• Clean Technology
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• v.19 no.4
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• pp.476-480
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• 2013

The growth behavior of $CH_4$ and $SF_6$ mixture gas hydrate has been investigated by a combined approach of Raman spectroscopy and molecular modeling. Raman spectroscopy results presented that when $CH_4$ is used only, $CH_4$ guest molecule is inserted first into the large cavity of the host structure built by $H_2O$ molecules and then into the small cavity to stabilize the whole gas hydrate structure. In the other hand, when $SF_6$ is mixed together, $SF_6$ is favored over (or competing with) $CH_4$ in being inserted into the large cavity and the small cavity still prefers $CH_4$ insertion. The calculations of binding energies clearly supported this. While $SF_6$ has a binding energy of -26.9 kcal/mol a little lower than -24.2 kcal/mol of $CH_4$ in the large cavity, $SF_6$ and $CH_4$ has 1.2 kcal/mol and -22.0 kcal/mol, respectively, in the small cavity. It indicates that the sizable $SF_6$ is not preferred in the small cavity but has a relative energetic advantage over $CH_4$ in the large cavity.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.769-774
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• 2005

Fluosilicic acid(H2SiF6) is recovered as an aqueous solution which absorbs $SiF_4$ produced from the manufacturing of industrial-graded H3PO4 or HF. Generally, fluosilicates are the salts produced by the reaction of H2SiF6 and metal salts. Addition of fluosilicates to cement endows odd properties through unique chemical reaction with the fresh and hardened cement. This study was performed to know mechanical properties and watertightness using fluosilicates based composite made from fluosilicates and other compounds. Mix proportions for experiments were modulated at 0.45 of water to cement ratio and $0.0-2.0\%$ of adding ratio of fluosilicates based composite. Evaluation for mechanical properties of concrete was conducted to know fresh state of concrete, hardening state of concrete, and watertightness. Evaluation for watertightness of concrete was carried out permeability, absorption test and porosity analysis. In addition. Scanning Electron Microscopy(SEM) and Energy Dispersive X-Ray(EDX) used for investigating micro-structure and atomic component distributed in hardened concrete. It is ascertained that characteristics of mechanical properties and watertightness was more improved than non-added because of packing role of fluosilicates based composite and pozzolanic reaction of soluble $SiO_2$. Also, concrete added fluosilicates based composite had a tendency to delay setting time and only $0.5\%$ addition of fluosilicates based composite delayed 150 minutes compared with non-added.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.29-32
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• 1999

$GaF_3$ films were directly grown on p' and p-type GaAs(100) substrates using a $SF_6$ plasma discharge system. GaAs MIS(Meta1-Insulator-Semiconductor) capacitor was successfully fabricated for about 1 hour at temperature $290^{\circ}C$ using the as-grown $GaF_3$ films. The as-grown films on p'-GaAs exhibited a current density of less than 6.68 $\times$ $1O^{-9}$ A/$cm^2$ at a breakdown field of 500kV/cm and a refractive index of 2.0 ~ 2.3 at a wavelength of 632.8 nm. The dielectric constant was about 5 derived from 1 MHz capacitance-voltage (C-V) measurements. Dielectric dispersion of the fluoridated films on p'-GaAs measured ranged from 100 Hz to 10 MHz was not observed.

• Korean Journal of Heritage: History & Science
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• v.55 no.3
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• pp.120-129
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• 2022

