• YAKHAK HOEJI
• /
• v.36 no.4
• /
• pp.315-320
• /
• 1992

The amino acid threonine was produced from glycine and ethanol in a reaction mixture using resting cells of a newly isolated gram-negative methylotrophic bacterium, capable of growth on methanol. The isolate could utilize $C_1$ compounds and a variety of multicarbon substrates as sole carbon and energy source. To obtain cells of isolate with high threonine producing activity, we investigated optimum cultural conditions. Optimal growth was at the initial concentration of 0.5%(v/v) methanol, at $30^{\circ}C$ and pH 7.0. The growth was not affected by antibiotics inhibiting cell wall synthesis, but was completely suppressed by those inhibiting protein synthesis. The optimum reaction conditions from threonine production by resting cells of this strain were found.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1997.10a
• /
• pp.13-19
• /
• 1997

From the formation of the monodispersed silica particle which is a valuable for the industry by Sol-Gel process, the effects of the parameters participated in the process, the growth mechanism and the characteristics of silica particles for each rection conditions are investigated. To investigate about the formation of final silica particles, the suspension which performs the polymerization is reacted with molybdic acid, and the evolutions of TEOS and silica particle size are investigated in the reaction time ？ 새 the characteristics of molybdic acid with the suspension. From the results, a constant number of silica particle is formed at early reaction stage. Silica particles grow through the aggregation of smaller particles and nucleation is rate-limiting step for the growth of particles. In the conditions of this study, spherical silica particles are formed, [NH$_3$] and [$H_2O$] concentration increase the particle size but particle size decrease with [$H_2O$] concentration which is a certain above region. Average particle sizes are 187.4~483.3 nm and standard deviations in the average particle size are 1.7~2.9% with each experimental condition. From the BET results, specific surface area is 5.5~23.4 $m^2$/g and these values decrease with increase size. The average pore size is 50~70$\AA$.

• Applied Microscopy
• /
• v.24 no.3
• /
• pp.78-86
• /
• 1994

A TEM study on proeutectoid ${\alpha}$ reaction at sub-eutectoid temperatures has been made in hypoeutectoid Ti-3.gw/o Co and Ti-5.2w/o Fe alloys. Widmanstatten ${\alpha}$ plates were formed in both alloys within the ${\beta}$ matrix with some modification of degenerate forms. These degenerate plates were formed by the sympathetic nucleation of ${\alpha}$ plates at ${\alpha}:{\beta}$ interphase boundaries. Three types of sympathetic nucleation, i.e., edge-to-edge, face-to-edge, face-to-face, were found in both alloys. The edge-to-edge sympathetically nucleated crystals formed a low-angle boundary between two crystals. The ${\alpha}:{\beta}$ interphase boundaries were found to be partially coherent interfaces which consist of regularly spaced misfit dislocations. The growth of these interphase boundaries were accomplished by the lateral movement of growth ledges. The intersection points of two ${\alpha}$ plates or the low angle boundaries which had formed by edge-to-edge sympathetic nucleation played a role as the potential sources of growth ledges during the growth of plate. The interfacial structures and the spatial morphologies of the degenerate proeutectoid ${\alpha}$ plates would be expected to influence the nucleation and growth of the succeeding eutectoid decomposition process.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.2 no.1
• /
• pp.51-59
• /
• 1992

Effect of agglomeration of $Nb_20_5$ of the same primary particle size on formation reaction and sintering of $Pb(Mg_{1/3}\;Nb_{2/3})O_3$ was examined. Both solid state reaction and molten salt synthesis were adopted. With decreasing agglomeration of $Nb_20_5$ increased the rate of formation reaction of perovskite PMN in solid state reaction, but had little influence in molten salt synthesis. It was concluded that the increase in the inhomogeneity of the dispersion state of intermediate pyrochlore with increasing agglomeration of $Nb_20_5$ retarded the formation reaction of perovskite PMN in solid state reaction, while had little influnce in molten salt synthesis due to its solution - precipitation mechanism -mainly depends on powder surface area.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.6 no.2
• /
• pp.129-140
• /
• 1996

In this study, we have prepared corundum ($\alpha$-Al_{2}O_{3}$) single crystals from aluminum hydroxides by hydrothermal growing process and have investigated the reaction conditions. The hydrothermal conditions were mainly affected by reaction temperature, seed crystal and reaction time. Especially, seed crystal has strong effects on the particle size and crystallity of products. By adding seed crystal in Japanese gibbsite solution as the nutrient, hydrothermal reaction was performed for 2 hours at the reaction temperature of $460^{\circ}C$, to produce corundum powders which had weight mean particle diameter of $11\;\mu\textrm{m}$ with hexagonal crystal, Without adding seed crystal in Russian gibbstite solution, corundum powders that have weight mean particle diameter of $6\;\mu\textrm{m}$ with hexagonal crystals were also formed after 2 hours operation at the reaction temperature of $420^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.22 no.7
• /
• pp.549-554
• /
• 2009

