• Bulletin of the Korean Chemical Society
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• 제24권11호
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• pp.1649-1654
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• 2003

We have investigated substituent effect on the stabilization energies, and nucleus-independent chemical shifts of pentafulvalenes and on the electronic structures of the corresponding polypentafulvalenes to design environmentally stable semiconductive or conductive polymers. Geometrical optimizations of the molecules were carried out at the density functional level of theory with B3LYP hybrid functional and 6-311+G(d) basis set. Stabilization energies were estimated using isodesmic and homodesmotic reactions. As a criterion of aromaticity nucleus-independent chemical shifts of the molecules were computed using GIAO approach. For the polymers the geometrical parameters were optimized through AM1 band calculations and the electronic structures were obtained through modified extended Huckel band calculations. It is found that strong electronwithdrawing substituents increase isodesmic and homodesmotic stabilization energies of pentafulvalene, though it does not increase the aromaticity. Nitro-substituted pentafulvalene is estimated to have stabilization energy as much as azulene. However, substitution either with electron-donating groups or with electronwithdrawing groups does not significantly affect the electronic structures of polypentafulvalene and poly (vinylenedioxypentafulvalene).

• Carbon letters
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• 제9권4호
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• pp.308-315
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• 2008

In the present study, fast isothermal stabilization processes for rayon precursor fabrics were performed at $350^{\circ}C$ and $400^{\circ}C$ within 3 minutes and the chemical and physical characteristics of the stabilized fabrics were investigated. In addition, rayon precursor fabrics were pre-treated with three different phosphorous-based flame retardants and then stabilized. The effect of flame retardants on the chemical composition, thermal shrinkage, weight change, thermal stability and XRD results was examined, comparing with those of the precursor fabrics. The result showed that the stabilization of rayon fabrics was most effective as the stabilization temperature was $350^{\circ}C$, the stabilization time was 3 min, and the pre-treatment with phosphoric acid of 1 vol%. The carbon contents of stabilized rayon fabrics were increased with increasing stabilization temperature and time, whereas the oxygen contents were decreased. Also, it is likely that the pre-treatment with phosphoric acid plays a role in retarding the change of chemical structure of rayon fabric. The XRD result was quite consistent with the result showing the effect of phosphoric acid on the chemical composition, thermal shrinkage and weight reduction of rayon fabric.

• 한국응용과학기술학회지
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• 제26권4호
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• pp.440-450
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• 2009

Metal(Zinc) soap and mixed metal(Zn/Ba) soap were synthesized with good structures and characterized by IR and H-NMR. The H-NMR spectrums of the synthesized soaps were in very good accordance with the structures proposed by earlier workers. The mixed metal soaps with various costabilizers(acid or metal content effect), which added in order to investigate the thermal stabilization effect at low and high temperature, were investigated the thermal stabilization effect. The temperature effect is relation to the metal content effect than acid effect. In case of mixed metal soap, the high thermal stabilization effect improved with increasing Barium content. As the Zinc content increase the low temperature thermal stabilization effect improved, but the high temperature thermal stabilization effect showed an opposite tendency.

• 대한화학회지
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• 제42권1호
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• pp.135-140
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• 1998

High oxygen pressures appear an important tool in Solid State Chemistry. Two main routes can be developed: (i) the stabilization of thermally unstable oxides, used as precursors, in order to open the synthesis of new materials, (ii) the stabilization of the highest oxidation states of transition metals. This paper is essentially devoted to this second research axis. The methodology developed for preparing new oxides containing Fe(Ⅴ), Ir(Ⅵ), high spin Fe(Ⅳ) and Cu(Ⅲ) is described.

• 접착 및 계면
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• 제11권1호
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• pp.15-25
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• 2010

본 연구에서는 레이온직물에 대하여 $180^{\circ}C$ 및 $200^{\circ}C$의 비교적 낮은 온도영역에서 장시간 동안 등온 안정화공정을 수행하였다. 등온 안정화공정 전과 후의 변화된 레이온직물의 중량감소율, 치수변화율, X-선 회절, 그리고 전자현미경을 사용하여 섬유 형태를 관찰한 결과, 레이온 프리커서 섬유의 화학적, 물리적 변화는 $200^{\circ}C$ 이하의 안정화온도에서도 지속적이면서 서서히 진행되는 것으로 확인되었다. 그리고 안정화공정 전에 사용한 네 종류의 화학전처리제는 레이온직물의 특성변화에 서로 다른 영향을 주는 것으로 조사되었다. 결과적으로, 주어진 안정화 조건하에서 $H_3PO_4$와 $Na_3PO_4$$는 레이온직물의 안정화 반응을 촉진시키는 역할을 하는 반면, $NH_4Cl$과 $ZnCl_2$는 안정화 반응을 더디게 하거나 지연시키는 역할을 하는 것으로 판단되었다. 또한 $350^{\circ}C$에서 행한 2차 안정화에서는 $H_3PO_4$가 상대적으로 가장 낮은 직물의 중량감소율을 보여주었으며, 난연 기능을 가지고 있는 인산이 2차 안정화 단계에서도 후속 반응을 다소 더디게 하는데 기여한 것으로 사료되었다.

