• Nuclear Engineering and Technology
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• v.50 no.1
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• pp.43-53
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• 2018

It is important to clarify the characteristics of flow regimes underlying the debris bed formation behavior that might be encountered in core disruptive accidents of sodium-cooled fast reactors. Although in our previous publications, by applying dimensional analysis technique, an empirical model, with its reasonability confirmed over a variety of parametric conditions, has been successfully developed to predict the regime transition and final bed geometry formed, so far this model is restricted to predictions of debris mixtures composed of spherical particles. Focusing on this aspect, in this study a new series of experiments using nonspherical particles have been conducted. Based on the knowledge and data obtained, an extension scheme is suggested with the purpose of extending the base model to cover the particle-shape influence. Through detailed analyses and given our current range of experimental conditions, it is found that, by coupling the base model with this scheme, respectable agreement between experiments and model predictions for the regime transition can be achieved for both spherical and nonspherical particles. Knowledge and evidence from our work might be utilized for the future improvement of design of an in-vessel core catcher as well as the development and verification of sodium-cooled fast reactor severe accident analysis codes in China.

• Journal of the Korean Ceramic Society
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• v.31 no.9
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• pp.1076-1086
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• 1994

This study covers synthetic effect of the various hydrothermal treatments on formation of artificially made kaolinite mineral. The hydrothermal treatment includes the temperature treatment with time duration, addition of seeds, particle size of the starting material used, pH variation and the different types of organic acids. A colloidal silica and alumina sol which are commercially available are used for this study. A colloidal silica and alumina sol are mixed by the atomic ratio of Al/Si = 1, based on the theoretical kaolinite composition and calcined at $600^{\circ}C$ for 8 hours duration. It was found that the kaolinitic clay mineral was well developed; thereby, the different patterns of crystalline mineral are appeared. Spherical type as a crystal form was distinctively formed at the temperature of 20$0^{\circ}C$ to 25$0^{\circ}C$ with short duration time, while platy type as a crystal was highly yielded at 300~35$0^{\circ}C$. Moreover, by adding more than 20 wt% of seed as the natural kaolinitic clay to the starting material is widely distributed and developed when 2 ${\mu}{\textrm}{m}$ or less particle size of the starting material is used; also, when they are heat-treated at the temperature of 25$0^{\circ}C$ with 5 hours duration. With respect of the effect of pH variation on formation of the synthetic kaolinite minerals, the crystalline minerals are highly yielded at less than pH 2 and gradually diminished at more than pH9. Regarding to the effect of different acids on development of the kaolinite mineral, the organic acids with high chelating capacity produces good formation of crystalline minerals; whereas, amine radical-(NH2) is not an effective agent to generate the crystalline minerals.

• Journal of the Korean Ceramic Society
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• v.35 no.6
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• pp.543-550
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• 1998

A process for the preparation of spherical tungsten oxide powders by the emulsion evaporation method was developed. The characteristics of the powders thus prepared were examined by means of TGA X-ray diffraction SEM and image analysis. The emulsion was prepared by fast mixing of tungsten containing aque-ous phase and the organic phase which contained kerosene surfactant and paraffin oil. The precursor was made by evaporating the emulsion in the kerosene bath at $160^{\circ}C$ and then calcined at $650^{\circ}C$ in order to pro-duce tungsten oxide powders. The average particle size of the tungsten oxide powders was $0.5\;\mu\textrm{m}$ and their shapes were spherical. Water-in-oil type emulsion wasmore advantageous to make less agglmerated. $W_{3}$ powders than the oil-in-water type emulsion for the emulsion evaporation experiments. As the HLB value of the surfactant increased and the concentration of tungsten ions in the aqueous phase decreased the mean particle size of tungsten oxide powders decreased whereas agglomeration increased. The optimum con-centration of Span 80 was 8 percent by volume and the optimum stirring speed in the emulsion formation was 5000 rpm in order to obtain find less agglomerated $W_{3}$ powders.

• Journal of the Korean Ceramic Society
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• v.35 no.11
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• pp.1171-1181
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• 1998

$SrZr_{0.95}$$Y_{0.05}$$O_{2.975}$ powder was synthesized by ultrasonic spray pyrolysis using a solution that Sr carbonate and Zr and Y nitrates were dissolved in a citric acid solution. The processes of particle formation were in-vestigated with respect to solution properties and pyrolysis temperature. With changing the solution con-centration form 0.1M to 0.01M there was a tendency that average sizes of droplets and particles were de-creased and their size distributions were narrowed. Citrate functional groups converted the droplets into gel particles which prevented an inhomogeneous precipitation of the metal ions and facilitated the diffusion of gases during thermal decomposition. As a result the powder having spherical particles without hollow par-ticles could be prepared. Low pyrolysis temperature led to amorphous particles due to incomplete pyrolysis and made the particles difficult to maintain spherical shape due to retarded gelation of the droplets. Whereas higher pyrolysis temperature produced hollow and broken particles because the droplets un-derwent rapid gelationand decomposition. The particles obtained at two pyrolysis temperature $500^{\circ}$and $1000^{\circ}C$ consisted of a perovskite phase and a very small amount of $SrCO_3$ However after calcination at $1000^{\circ}C$ the particles contained a single perovskite phase having an average particle size of 0.63${\mu}{\textrm}{m}$ and an apparent density near to the theoretical density.

