• Journal of the Korean Ceramic Society
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• v.35 no.6
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• pp.559-568
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• 1998

Studies of preparation condition and characteristics of AUC(ammonium uranyl carbonate) were carried out to optimize AUC process with different reactor sizes and precipitation methos. As results four types of precipitates with different chemical compositions and morphologies were obtained from the reaction of {{{{ {(NH }_{4 }) { }_{2 } {CO }_{3 } }} with {{{{ {UO }_{2 }( {NO }_{3 }) { }_{2 } }} solution. A phase diagram has been made and crystal structure and chemical composition of each phase have been characterized by using SEM X-ray IR and thermal analysis. It was found that ammonium uranyl carbonate {{{{ {(NH }_{4 }) { }_{4 } {UO }_{2 } {(CO }_{3 }) { }_{3 } }} with monoclinic crystal morphology could be syn-thesized when the mole ratio of in {{{{ {(NH }_{4 }) { }_{2 } {CO }_{3 }/ {UO }_{2 } {(NO }_{3 }) { }_{2 } }} in the solution was higher than 5 Also a mechanism and a precipitating condition on rounding of the AUC particle were examined in the course of the AUC pre-cipitation. The rounding of the AUC particle was possible only by external circulation using pump not by internal circulation using agitator.

• Korean Journal of Materials Research
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• v.12 no.12
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• pp.947-954
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• 2002

HCl concentration and reaction time are the decisive factors in determining the structure of precipitates in the process of synthesis of $TiO_2$ particles from aqueous $TiOCl_2$ solution by precipitation and the volumetric proportion of brookite phase in $TiO_2$ particles can be controlled by these two factors. As reaction rate increases with increase of reaction temperature, the reaction time, at which maximum volumetric proportion of brookite phase in $TiO_2$ particles was obtained, was reduced. The brookite was transformed directly to rutile phase with only increase of reaction time. And precipitation was delayed with increase of HCl concentration because the amount of $H_2$O, which is necessary source of oxygen for conversion of $Ti^{+4}$ to $TiO_2$, was relatively reduced with increase of that. Brookite in the mixture phase powder was finally transformed to rutile phase via anatase through heat-treatment.

• Microbiology and Biotechnology Letters
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• v.42 no.1
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• pp.25-31
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• 2014

Fractional precipitation is a simple method for purifying (+)-dihydromyricetin extracted from biomass. However, the fractional precipitation process has been inherently problematic due to the lengthy precipitation time that is required. The fractional precipitation time was shortened and (+)-dihydromyricetin yield was improved by increasing the surface area per working volume (S/V) of the reacting solution through the addition of a cation exchange resin (Amberlite 200, Amberlite IR 120Na, Amberlite IR 120H, or Amberlite IRC 50). Most of the (+)-dihydromyricetin (>90%) could be obtained after about 16 h of fractional precipitation using Amberlite 200. Since high-purity (+)-dihydromyricetin can be obtained at a high yield and the precipitation time can be reduced by increasing the surface area available for precipitation, this improved method is expected to minimize solvent usage and the size and complexity of the high performance liquid chromatography operation required for (+)-dihydromyricetin purification.

• Journal of the Korean Ceramic Society
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• v.48 no.4
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• pp.263-268
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• 2011

ZnO hexagonal rods grown in aqueous solution can be changed into a tubular shape by two-step aging in the course of the growing process. In the first step, hexagonal ZnO rods is grown by aging at $90^{\circ}C$ under a highly supersaturated aqueous solution giving rise to a fast precipitation rate. Meanwhile, during the second step aging at $60^{\circ}C$ in the same aqueous solution, the hexagonal polar face (001) having higher surface energy than (010) side planes dissolves to minimize surface energy. Hence the flat (001) face changes to a craterlike face and the hexagonal rod length of ZnO decreases at an initial-stage of this step aging. The formation of the (101) wedge-type faces is ascribed to the resultant of competitive reactions between the dissolution of polar face minimizing the surface energy which is a dominant reaction at the initial stage and the precipitation reaction dissipating supersaturation. At a later stage of the second-step the reaction rates of these two processes in the aqueous solution become similar and the overall reaction is terminated.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.2
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• pp.99-104
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• 2012

The co-precipitation technique has been applied to synthesize biphasic calcium phosphate (BCP). $Ca(NO_3)_2{\cdot}4H_2O$ and $(NH_4)_2HPO_4$ as the starting materials was used. X-ray diffraction (XRD) and Fourier transformed infrared (FT-IR) spectroscopy were used to characterize the structure of as-synthesized and calcined BCP powders. After immersion in Hanks' Balanced Salt Solution (HBSS), for 1 week a precipitation started to be formed with individual small granules on the specimen surface. An MTT assay indicated that BCP powders have no cytotoxic effects on MG-63 cells, and that they have good biocompatibility.

