• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1209-1217
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• 1994

Monodispersed alumina-zirconia fine powders were prepared by controlled hydrolysis of alkoxides. These powders and the sintered bodies were characterized. Aluminium alkoxide and zirconium alkoxide were dissolved into complex solvent with butanol and n-propanol, and by acetonitrile added hydrolytic solution, hydrolysis rate was controlled. The oil, as a dispersant, was added in hydrolytic solution, and then prepared powders were nano-sized and well-monodispersed. In the case of hydroxypropyl celluose (HPC) as a dispersant, it was added in complex solution with butanol and iso-propanol, sub-micrometer sized and well-monodispersed powders could be prepared. The value of relative density (R.D.) and tetragonal phase fraction of zirconia in the sintered body made by nano-meter sized powders were respectively higher than those in the case of sub-micrometer sized one.

• Journal of the Korean Ceramic Society
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• v.34 no.4
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• pp.394-398
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• 1997

Mn-Zn ferrite powders were prepared by alcoholic dehydration, using coprecipitation method. Then the effects of organic dispersant and polymeric binder concentration on stability and casting of slurry were discussed. Citric acid, the organic dispersant and polyvinylacohol(PVA), the non-ionic binder, were selected as additives of slurry. With variation of concentration of water, citric acid and polyvinylalcohol(PVA), optimum forming conditions were determined from viscosity and density. To compare with dry process, density and microstructure of sintered body formed by uniaxial die pressing were observed.

• Journal of the Korean Ceramic Society
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• v.37 no.10
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• pp.944-948
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• 2000

TiCl$_4$, 물 및 propanol의 혼합용액으로부터 가수분해하여 미립의 TiO$_2$분말을 제조할 때 HPC 첨가와 HPC 존재하에서 TiCl$_4$mole 농도 및 유기용매 처리를 했을 때 입자크기, 응집성 및 형태 등을 관찰하였다. HPC는 TiO$_2$합성시 steric dispersant로 작용하여 응집을 적게 하는 경향을 나타내었고 HPC를 첨가한 상태에서 TiCl$_4$의 mole 농도 변화는 입자크기에 크게 영향을 주었는데 TiCl$_4$mole 농도가 증가함에 따라 입자크기는 증가하였다. 또한 유기용제 처리는 분산 효과가 있었다.

• Journal of the Korean Ceramic Society
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• v.52 no.5
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• pp.315-319
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• 2015

Yttria-stabilized zirconia (YSZ)-based micro tubular SOFC single cells were fabricated by electrophoretic deposition (EPD) process. Stable slurries for the EPD process were prepared by adding phosphate ester (PE) as a dispersant in order to control the pH, conductivity, and zeta-potential. NiO-YSZ anode support, NiO-YSZ anode functional layer (AFL), and YSZ electrolyte were consecutively deposited on a graphite rod using the EPD process; materials were then co-sintered at $1400^{\circ}C$ for 4 h. The thickness of the deposited layer increased with increasing of the applied voltage and the deposition time. A YSZ-based micro tubular single cell fabricated by the EPD process exhibited a maximum power density of $0.3W/cm^2$ at $750^{\circ}C$.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06b
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• pp.129-153
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• 1996

In aqueous slurry processing of silicon nitride, the interaction of dispersant and binder on the surface of particles was studied to identify the effect of these additives on ceramic powder processing. Polymethacrylic acid (PMAA) and polyvinyl alcohol (PVA) were used as dispersant and binder, respectively. the adsorption isotherms of PMAA and PVA for the silicon nitride suspension were determined, while the adsorption of PMAA was differentiated in the mixed additive system by ultraviolet spectroscopy. These experiments were done in order to investigate the effect of these organic additives on the physicochemical properties of silicon nitride suspensions. The electrokinetic behavior of silicon nitride was subsequently measured by electrokinetic sonic amplitude (ESA). As PMAA adsorbed onto silicon nitride, the isoelectric point (pHicp) shifted from pH=6.7 to acidic pH, depending on the surface coverage of PMAA. However, adsorption of PVA did not change the pHicp of suspensions, but did decrease the surface potential of silicon nitride moderately. The rheological behavior of silicon nitride suspensions was measured to assess the stability of particles in aqueous media, and was correlated with the electrokinetic behavior and adsorption isotherm data for silicon nitride.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.12
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• pp.751-756
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• 2017

A molding-type power inductor is an inductor that uses a hybrid material that is prepared by mixing a ferrite metal powder coated with an insulating layer and an epoxy resin, which is injected into a coil-embedded mold and heated and cured. The fabrication of molding-type inductors requires various techniques such as for coil formation and insertion, improving the magnetic properties of soft magnetic metal powder, coating an insulating film on the magnetic powder surface, and increasing the packing density by well dispersing the powder in the epoxy resin. Among these aspects, researches on additives that can disperse the metal soft magnetic powder having the greatest performance in the epoxy resin with high charge have not been reported yet. In this study, we investigated the effect of silanes, KBM-303 and KBM-403, and a commercial dispersant on the dispersion of metal soft magnetic powders in epoxy resin. The sedimentation height and viscosity were measured, and it was confirmed that the silane KBM-303 was suitable for dispersion. For this silane, the packing density was as high as about 72.49%. Moreover, when 1.2 wt% of dispersant BYK-103 was added, the packing density was about 80.5%.