Al thin films were synthesized on TiN/Si substrate by MOCVD using N-methylpyrrolidine alane (MPA) precursor. Effects of substrate temperature, reaction pressure on the deposition rate, surface roughness and electrical resistivity were investigated. The early stage of Al thin film formation was analyzed by in-situ surface reflectivity measurement with a laser and photometer apparatus. From the Arrhenius plot of deposition rate vs. substrate temperature, it was found that the activation energy of surface reaction was 91.1kJ/mole, and the transition temperature from surface-reaction-limited region to mass-transfer-limited region was about $150^{\circ}C$. The growth rate increased with the reaction pressure, and average growth rates of $200{\sim}1,200nm/min$ were observed at various experimental conditions. Surface roughness of the film increased with the film thickness. The electrical resistivity of Al film was about $4{\mu}{\Omega}{\cdot}cm$ in the case of optimum condition, and it was close to the value of the bulk Al, $2.7{\mu}{\Omega}{\cdot}cm$.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.26 no.6
• /
• pp.258-262
• /
• 2016

Foam reaction injection molding (FRIM) is a widely used process for manufacturing polyurethane foam with complex shapes. The modified theoretical model for polyurethane foam forming reaction during FRIM process was established in our previous work. In this study, using the modified model, parametric study for FRIM process was performed in order to optimize experimental conditions of FRIM process such as initial temperature of mold, thickness of mold, and injection amount of polymerizing mixture. In addition, we applied the modified model to real application of refrigerator cabinet to determine optimal manufacturing conditions for polyurethane FRIM process.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.10 no.1
• /
• pp.73-79
• /
• 2000

Highly porous amorphous silica obtained from a serpentine mineral by hydrochloric acid treatment was used to produce a zeolite A through the hydrothermal reaction under atmospheric pressure. An optimum synthesis condition of the zeolite A was achieved at $80^{\circ}C$ for two hours with a mole ratio of $Na_2O/SiO_2$1.5. Additionally, it was found that a hydroxysodalite zeolite was formed under the experimental conditions over the reaction temperature of $80^{\circ}C$ and the reaction time of 120 minutes even though the crystallization of zeolite proceeds rapidly as the reaction temperature and the alkalinity becomes higher.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.6 no.4
• /
• pp.501-508
• /
• 1996

Strontium barium niobate powders were prepared by NaCl-KCl molten salt, and reaction process and morphology change of strontium barium niobate were investigated as a function of reaction temperature, time, and amount of molten salt. With increasing the reaction temperature and time, the reacted fraction was increased and the morphology of powder was changed from lumpy shape into meedle-like shape. With increasing the amount of molten salt, reacted fraction was increased rapidly, but the morphology of powder was changed from needle-like shape into spherical shape. Strontium barium niobate powder, over 90 % in fraction reacted, was obtained from the reaction conditions at $1000^{\circ}C$ for small flux ratio (=1) and at $650^{\circ}C$ for large flux ratio (=4).

• Korean Journal of Microbiology
• /
• v.23 no.4
• /
• pp.297-301
• /
• 1985

The dependence of activities of Aspergillus phoenicis on the culture conditions in the progesterone transformation reaction was investigated. In the beginning of the reaction, $6{\beta},\;11{\alpha}-dihydroxyprogesterone$ was not produced even at high concentration of $11{\alpha}-hydroxyprogesterone$. However, large amount of the product was obtained after the complete exhaustion of progesterone. When spores of A.phoenicis replaced mycelia as enzyme source, $11{\alpha}-hydroxyprogesterone$ was produced after a considerably long indyction period, and its maximum production rate followed the exponential growth phase. The $6{\beta}-hydroxylation\;of\;11{\alpha}-hydroxyprogesterone$ continued, even after the stationary growth phase. A. phoenicis showed high enzyme activity for these reactions when the phosphate buffer solutions were used in place of the ordinary culture medium. The buffer solutions of low pH gave more yield of $11{\alpha}-hydroxyprogesterone$ than those of high pH. However, the addition of flucose to the buffer solutions did not activate the transformation reaction. The presence of progesterone seems to be necessary for the induction of enzymes for the $6{\beta}-hydroxylation\;of\;11{\alpha}-hydroxyprogesterone\;since\;6{\beta},\;11{\alpha}-dihydroxyprogesterone$ is not produced in the reaction medium containing only $11{\alpha}-hydroxyprogesterone$ as a substrate.