• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.553-560
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• 1997

A fine $\alpha$-Al2O3 powder was prepared by sol-gel process for membrane application. And it was carried out by adding 1.5wt% $\alpha$-Al2O3 powders(mean size : 87 nm) as seeds to the prepared sols and by controlling the heating schedule (the heating rate and the soaking time) to prevent the microstructural change, which occured during $\theta$-to $\alpha$Al2O3 phase transformation. The seeded $\alpha$-Al2O3 particles acted as the heterogeneous nucleation sites for the $\alpha$-Al2O3 nucleation during the transformation of $\theta$- to $\alpha$-Al2O3 and resulted in increasing the driving force of phase transformation to activate the formation of $\alpha$-Al2O3 phase at 82$0^{\circ}C$. By $\alpha$-Al2O3 seeding and controlling of heating condition the phase transformation of $\theta$- to $\alpha$-Al2O3 was accomplished at low temperature and the grain growth process was depressed. Therefore, the unsupported membrane could be fabricated in $\alpha$-Al2O3 . The average diameter of pores in the fabricated membrane was 7 nm and the porosity was 47%.

• Korean Journal of Materials Research
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• v.21 no.10
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• pp.542-545
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• 2011

Half-Heusler alloys are a potential thermoelectric material for use in high-temperature applications. In an attempt to produce half-Heusler thermoelectric materials with fine microstructures, TiCoSb was synthesized by the mechanical alloying of stoichiometric elemental powder compositions and then consolidated by vacuum hot pressing. The phase transformations during the mechanical alloying and hot consolidation process were investigated using XRD and SEM. A single-phase, half- Heusler allow was successfully produced by the mechanical alloying process, but a minor portion of the second phase of the CoSb formation was observed after the vacuum hot pressing. The thermoelectric properties as a function of the temperature were evaluated for the hot-pressed specimens. The Seebeck coefficients in the test range showed negative values, representing n-type conductivity, and the absolute value was found to be relatively low due to the existence of the second phase. It is shown that the electrical conductivity is relatively high and that the thermal conductivities are compatibly low in MA TiCoSb. The maximum ZT value was found to be relatively low in the test temperature range, possibly due to the lower Seebeck coefficient. The Hall mobility value appeared to be quite low, leading to the lower value of Seebeck coefficient. Thus, it is likely that the single phase produced by mechanical alloying process will show much higher ZT values after an excess Ti addition. It is also believed that further property enhancement can be obtained if appropriate dopants are selectively introduced into this MA TiCoSb System.

• Transactions of Materials Processing
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• v.12 no.6
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• pp.588-596
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• 2003

The relationships between evolution of microstructure and mechanical properties of porous Al-3Si-2Mg-2Cu alloy after the foaming and various heat treating were investigated. The foamed alloy having various densities were manufactured by powder compact foaming and heat treated. Then compression test was performed with deformation rate of 0.5/s. The ultimate compression strength was not changed after solution heat treatment but the flow curve after ultimate strength showed very smooth and uniform plateau region. This change of flow curve means that the deformation mechanism is altered from brittle fracture to ductile deformation and the energy absorption property of Al foam is dramatically improved. The improvement of energy absorption without any detriment of mechanical properties is due to that the very brittle precipitation like Al-Cu and Al-Mg was uniformly dissolved in Al matrix after solution heat treatment. And various mechanical properties of Al alloy porous material were improved by 40% with aging of $200^{\circ}C$ and 50min. These improvements are ascribe to the various fine precipitates like $\Omega$ and $\theta$'.

• YAKHAK HOEJI
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• v.37 no.2
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• pp.172-181
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• 1993

The purpose of this study was to evaluate the clinical efficacy and safety of NRM which was newly developed as a combination product containing antacids, digestive enzyme and herbal drugs, and OTA powder, called OHTA'S ISAN on the morret, for the treatment of various symptoms in upper gastrointestinal diseases. 63 patients were recruited, 36 as a treated group with NRM and 27 as a controlled one with OTA. Patients were randomly allocated to receive either NRM or OTA t.i.d. for treatment of upper G-1 symptoms and undergone endoscopic, symptomatic and clinical laboratory assessments before and after 2 weeks. The results were as follows; 1. The general improvement rates of subjective symptoms in upper G-1 diseases were observed in 100%(32/32) for NRM and in 92%(23/25) for OTA. 2. The overall effective rates in terms of the symptoms and endoscopic findings were 88.9%(32/36) for NRM and 85.2%(23/27) ,or OTA respectively. 3. In NRM group, no significant side effects by NRM were observed except a mild and transient vomiting in one patient, but in OTA group treatment was discontinued due to nousea in one patient, However, there were no clinically significant changes detected in the laboratory parameters. According to the result of this trial, it is cocluded that NRM was safe and effective and (but not statistically significant) was superior to OTA in the treatment of gastrointestinal diseases caused by gastritis, gastric and duodenal ulcer, functional gastrointestinal disorder, non-ulcer dyspepsia etc.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.196-201
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• 2001

Electro-Rheological(ER) fluids change their apparent viscosity according to the electric field strength. Therefore, there are many practical applications using the ER fluids. ER effect on the dispersive system of polarizable fine powder/dielectric oil has been investigated. The electrical and rheological properties of starch based ER fluid were reported. Yield stress of the fluids were measured on the couette cell type rheometer as a function of electric fields, particle concetrations, and temperatures. The electric field is applied by high voltage DC power supply, The outer cup is connected to positive electrode(+) and the bob becomes ground(-). And the temperatures the viscosity(or shear stress) versus shear rates were measured. In this experiment shear rates were increased from 0 to 200s$^{-1}$ in 2 minutes. This thesis presents Bingham properties of ER fluids subjected to temperature variations. The temperature dependence of the viscosity was determined for ER fluids consisting of 35 weight % starch particles in automatic transmission oil.

