• Journal of Industrial and Engineering Chemistry
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• 제67권
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• pp.316-325
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• 2018

Aluminum based metal-organic framework using a di-carboxylate linker succinic acid (Al-SA MOF), are synthesized in water with minimal generation of secondary pollutants. The physicochemical properties of Al-SA MOF were examined, followed by its utility for the adsorption of Acid Black 1 (AB1) in aqueous media. Influences of key parameters such as pH, contact time, initial AB1 concentration,temperature, and selectivity on the adsorption process were assessed. A series of adsorption mechanisms are proposed, which involve electrostatic, hydrogen bonding, and hydrophobic interactions. These findings suggest that Al-SA MOF is a potent candidate in removing complex azo dyes molecules from aqueous media.

• Advances in nano research
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• 제16권5호
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• pp.435-444
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• 2024

Microscopic defects within the microstructure of hardened cement paste are the main source of weakness in concrete. As a solution, nano-graphene oxide (GO) can be employed to improve the cement paste microstructure. However, there is a number of disadvantages, e.g., fluidity reduction and non-uniform dispersion. The present study sought to modify GO by fabricating a copolymer (PSGO) in a novel process to exploit the advantages of nano-GO while minimizing its disadvantages. Using 0.03wt% copolymerled to 38.8% higher tensile strength, 29.3% higher compressive strength and 25% higher workability. The SEM images revealed that GO and modified GO enhanced concrete by secondary hydration and bonding with C-S-H, creating a firm, integrated, and foil-like structure, and reducing the crack size and depth.

• 헤리티지:역사와 과학
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• 제55권2호
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• pp.200-211
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• 2022

청자 투각고리문 의자는 4점 일괄유물로 경기도 개성에서 출토된 것으로 전해진다. 청자 의자는 고려시대 당시 청자 제작기술의 우수성과 화려한 생활상을 보여주는 등 미술사적으로 가치가 높아 보물로 지정 관리되어 왔다. 그러나 일괄유물 중 1점의 경우 과거 수리 복원된 것으로, 처리 재료의 열화, 처리자의 미숙함 등으로 인해 미적가치가 하락되었고, 구조적으로 불안하여 재처리의 필요성이 제기되었다. 처리 전 보존상태를 조사한 결과, 물리적 손상은 전반적으로 제조상 결함부위를 중심으로 인위적 손상이 가중되어 구조적으로 취약한 상태를 보였다. 균열부위 및 탈락된 편은 접합면이 맞지 않고 접착제가 청자 표면에 흐른 자국과 접착제 표면에 분진 등 2차적 오염물이 생겨 변질된 상태였다. 수리복원 상태를 조사하기 위해 자외선과 확대현미경을 이용하여 균열부의 접합 부위의 위치와 범위, 상태를 파악하였다. 적외선분광 분석(FT-IR)과 휴대용 X-선 형광분석을 실시하여 보존처리에 사용한 재료를 분석한 결과, 접착제로 셀룰로오스계 수지와 에폭시계 수지가 사용된 것을 확인하였다. 또한 일부 힘을 받는 접합부위에서는 접합강도를 높이기 위해 접착제에 석고(CaSO₄·2H₂O) 또는 골분(Ca₁₀ (PO₄)₆(OH)₂)을 첨가한 것을 알 수 있었다. 상태조사 결과를 바탕으로, 유물의 보존처리는 기존 접합된 상태에서 전면 해체하고 물리적으로 취약한 부분을 중심으로 접합·복원을 통해 보강하는데 중점을 두었다. 기존에 사용된 접착제를 제거하고 해체한 결과, 청자 의자는 크게 상부와 하부, 굽다리, 일부 고리 문 등 총 6개 편으로 분리되었다. 해체 후 접합면에 남아 있는 잔류 접착제 및 오염물은 화학적 및 물리적으로 제거하고 스팀세척기로 파단면 세척을 통해 재접합의 효율을 높였다. 유물의 접합은 접합부위와 크기에 따라 접착제를 다르게 적용하였다. 편의 위치만 고정하는 접합부에는 시아노아크릴계 수지 Loctite^® 401을 사용하고 구조적으로 안정화시키는 부분에는 가역성을 위해 아크릴계 수지인 Paraloid^® B-72 20%(in xylene)로 단면처리한 후 에폭시계 수지 Epo-tek^® 301-2를 이용하여 접합하였다. 상·하부 접합 같이 힘을 받는 부위는 Epo-tek^® 301-2에 Kaolin을 첨가하여 접합강도를 보강하였다. 연속되는 문양으로 추정 가능한 고리문의 결실 부분은 SN-Sheet로 뼈대를 만들고 Wood epos^®로 파손단면을 연결하여 모델링하면서 고리문을 복원하였다. 그 외 접합하면서 생긴 복원 부위는 심미적 및 구조적 안정화를 위해 Wood epos^®로 메움처리하였다. 복원부위 및 메움처리한 부분은 추후 전시활용에 있어 이질감이 없도록 색맞춤하였다. 다양한 과학기술을 활용한 조사와 처리과정은 체계적으로 기록하여 보존 관리하는데 기초자료로 활용하도록 하였다.

