• Journal of the Korean Ceramic Society
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• v.18 no.3
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• pp.163-170
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• 1981

The crystallization of $Li_2O-SiO_2$ system glasses and the effect of phase separtion to crystal nucleation were studied. The crystallization temperatures of various glasses were determined by DTA and glasses were nucleation heat treated at the temperatures ranging from 45$0^{\circ}C$ to 5$25^{\circ}C$. These glasses were thengown at $700^{\circ}C$ to observable size in the optical microscope. Crystal nucleation rates of various glasses were obtained by estimating the number of crystals per unit volume. The main crystal phase of these glasses identified by X-ray diffraction was lithium disilicate ($Li_2O$.$2SiO_2$). It was found that the crystal nucleation rate of glass (19.5% $Li_2P$-80.5% $SiO_2$), the nearest composition to lithium disilicate, was higher than other glasses. The opalescence caused by phase separation was observed in the nucleation heat treated glass (16.3% $Li_2O$-83.7% $SiO_2$). The result from nucleation density measurement of this glass indicated that the nucleation was enhanced during early stage of phase separation. The molphologies of crystals in glasses and crystal growth rate at $600^{\circ}C$ were also discussed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.1
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• pp.64-69
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• 2019

Methylammonium lead triiodide ($MAPbI_3$)-based perovskite solar cells potentially have potential advantages such as high efficiency and low-cost manufacturing procedures. However, $MAPbI_3$ is structurally unstable and has low phase-change temperatures ($30^{\circ}C$ and $130^{\circ}C$); it is necessary to solve these problems. We investigated the crystal structure and phase separation using real-time temperature-change X-ray diffraction, transmission electron microscopy, and electron energy loss spectroscopy. $MAPbI_3$ has a tetragonal structure, and at about $35^{\circ}C$ the c-axis contracts, transforming $MAPbI_3$ into the related cubic crystal structure. In addition, at $130^{\circ}C$, phase separation occurs in which $CH_3NH_2$ and HI at the center of the unit cell of the perovskite structure are extracted by gas, leavingand only $PbI_2$ of the three-component structure, is produced as the final solid product.

• Korean Chemical Engineering Research
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• v.57 no.3
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• pp.392-399
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• 2019

A highly transparent interfacial layer (HTIL) to enhance the performance of dye-sensitized solar cells (DSSCs) was prepared via a polymer-assisted (PA) approach. Poly(vinyl chloride)-graft-poly(oxyethylene methacrylate) (PVC-g-POEM) was synthesized via atom-transfer radical polymerization (ATRP) and was used as a sacrificial template. The PVC-g-POEM graft copolymer induced partial coordination of a hydrophilic titanium isopropoxide (TTIP) sol-gel solution with the POEM domain, resulting in microphase separation, and in turn, the generation of mesopores upon calcination. These phenomena were confirmed using Fourier-transform infrared (FT-IR) spectroscopy, UV-visible light transmittance spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis. The DSSCs incorporating HTIL60/20 (consisting of a top layer with a pore size of 60 nm and a bottom layer with a pore size of 20 nm) exhibited the best overall conversion efficiency (6.36%) among the tested samples, which was 25.9% higher than that of a conventional blocking layer (BL). DSSC was further characterized using the Nyquist plot and incident-photon to electron conversion efficiency (IPCE) spectra.

• Structural Engineering and Mechanics
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• v.84 no.6
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• pp.733-741
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• 2022

The amount of natural gas that is used on a worldwide scale is continuously going up. Natural gas and acidic components, such as hydrogen sulfide and carbon dioxide, cause significant corrosion damage to transmission lines and equipment in various quantities. One of the fundamental processes in natural gas processing is the separation of acid gases, among which the safety and environmental needs due to the high toxicity of hydrogen sulfide and also to prevent wear and corrosion of pipelines and gas transmission and distribution equipment, the necessity of sulfide separation Hydrogen is more essential than carbon dioxide and other compounds. Given this problem's significance, this endeavor aims to extend the lifespan of the transmission lines' pipes for gas and oil. Zinc oxide nanoparticles made from the environmentally friendly source of Allium scabriscapum have been employed to accomplish this crucial purpose. This is a simple, safe and cheap synthesis method compared to other methods, especially chemical methods. The formation of zinc oxide nanoparticles was shown by forming an absorption peak at a wavelength of about 355 nm using a spectrophotometric device and an X-ray diffraction pattern. The size and morphology of synthesized nanoparticles were determined by scanning and transmission electron microscope, and the range of size changes of nanoparticles was determined by dynamic light scattering device.

