• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 1998년도 가을 학술발표회논문집
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• pp.61-65
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• 1998

Epoxy resins are currently one of the most widely used thermoset polymers. Applications on epoxy-based materials range from common to structural adhesives as well as to matrix materials for high performance composites. The outstanding versatility of this resin can be related to the reactivity of the epoxy group, which can be opened by a large number of different chemical compounds, such a aliphatic and aromatic amines, anhydrides and poly-amides. (omitted)

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 1998년도 가을 학술발표회논문집
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• pp.98-101
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• 1998

Segmented polyurethane elastomers are an important class of polymeric materials consisting of thermodynamically incompatible hard and soft segments. Due to the chemical structural difference between the hard and soft segments, a microphase separation occurs, consisting of crystalline hard domains and amorphous soft domains. (omitted)

• 한국응용과학기술학회지
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• 제15권3호
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• pp.13-19
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• 1998

This study was carried out to investigate characteristics and Pb(II) removal effect of natural Muan, Seosan, Kangjin clays in the batch mode test to develope the low-priced treatment agent of wastewater which contain heavy metals in order structural, optical properties and chemical compositions of natural clays from domestic have been investigated to have high specific surface area and have minerals such as $SiO_2$ and $Al_2O_3$. As a result, removal effects of Pb(II) ions on clays were reached at equilibrium in aqueous solutions by stirring about 20minutes. The removal effect of Pb(II) ions was best for Seosan clay than Muan or Kangjin clays in terms of fixed time. The results show the possibility of continuous treatment system of wastewater which contain heavy metals by using natural clays from domestic.

• 공업화학
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• 제10권4호
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• pp.615-619
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• 1999

스테아릴트리메틸암모늄 이온만 삽입된 몬모릴로나이트는 나노복합재료를 형성하지 못하였다. 그러나 스테아릴트리메틸암모늄과 m-페닐렌디암모늄 염이 함께 삽입된 몬모릴로나이트와 diglycidyl ether of bisphenol A(DGEBA)와 가열하면 중합반응이 일어나 폴리에테르-몬모릴로나이트의 나노복합재료를 합성하였다. 합성한 나노복합재료를 XRD과 TEM을 통하여 에폭시 메트릭스내의 몬모릴로나이트의 실리케이트층이 한층 균일하게 분산되어 있음을 확인하였다. 그리고 각각의 실리케이트 층간거리는 $250{\sim}500{\AA}$ 정도였다.

• Transactions on Electrical and Electronic Materials
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• 제7권1호
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• pp.36-41
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• 2006

In this paper, the time evolution of undoped GaN epilayers on a low-temperature GaN buffer layer grown on c-plane sapphire at a low pressure of 300 Torr was studied via a two-step growth condition in a horizontal MOCVD reactor. As a function of the growth time at a high-temperature, the surface morphology, structural quality, and optical and electrical properties were investigated using atomic force microscopy, high-resolution x-ray diffraction, photoluminescence, and Hall effect measurement, respectively. The root-mean-square roughness showed a drastic decrease after a certain period of surface roughening probably due to the initial island growth. The surface morphology also showed the island coalescence and the subsequent suppression of three-dimensional island nucleation. The structural quality of the GaN epilayer was improved with increasing growth time considering the symmetrical (002) and asymmetrical (102) rocking curves. The variations of room-temperature photoluminescence, background carrier concentration, and Hall mobility were measured and discussed.

• Advances in concrete construction
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• 제9권1호
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• pp.9-22
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• 2020

The present work looks at the possibilities of recycling more than once demolished concrete as coarse aggregates, to produce new concrete. Different concrete mixes were made with substitutions of 50%, 75% and 100% of recycled concrete aggregates respectively as coarse aggregates. The physico-mechanical characterization tests carried out on the recycled concrete aggregates revealed that they are suitable for use in obtaining a structural concrete. The resulting concrete materials had rheological parameters, compressive strengths and tensile strengths very slightly lower than those of the original concrete even when 100% of two cycles recycled concrete aggregates were used. The durability of the recycled aggregates concrete was assessed through water permeability, water absorption and chemical attacks. The obtained concretes were thought fit for use as structural materials. A linear regression was developed between the strength of the material and the number of cycles of concrete recycling to anticipate the strength of the recycled aggregates concrete. From the results, it appear clear that recycling demolished concrete represents a valuable resource for aggregates supply to the concrete industry and a the same time plays a key role in meeting the challenge for a sustainable development.

