• Journal of the Microelectronics and Packaging Society
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• v.7 no.3
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• pp.7-11
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• 2000

The low-voltage driven $SrTiO_3$ceramic varistor device was fabricated from $SrTiO_3$ powders prepared by co-precipitation method with $CuO-SiO_2$additives. Compare with conventional process, this process has advantages such as the reduction of the sintering temperature of $SrTiO_3$ ceramics by 100-$150^{\circ}C$ and the simplification of processing procedure. The non-linear coefficient value ($\alpha$) of the varistor showed 8.47 when it was sintered at $1350^{\circ}C$ for 2 h with 5 wt% additives in reducing atmosphere of 5% $H_2/N_2$ mixed gas. The low-voltage driven $SrTiO_3$ceramic varistor was obtained which has a breakdown voltage as low as 7 V.

• Korean Journal of Materials Research
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• v.32 no.4
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• pp.216-222
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• 2022

The capacity of high nickel Li(Ni_xCo_yMn_1-x-y)O₂ (NCM, x ≥ 0.8) cathodes is known to rapidly decline, a serious problem that needs to be solved in a timely manner. It was reported that cathode materials with the {010} plane exposed toward the outside, i.e., a radial structure, can provide facile Li⁺ diffusion paths and stress buffer during repeated cycles. In addition, cathodes with a core-shell composition gradient are of great interest. For example, a stable surface structure can be achieved using relatively low nickel content on the surface. In this study, precursors of the high-nickel NCM were synthesized by coprecipitation in ambient atmosphere. Then, a transition metal solution for coprecipitation was replaced with a low nickel content and the coprecipitation reaction proceeded for the desired time. The electrochemical analysis of the core-shell cathode showed a capacity retention of 94 % after 100 cycles, compared to the initial discharge capacity of 184.74 mA h/g. The rate capability test also confirmed that the core-shell cathode had enhanced kinetics during charging and discharging at 1 A/g.

• KSBB Journal
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• v.27 no.3
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• pp.157-160
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• 2012

When iron oxide magnetic nanoparticles were synthesized by co-precipitation method using aqueous ammonia as reducing agent, the synthesized particles were aggregated and thus precipitation occurred. Using Magnolia kobus leaf extract as reducing agent, spherical nanoparticles of 50~200 nm were synthesized with low yield. By using both Magnolia kobus leaf extract and aqueous ammonia as reducing and stabilizing agents, smaller nanoparticles of 40~120 nm could be synthesized with various shapes. The synthesized magnetic nanoparticles were characterized with field emission transmission electron microscopy (FE-TEM) and scanning electron microscopy (SEM). TEM and SEM images showed that the magnetic nanoparticles are a mixture of triangles, tetragons, rods and spherical structures.

• Journal of the Korean Applied Science and Technology
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• v.25 no.4
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• pp.511-517
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• 2008

We make high-functional inorganic-composite pearlescent pigment material that coated with carmine on the plate-type particle such as mica. In this experiment, we synthesized composite powder using pH control precipitation method. We make an experiment with changing as synthesis factors that are concentrations of starting material and precipitation materials. We analyzed pearlescent powder's shape, and crystallization with FE-SEM, XRD, and EDS. Optimum condition for preparation of carmine coated mica pearlescent pigment is pH $4.5{\sim}5.5$.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.861-862
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• 2009

Precipitated iron-based catalysts are highly promising for the Fischer-Tropsch synthesis (FTS), in particular for the low temperature FTS below $280^{\circ}C$, because of their high activity and low cost. $SiO_2$ is an essential promoter for the precipitated iron-based catalysts to improve the attrition strength and physical stability. In this study, we carried out FTS over precipitated iron-based catalysts with and without $SiO_2$ in a fixed-bed reactor. The catalysts were prepared by a conventional co-precipitation method. In case of the catalysts with $SiO_2$, we used two comparative preparation methods, i.e., incorporation of $SiO_2$ before precipitation (denoted as precipitated $SiO_2$) and after precipitation (denoted as binder $SiO_2$), respectively. The addition of $SiO_2$ crucially affects both physico-chemical properties and catalytic peformance of precipitated iron-based catalysts.