• Membrane Journal
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• v.32 no.6
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• pp.456-464
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• 2022

Hydrogen permeation performance was analyzed by manufacturing Pd and Pd-Cu membranes through electroless plating. As a support for the Pd and Pd-Cu membranes, α-Al₂O₃ ceramic hollow fiber were used. Pd-Cu membrane was manufactured through sequential electroless plating, and then annealing was performed at 500°C, for 18 h in a hydrogen atmosphere to make Pd and Cu alloy. After annealing, the Pd-Cu membrane confirmed that the alloy was formed through EDS (Energy Dispersive X-ray Spectroscopy) and XRD (X-ray Diffraction) analysis. In addition, the thickness of the Pd and Pd-Cu plating layers were measured to be about 3.21 and 3.72 µm, respectively, through SEM (Scanning Electron Microscope) analysis. Hydrogen permeation performance was tested for hydrogen permeation in the range of 350~450°C and 1~4 bar in hydrogen single gas and mixed gas (H₂, N₂). In a single hydrogen gas, Pd and Pd-Cu membranes have flux of up to 54.42 and 67.17 ml/cm²⋅ min at 450 °C and 4 bar. In the mixed gas, it was confirmed that the separation factors of 1308 and 453 were obtained under the conditions of 450 °C and 4 bar.

• Membrane Journal
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• v.14 no.2
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• pp.99-107
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• 2004

Carbon molecular sieve (CMS) membranes were prepared by pyrolysis of polyimides having carboxylic acid groups and applied to the hydrogen separation. The polymeric membranes having carboxylic acid groups showed different steric properties as compared with polymeric membranes having other side groups ($-CH_3$ and $-CF_3$) because of the hydrogen bond between the carboxylic acid groups. However, the microporous CMS membranes were significantly affected by the decomposable side groups evidenced from the wide angle X-rat diffraction, nitrogen adsorption isotherms, and single gas permeation measurement. Furthermore, the gas separation properties of the CMS membranes were essentially affected by the pyrolysis temperature. As a result, the CMS membranes Prepared by Pyrolysis of polyimide containing carboxylic acid froups at $700^{\circ}C$ showed the $H_2$ permeability of 3,809 Baller [$1{\times}10^{-10}$ H $\textrm{cm}^$(STP)cm/$\textrm{cm}^2$.s.cmHg], $H_2$/$N_2$, selectivity of 46 and $H_2$/$CH_4$ selectivity of 130 while the CMS membranes derived from polyimide showed the H$_2$ permeability of 3,272 Barrer, $H_2$/$N_2$ selectivity of 136 and $H_2$/$CH_4$ selectivity of 177.

• Membrane and Water Treatment
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• v.7 no.3
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• pp.223-240
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• 2016

In this study, poly(vinyl-alcohol) and water insoluble ${\beta}$-cyclodextrin polymer (${\beta}$-CDP) cross-linked with citric acid, have been used as macrocyclic carrier in the preparation of polymer inclusion membranes (PIMs) for aniline (as molecule model) extraction from aqueous media. The obtained membranes were firstly characterized by X-ray diffraction, Fourier transform infrared and water swelling test. The transport of aniline was studied in a two-compartment transport cell under various experimental conditions, such as carrier content in the membranes, stirring rate and initial aniline concentration. The kinetic study was performed and the kinetic parameters were calculated as rate constant (k), permeability coefficient (P) and flux (J). These first results demonstrated the utility of such polymeric membranes for environmental decontamination of toxic organic molecules like aniline. Predictive modeling of transport flux through these materials was then studied using design of experiments; the design chosen was a two level full factorial design $2^k$. An empirical correlation between aniline transport flux and independent variables (Poly ${\beta}$-CD membrane content, agitation speed and initial aniline concentration) was successfully obtained. Statistical analysis showed that initial aniline concentration of the solution was the most important parameter in the study domain. The model revealed the existence of a strong interaction between the Poly ${\beta}$-CD membrane content and the stirring speed of the source solution. The good agreement between the model and the experimental transport data confirms the model's validity.