• Journal of the Korean Applied Science and Technology
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• v.18 no.4
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• pp.273-284
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• 2001

A series of microcapsule were synthesized by using several PCM(Phase Change Material) as a core material and gelatin/arabic gum, melamine/formaldehyde as a shell material. Coacervation technique and in situ polymerization were adopted in synthesizing microcapsules. In the microencapsulation by coacervation, tetradecane and octadecane were used as core materials. In the microencapsulation by situ polymerization tetradecane, pentadecane, hexadecane, heptadecane, octadecane, and nonadecane were used as core material. The synthesized microcapsule was examined to observe the shape of the microcapsule. The particle size analysis was performed by particle size analyzer. The thermal properties(e.g. melting point, heat of melting, crystallization temperature, heat of crystallization, differences between melting point and crystallization temperature) were obtained by DSC(Differential Scanning Calorimeter). The stirring rate effect was investigated during the microencapsulation. It was found that with increasing the stirring rate much smaller microcapule was produced. However, this did not necessarily lead to formation of spherical microcapsule.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.1 no.1
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• pp.107-116
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• 1991

Fine $PbTiO_3$ Particles were synthesized from the $Pb(NO_3)_2$and $TiO(NO_3)_2$ solution by the spray pyrolysis method using the ultrasonic vibrator as a mist generator. The obtained particles were characterized. The mechanisms of particle formation were discussed in comparison with those if other particles, such as $BaTiO_3$, $ZnO_2$, ZnO ....., in the same spray pyrolysis process.

• Korean Journal of Materials Research
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• v.28 no.3
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• pp.189-194
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• 2018

Porous graphites were synthesized by removing the template in HF after cabothermal conversion for 3 h at $900^{\circ}C$, accompanied by intercalations of pyrolyzed fuel oil (PFO) in the interlayer of Co or Ni loaded magadiite. The X-ray powder diffraction pattern of the porous graphites exhibited 00l reflections corresponding to a basal spacing of 0.7 nm. The particle morphology of the porous graphites was composed of carbon plates intergrown to form spherical nodules resembling rosettes like a magadiite template. TEM shows that the cross section of the porous graphites is composed of layers with very regular spaces. In particular, crystallization of the porous graphite was dependent on the content of Co or Ni loaded in the interlayer. The porous graphite had a surface area of $328-477m^2/g$. This indicates that metals such as Co and Ni act as catalysts that accelerate graphite formation.

• Journal of the Korean Ceramic Society
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• v.26 no.3
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• pp.445-451
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• 1989

Hydrolysis of aluminum isopropoxide with excess water in the presence of excess isopropyl alcohol resulted in the formation of boehmite in independence of temperature of hydrolysis and aging. Stoichiometric and substoichiometric amount of water hydrolyzed aluminum isopropoxide to pseudo-boehmite and amorphous one, respectively. $\alpha$-Al2O3 with 0.3${\mu}{\textrm}{m}$ in median size was produced by calcination of boehmite, bseudo-boehmite and amorphous boehmite at 125$0^{\circ}C$, 120$0^{\circ}C$, and 115$0^{\circ}C$ for one hour, respectively. Singnificant reduction in particle size was found during transition from $\theta$-Al2O3 to $\alpha$-Al2O3. $\alpha$-Al2O3 produced in this study was relatively uniform spherical and its purity was found to be over 99.9%.

• Journal of Powder Materials
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• v.20 no.5
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• pp.359-365
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• 2013

In this study, we fabricated $Nd_2Fe_{14}B$ hard magnetic powders with various sizes via spray drying combined with reduction-diffusion process. Spray drying is widely used to produce nearly spherical particles that are relatively homogeneous. Thus, the precursor particles were prepared by spray drying using the aqueous solution containing Nd salts, Fe salts and boric acid with the target stoichiometric composition of $Nd_2Fe_{14}B$. The mean particle sizes of the spray-dried powders are in the range from one to seven micrometer, which are adjusted by controlling the concentrations of precursor solutions. After debinding the as-prepared precursor particles, ball milling was also conducted to control the particle sizes of Nd-Fe-B oxide powders. The resulting particles with different sizes were subjected to subsequent treatments including hydrogen reduction, Ca reduction and washing for CaO removal. The size effect of Nd-Fe-B oxide particles on the formation of $Nd_2Fe_{14}B$ phase and magnetic properties was investigated.

• Journal of Microbiology and Biotechnology
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• v.24 no.10
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• pp.1354-1367
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• 2014

In the present work, we describe a simple, cheap, and unexplored method for "green" synthesis of silver nanoparticles using cell extracts of the cyanobacterium Anabaena doliolum. An attempt was also made to test the antimicrobial and antitumor activities of the synthesized nanoparticles. Analytical techniques, namely UV-vis spectroscopy, X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and TEM-selected area electron diffraction, were used to elucidate the formation and characterization of silver-cyanobacterial nanoparticles (Ag-CNPs). Results showed that the original color of the cell extract changed from reddish blue to dark brown after addition of silver nitrate solution (1 mM) within 1 h, suggesting the synthesis of Ag-CNPs. That the formation Ag-CNPs indeed occurred was also evident from the spectroscopic analysis of the reaction mixture, wherein a prominent peak at 420 nm was noted. TEM images revealed well-dispersed, spherical Ag-CNPs with a particle size in the range of 10-50 nm. The X-ray diffraction spectrum suggested a crystalline nature of the Ag-CNPs. FTIR analysis indicated the utilization of a hydroxyl (-OH) group in the formation of Ag-CNPs. Ag-CNPs exhibited strong antibacterial activity against three multidrug-resistant bacteria. Additionally, Ag-CNPs strongly affected the survival of Dalton's lymphoma and human carcinoma colo205 cells at a very low concentration. The Ag-CNPs-induced loss of survival of both cell types may be due to the induction of reactive oxygen species generation and DNA fragmentation, resulting in apoptosis. Properties exhibited by the Ag-CNP suggest that it may be used as a potential antibacterial and antitumor agent.