• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.17 no.2
• /
• pp.69-74
• /
• 2007

[ $0.6Pb(Sc_{1/2}Ta_{1/2})O_3-0.4PbTiO_3$ ] (hereafter PSTT) ceramics were prepared by the molten salt synthesis (MSS) method using KCI as a flux. Formation of perovskite phase was investigated by a differential thermal analysis (DTA) and X-ray diffraction (XRD) analysis in the temperature range from $600^{\circ}C$ to $850^{\circ}C$. A 92% perovskite phase was synthesized at $750^{\circ}C$ for 2 hrs using the MSS method, while 82% perovskite phase was synthesized at $850^{\circ}C$ for 4ks using the calcining of mixed oxide (CMO) method. This result could be due to the improvement in reactivity of $Sc_2O_3$ by melting of KCI. The MSS specimen sintered at $1,100^{\circ}C$ for 4hrs showed a dielectric constant of 11,200, a remnant polarization of $13.5{\mu}C/cm^2$ and a coercive field of 10.198 kV/cm, which was discussed in view of the microstructure.

• Economic and Environmental Geology
• /
• v.53 no.2
• /
• pp.159-166
• /
• 2020

In this research, we investigate the effect of microwave pretreatment on the recovery of gold from the gold concentrates by thiourea leaching. The changes in mineral phases by decomposition of pyrites in the gold concentrates using microwave were observed, and the result of microwave irradiation showed that the temperature of the irradiated sample increases with increasing irradiation time. With the reaction of temperature increases, Sulfur (S) in pyrites was converted to sulfur dioxide (SO₂), and then the content of S in the sample was reduced. The analytical results of XRD and SEM-EDS showed that pyrites are converted to magnetite and hematite, and its surfaces are changed to a porous shape where micro-cracks are developed. The Au leaching efficiency from the irradiated gold concentrates using thiourea-mixed solvent increased with the increases of irradiation time and solvent concentration. The experimental results considering leaching parameters indicate that the mechanism of microwave irradiation increases the maximum leaching efficiency and leaching rate of the gold concentrates, and the solvent does a role for the increasing of leaching rate constant.

• Journal of Korean Society of Environmental Engineers
• /
• v.33 no.8
• /
• pp.583-590
• /
• 2011

The effect of the physical parameters in the reactor (aeration depth, bubble size, and surface area) and the alkalinity of the solution on the ammonia stripping by bubbling were evaluated. When an airflow of 30 L/min was bubbled below the solution surface in the range 6-53 cm, the ammonia removal rate were observed to be the same regardless of the bubbling depths. At pH 10.0 and a temperature of $30^{\circ}C$, the average rate constant and the standard deviation were $0.178h^{-1}$ and 0.004. No appreciable changes in the ammonia removal rate were also observed with varying the bubble size and the air-contacting surface area. Alkalinity of the solution was found to affect the ammonia removal rate indirectly. This is expected because the pH of the solution would vary with dissolution of gaseous $CO_2$ by air bubbling. The real wastewaters from landfill site and domestic wastewater treatment plant were tested. In the case of domestic wastewater (pH = 7.1, alkalinity = 75 mg/L), the ammonia removal rate was poor even with the control of pH to 9.3. The raw landfill leachate (pH = 8.0, alkalinity = 6,525 mg/L), however, showed the appreciable removal rate with increasing pH during aeration. When the initial pH of the leachate was adjusted 9.4, the removal rate was significantly increased without changing the pH during aeration.

• Microbiology and Biotechnology Letters
• /
• v.9 no.4
• /
• pp.197-205
• /
• 1981

Penicillin amidase of Bacillus megaterium was recovered from the fermentation broth by adsorption on celite and immobilized by entrapping the adsorbed enzyme in acrylamide gel. The operational stability in column reactor was greatly increased by entrappment as compared with that of without entrappment. The optimum pH of the immobilized enzyme was 8.7 with broader activity profile than that of the free enzyme, while the most stable pH range appeared to be between pH 7.5 and 8.0. The optimum temperature was shifted to 5$0^{\circ}C$ from 45$^{\circ}C$ for the soluble enzyme. The values of Km and the inhibition constants for 6-APA( $K_{ia}$ ) and phenylacetic acid ( $K_{ip}$ ), were 4.55 mM, 36.5mM, and 10.5mM, respectively. No significant internal pore diffusion limitation was found since the value of effectiveness factor was 0.95. The operational half life in a column reactor at pH 8.0 was 6.8 days at 4$0^{\circ}C$ and 47 days at 3$0^{\circ}C$, whereas that of without entrappment was only 1 day and 4 days, respectively. The performance of a batch and a column reactor was also discussed with respect to the productivity. The results demonstrated that the entrappment of an adsorbed enzyme for the enhancement of the operational stability of the immobilized enzyme was useful especially when an extracellular enzyme was used.

• Current Research on Agriculture and Life Sciences
• /
• v.8
• /
• pp.29-34
• /
• 1990

This study was conducted to examine the influence of heat treatment on the $NH_4{^+}$ adsorption by zeolite and to determine the $NH_4{^+}$ loss from $NH_4-$ zeolite during the incubation. The dominant clay minerals of zeolite were clinoptiloiite and mordenite. $NH_4{^+}$ adsorption by zeolite was equilibrated at a 4hrs-shaking. The content of exchangeable $K^+$ of zeolite was increased with increase in the temperature of heat treatment but the amount of $NH_4{^+}$ adsorbed by zeolite was decreased. The amount of $NH_4{^+}$ in the soil treated with ammonium sulfate was decreased during incubation under the submerged condition but the amount of $NH_4{^+}$ adsorbed by zeolite was not decreased in the same course of incubation. It was estimated that $NH_4{^+}$ adsorbed by zeolite was resistant to $NH_4{^+}$-N loss by various reactions.