• Membrane and Water Treatment
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• v.10 no.2
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• pp.165-178
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• 2019

Mixed matrix membranes (MMMs) of poly (vinyl alcohol) (PVA) containing certain amounts of H-${\beta}$ zeolite for pervaporation were manufactured by using a solution casting protocol. These zeolite-embedded membranes were then characterized with scanning electron microscope (SEM), X-ray diffraction (XRD) and swelling tests. The membrane separation performance has been examined by means of isopropanol (IPA) dewatering from its highly concentrated aqueous solutions via response surface methodology (RSM). The results have demonstrated that the influences of feed IPA composition (85-95 wt.%), feed temperature ($50-70^{\circ}C$), zeolite loading (15-25 wt.%) and their interactive influences are all statistically significant on both pervaporation flux ($398-1228g/m^2{\cdot}h$) and water/isopropanol separation factor (617-2001). The quadratic models based on the RSM analysis have performed excellently to correlate experimental data with very high determination coefficients and very low relative standard deviations. The optimal pervaporation predictions given by using the RSM models demonstrate a total flux of $953g/m^2{\cdot}h$ and separation factor of 1458, and are excellently verified by experimental results. As reflected by these results, PVA MMMs embedded with hydrophilic $H-{\beta}$ zeolite entities have performed considerably better than its pure counterpart and indicated great potential for isopropanol dehydration applications.

• Korean Journal of Materials Research
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• v.31 no.11
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• pp.593-600
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• 2021

Herein, a series of g-C₃N₄ modified Bi₂MoO₆ nanocomposites using Bi₂MoO₆ and melamine as original materials are fabricated via sintering process. For presynthesis of Bi₂MoO₆ an ultrasonic-assisted hydrothermal technique is researched. The structure and composition of the nanocomposites are characterized by Raman spectroscopy, X-ray diffraction (XRD), and high-resolution field emission scanning electron microscopy (SEM). The improved photoelectrochemical properties are studied by photocurrent density, EIS, and amperometric i-t curve analysis. It is found that the structure of Bi₂MoO₆ nanoparticles remains intact, with good dispersion status. The as-prepared g-C₃N₄/Bi₂MoO₆ nanocomposites (BMC 5-9) are selected and investigated by SEM analysis, which inhibits special morphology consisting of Bi₂MoO₆ nanoparticles and some g-C₃N₄ nanosheets. The introduction of small sized g-C₃N₄ nanosheets in sample BMC 9 is effective to improve the charge separation and transfer efficiency, resulting in enhancing of the photoelectric behavior of Bi₂MoO₆. The improved photoelectronic behavior of g-C₃N₄/Bi₂MoO₆ may be attributed to enhanced charge separation efficiency, photocurrent stability, and fast electron transport pathways for some energy applications.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.6
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• pp.615-624
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• 2016

In this study, two rectangular barges in close proximity were simulated to analyze the characteristics of motion responses due to hydrodynamic interactions. Using a numerical solution from DNV-GL SESAM, coupled stiffness matrix terms for these same FEM models were added to the multiple body modes in the surge direction. Potential theory was used to calculate the first order radiation and diffraction effects on the simulated barge models. In the results, the sheltering effect of the barges was not shown at 1.3 rad/s with hull separation of 20 m in transverse waves. The separation effect between the barges was more clear with longitudinal waves and a shallow water depth. However, sway forces were influenced by hull separation with transverse waves. The peaks for sway and heave motion and sway force occurred at higher frequencies as hull separation narrowed with longitudinal and transverse waves. Given a depth of 10 m, the sway motion on the lee side of a coupled barge made a significant difference in the range of 0.2-0.8 rad/s with transverse and oblique waves. Also, the peaks for sway force were situated at lower frequencies, even when incident waves changed.