• Carbon letters
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• 제12권4호
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• pp.229-235
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• 2011

Isotactic polyacrylonitrile (PAN) with triad isotacticity of 0.53, which was determined by $^{13}C$ NMR, using dialkylmagnesium as an initiator, was successfully synthesized. Isothermal treatment of iso-PAN was conducted in air at 200, 220, 250 and $280^{\circ}C$. Structural evolutions and chemical changes were studied with Fourier transformation infrared and wide-angle X-ray diffraction during stabilization. A new parameter $CNF={I_{2240cm}}^{-1}/ ({I_{1595cm}}^{-1}+f^*{I_{1595cm}}^{-1})$ was defined to evaluate residual nitrile groups. Crystallinity and crystal size were calculated with X-ray diffraction dates. The results indicated that the nitrile groups had partly converted into a ladder structure as stabilization proceeded. The rate of reaction increased with treatment temperature; crystallinity and crystal size decreased proportionally to pyrolysis temperature. The iso-conversional method coupled with the Kissinger and Flynn-Wall-Ozawa methods were used to determine kinetic parameters via differential scanning calorimetry analysis with different heating rates. The active energy of the reaction was 171.1 and 169.1 kJ/mol, calculated with the two methods respectively and implied the sensitivity of the reaction with temperature.

• 한국세라믹학회지
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• 제48권1호
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• pp.20-25
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• 2011

Since 1980's, many mines have been closed and abandoned due to the exhaustion of deposits and declining prices of international mineral resources. Because of the lack of post management for these abandoned mines, Farm land and rivers were contaminated with heavy metal ions and sludge. We studied on the solidification/stabilization of heavy metal ions, chromium ions and lead ions, using magnesia-phosphate cement. Magnesia binders were used calcined-magnesia and dead-burned magnesia. Test specimens were prepared by mixing magnesia binder with chromium ions and lead ions and activators. We analyzed the hydrates by reaction between magnesiaphosphate cement and each heavy metal ions by XRD and SEM-EDAX, and analyzed the content of heavy metal ions in the eruption water from the specimens for the solidification and stabilization of heavy metal ions by ICP. The results was shown that calcined magnesia binder is effective in stabilization for chromium ions and dead-burned magnesia binder is effective in stabilization for lead ions.

• 한국환경농학회지
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• 제37권3호
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• pp.179-188
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• 2018

BACKGROUND: Reclamation of heavy metal-contaminated agricultural fields has intensively been done to ensure the soil quality and food security. This study evaluated the efficiency and longevity of current physical and chemical approaches for heavy metal-contaminated soils. METHODS AND RESULTS: Concentrations of 0.1 N HCl-leachable trace metals of Cd, Pb, and As from the stabilizing agents-treated soils decreased by 50%, 70%, and 40%, respectively, compared to the control. Among the stabilizing agents, the $CaCO_3$ was the best for stabilization. For physical stabilization, the soil dressing reduced the concentrations of Cd, Pb, and As by 88%, 94%,and 88%, respectively, compared to the control. Moreover, the dilution of the contaminated soils decreased the metals by an average of 25.3% when compared with the control. The longevity of each stabilization method was determined by using the availability assessment of heavy metals in the soils. Results showed that the leaching methods using HCl and $NH_4NO_3$ had 120 and 32 weeks longevity, respectively. Interestingly, any stabilization efficacy was not found over the time for Cd and Pb (i.e., cation metals), whereas the stabilization efficacy of As was sharply decreased under 50% after 32 weeks. However, the change of metal concentration was not significant with the physical stabilization compared to the chemical stabilization. CONCLUSION: The stabilization methods should carefully be selected based on long-term monitoring under climate conditions.

• Korean Chemical Engineering Research
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• 제45권3호
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• pp.269-276
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• 2007

$TiO_2$ 함유 피치섬유의 최적 안정화 조건을 도출하기 위하여 $TiO_2$의 함유량을 달리하여 피치섬유를 제조한 후, 여러가지 안정화 조건에 대한 섬유의 특성 변화와 금속입자의 거동을 관찰하였다. 공기에 의한 피치섬유의 안정화시 안정화온도가 높고, $TiO_2$ 함유량이 적을수록 산화에 의한 무게증가가 컸다. 안정화된 섬유를 탄화하면 수율은 71~82 wt.% 수준인데, $TiO_2$가 활성촉매 역할을 하여 $TiO_2$의 함유량이 많을수록 탄화수율은 낮았다. 안정화 과정에서 열가소성의 피치섬유는 산소의 도입으로 카르보닐기(C=O)와 카르복실기(-COOH) 등이 형성되며 동시에 이들이 가교결합을 이루고 수소를 탈리시켜 열경화성 섬유로 전환되었다. 활성탄소섬유의 기공크기는 $TiO_2$ 함유량이 증가함에 따라 점점 커졌으며, 주사전자현미경과 투과전자현미경을 통하여 섬유의 표면과 내부에 분포된 $TiO_2$ 입자와 분포를 관찰한 결과 안정화, 탄화 및 활성화공정 중 일부 $TiO_2$가 서로 뭉침을 알 수 있었다. 최종적으로 0.5 wt.% $TiO_2$ 함유 석유계 피치섬유는 $280^{\circ}C$에서 3 hr를 최적 안정화 조건으로 제시할 수 있었다.

• 접착 및 계면
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• 제14권3호
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• pp.146-159
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• 2013

본 연구에서는 $350^{\circ}C$에서 4 min 이내로 빠르게 등온 안정화공정을 통해 얻어진 레이온직물의 화학조성, 물리적 특성, X-선 회절 패턴, 열안정성 그리고 직물 형상에 미치는 초음파세척 및 화학전처리의 영향을 조사하였다. 안정화공정 동안 레이온직물에서 발생하는 중량감소와 열수축을 줄이고 안정화반응을 촉진시키기 위하여 안정화공정 전에 레이온직물을 먼저 초음파 세척하고 $NH_4Cl$, $Na_3PO_4$, $H_3PO_4$ 및 $ZnCl_2$로 화학전처리 공정을 수행하였다. 결과는 초음파세척 및 화학전처리가 안정화된 레이온직물의 중량감소, 열수축, 미세구조 변화, 탄소함량, 열안정성, 및 직물 형상에 영향을 주었으며, 사용한 안정화시간과 화학전처리제의 종류에 의존하였다.