• Macromolecular Research
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• 제12권2호
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• pp.172-177
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• 2004

We have studied the lamella-level morphology of poly(ethylene terephthalate) (PET)/polycarbonate (PC) blends using small-angle X-ray scattering (SAXS). Measurements were made as a function of the holding time in the melt. We determined the morphological parameters at the lamellar level by correlation function analysis of the SAXS data. An increased amorphous layer thickness was identified in the blend, indicating that some PC was incorporated into the interlamellar regions of PET during crystallization. The blend also exhibits a larger lamella crystalline thickness (l$\sub$c/) than that of pure PET. A possible reason for the increase in l$\sub$c/ is that the inclusion of the PC molecules in the interlamellar regions causes an increase in the surface free energy of folding. At the early stage of isothermal crystallization, we observed a rapid drop in the value of l$\sub$c/ in the blend; this finding indicates that a relatively large fraction of secondary crystals form during the primary crystallization. In contrast, the value of l$\sub$c/ for the sample that underwent a prolonged holding time increased with time in the secondary crystallization-dominant regime; this observation suggests that the disruption of chain periodicity, which results from transesterification between the two polymers, favors the development of fringed micellar crystals that have larger values of l$\sub$c/ rather than the development of normal chain-folded crystals.

• 한국주조공학회지
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• 제15권6호
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• pp.566-573
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• 1995

In this study, the microstructural characteristics such as primary silicon, eutectic silicon, $SiC_p$ dispersion behavior, compound amount and Si solubility in $Al/SiC_p$ composite fabricated by the squeeze casting under various conditions were investigated systematically. As applied pressure(MPa) increases, cooling rate and compound amount are increased. In gravity casting, the cooling rate of hypereutectic composite is slower than of hypoeutectic composite by exothermic reaction of primary Si crystallization. But the cooling rate of hypereutectic composite is faster than that of hypoeutectic composite fabricated by same applied pressure, because amount of primary Si crystallization in hypereutectic composite was decreased, on the contrary, primary ${\alpha}-Al$ in hypoeutetic composite was increased due to increase of Si solubility in matrix by applied pressure. The crystalized primary silicon in hypereutectic composite fabricated by squeeze casting become more fine than that in non-pressure casting This is because mush zone became narrow due to increase of Si content of eutectic composition by pressure and time for growth of primary silicon got shorter according to applied pressure. It is turned out that eutectic temperature and liquidus are decreased by the increasing of squeeze pressure in all the composite due to thermal unstability of matrix owing to increasing of Si solubility in matrix by the increasing of applied pressure, as indicated in thermal anaiysis(DSC) results.

• 한국세라믹학회지
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• 제39권4호
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• pp.420-426
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• 2002

가열가수분해반응에 의하여 제조된 구형의 $ZrO_2$ 겔을 수열결정화시켜 순수한 $ZrO_2$ 분말과 $Y2_O_3$, CaO 등 상안정화제가 도핑된 $ZrO_2$ 분말을 합성하였다. 합성된 $ZrO_2$ 결정분말들은 평균 10nm 크기의 일차 입자들로 구성된 이차입자들이었다. 이차입자의 평균 크기는 $0.4{\mu}m$였고, 수열결정화과정에서 겔의 구형 형상이 그대로 유지되었으며 일차 입자들 사이에는 약한 응집으로 존재하였다. 입자모양, 크기, 상분율, 도핑된 분율 등을 SEM, TEM, XRD, ICP로 연구하였고 구형 겔의 수열결정화기구를 논의하였다.

• Macromolecular Research
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• 제11권1호
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• pp.25-35
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• 2003

A series of random poly(ethylene-co-1,4-butylene terephthalate)s (PEBTs), as well as poly(ethylene terephthalate) (PET) and poly(1,4-butylene terephthalate) (PBT), were synthesized by the bulk polycondensation. Their composition, molecular weight, and thermal properties were determined. All the copolymers are crystallizable, regardless of the compositions, which may originate from both even-atomic-numbered ethylene terephthalate and butylenes terephthalate units that undergo inherently crystallization. Non-isothermal crystallization exotherms were measured over the cooling rate of 2.5-20.0 K/min by calorimetry and then analyzed reasonably by the modified Avrami method rather than the Ozawa method. The results suggest that the primary crystallizations in the copolymers and the homopolymers follow a heterogeneous nucleation and spherulitic growth mechanism. However, when the cooling rate increases and the content of comonomer unit (ethylene glycol or 1,4-butylene glycol) increases, the crystallization behavior still becomes deviated slightly from the prediction of the modified Avrami analysis, which is due to the involvement of secondary crystallization and the formation of relatively low crystallinity. Overall, the crystallization rate is accelerated by increasing cooling rate but still depended on the composition. In addition, the activation energy in the non-isothermal crystallization was estimated.