• Journal of the Korean Ceramic Society
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• v.20 no.4
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• pp.305-314
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• 1983

In order to enhance the rate of th nitridation and to give the high density of reaction-bonded silicon nitride MgO powder as nitriding aid were added to silicon powders and the mixture was pressed isostatically into compacts which were nitrided in the furnace of 1, 35$0^{\circ}C$ where 95% $N_2$-5% $H_2$ gases were flowing. As the other nitriding aid $Mg(NO_3)_2 6H_2O$ was selected, A slip made of magnesium nitrate solution and fine silicon particles was spray-dried and then decomposed at 30$0^{\circ}C$. Magnesium oxide-coated silicon powders were formed into compacts prior to the nitridation on the same condition as the former. Magnesium nitrate (MgO, produced from the decomposition of magnesium nitrate) was more effective for the formation of the $\beta$-phase in the initial stage of the nitridation probably due to the easy formation of $MgO-SiO_2$-metal oxide eutectic melt. It has been confirmed that forsterite was formed as a result of the reaction between MgO and $SiO_2$ film of silicon surface. It was considered that MgO produced from magnesium nitrate may be finer more reactive and more uniformly distributed on the surface of silicon particles than original MgO. The higher the forming pressure was the more the $\beta$-phase was formed.

• Journal of the Korean Ceramic Society
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• v.46 no.5
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• pp.534-539
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• 2009

Reaction Bonded Silicon Carbide(RBSC) has been used for engineering ceramics due to low-temperature fabrication and near-net shape products with excellent structural properties such as thermal shock resistance, corrosion resistance and mechanical strength. Recently, attempts have been made to develop hot gas filter with gradient pore structure by RBSC to overcome weakness of commercial clay-bonded SiC filter such as low fracture toughness and low reliability. In this study a fabrication process of porous RBSC with multi-layer pore structure with gradient pore size was developed. The support layer of the RBSC with multi-layer pore structure was fabricated by conventional Si infiltration process. The intermediate and filter layers consisted of phenolic resin and fine SiC powder were prepared by dip-coating of the support RBSC in slurry of SiC and phenol resin. The temperature of $1550^{\circ}C$ to make Si left in RBSC support layer infiltrate into dip-coated layer to produce SiC by reacting with pyro-carbon from phenol resin.

• Journal of the Korean Ceramic Society
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• v.55 no.5
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• pp.473-479
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• 2018

Highly toxic gases such as hydrogen sulfide ($H_2S$), carbon dioxide ($CO_2$), and ammonia ($NH_3$) are generated by both nature and human activities and affect human health. In this research, activated carbon combined with $Ca(OH)_2$ and $CaCO_3$ (AC-CO and AC-CC, respectively) were fabricated and applied in absorbing toxic gases from air pollutants. Activated charcoal powder was compressed in the form of pellets and used in the designated conditions. The optimum operating conditions and material properties, such as adsorption capacity, effect of weight ratio of the mixture, and hardness, have been investigated after combining with the calcium derivative. The good performance exhibited in this study suggests that this material is expected to be an effective and economically viable adsorbent for $NH_3$, $CO_2$, and $H_2S$ removal from the air system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.313-313
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• 2008

Aerosol Deposition(AD) method is based on the impact consolidation phenomenon of ceramic fine particles at room temperature. AD is promising technology for the room temperature deposition of the dielectrics thin films with high quality. Embedding of passive components such as capacitors into printed circuit board is becoming an important strategy for electronics miniaturization and device reliability, manufacturing cost reduction. So, passive integration using aerosol deposition. In this study, we examine the effects of the characteristics of raw powder on the thickness, roughness, electrical properties of $BaTiO_3$ thin films. Thin films were deposited on the copper foil and copper plate. Electrical and material properties was investigated as a change of annealing temperature. We final aim the effects of before and after of laminated on the electrical properties and suit of embedded capacitor.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.53-53
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• 2008

Piezoelectric transformers have been widely used such as DC-DC convertor, invertor, Ballast, etc. Because, the y have some merits compared with electro-magnetic transformers such as step-up ratio, high efficiency, small size and lg hit weight, etc. Piezoelectric transformer require high electromechanical coupling factor kp in order to induce a large out put power in proportional to applied electric field. And also, high mechanical quality factor Qm is required to prevent mechanical loss and heat generation. In general, PZT system ceramics should be sintered at high temperatures between 1200 and $1300^{\circ}C$ in order to obtain complete densification. Accordingly, environmental pollution due to its PbO evaporation. Hence, to reduce its sintering temperature, various kinds of material processing methods such as hot pressing, high energy mill, liquid phase sintering, and using ultra fine powder have been performed. Among these methods, liquid phase sintering is basically an effective method for aiding densification at low temperature. In this study, In order to comparis on low temperature sintering and solid state sintering piezoelectric transformers, rosen type transformers were fabricated u sing two PZT ceramics compositions and their electrical properties were investigated.