• Resources Recycling
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• v.30 no.6
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• pp.36-42
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• 2021

Spent lithium-ion batteries are treated by reduction-smelting at high temperatures to recover valuable metals. Solvent extraction and precipitation of the HCl leaching solution of reduction-smelted metallic alloys resulted in a filtrate containing Ni(II) and a small amount of Si(IV). Adsorption and precipitation experiments were conducted to recover pure Ni(II) compounds from the filtrate. Si(IV) was selectively loaded onto polyacrylamide, but this method did not efficiently filter the solution due to an increase in viscosity. The addition of Na₂CO₃ as a precipitant to the filtrate led to the simultaneous precipitation of Ni(II) and Si(IV). However, it was possible to recover nickel oxalate with a purity higher than 99.99% by selectively precipitating Ni(II) with the addition of Na₂C₂O₄ as a precipitant.

• Journal of the Korean Magnetics Society
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• v.18 no.3
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• pp.120-125
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• 2008

In this study, NiCoZn ferrites with the variation of sintering temperature and chemical composition were prepared by the coprecipitation. Microstructures Crystal structure of NiCoZn ferrites were analyzed by XRD and their electric magnetic characteristics were analyzed by LCR meter and their morphology observed by SEM. We identified that these powders have a typical NiCoZn spinel structure and nanoparticles average size of 40 nm. The impurity, the initial permeability and the Q factor value are the lowest of sintered NiCoZn ferrite at $1250^{\circ}C$. Also, we measured S-parameter for $(Ni_{0.4}Co_{0.1}Zn_{0.5})Fe_2O_4$ which showed a maximum reflection loss of -3.1 dB at 6 GHz for the 2 mm thick sample. From this result, we found that the NiCoZn ferrite can be used in ferrite microwave-absorbing application at a higher frequency region (> 6 GHz).

• Journal of Korean Society of Water and Wastewater
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• v.31 no.4
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• pp.329-338
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• 2017

The problem of disposal of brine due to increased MD/RO desalination plant has recently become a big social issue. The chlor-alkali process through electrolysis of brine has been studied as a method to overcome this problem. In order to increase the electrolysis efficiency, a pretreatment process for removal of hard substances must be preceded. In this study, we investigated the mechanism of removal of hardness through chemical precipitation. As a result, Ca was greatly influenced by addition of $Na_2CO_3$, and Mg was strongly influenced by pH. Also, the addition of NaOH and $Na_2CO_3$ enabled simultaneous removal of Ca and Mg, and showed a removal efficiency of 99.9% or more. Finally, the residual concentrations of Ca and Mg in the brine after the reaction were 0.14 and 0.13 mg/L, respectively. Saturation index was calculated using Visual MINTEQ 3.1, and solid phase analysis of the precipitate was performed by FE-SEM and PXRD analysis. It was confirmed that precipitate formed by the formation of calcite and brucite.

• Korean Chemical Engineering Research
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• v.46 no.5
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• pp.868-874
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• 2008

The Ni based adsorbent was prepared by co-precipitation method and its performance for removing carbon monoxide was investigated. Here, silica, aluminium silicate and ${\gamma}$-alumina were used for carriers of catalyst. $Ni(NO_3)_2{\cdot}6H_2O$ and $Ni(CH_3COO)_2{\cdot}4H_2O$ were utilized for Ni precursors. Precipitants were urea and citric acid. After precipitation of Ni salt on the carrier and following reduction using $H_2$ gas, adsorbent was prepared and its performance was analyzed based on EDS, TPR and XRD experiments. In accordance with change of precipitation agents, Ni salts on carrier, carriers and reduction condition. Adsorbent performance for removing carbon monoxide was investigated. The adsorbent with 54.8 wt% Ni prepared using urea precipitant under reduction condition at $500^{\circ}C$ for 3 h exhibited the best CO removal performance.

• Journal of the Korean Geotechnical Society
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• v.33 no.9
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• pp.61-69
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• 2017

This study presents the experimental results of $CaCO_3$ formation in sand by the Enzyme Induced Carbonate Precipitation (EICP) method. Concentration of $CaCO_3$ with elapsed reaction time is calibrated by standardized procedure by measuring $CO_2$ pressure, and it increases with time towards asymptotic value. Jumunjin sand saturated with EICP solution shows that both shear wave velocity and electrical conductivity sharply increase as the reaction starts to approach to the constant values after 50 hours of reaction time. Urease concentration of 0.5 g/L exhibits 224% higher final shear wave velocity than that of 0.1 g/L. The nucleation models hint that carbonate tends to precipitate not only at grain contacts but also at grain surfaces. Regardless of urease concentration, electrical conductivity and shear wave velocity follow the unique path. The scanning electron microscopic images and X-ray computed tomographic images validate the spatial configuration of produced $CaCO_3$ in soils.