• Korean Journal of Crystallography
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• v.6 no.1
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• pp.14-26
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• 1995

The growth mechanism of diamond thin films, deposited by Hot Filament CVD, was investigated through observation of changes in their surface morphology as a function of the substance temperature and deposition time. Amorphous carbon or DLC thin films were deposited at low substrate temperature. Diamond films consisting of square-shaped particles, whose surfaces are (100) planes, were deposited at an intermedate temperature. At high substrate temperatures, diamond films consisting of the particles showing both (100) and (111) plane were deposited. The (100) proferred orientation of the diamond films are believed to be due to a relatively high supersaturation during deposition, and the growth condition for the diamond films having (100) preferred orientation can be applied to the single crystal growth since no twins are generated on the (100) plane. The grain size of the diamond films did not change with increasing temperature and its increasing rate with increasing deposition time was the same irrespective of the substrate temperature. However, the nucleation density increased with substrate temperature and its increasing rate with deposition time was much higher for the films deposited at higher substrate temperature.

• The Korean Journal of Mycology
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• v.13 no.2
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• pp.105-109
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• 1985

Isolates of the different species groups of Trichoderma from the mushroom culture beds were identified according to Rifai's classification and influence of antibiotics produced by them against the oyster mushroom was examined. Trichoderma islolates were identified as Trichoderma hamatum, Trichoderma viride and Trichoderma koningii. Among the Trichoderma isolates, fungistatic action of Trichoderma viride was found to be most remarkable. Pleurotus ostreatus and Pleurotus sajor-caju were the most susceptable of the edible mushrooms tested, followed by Lentinus edodes, Flammulina velutipes and Auricularia auricula. A needle-shaped crystal gained from the chloroform extract of the culture filtrate of Trichoderma viride repressed distinctively the mycelial growth of the oyster mushroom. The grade of repression of the crystal at 500ppm and 1/10 aequ­ous solution of the chloroform extract against the oyster mushroom, seemed equal to that of cycloheximide at $100{\sim}200ppm$.

• Journal of the Korean Ceramic Society
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• v.53 no.6
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• pp.670-675
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• 2016

Calcium phosphate crystallites were prepared by wet chemical method for use in artificial bone. In order to obtain ${\beta}$-tricalcium phosphate (TCP), nano-crystalline calcium phosphate (CaP) was precipitated at $37^{\circ}C$ and at $pH5.0{\pm}0.1$ under stirring using highly active $Ca(OH)_2$ in DI water and an aqueous solution of $H_3PO_4$. The precipitated nano-crystalline CaP solution was kept at $90^{\circ}C$ for the growth of CaP crystallites. Through the growing process of CaP crystallites, we were able to obtain various sizes of rectangular CaP crystallites according to the crystal growing times. Dry nano-crystalline CaP powders at $37^{\circ}C$ were mixed with dry macro-crystalline CaP crystallites and the shaped mixture sample was fired at $1150^{\circ}C$ to make a ${\beta}-TCP$ block. Several tens of nm powders were uniformly coated on the surface, which was comprised of powders of several tens of ${\mu}m$, using a vibrator. The mixing ratio between the nanometer powders and the micrometer powders greatly affected the mechanical strength of the mixture block; the most appropriate ratio of these two materials was 50 wt% to 50 wt%. The sintered block showed improved mechanical strength, which was caused by the solid state interaction between the nano-crystalline ${\beta}-TCP$ and the macro-crystalline ${\beta}-TCP$.

• The Korean Journal of Ceramics
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• v.5 no.2
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• pp.131-136
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• 1999

Yttria stabilized zirconia(YSZ) films were deposited on porous NiO substrates and quartz plates by the thermal CVD using $ZrCl_4, YCl_3$ as precursors, and $O_2$ as a reactive gas at atmospheric pressure. The evaporation temperature of $ZrCl_4$ was varied from $250^{\circ}C$ to $550^{\circ}C$ while the temperatures of $YCl_3$ and the substrate were varied from $1000^{\circ}C$ to $1030^{\circ}C$. As the evaporation temperature of $ZrCl_4$ increased, the deposition rate of $ZrO_2$ decreased, contrary to our expectation. As a result of the decreased deposition rate of $ZrO_2$, the yttria content increase. The high evaporation temperature of $ZrCl_4$ makes the well-faceted crystal while the low evaporation temperature leads to the cauliflower-shaped structure. The dependence of the evaporation temperature on the growth rate and the morphological evolution was interpreted by the charged cluster model.

• Journal of the Korean Ceramic Society
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• v.17 no.1
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• pp.20-26
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• 1980

The crystallization behaviors of slag-based glass in $CaO-MgO-Al_2O_3-SiO_2(-Na_2O)$ system have been studied. The mother glass containing 16.50 CaO, 7.50MgO, 19.70Al2O3, 50.80SiO3 and 2.09wt% $Na_2O$ was prepared by using Korean domestic raw materials such as granulated slag, serpentine, sea sand and etc. The glass-ceramics composed of major crystalline phase diopside was produced by the heat treatment in a temperature range from 850$^{\circ}$ to 9$25^{\circ}C$ for 0-6hr. The composition and morphology of diopside phase formed in the system were examined by X-ray diffraction analysis and electron microscopy. The kinetic measurements such as J.M. A plot and Arrhenius plot indicated that the process of nucleation of the initially formed diopside phase could be described from the view point of instantaneous nucleation. It was also demonstrated that the linear crystal growth of diopside phase was proceeded by short range diffusion of $Mg^{2+}$ and $Ca^{2+}$ ion. The microstructures of the resulting glass-ceramics were consisted of leafroidal shaped crystalline aggregations.

