• Ocean and Polar Research
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• v.26 no.3
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• pp.515-521
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• 2004

The processes of formation and dissociation of gas hydrates were investigated by monitoring pressure and temperature variations in a pressure cell in order to understand the kinetic behavior of gas hydrate and the controlling factors fur the phase transition of gas hydrate below freezing. Gas hydrates were made kom guest gases ($CH_4,\;CO_2$, and their mixed-gas) and fine ice powder. We found that formation and dissociation speeds of gas hydrates were not controlled by temperature and pressure conditions alone. The results of this study suggested that pressure levels at the formation of mixed-gas hydrate determine the transient equilibrium pressure itself.

• Journal of Industrial Technology
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• v.40 no.1
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• pp.25-32
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• 2020

In this study, the effects of thermodynamic hydrate inhibitors on hydrate formation and dissociation behaviors were identified. The nucleation and growth of CP hydrate in the presence of methanol were monitored by optical microscope. Cyclopentane was used to demonstrate the oil phase in the pipeline in this study. Hydrate morphology, required time for hydrate formation, hydrate dissociation temperature were also identified by experiments. With the addition of methanol in water solution, the hydrate nucleation as well as hydrate growth were delayed. Moreover, hydrate morphology was also varied with the addition of methanol. Hydrate formation and dissociation temperature also decrease as the concentration of methanol increases.

• Bulletin of the Korean Chemical Society
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• v.26 no.11
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• pp.1682-1688
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• 2005

Using the ASED-MO (Atom Superposition and Electron Delocalization-Molecular Orbital) theory, we investigated carbon formation and carbon hydrogenation for $CO_2$ methanation on the Ni (111) surface. For carbon formation mechanism, we calculated the following activation energies, 1.27 eV for $CO_2$ dissociation, 2.97 eV for the CO, 1.93 eV for 2CO dissociation, respectively. For carbon methanation mechanism, we also calculated the following activation energies, 0.72 eV for methylidyne, 0.52 eV for methylene and 0.50 eV for methane, respectively. We found that the calculated activation energy of CO dissociation is higher than that of 2CO dissociation on the clean surface and base on these results that the CO dissociation step are the ratedetermining of the process. The C-H bond lengths of $CH_4$ the intermediate complex are 1.21 $\AA$, 1.31 $\AA$ for the C${\cdot}{\cdot}{\cdot}H_{(1)}$, and 2.82 $\AA$ for the height, with angles of 105${^{\circ}}$ for ∠ $H_{(1)}$CH and 98${^{\circ}}$ for $H_{(1)} CH _{(1)}$.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.630-633
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• 2005

Some gases can be formed into hydrate by physical combination with water under appropriate temperature and pressure condition. Besides them, it was found that the pore size of the sediments can affect the formation and dissociation of hydrate. In this study, formation temperatures of carbon dioxide and methane hydrate have been measured using isobaric method to investigate the effects of flow rates of gases on formation condition of hydrate in porous rock samples. The flow rates of gases were controlled using a mass flow controller. To minimize Memory effect, system temperature increased for the dissociation of gas hydrates and re-established the initial saturation. The results show that the formation temperature of hydrate decreases with increasing the injection flow rate of gas. This indicates that the velocity of gas in porous media may act as kinds of inhibitor for the formation of hydrate.

• Korean Journal of Materials Research
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• v.18 no.11
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• pp.604-609
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• 2008

The sintering behavior of zircon with silica was investigated. Zircon with 5 vol% of sedimentation $SiO_2$ resulted in the apparent density of $4.45\;g/cm^3$, the diametral tensile strength of $12.125\;kgf/cm^2$, and the micro Vickers hardness of 1283 HV. The dissociation temperature and mechanical characteristics of the $ZrSiO_4$ were changed with different kinds of $SiO_2$. $SiO_2$ addition prevented dissociation of $ZrSiO_4$. Zircon with 5 vol% of sedimentation $SiO_2$ and with 5 vol% of fused $SiO_2$ resulted in increased diametral tensile strength and increased micro Vickers hardness by suppression of $ZrSiO_4$ dissociation and low temperature liquid $SiO_2$ formation. Zircon with fumed $SiO_2$ and quartz $SiO_2$ resulted in decreased diametral tensile strength and decreased micro Vickers hardness because of cristobalite and quartz phase formation and high temperature liquid $SiO_2$ formation. Zircon with 10 vol% of $SiO_2$ resulted in decreased diametral tensile strength and decreased micro Vickers hardness because of weak particle coupling due to excess formation of liquid $SiO_2$.