• Bulletin of the Korean Chemical Society
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• 제33권5호
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• pp.1547-1550
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• 2012

Second-order rate constants ($k_N$) have been measured spectrophotometrically for the reactions of benzyl 2-pyridyl carbonate $\mathbf{3}$ and $t$-butyl 2-pyridyl carbonate $\mathbf{3}$ with a series of alicyclic secondary amines in MeCN at $25.0{\pm}0.1^{\circ}C$. Substrate $\mathbf{4}$ is much less reactive than $\mathbf{3}$ and the steric hindrance exerted by the bulky $t$-Bu group in $\mathbf{4}$ has been attributed to its decreased reactivity. The Br${\o}$nsted-type plots for the reactions of $\mathbf{3}$ and $\mathbf{4}$ are linear with ${\beta}_{nuc}=0.57$ and 0.45, respectively. Thus, the reactions have been concluded to proceed through a concerted mechanism, although the current reactions were expected to proceed through a stepwise mechanism with a zwitterionic tetrahedral intermediate $T^{\pm}$. It has been proposed that the rate of leaving-group expulsion is accelerated by the intramolecular H-bonding interaction in $T^{\pm}$ and the "push" provided by the RO group through the resonance interaction. Thus, the enhanced nucleofugality forces the reactions to proceed through a concerted mechanism. The reactivity-selectivity principle (RSP) is not applicable to the current reaction systems, since the reaction of the less reactive $\mathbf{4}$ results in a smaller ${\beta}_{nuc}$ than that of the more reactive $\mathbf{3}$. Steric hindrance exerted by the bulky $t$-Bu group in $\mathbf{4}$ has been suggested to be responsible for the failure of the RSP.

• Bulletin of the Korean Chemical Society
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• 제33권9호
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• pp.2971-2975
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• 2012

Second-order rate constants $k_N$ have been measured spectrophotometrically for nucleophilic substitution reactions of t-butyl 4-pyridyl carbonate 8 with a series of alicyclic secondary amines in $H_2O$ at $25.0{\pm}0.1^{\circ}C$. The Br${\emptyset}$nsted-type plot for the reactions of 8 is linear with ${\beta}_{nuc}$ = 0.84. The ${\beta}_{nuc}$ value obtained for the reactions of 8 is much larger than that reported for the corresponding reactions of t-butyl 2-pyridyl carbonate 6 (i.e., ${\beta}_{nuc}$ = 0.44), which was proposed to proceed through a forced concerted mechanism. Thus, the aminolysis of 8 has been concluded to proceed through a stepwise mechanism with a zwitterionic tetrahedral intermediate $T^{\pm}$, in which expulsion of the leaving-group from $T^{\pm}$ occurs at the rate-determining step (RDS). In contrast, aminolysis of benzyl 4-pyridyl carbonate 7 has been reported to proceed through two intermediates, $T^{\pm}$ and its deprotonated form $T^-$ on the basis of the fact that the plots of pseudo-first-order rate constant $k_{obsd}$ vs. amine concentration curve upward. The current study has demonstrated convincingly that the nature of the leaving and nonleaving groups governs the reaction mechanism. The contrasting reaction mechanisms have been rationalized in terms of an intramolecular H-bonding interaction, steric acceleration, and steric inhibition.