The purpose of this study is to analyze the chemical composition of smalt pigments used in 10 large Buddhist paintings in the Joseon Dynasty using energy dispersive X-ray spectroscopy, and to clarify the material and characteristics by observing morphological characteristics using polarized light microscopy and a scanning electron microscope. Through chemical composition analysis, the smalt of all 10 large Buddhist paintings is judged to be potash glass using SiO₂ as a former and K₂O as a flux. In addition to the components related to cobalt ore used as a colorant, the paintings were found to contain high levels of As₂O₃, BaO, and PbO. The smalt particles did not have specific forms, and were blue in color, with various chromaticity. In some particles, conchoidal fracture, spherical bubbles, and impurities were observed. Through backscattered electron images, it was found that the smalt from paintings produced in the early 18th century AD had a high level of As, but the smalt from paintings produced from the mid-18th century AD onwards exhibited various contrast differences from particle to particle, and there was smalt with high levels of As, Ba, and Pb. Through the above results, the large Buddhist paintings in the Joseon Dynasty are divided into three smalt types. Type A is a type with high As₂O₃, type B is a type with high BaO, and type C is a type with high PbO. Looking at the three types of smalt pigments by the period of production, although some in-between periods were not detected, type A was confirmed to have been used from 1705 to 1808, while type B and type C were shown to have appeared in 1750 and used until 1808. This reveals that only one type of smalt was used until the early 18th century AD, and from the middle of the 18th century AD, several types of smalt were mixed and used in one large Buddhist painting. Studies such as this research are expected to provide insights into the characteristics of the smalt pigments used to produce large Buddhist paintings at the time.

• Applied Chemistry for Engineering
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• v.4 no.2
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• pp.318-323
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• 1993

Pentachloroethane($CHCl_2CCl_3$) was synthesized and reacted with hydrogen fluoride using antimony pentahalide catalyst($SbCl_xF_y$) in order to manufacture HCFC-123$(CF_3CHCl_2)$, a potential CFC-11$(CFCl_3$) substitute candidate. Products analyses showed the fluorination proceeds through fluorine-chlorine exchanges between $HF/SbCl_xF_y$ and $SbCl_xF_y/CCl_3CHCl_2$ respectively. The degree of fluorination of $CCl_3$ group in pentachloroethane was greatly affected on the reaction temperature, but the effect of catalyst concentration was relatively small. Mechanistic study was also performed to elucidate the pathway to the formation of side-products such as $CCl_3CFCl_2$, $CFCl_2CFCl_2$ and $CF_2ClCFCl_2$.

• Korean Chemical Engineering Research
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• v.54 no.3
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• pp.387-393
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• 2016

Fluorinated polyurethane coating solutions were synthesized from perfluoroalkyl alcohol, toluene diisocyanate, and polycarbonate diol as starting materials. Next, coating films were prepared by spin-coating the fluorinated polyurethane coating solutions on the PC substrates, followed by thermal curing at $120^{\circ}C$. The obtained fluorinated polyurethane coating films were characterized by FT-IR spectroscopy, UV-Vis spectrometer, contact angle tester and pencil hardness tester. Contact angle measurements of water on the coating films showed that the addition of perfluoroalkyl alcohol improved the water repellency and increased the contact angle from $81^{\circ}C$ to $111^{\circ}C$. However, the pencil hardness of coating films exhibited a constant grade of H, irrespective of the addition of perfluoroalkyl alcohol.

• Membrane Journal
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• v.30 no.5
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• pp.326-332
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• 2020

In this study, polymer-fluorinated silica composite hollow fiber membranes were fabricated and applied to a membrane contactor for the recovery of methane dissolved in the anaerobic effluent. To prepare the composite membranes, porous hollow fiber substrates were fabricated with Ultem^®, a commercial polyetherimide (PEI). Subsequently, fluorinated silica particles were synthesized and coated on the surface via strong covalent bonding. Due to the high porosity, our membrane showed a CH₄ flux of 8.25 × 10^-5 ㎤ (STP)/㎠·s at the liquid velocity of 0.03 m/s which is much higher that that of commercial polypropylene membrane designed for degassing processes. This is attributed to our membrane's high porosity as well as a superior surface hydrophobicity (120~122°) resulted from the coating with fluorinated silica nanoparticles.

