replica of the original structure of polymeric foam. To accomplish these objectives industrial waste foams, polyurethane (PU) and polyvinyl alcohol (PVA) foams, were used as a polymeric template. Results indicated that the porosity of the polyurethane and polyvinyl alcohol foams were about 99% and 97%. Their average cell sizes were approximate 200 and 50 micrometres, respectively. The cell characteristics of polymer foams exhibited the character of a high permeability material that can be able to dip with ceramic slurry, which was synthesized with various viscosities, during a catalyst preparation step. Next, morphology of ceramic foams was explored using scanning electron microscopy (SEM), and catalyst properties, such as; temperature profile of catalyst reduction, metal dispersion, and surface area, were also characterized by $H_2-TPR$ and $H_2-TPD$ techniques, and BET, respectively. From the results, it was found that metal-particle dispersion was relatively high about 5.89%, whereas the surface area of ceramic foam catalysts was $64.52m^2/g$. Finally, the catalytic behaviour toward hydrogen production through the dry reforming of methane using a fixed-bed reactor was evaluated under certain operating conditions. The approaches from this research provide a direction for further improvement of marketable environmental friendly catalyst production.

• Journal of the Korean Ceramic Society
• /
• v.34 no.1
• /
• pp.79-87
• /
• 1997

Anti-reflective and anti-static double layered films were prepared on the VDT panel by sol-gel spin-coating method. Their electrical, opticla, and mechanical properties were investigated. The outer SiO2 film with low re-fractive index was coated over the inner ATO(Antimony-doped Tin Oxide)-SiO2 film which was prepared by mixing ATO sol with SiO2 at molar ratio of 68:32 to satisfy the interference condition of double layers. The heat treatment was conducted at 45$0^{\circ}C$ for 30 min where residual organics were completely removed. The sheet resistance of ATO single layer showed the minimum value of 6$\times$107$\Omega$/$\square$ at 3 mol% addition of Sb and that of SiO2/ATO-SiO2 increased slightly with increasing SiO2 mol% up to 30 mol%, and then increased steeply to the value of 3$\times$108$\Omega$/$\square$ at 32 mol%. The reflectance of double layered films was about 0.64% at the wavelength of 550nm and the transmittance increased about 3.20%. The hardness of double layered films was almost the same as that of uncoated VDT panel, 471.4kg.f/mm2.