• Bulletin of the Korean Chemical Society
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• v.19 no.6
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• pp.671-676
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• 1998

The formation and dissociation rates of $Ce^{3+}$ Complexes of the 1,4,7,10-tetraaza-13,16-dioxacyclooctadecane-NN', N",N"'-tetraacetic acid (1), 1,4,7,10-tetraaza-13,16-dioxacyclooctadecane-N,N',N",N"'-tetramethylacetic acid (2), and 1,4,7,10-tetraaza-13,16-dioxacyclooctadecane-N,N',N",N"'-tetrapropionic acid (3) have been measured by the use of stopped-flow spectrophotometry. Observations were made at 25.0±0.1 ℃ and at an ionic strength of 0.10 M $NaClO_4$. The complexation of $Ce^{3+}$ ion with 1 and 2 proceeds through the formation of an intermediate complex $(CeH_3L^{2+})^*$ in which the $Ce^{3+}$ ion is incompletely coordinated. This may then lead to be a final product in the rate-determining step. Between pH 4.76 and 5.76, the diprotonated $(H_2L^{2-})$ from is revealed to be a kinetically active species despite of its low concentration. The stability constants $(logK(CeH_3L^{2+}))$ and specific water-assisted rate constants $(k_{OH})$ of intermediate complexes have been determined from the kinetic data. The dissociation reactions of $Ce^{3+}$ complexes of 1, 2, and 3 were investigated with $Cu^{2+}$, ions as a scavenger in acetate buffer. All complexes exhibit acid-independent and acid-catalyzed contributions. The effect of buffer and $Cu^{2+}$ concentration on the dissociation rate has also been investigated. The ligand effect on the dissociation rate of $Ce^{3+}$ complexes is discussed in terms of the side-pendant arms and the chelate ring sizes of the ligands.

• Membrane Journal
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• v.15 no.2
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• pp.175-186
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• 2005

An electrodialysis process was operated for a long period to investigate the scale formation on the membrane surface. During the desalination process, concentration of $Ca^{2+}$ and $SO_4^{2-}$ ions increased continuously in the concentrate compartment and eventually caused precipitation on the cation exchange membrane (Neosepta CMX) surface. During the initial scale formation, the performance of the process and membrane characteristics did not show significant changes, except the decrease in limiting current density of the CMX membrane occurring due to increase in the salt concentration in the concentrate compartment. Eventually, the limiting current density of the fouled CMX membrane dropped significantly to $300\;A/m^2$ as water dissociation occurred in the CMX membrane. It was concluded that the fouling was caused mainly by the scale formation on the cation exchange membrane surface in the concentrate and consequent water dissociation. Also the scale formation was reasonably predicted by the solubility of $CaSO_4$.

• Bulletin of the Korean Chemical Society
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• v.18 no.10
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• pp.1054-1056
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• 1997

• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.186-187
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• 2008

Electrical resistivity in hydrate-bearing sediments is sensitive to porosity, gas hydrate saturation, gas content, pore fluid composition, and temperature, so electrical measurements such as well logs and electromagnetic surveys have been used to explore gas hydrate-bearing formation. The high pressure tomography cell is designed considering the effect of electrode configuration and electrical shielding on tomography measurements and the safety. The evolution of electrical conductivity during $CO_2$ hydrate formation and dissociation reflects the combined effects of concurrent changes that include ionization of dissolved $CO_2$, temperature-dependent ionic mobility, changes in the degree of saturation, ion exclusion, surface conduction, and porosity changes. Measurements during hydrate formation and dissociation require careful analysis to properly interpret signatures, in particular when out-of plane conductivity anomalies prevail.

• Journal of Animal Reproduction and Biotechnology
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• v.38 no.1
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• pp.10-16
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• 2023

Intermuscular fat is essential for enhancing the flavor and texture of cultured meat. Mesenchymal stem cells derived from intermuscular adipose tissues are a source of intermuscular fat. Therefore, as a step towards developing a platform to derive intermuscular fat from mesenchymal stem cells (MSCs) for insertion between myofibrils in cultured beef, an advanced protocol of intermuscular adipose tissue dissociation effective to the isolation of MSCs from intermuscular adipose tissues was developed in cattle. To accomplish this, physical steps were added to the enzymatic dissociation of intermuscular adipose tissues, and the MSCs were established from primary cells dissociated with physical step-free and step-added enzymatic dissociation protocols. The application of a physical step (intensive shaking up) at 5 minutes intervals during enzymatic dissociation resulted in the greatest number of primary cells derived from intermuscular adipose tissues, showed effective formation of colony forming units-fibroblasts (CFU-Fs) from the retrieved primary cells, and generated MSCs with no increase in doubling time. Thus, this protocol will contribute to the stable supply of good quality adipose-derived mesenchymal stem cells (ADMSCs) as a fat source for the production of marbled cultured beef.