• Korean Journal of Soil Science and Fertilizer
• /
• v.31 no.3
• /
• pp.259-265
• /
• 1998

A field experiment was conducted to investigate changes of $NH_4-N$, N uptake, N use efficiency and rice yield by the Latex coated urea(LCU) application on wet-seeding rice from 1994 to 1997. Nitrogen deficiency symptom appeared when LCU was applied as basal dressing continuously until the ripening stage during normal temperature year, but was completed at heading stage during year at high temperature. Percentage recovery of fertilizer N was higher in LCU than in urea but decreased in high temperature. Turn over of N applied as LCU to grain increased more during years high temperature than the normal year. Rice yield with LCU treatment compared to conventional treatment was similar during the normal year but decreased by 6% during year of high temperature. Top dressing of urea at panicle initiation stage in addition to basal dressing of LCU increased rice yield to 12%.

• Journal of the Korea Organic Resources Recycling Association
• /
• v.10 no.1
• /
• pp.120-127
• /
• 2002

This study was carried out to evaluate the effects of initial concentration on composting of diesel-contaminated soil. Silt loam was used in this study. Target contaminant, diesel oil, was spiked at about 2,000, 4,000, and 10,000mg/kg of dry soil, respectively. Mix ratio of soil to sludge was 1:0.3 as wet weight basis. Temperature was maintained at $20^{\circ}C$ Volatilization loss of TPH was 0.7-3.5% of the initial concentrations. Volatilization loss of TPH was not increased in proportion to the initial concentration. After 30 days of operation, 86% and 94% of the initial concentrations at about 2,000 and 10,000mg TPH/kg were biodegraded. Normal alkanes were degraded more rapidly than TPH. The compounds of C12 to C14 were volatilized greatly among n-alkanes. The first order degradation rate constants of about 2,000, 4,000, and 10,000mg TPH/kg were 0.079, 0.069, and 0.061/day, respectively. Produced-$CO_2$ and degraded-TPH were correlated highly regardless of the initial TPH concentration(r = 0.97-0.99).

• Journal of the Korean Chemical Society
• /
• v.23 no.4
• /
• pp.248-258
• /
• 1979

Glucose 6-phosphate dehydrogenase of Leuconostoc mesenteroides which was purifid by an affinity chromatography was studied on the characterization, kinetics and chemical modification. The apparent molecular weight of the enzyme was 112,000 by the gel filtration method of Sephadex G-200 column. The optimum temperature of $NAD^+$-linked reation was 50$^{circ}C$ and the activation energy and the heat of inactivation were 8.36 kcal/mole and -58.2kcal/mole, respectively. The steady state kinetic study showed KG6P, Kemp, and CX KNADP to be 76.9 PM, 7.46${\mu}M$ and 7.14 ${\mu}M$, respectively, and KGGP, KNAD,and aKNm to be 53.7${\mu}M$, 115.2${\mu}M$ and 702.2${\mu}M$ for the $NAD^+$-linked reaction at pH 7.8, optimum pH. The pH dependent kinetic constants suggested that the two ionizing groups whose pKa is 7.2 .and pKb is 9.0-9.6 were involved in the enzyme-substrate interaction. Evidence by photooxidation and carboxymethylation of the enzyme suggested that the imidazole group of histidine with pKa group may participate in the catalytic site.

• Journal of the Korean Magnetics Society
• /
• v.13 no.2
• /
• pp.64-69
• /
• 2003

Ba-ferrite thin films were prepared on Si substrate with ${\alpha}$-Fe$_2$O$_3$ underlayer by a pulsed laser deposition system and characterized by X-ray, SEM, Mossbauer spectroscopy and VSM. The appropriate conditions of pulsation in ${\alpha}$-Fe$_2$O$_3$ and Ba-ferrite were the oxygen pressure of 0.1 Torr at a substrate temperature of 400$^{\circ}C$. Ba-ferrite crystals had the forms of ellipsoidal or needle and the grains shaped the more lumps with increasing the film thickness. Mossbauer spectroscopy assured that the direction of atomic spin in Fe ion was not random but had the tendency of arrangement normal to the substrate. The coercive force and squareness of hysteresis were larger in normal than in plane to the substrate but, the magnetic saturation moment was contrary to them. The spin arrangement was strongly affected by ${\alpha}$-Fe$_2$O$_3$ underlayer and the high coercive force and squareness were influenced by this. The crystal structure was conformed to be a Magntoplumbite symmetry with the hexagonal unit cell and the lattice constant of a increased with increasing film thickness, while c decreased

• Journal of the Korean Magnetics Society
• /
• v.17 no.2
• /
• pp.60-64
• /
• 2007

Ba-Ferrite single crystals were prepared and characterized by X-ray, SEM and Mossbauer spectroscopy. The single crystal layers was cut in the c-axis and radiated to the surface by ${\gamma}-rays$ for Mossbauer spectroscopy. We found out that the spin states in Fe atoms were parallel to the ${\gamma}-rays$ direction. The temperature dependence of the hyperfine field is almost similar to that of powder samples. The crystal structure is a Magnetoplumbite without any other phases and the lattice parameters are found out with $a_0=5.892{\AA},\;b_0=5.892{\AA},\;c_0=23.198{\AA}$. $M\"{o}ssbauer$ spectrum in single crystal have 5 sets off absorption lines in each Fe site when the ${\gamma}-rays$ have the same radiation direction with the c-axis in the crystal, which mean that the whole crystal bulk formed only one crystal and same spin direction. The hysteresis curve shows the saturation moment and coercive force of 70.71 emu/g and 320 Oe respectively.