• Carbon letters
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• 제4권1호
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• pp.1-9
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• 2003

Recently, the control of pore-characteristics of nano-porous materials has been studied extensively because of their unique applications, which includes size-selective separation, gas adsorption/storage, heterogeneous catalysis, etc. The most widely adopted techniques for controlling pore characteristics include the utilization of pillar effect by metal oxide and of templates such as zeolites. More recently, coordination polymers constructed by transition metal ions and bridging organic ligands have afforded new types of nano-porous materials, porous metal-organic framework(porous MOF), with high degree and uniformity of porosity. The pore characteristics of these porous MOFs can be designed by controlling the coordination number and geometry of selected metal, e.g transition metal and rare-earth metal, and the size, rigidity, and coordination site of ligand. The synthesis of porous MOF by the assembly of metal ions with di-, tri-, and poly-topic N-bound organic linkers such as 4,4'-bipyridine(BPY) or multidentate linkers such as carboxylates, which allow for the formation of more rigid frameworks due to their ability to aggregate metal ions into M-O-C cluster, have been reported. Other porous MOF from co-ligand system or the ligand with both C-O and C-N type linkage can afford to control the shape and size of pores. Furthermore, for the rigidity and thermal stability of porous MOF, ring-type ligand such as porphyrin derivatives and ligands with ability of secondary bonding such as hydrogen and ionic bonding have been studied.

• 마이크로전자및패키징학회지
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• 제29권3호
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• pp.13-23
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• 2022

환경이슈로 인해 전기자동차에 대한 수요 및 관심이 급증하고 있다. 전기자동차의 성능 향상에는 핵심 부품인 자동차 배터리의 성능향상, 그리고 배터리 접합기술의 발전이 수반되어야 한다. 알루미늄 합금은 전기자동차 산업에서 가장 폭넓게 사용되는 금속이며, 알루미늄 접합은 전기자동차 이차전지를 구성하는 모든 공정에서 이용된다. 따라서 본 논문에서는 알루미늄, 알루미늄 합금의 특성과 다양한 알루미늄 접합 기술에 대한 지식을 기반으로, 차량용 이차전지에서 이용되는 주요한 접합기술과 차세대 접합기술을 검토한다. 또한 그 과정에서 접합이 이용되는 자동차 이차전지 셀의 구조, '셀-모듈-팩'의 집적 순서와, 접합 기술이 요구하는 다양한 환경적 조건들을 설명한다.

• 대한소아치과학회지
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• 제32권4호
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• pp.595-603
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• 2005

와동 형성시 박테리아에 감염된 상아질이나 법랑질을 완전히 제거하지 않는 것은 수복학적 측면에서 볼 때 잠재적 문제점이 된다. 수복물 하방에서의 박테리아의 활동에 의해 술후 과민반응, 치수의 염증. 이차 우식 등이 진행될 수 있다. 와동세척제는 와동 형성 후 잔존 박테리아의 제거를 위해 효과적으로 사용될 수 있지만 상아세관에 잔유물을 남겨 상아질 결합제와 치질간의 긴밀한 결합을 방해하여 미세누출을 증가시키고 결합강도를 약화시킬 가능성이 있다. 본 연구는 2% 클로르헥시딘을 함유하는 와동 세척제인 $Consepsis^{(R)}$(Ultradent, USA)가 $Adper^{TM}$ $Scotchbond^{TM}$ Multi-Purpose(3M ESPE, USA), $Adper^{TM}$ Single Bond(3M ESPE, USA), $Adper^{TM}$ $Prompt^{TM}$ $L-Pop^{TM}$(3M ESPE, USA)의 결합에 미치는 영향을 평가하기 위하여 발거된 제 3대구치 120개를 이용하여 $Consepsis^{(R)}$ 와동 세척제를 사용한 군과 사용하지 않은 군으로 나누어 전단결합강토 측정과 수복물 변연에 나타나는 미세누출 정도를 색소 침투 평가 방법으로 분석함으로써 다음과 같은 결론을 얻었다. 1. $Consepsis^{(R)}$ 와동 세척제의 사용 유무는 $Adper^{TM}$ $Scotchbond^{TM}$ Multi-Purpose, $Adper^{TM}$ Single Bond, $Adper^{TM}$ $Prompt^{TM}$ L-Pop의 전단결합강토에 있어 통계학적으로 유의한 차이를 보이지 않았다(p>0.05). 2. $Consepsis^{(R)}$와동 세척제의 사용 유무는 $Adper^{TM}$ $Scotchbond^{TM}$ Multi-Purpose, $Adper^{TM}$ Single Bond, $Adper^{TM}$ $L-Pop^{TM}$ $L-Pop^{TM}$의 미세누출 양상에 있어 통계학적으로 유의한 차이를 보이지 않았다(p>0.05).