• Bulletin of the Korean Chemical Society
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• 제23권2호
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• pp.241-244
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• 2002

Using ab initio method, we have studied the structural stabilities, the electronic structures and properties between the two isomers with $C_{2h}$ and $C_{2v}$ symmetry of AlN four-membered-ring single precursors $[Me_2AlNHR]_2$ (R = Me, $^iPr$, and $^iBu$). In the viewpoint of bond lengths in optimized structures, the N-C bonds are considerably affected by the change of the R groups bonded to nitrogen, but the bonding characters of the Al-N and Al-C bonds are little affected. Also the structural stabilities between the two isomers with $C_{2h}$ and $C_{2v}$ symmetry by using Hartree-Fock (HF) and the second order Moeller-Pleset (MP2) calculations agree well with the experimental results for the relative stability of bis(dimethyl- m-isopropylamido-aluminum) (BDPA) and bis(dimethyl- m-t-butylamido-aluminum) (BDBA), while the semiempirical AM1 and PM3 calculations for BDPA were reverse. Thus, our results may aid in designing an optimum precursor for a given process by explaining the experimental results through the elimination of the R groups bonded to nitrogen.

• Bulletin of the Korean Chemical Society
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• 제32권8호
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• pp.2623-2627
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• 2011

We investigated the surface structure and wetting behavior of octaneselenolate self-assembled monolayers (SAMs) on Au(111) formed in a 50 ${\mu}M$ ethanol solution according to immersion time, using scanning tunneling microscopy (STM) and an automatic contact angle (CA) goniometer. Closely-packed, well-ordered alkanethiol SAMs would form as the immersion time increased; unexpectedly, however, we observed the structural transition of octaneselenolate SAMs from a molecular row phase with a long-range order to a disordered phase with a high density of vacancy islands (VIs). Molecularly resolved STM imaging revealed that the missing-row ordered phase of the SAMs could be assigned as a $(6{\times}{\surd}3)R30^{\circ}$ superlattice containing three molecules in the rectangular unit cell. In addition, CA measurements showed that the structural order and defect density of VIs are closely related to the wetting behaviors of octaneselenolate SAMs on gold. In this study, we clearly demonstrate that interactions between the headgroups and gold surfaces play an important role in determining the physical properties and surface structure of SAMs.

• Structural Engineering and Mechanics
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• 제58권1호
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• pp.143-161
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• 2016

Utilization of mineral and chemical admixtures in concrete technology has led to changes in the formulation and mix design in recent decades, which has, in turn, made the concrete stronger and more durable. Lightweight concrete is an excellent solution in terms of decreasing the dead load of the structure, while self-compacting concrete eases the pouring and removes the construction problems. Combining the advantages of lightweight concrete and self-compacting concrete is a new and interesting research topic. Considering its light weight of structure and ease of placement, self-compacting lightweight concrete may be the answer to the increasing construction requirements of slender and more heavily reinforced structural elements. Twenty one laboratory experimental investigations published on the mix proportion, density and mechanical properties of lightweight self-compacting concrete from the last 12 years are analyzed in this study. The collected information is used to investigate the mix proportions including the chemical and mineral admixtures, light weight and normal weight aggregates, fillers, cement and water. Analyzed results are presented in terms of statistical expressions. It is very helpful for future research to choose the proper components with different ratios and curing conditions to attain the desired concrete grade according to the planned application.

• 한국진공학회지
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• 제11권2호
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• pp.97-102
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• 2002

유기금속화학기상증착방법 (metal-organic chemical vapor deposition : MOCVD)을 이용하여 실리콘 (100) 기판위엔 ZnO막을 증착하였다. 공정온도 ($250^{\circ}C$~$400^{\circ}C$)와 Ar과 $O_2$가스의 유량 비 변화에 따른 ZnO막의 특성변화를 조사하였다. 막의 결정성은 공정온도가 증가함에 따라 향상되었으며 $400^{\circ}C$에서 $0.4^{\circ}$의 반치폭(full width at half maximum : FWHM)을 얻었다. 공정온도 변화에 따른 표면 평활도(surface smoothness)변화는 결정성과 반대의 경향성을 보였다.