• Journal of the Korean Ceramic Society
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• v.56 no.4
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• pp.360-364
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• 2019

PZT suspensions for photo-curable 3D printing were fabricated and their characteristics were evaluated. After mixing the PZT, photopolymer, photo-initiator, and dispersant for 10 min by using a high-shear mixer, the viscosity characteristics were investigated based on the powder content. To determine an appropriate dispersant content, the dispersant was mixed at 1, 3, and 5 wt% of the powder and a precipitation test was conducted for two hours. Consequently, it was confirmed that the dispersibility was excellent at 3 wt%. Through thermogravimetric analysis, it was confirmed that weight reduction occurred in the photopolymer between 120? and 500?, thereby providing a debinding heat treatment profile. The fabricated suspensions were cured using UV light, and the polymer was removed through debinding. Subsequently, the density and surface characteristics were analyzed by using the Archimedes method and field-emission scanning electron microscopy. Consequently, compared with the theoretical density, an excellent characteristic of 97% was shown at a powder content of 87 wt%. Through X-ray diffraction analysis, it was confirmed that the crystallizability improved as the solid content increased. At the mixing ratio of 87 wt% powder and 13 wt% photo-curable resin, the viscosity was 3,100 cps, confirming an appropriate viscosity characteristic as a stereolithography suspension for 3D printing.

• Journal of the Korean Ceramic Society
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• v.32 no.2
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• pp.189-196
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• 1995

Materials retaining electrolyte of a phosphoric acid fuel cell (PAFC) have been prepared with SiC powder to SiC whisker mixing ratios of 1:1, 1:2, 1:3, 1:4, 0:1 by a tape casting method. When 3wt% dispersant (sorbitan monooleate) is added to a matrix, the porosity of the matrix decreases a little while the bubble pressure and area of the matrix increase remarkably in comparison with no dispersant content. Effect of the electrolyte resistance and the polarization resistance on perfomance of a PAFC has been investigated using A.C. impedance spectroscopy. With the increase of whisker content, the electrolyte resistance decreases due to the increase of porosity and acid absorbancy, and the polarization resistance increases due to the increase of surface roughness. The polarization resistance affects current density predominantly at the higher potential than 0.7V becuase the polarization resistance is considrably larger than the electrolyte resistance. Both the electrolyte resistance and the polarization resistance affect current density near 0.7V of the fuel cell operating potential because they have similar values. The electrolyte resistance affects current density predominantly at the lower potential than the fuel cell operating potential because the electrolyte resistance is larger than the polarization resistance.

• Transactions of Materials Processing
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• v.31 no.5
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• pp.290-295
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• 2022

Recently, the use of high-tech ceramic parts in functional electronic parts, automobile parts and semiconductor equipment parts is increasing. These ceramics materials are required to have high reproducibility, reliability, large size and complex shapes. The researchers initiated the work to develop a new shaping method called gel casting, which allows high performance ceramic materials with a complex shape to be produced. The manufacturing process parameters of gel casting include uniform mixing of the initiator, bubble removal, and slip injection. In this study, we analyzed the dispersion and gelation characteristics according to the change in the additive content of the alumina slurry in the gel casting process. The alumina slurry for gel casting was prepared by mixing a solvent, a monomer and a dispersant through a ball mill. Alumina powder and a gelation initiator were added to the mixed solution, and ball milling was performed for 24 hours. A viscosity of 6,435 cps and a stable zeta potential value were obtained under the conditions of alumina powder content of 55 vol% and dispersant 2.0 wt%. After curing for 12 hours by adding aps 0.1wt%, TEMED 0.2wt%, and Monomer 3, 5wt%, it was possible to separate from the molding cup, confirming that the gelation was completed.

• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.280-285
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• 2000

The electrolyte, $(HO)_2C_6H_2(SO_3Na)_2H_2O $(Tiron), disperses efficiently alumina powder in aqueous media and stable suspensions with 60 vol% solid loading can be prepared. The strong adsorption of this additive is mainly due to the ability of the molecule to form chelate rings with the particle surface but electrostatic interactions between the surface charge and the anionic dispersant strongly influence the amount of Tiron adsorbed. By using a cationic exchange route to substitute the counter ion which neutralizes the sulfonate groups, new molecules of dispersant have been prepared, either with mineral cations as $Li^+,\; Na+^,\; NH_4^\;+$, or with organic cations as counter ion but organic counter ions lead to less to less viscous suspensions than $Na^+$ in particular when the number of carbon atoms of the aliphatic chain increases from 1 to 3.