• Journal of Korean society of Dental Hygiene
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• v.12 no.1
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• pp.113-122
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• 2012

Objectives : This study was carried out to investigate the caries resistant effect of fluoride by dental polishing prior to fluoride application in vitro. Methods : Artificial caries lesion was made on the surface of specimen enamel taken from cow's permanent cuspid on the part of labial surface after resin embedding and polishing. Artificial dental plaque was formed on the 72 dental specimen 25~45 VHN(Vickers Hardness Number) which were divided into three groups(fluoride varnish, APF gel, control) with dental polishing and without polishing respectively. Fluoride varnish and APF gel group with 20 second polishing or without polishing were immersed in the artificial saliva respectively. Control group with or without polishing were immersed in the artificial saliva. Results : 1. Significant difference was not found by fluoride varnish between polishing group and non polishing group (p>0.01). 1) polishing group. The changes of Vickers Hardness Number(VHN) were $14.49{\pm}13.73$. 2) non-polishing group. The changes of VHN were $11.67{\pm}5.39$. 2. Significant difference was not found by APF gel between polishing group and non polishing group (p>0.01). 1) polishing group. The changes of VHN were $8.48{\pm}8.37$. 2) non-polishing group. The changes of VHN were $5.32{\pm}2.59$. Conclusions : Showed no significant difference between polishing group and non-polishing group regardless of fluoride materials (fluoride varnish, APF gel).

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1999.10a
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• pp.105-105
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• 1999

핵연료 피복관은 핵연료에서 방사성 핵분열생성물의 방출을 저지하는 가장 뚱요한 방어막인데, 현재 지르칼로이 4가 피복관의 재료로 사용되고 있다. 사용후 핵연료는 원자력발전소내 습식 저장조에 저장되고 있으나, 지속적인 관리와 장소확보의 용이 성으로 인해 건식 저장조를 사용하는 추세에 있다. 본 연구에선 건식 저장조에 장 기간 저장되는 핵연료 피복관에 주변 환경으로부터 오염될 수 있는 소금기나 기름 등이 지르칼로이의 공기중 산화에 미치는 영향의 존재를 밝히려 한다. 현재 고리 원자력발전소에서 사용중인 핵연료 피복관을 1cm정도 높이로 자르고, 피복관 표면 을 ASTM -G2-88 방법으로 처리한 후 산화실험을 수행하였다. 산화정도는 간헐적 (intermittent) 방법을 사용하여 시편의 무게를 측정하여 구하였으며, 산화온도는 $400-500^{\circ}C$로 하였다. 소금이 흡착이 된 경우, 산화 속도는 흡착이 안된 시편보다 가속되었으며, 거의 이차법칙을 따르고 있다. 산화막 위의 흡착물의 영향을 알아보기 위해, 지르칼로이를 $500^{\circ}C$ 수증기에 $5g/m^2$ 두께로 산화시킨 후, 다시 산화실험을 수행하였다. 사용한 흡착물은 LiF, NaF, KF, NaCI 이다. 흡착물들은 산화를 대체로 가속시켰으며, NaF, KF, NaCI 순으로 그 영향력이 컸다. 그러나, LiF는 산화에 전혀 영향을 미치지 않았다. SIMS를 사용하여 각 시편의 두께에 따른 흡착물의 분포 를 알아보았다. 음이온(CI, F)과 양이온(Na, Li, K)이 산화막과 금속 경계면까지 관 찰되었으며, 음이온과 양이온의 분포는 대게 동일하였다. LiF의 경우 산화막에서 이들의 농도가 급격히 떨어지고 있음을 알 수 있었다. 산화막 내에서 이들 흡착물의 확산이 산화속도 가속의 원인이며 이들 흡착물중 CI과 F는 산화막과 금속 겸계면 에서 새로 생성되는 산화막의 강도에 영향을 미쳐, 일찍 미세균열을 만들기 시작하여 산화를 가속시키는 것으로 판단된다.

• Applied Chemistry for Engineering
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• v.27 no.6
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• pp.573-576
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• 2016

In this study, hydrogenation of 1,2,3,3,3-pentafluoropropene was performed to produce R-1234yf as an environmentally friendly refrigerant. Palladium based carbon was prepared as a catalyst in the hydrogenation reaction. The effect of reaction conditions including the weight hourly space velocity (WHSV), reaction temperature and ratio of hydrogen and reactants on the catalytic performance was investigated. Under the identical reaction conditions, the effect of WHSV on the main product selectivity was insignificant, but a high reaction temperature was essential for the good product selectivity. A high product selectivity was also obtained when the ratio of hydrogen and reactants kept less than 1.5. Moreover, a correlation model involving the statistical approach to predict product yields was developed.