• Journal of Microbiology
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• v.37 no.4
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• pp.206-212
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• 1999

In order to isolate a Fe(III)-reducer from the natural environment, soil samples were collected from various patty fields and enriched with ferric citrate as a source of Fe(III) under anaerobic condition. Since the enrichment culture was serially performed, the Fe(III)-reduction activity was serially diluted and cultivated on an agar plate containing lactate and ferric citrate in an anaerobic glove box. A Gram negative, motile, rod-shaped and facultative anaerobic Fe(III)-reducer was isolated based on its highest Fe(III)-reduction activity, Bacterial growth was coupled with oxidation of lactate to Fe(III)-reduction, but the isolate fermented pyruvate without Fe(III), The isolate reduced an insoluble ferric iron (FeOOH) as well as a soluble ferric iron (ferric citrate). Using the BBL crystal enteric/non-fermentor identification kit and 16S rDNA sequence analysis, the isolate was identified as Shewanella putrefaciens IR-1.

• Korean Journal of Materials Research
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• v.10 no.9
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• pp.648-655
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• 2000

Synthesis of the crystalline film was investigated under the diamond growth condition with altering the addition of the nitrogen from 0% to 95%. With increasing the nitrogen concentration, surface morphology of the film was changed from the diamond film with {100} growth plane to the non-faceted diamond film with nano-scale grains. It also showed that the deposition of the diamond film could be synthesized using only methane and nitrogen gases without hydrogen gas. Separated particles with diamond structure showed an octahedral shaped I the nitrogen ranges between 30% and 80%, and newly formed hexagonal crystals are observed when substrate temperature with diamond structure, however, also identify that the hexagonal crystal was SiCN composite composed of Si, C and N atoms.

• Korean Journal of Materials Research
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• v.29 no.10
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• pp.609-616
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• 2019

Oxide coatings are formed on die-cast AZ91D Mg alloy through an environmentally friendly plasma electrolytic oxidation(PEO) process using an electrolytic solution of $NaAlO_2$, KOH, and KF. The effects of PEO condition with different duty cycles (10 %, 20 %, and 40 %) and frequencies(500 Hz, 1,000 Hz, and 2,000 Hz) on the crystal phase, composition, microstructure, and micro-hardness properties of the oxide coatings are investigated. The oxide coatings on die-cast AZ91D Mg alloy mainly consist of MgO and $MgAl_2O_4$ phases. The proportion of each crystalline phase depends on various electrical parameters, such as duty cycle and frequency. The surfaces of oxide coatings exhibit as craters of pancake-shaped oxide melting and solidification particles. The pore size and surface roughness of the oxide coating increase considerably with increase in the number of duty cycles, while the densification and thickness of oxide coatings increase progressively. Differences in the growth mechanism may be attributed to differences in oxide growth during PEO treatment that occur because the applied operating voltage is insufficient to reach breakdown voltage at higher frequencies. PEO treatment also results in the oxide coating having strong adhesion properties on the Mg alloy. The micro-hardness at the cross-section of oxide coatings is much higher not only compared to that on the surface but also compared to that of the conventional anodizing oxide coatings. The oxide coatings are found to improve the micro-hardness with the increase in the number of duty cycles, which suggests that various electrical parameters, such as duty cycle and frequency, are among the key factors controlling the structural and physical properties of the oxide coating.

• Korean Journal of Crystallography
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• v.3 no.2
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• pp.120-128
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• 1992

Single crysals of BaTiO3 were grown by TSSG technique at various cooling rates. Morpolo girts, defects and domain structures of the grown crystals were investigated. At the cooling rates below 0.5℃/hr, equant single crystals were obtained and the 11111 faces were dominantly developed. If the cooling rate was much faster or if the vortical temperature gradient in the so lotion was very large, the solution became unstable and the needle formed BasTil04 o crystals were precipitated. Two sets of parallel lamella domains are arranged perpendicular to each other and the irregularly shaped boundaries are fixed between them. These sets of domains show remarkable orientation contrast in x-ray topography. Heating the crystal above 127℃, the phase transition from tetragonal to cubic occurs. The phase transition front (PTF) moves in the direction of temperature gradient. Domains in the tetragonal phase are successively rearranged and regular strain patterns appear in the cubic phase. The habit plane of PTF in BaTi03 is found to deviate from a l1101 lattice plane by app roximately 9°.

• Journal of the Korean Ceramic Society
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• v.52 no.4
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• pp.273-278
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• 2015

${\alpha}-Al_2O_3$ was synthesized by solvothermal synthesis using ${\alpha}-Al_2O_3$ seed, precursor of fine boehmite (Al(OOH)) or gibbsite ($Al(OH)_3$), and 1, 4-butanediol solvent. The seed content and precursor type were selected as variables in order to synthesize ${\alpha}-Al_2O_3$. The formation time of ${\alpha}-Al_2O_3$ was reduced and the size of the particles was decreased with addition of the seed. When the seed content was increased, the size of the synthesized ${\alpha}-Al_2O_3$ was reduced. Morphologies of the as-synthesized ${\alpha}-Al_2O_3$ with ${\alpha}-Al_2O_3$ seed were polyhedron-shaped, while the shape was plate-like or polyhedral without the seed, depending on the additives or the average particle size of the boehmite precursor. The aggregation of as-synthesized ${\alpha}-Al_2O_3$ from boehmite was smaller than that from gibbsite. As-synthesized ${\alpha}-Al_2O_3$, with 140 nm size, was obtained by using the seed and boehmite precursor.