• 대한소아치과학회지
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• 제25권1호
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• pp.103-115
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• 1998

Adhesion of composite resin to tooth structure has been of tremendous signgicance in clinical dentistry. Due to the lack of adhesion between composite restorative resins and enamel and dentin, microleakage occurs at the tooth/restoration interface. This may lead to discoloration, secondary caries, marginal breakdown, postoperative sensitivity, and even pulpal pathology. According to extensive use of composite resin, every effort on improving bonding strength and reducing microleakage between a tooth and composite resin has been continued. This study was conducted to determine the difference in microleakage in enamel and dentin treated with air-abrasion, acid etching and combination when restored with composite resin. Class V cavities were prepared on 30 premolars. The specimens were divided into following groups. group 1:air-abrasion+Scotchbond Multi-purpose group 4 :air-abrasion+All-Bond 2 group 2:acid etching+Scotchbond Multi-purpose group 5 :acid etching+All-Bond 2 group 3:combination+Scotchbond Multi-purpose group 6 :combination+All-Bond 2 #combination:air-abrasion + acid etching The specimens were filled with Z-100 after application of Scotchbond Multi-purpose and All-Bond 2. Thermocycling was conducted by alternately dipping the specimens in $5^{\circ}C$ and $55^{\circ}C$ water for 30 seconds 500 times. 1% methylene blue was applied and the specimens were left for 24 hours at $37^{\circ}C$. After washing out the dye, the tooth was sectioned buccolingually along the axis. The sectioned surface was observed with stereoscope for dye penetration. The author has measured the microleakage in teeth prepared with air-abrasion, acid ethching and combination to study the difference in microleakage following different methods of tooth surface treatment and has come to following results. 1. In comparing microleakage between groups, group 1 and 4 showed statistically significant difference from group 2, 3, 5 and 6(p<0.05). There was no significant difference among group 2, 3, 5, 6(p>0.05) nor between group 1 and 4(p>0.05). 2. In comparing microleakage among tooth surface treatment methods, Air-abrasion group showed significantly more microleakage than acid etching group and combination(airabrasion + acid etching) group(p<0.05). Combination(acid etching+air-abrasion)group tended to show lesser microleakage than acid etching group, but this was not statistically significant(p>0.05). 3. In comparing microleakage between bonding agents, there was no statistically significant difference between Scotch bond Multi-purpose and All-Bond 2(p>0.05).

• 한국재료학회지
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• 제22권12호
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• pp.696-700
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• 2012

(Na, K) $NbO_3$ thick film was successfully achieved using a sol-gel coating process with the addition of polyvinylpyrrolidone (PVP) to a metal alkoxide solution. The transparent coating solution, mixed with Nb:PVP = 1:1 in a molar ration, was synthesized by evaporating the solvent to over 62.5 wt%. Additive PVP increased the viscosity of the solution so that the coating thickness could be enhanced. The thickness of the (Na, K) $NbO_3$ film assisted by PVP was ca. 320 nm at the time of deposition; this value is four times thicker than that of the sample fabricated without PVP. Also, due to PVP binding with the OH groups of the metal alkoxide, the condensation reaction in the film was suppressed. The crystalline size of the (Na, K) $NbO_3$ films assisted by PVP was ca. 15 nm smaller than that of the film fabricated without PVP. After the sintering process at $700^{\circ}C$, the (Na, K) $NbO_3$ films were mainly composed of randomly oriented (Na, K) $NbO_3$ phase of perovskite crystal structure, including a somewhat secondary phase of $K_2Nb_4O_{11}$. However, by adding PVP, the content of the secondary phase became quite smaller than that of the sample without PVP. It was thought that the addition of PVP might have the effect of restraining the loss of potassium and that PVP could hold metalloxane by strong hydrogen bonding before complete decomposition. Therefore, the film thickness of the (Na, K) $NbO_3$ films could be considerably advanced and made more crack-free by the addition of PVP.