• International Journal of Industrial Entomology and Biomaterials
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• v.27 no.1
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• pp.203-208
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• 2013

Sericin is usually abandoned after the degumming process. However, it could be a valuable bioresource if an economically efficient recovery process could be set up. In this study, sericin was recovered directly from the degummed waste solution by adding calcium chloride, which induced the precipitation of the surfactant, sodium oleate, by charge interaction. The recovery yield was maximum when 10% of calcium chloride was added. Further increase in the calcium chloride concentration induced the precipitation of sericin. The recovered sericin had a molecular weight distribution similar to that of the hot-water-extracted sericin; but some highmolecular- weight sericin could not be recovered. The secondary structure and amino acid composition of the recovered sericin were similar to those of conventional hot-water-extracted sericin. We expect that sericin recovered from the degummed waste solution could be an alternative to the hot-water-extracted sericin, which is widely used in various applications.

• Journal of Powder Materials
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• v.10 no.5
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• pp.310-317
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• 2003

Two-component ceramic (alumina-zirconia) composites were fabricated by a soft-solution process in which polyethylene glycol (PEG) was used as a polymeric carrier. Metal salts and PEG were dissolved in ethyl alcohol without any precipitation in 1:1 volume ratio of alumina and zirconia. In the non-aqueous system, the flammable solvent made explosive, exothermic reaction during drying process. The reaction resulted in formation of volume expanded, porous precursor powders by a vigorous decomposition of organic components in the precursor sol. The PEG content affected the grain size of sintered composites as well as the morphology of precursor powders. The difference of microstructure in sintered composite was attribute to the solubility and homogeneity of metal cations in precursor sol. At the optimum amount of the PEG polymer, the metal ions were dispersed effectively in solution and a homogeneous polymeric network was formed. It made less agglomerated particles in the precursor sol and affected on uniform grain size in sintered composite.

• Nuclear Engineering and Technology
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• v.32 no.6
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• pp.595-604
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• 2000

Flow-Accelerated Corrosion Behavior of SA106 Gr.C steel in room temperature alkaline solution simulating the CANDU primary water condition was studied using Rotating Cylinder Electrode. Systems of RCE were set up and electrochemical parameters were applied at various rotating speeds. Corrosion current density decreased up to pH 10.4 then it increased rapidly at higher pH. This is due to the increasing tendency of cathodic and anodic exchange half-cell current. Corrosion potential shifted slightly upward with rotating velocity. Passive film was formed from pH 9.8 by the mechanism of step oxidation and the subsequent precipitation of ferrous species into hydroxyl compound. Above pH 10.4, the film formation process was active and the film became stable. Corrosion current density showed increment in pH 6.98 with the rotating velocity, while it soon saturated from 1000 rpm above pH 9.8. This seems that activation process which represents formation of passive film on the bare metal surface controls the entire corrosion process

• Applied Chemistry for Engineering
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• v.19 no.1
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• pp.66-72
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• 2008

Manganese hydrogen phosphate hydrate, $MnHPO_4{\cdot}2.25H_2O$, is a major constituent of the pre-conditioning compositions for the manganese phosphate coating treatment over carbon steel substrate. This compound is conventionally produced by the synthesis in the aqueous solution process followed by the filtration and drying processes and a series of size reduction and classification processes in dry state. However, it is evident that the conventional process is neither environment-friendly nor cost-effective. In this work, a new process principle was examined based on the controlled double-jet precipitation technology to produce the manganese chemical product of fairly uniform particle size distribution in an aqueous solution media. The effects of stabilizing agents were comparatively studied by the scanning electron microscope analysis in a uniformity point of view of the resulting particle size. Polyvinylpyrrolidone and Gum Arabic were excellent in controlling the crystal growth step, resulting in fairly uniform size distributions of the particles from the controlled double-jet process.

• Korean Journal of Materials Research
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• v.19 no.11
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• pp.588-595
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• 2009

The knowledge of grain growth of carbide particles is very important for manufacturing micrograined cemented carbides. In the present study, continuous and discontinuous grain growth in WC-Co and WC-VC-Co cemented carbides is investigated using the Monte Carlo computer simulation technique. The Ostwald ripening process (solution/re-precipitation) and the grain boundary migration process are assumed in the simulation as the grain growth mechanism. The effects of liquid phase fraction, grain boundary energy and implanted coarse grain are examined. At higher liquid phase content, mass transfer via solid/liquid interfaces plays a major role in grain growth. Growth rate of the implanted grain was higher than that of the matrix grains through solution/re-precipitation and coalescence with neighboring grains. The results of these simulations qualitatively agree with experimental ones and suggest that distribution of liquid phase and carbide particle/carbide grain boundary energy as well as contamination by coarse grain are important factors controlling discontinuous grain growth in WC-Co and WC-VC-Co cemented carbides. The contamination by coarse grains must by avoided in the manufacturing process of fine grain cemented carbides, especially with low Co.