• Journal of the Korean institute of surface engineering
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• v.28 no.4
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• pp.207-218
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• 1995

Tungsten(W) metal has excellent properties in heat-resistance, corrison-resistance and impact-resistance but W-Metal is hard to sinter because higher than $2,000^{\circ}C$ is required to sinter W-powder. Con-sequently, a deposit technique of Nikel Phosphorus(NiP) on W-powber by the liquid reduction precipitation method was performed. Sintering temperature of the resulting W-NiP composite was lowered around to $1,000^{\circ}C$, and the mechanical properties of the sintered body was studied. The most suitable conditions for NiP thin film deposit on W-Powder by the liquid reduction precipitation method, which are composition, concentration, pH and temperature of the liquid reduction solution, were considered. The activated sintering was carried out in a reducing condition furnace. Components and properties of the sintered body were investigated by the density and the hardness measurements, X- ray diffraction analysis, and microscopic photographs of the surface. Quantity of NiP thin film on W-powder could be varied by the change of the liquid reduction solution composition. The sintering temperature of W-NiP composite powder is lowered to $950^{\circ}C$ from $2,000^{\circ}C$ and the hardness is increased (ca. 720 Hv). Large shrinkage could be observed since density was increased from 5.5 to 11.0 g/$cm^2$ which 86.2% of theoretical density. W metal and $Ni_3P$ crystal were detected through X-ray diffraction on the sintered body. Perfectly activated sintering was observed by microscopic photographs.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.3
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• pp.95-100
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• 2016

In this work, tin oxides were obtained by the liquid reduction precipitation method and hydrothermal process using $SnCl_2{\cdot}2H_2O$, $N_2H_4$, and NaOH. Tin oxide crystals having different sizes and morphologies could be achieved. The powders were characterized by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FE-SEM). Depending on the molar ratio of the raw materials, tin oxide crystalline with the spherical and rectangular plate-like shape could be obtained, the crystal phase was SnO and $Sn_6O_4(OH)_4$. And the obtained SnO crystals by a hydrothermal reaction showed various shapes, such as, spherical, plate-like and flower-like architectures depending on the temperature conditions.

• Nuclear Engineering and Technology
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• v.50 no.6
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• pp.886-889
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• 2018

This article presented two-staged chemical precipitation for radioactive wastewater decontamination by using chemical agents. The total amount of radioactive wastewater was $35m^3$, and main radionuclides were Cs-137, Cs-134, and Co-60. Initial radioactivity concentration of the liquid waste was 2264, 17, and 9 Bq/L for Cs-137, Cs-134 and Co-60, respectively. Potassium ferrocyanide, nickel nitrate, and ferrum nitrate were selected as chemical agents at high pH levels 8-10 according to the laboratory jar tests. After the process, radioactivity was precipitated as sludge at the bottom of the tank and decontaminated clean liquid was evaluated depending on discharge limits. By this precipitation method decontamination factors were determined as 66.5, 8.6, and 9 for Cs-137, Cs-134, and Co-60, respectively. By using the potassium ferrocyanide, about 98% of the Cs-137 was removed at pH 9. At the bottom of the tank, radioactive sludge amount from both stages was totally $0.98m^3$. It was transferred by sludge pumps to cementation unit for solidification. By chemical processing, 97.2% of volume reduction was achieved. The potassium ferrocyanide in two-staged precipitation method could be used successfully in large-scale applications for removal of Cs-137, Cs-134, and Co-60.

• Journal of the Korean institute of surface engineering
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• v.57 no.2
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• pp.92-97
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• 2024

The LiBr aqueous solution, which is the absorption liquid of absorption refrigerator, must be replaced periodically because the concentration of impurities such as Cu²⁺, Fe²⁺, Ca²⁺, etc., increases due to corrosion of the tubes as the period of use increases, and the refrigeration efficiency decreases significantly. In order to reuse the waste absorption liquid, flocculation-precipitation method is mainly applied to precipitate the impurities, which requires hundreds of times the concentration of impurities and generates additional waste. In this study, a process for removing Cu ion impurities from cyclone electrolyzer by electrolytic reduction is presented in a small-scale facility without additional waste. It was confirmed that Cu ion impurities can be removed down to 1 ppm by electrolytic reduction process, and to further improve the removal rate, the mass transfer rate was increased by using a cyclone electrolyzer. The removal rate of Cu ions increased with the increase of flow rate and current density, and it was confirmed that Cu was removed at a rate of 1.48 ppm/h under the condition of 330 mL/sec and 2.5 mA/cm².

• Bulletin of the Korean Chemical Society
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• v.26 no.4
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• pp.563-568
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• 2005

The Pt/C and Pd/C catalysts were prepared from conventional chloride precursors by adsorption or precipitation-deposition methods. Their activities for hydrogenation reactions of cyclohexene and acetophenone were compared with those of commercial catalysts. The Pt/C and Pd/C catalysts obtained from the adsorption procedure reveal higher hydrogenation activity than commercial catalysts and the catalysts prepared by the precipitation-deposition method. Their improved performances are attributed to the decreased metal crystallite sizes of Pt or Pd formed on the active carbon support upon the adsorption of the precursors probably due to the same negative charges of the chloride precursor and the carbon support. Under the preparation conditions studied, the reduction of the supported catalysts using borohydrides in liquid phase is superior to a gas phase reduction by using hydrogen in the viewpoint of particle size, hydrogenation activity and convenience.

• 한국생물공학회:학술대회논문집
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• 2005.04a
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• pp.355-359
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• 2005

Fractional precipitation is a simple, efficient method for pre-purifying paclitaxel from plant cell cultures. The storage temperature of factional precipitation was optimized in terms of the yield and purity of paclitaxel with a fixed methanol concentration in water (61.5%, v/v), paclitaxel content in the crude extract (0.5%, w/v), and storage time (3 days). The greatest yield $({\sim}84%)$ was obtained with storage at a constant temperature $(0^{\circ}C)$ for 3 days. Conversely, the highest purity $({\sim}79%)$ was obtained with stepwise reduction in temperature over 3 days. For a constant storage temperature, the maximum purity $({\sim}67%)$ was obtained at $0^{\circ}C$. There was little difference in the yield of paclitaxel between -20 and $12^{\circ}C$. This pre-purification process serves to minimize solvent usage, and the size and complexity of the high-performance liquid chromatography (HPLC) operation required for paclitaxel purification.