• 한국세라믹학회지
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• 제50권6호
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• pp.434-438
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• 2013

Monodispersed 3Y-$ZrO_2$ spherical agglomerates were synthesized by thermal hydrolysis process followed by crystallization processes (hydrothermal treatment and calcination). The crystallization process affected the properties of the final particles, such as the primary particle size, the agglomeration state, and the fraction of $ZrO_2$ monoclinic phase. The hydrothermal treated spherical particles were porous microstructures (weak agglomerates) composed of small primary particles with a size of 14 nm, but the calcined spherical particles had a dense microstructure due to the hard aggregation between primary particles. While the calcined particles had a low green density due to the hard aggregation, hydrothermal treated ones were soft agglomerates and had a deflection point at 50 MPa due to the rearrangement of secondary spherical particles and the filling of the interstices with the primary particles. Finally, the green density of hydrothermally treated $ZrO_2$ particles was 58% at 200 MPa.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.375-375
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• 2007

In the conventional crystallization method, thepoly-Si TFTs show poor device-to-device uniformity because of the random location of the grain boundaries. However, our new crystallization method introduced in this paper employed substrate-embedded seeds on the highly ordered anodic alumina template to control both the location of seeds and the number of grain boundaries intentionally. In the process of excimer laser crystallization (ELC), a-Si film deposited on the anodic alumina by low pressure chemical vapor deposition (LPCVD) is transformed into fine poly-Si grains by explosive crystallization (XC) prior to primary melting. At the higher energy density, the film is nearly completely melted and laterally grown by super lateral growth (SLG) from remained small part of the fine poly-Si grains as seeds at the Si/anodic alumina interface. Resultant grain boundaries have almost linear functions of the number of seeds in concavities of anodic alumina which have a constant spacing. It reveals the uniformity of. device can be enhanced prominently by controlling location and size of pores which contains fine poly~Si seeds under artificial anodizing condition.

• 자원환경지질
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• 제34권6호
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• pp.617-625
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• 2001

Skaergaard 암체는 광범한 in situ 화성분화작용을 격은 층상관입암의 대표적인 예로 널리 알려져 있다. 따라서 이 암체는 폐쇄계에서 미량원소변이를 modeling 할 수 있는 적지가 될 것이다. 그러나, 기존의 연구에 의하면 본 암체의 전암 및 광물의 회토류는 폐쇄계로서의 예상된 경향을 보이지 않는다(Haskin and Haskin, 1968; Paster et al., 1974). 발표된 분배계수, 공존광물들의 mode,그리고 전암 및 광물의 미량원소함량을 사용한 미량원소modeling에 의하면 Skaergaard 암체의 희토류는 분화후기에 일어난 광범한 인회석 결정작용에 크게 영향을 받았음을 보여준다. 미량원소modeling은 Upper Border Series에서 간헐적으로 나타나는 인회석이 기존에 주장되어 온 바와 같은 liquldus상이 아니라 진화하는 magma의 미량원소함량에는 영향을 끼칠 수 없는 interstitial phase임을 시사한다. 분화작용 말기에 Skaerganrd 마그마가 대류를 멈추거나 소규모로 대류를 할 때, 마그마 암장의 상부에 축적되는 휘발성분에 기인한 증가된 $PH_2$O가 인회석이 UBS에서 정출 되는 것을 방해하였을 것이다. 이와 같은 인회석의 특성을 고려해서 Skaergaard분화작용을 modeling하면 희토류는 폐쇄계로서의 예상된 경향을 따른다 이와 같은 결과는 최종 20% 분화작용기간 중에 양적으로 상당한 양의 마그마의 주입이나 분출을 수반하는 그 어떤 Skaergaard 암체의 분화model도 배격한다.

• 폴리머
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• 제24권5호
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• pp.656-663
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• 2000

용융방사에 의한 선형 폴리락트산(polylactic acid, PLLA) 섬유가공에 있어서 가공 시 PLLA에 가해진 열 이력이 섬유의 기계적 특성과 결정화도에 미치는 영향을 살펴보았다. PLLA의 가공 시 가해진 열 이력에 의하여 PLLA의 분자량이 감소하며 이러한 분자량의 감소는 PLLA 섬유의 배향도 감소와 결정화도의 감소를 유발시킨다. 그 결과, PLLA 섬유의 인장강도와 탄성계수가 감소하며 신율이 증가됨을 확인할 수 있었다. PLLA의 용융방사에서 발현된 결정화는 PLLA의 느린 결정화 속도에 의하여 thermal induced crystallization보다는 stress induced crystallization에 기인함을 알 수 있었다. PLLA 섬유를 열처리하였을 경우, 상대적으로 분자량이 작고 열 이력을 받은 PLLA로 만들어진 섬유가 열 이력을 받지 않은 PLLA로 만들어진 섬유보다 결정화도가 높음을 확인하였다. 이로 보아 열처리에 의한 결정화도의 증가는 stress, Induced crystallization보다는 thermal induced crystallization에 기인함을 알 수 있었다.

• 한국주조공학회지
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• 제22권5호
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• pp.257-264
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• 2002

Effects of Ca content on the refinement of primary Si of Aluminum B390 alloy have been examined. Ca was found to have an effect on the refinement of primary Si particle. Primary Si particle size has been refined as Ca content of the melts decreased and cooling rate increased. A control of Ca content by the addition of $CuCl_2$ to the melt was the most efficient in the refinement of primary Si particles. The minimum size of primary Si particles in this study was $15.0\;{\mu}m$ when a residual content of Ca element in the alloy was 5ppm, Primary Si particle size was refined as primary Si crystallization temperature increased, which was attributed to the decrease of Ca content in the melts.

• 한국환경과학회지
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• 제8권2호
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• pp.227-231
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• 1999

This study was conducted to investigate the removal characteristics of $PO_4^{3-}-P$ contained in livestock wastewater using waste concrete. With small particle size, increased dosage and temperature of water, $PO_4^{3-}-P$ was well removed by waste concrete.$PO_4^{3-}-P$ was removed by adsorption reaction in low pH of the primary phase, but the crystallization reaction predominated for increasing pH with passed time. As a result of adapting the adsorption isotherm equation, $PO_4^{3-}-P$ removal was more affected by the crystallization reaction than the adsorption reaction. In the SEM micrograph, there was no evident change on the waste concreter surface. Particle size was plate-phase before reaction but appeared a dense form to progress in the crystallization reaction.