• Applied Chemistry for Engineering
• /
• v.10 no.3
• /
• pp.427-431
• /
• 1999

Copolyester resins for the coil coating process of aluminium and steel strip were synthesized and their thermal properties, molecular weight and solvent solution characteristics were examined. Copolyesters were obtained by two step reactions. The first step was to prepare bishydroxyethyl terephthalate (BHET), bishydroxyneopentyl terephthalate (BHNPT), bishydroxyethyl isophthalate (BHEI), bishydroxyneopentyl sebacate (BHNPS), bishydroxyneopentyl adipicate (BHNPA) and bishydroxyethyl adipicate (BHEA) oligomers by esterification reactions. The second step was the polycondensation reaction utilizing those oligomers to obtain relatively high molecular weight copolyesters (Mw = 30,000~59,000 g/mol) as measured by GPC. These copolyesters were amorphous polymers as shown by DSC without $T_m$ peaks probably due to the kink structure introduced by BHET oligomer and relatively large free volume by bulky BHNPT and BHNPS oligomers. The copolyester samples with half of BHET oligomer substituted by BHNPT while keeping BHEI (0.3 mole) and BHNPS (0.1 mole) ratio constant showed glass transition temperature above $40^{\circ}C$ and good solubility in toluene both at low ($-5^{\circ}C$) temperature and room temperature.

• Journal of the Korean Chemical Society
• /
• v.40 no.5
• /
• pp.295-301
• /
• 1996

A series of solid solutions of the $CaGa_1-xFexO_3-y$ system with the compositions of x=0.25, 0.50, 0.75, and 1.00 has been prepared at $1150^{\circ}C$ under an atmospheric air pressure. The structure, nonstoichiometric chemical formula, and the distribution of cations for the solid solutions are determined by X-ray diffraction analysis, Mohr salt titration, Mossbauer spectroscopic analysis. Their physical properties are discussed with electrical conductivity and magnetic measurements. The crystal system of all the compositions is a brownmillerite orthorhombic system from the X-ray diffraction analysis and the reduced lattice volume increases linearly with x value except that of the composition of x=0.25. All the solid solutions do not contain $Fe^{4+}$ ion and the mole number of oxygen vacancies or y value is 0.50 from Mohr salt analysis. The oxidation state of Fe ion, the coordination state, the structure change in the Brownmillerite-type structure, and the distribution of $Ga^{3+}$ and $Fe^{3+}$ ions are discussed with Mossbauer spectroscopic analysis. The electrical conductivity increases and activation energy decreases, as x value increases. The traditional semiconducting property of this system is described in terms of band theory. The compositions of x=0.50∼1.00 show a thermal magnetic hysteresis in the magnetic measurement with the cooling conditions, which is discussed in terms of the space group and Dzyaloshinsky-Moriya interaction.

• Journal of the Korean Chemical Society
• /
• v.55 no.3
• /
• pp.412-417
• /
• 2011

A series of homobinuclear complexes of the type [$M_2L(NO_3)_n(H_2O)_m$] where M=$UO_2$(VI), ZrO(IV), Th(IV); L=3-benzylidine-imino-5-p-sulphonamido phenyl azo-2-thiohyatoin(bispt), 3-furfurylidine-imino-5-p-sulphonamido phenyl azo-2-thiohydantoin(fispt),3-pyridyl-2'-methylene-imino-5-p-sulphonamido phenyl azo-2-thiohydantoin(pmispt) and 3-thienyl-2'-methylene-imino-5-p-sulphoanamido phenyl azo-2-thiohydantoin(tmispt); n=8 for Th(IV) and 4 for others, m=4 for bispt and 3 for others have been synthesized and characterized on the basis of elemental analysis, thermal analysis, molar conductance, magnetic moment and spectroscopic data (IR, electronic and $^1H$-NMR). In the light of this information, the ligands can be visualized as tetradentate co-ordinating through azomethine nitrogen, carbonyl oxygen to one metal centre where as azo nitrogen and thioimido nitrogen to the other metal centre yielding homo binuclear complexes of the above composition. The fungi toxicity of the ligands & their zirconyl complexes against some fungal pathogen has been studied.

• Journal of the Korean Chemical Society
• /
• v.54 no.4
• /
• pp.395-401
• /
• 2010

A series of macrocyclic complexes of the type [M(L/L')$(NO_3)_n$].$mH_2O$ and [VO(L/L')($SO_4$)].$2H_2O$, where L/L' is a Schiff base "3,4,10,11-tetraphenyl/tetramethyl-1,2,5,6,8,9,12,13-octaaza cyclotetradeca-2,4,9,11-tetraene-7,14-dithione" derived from thiocarbohydrazide (TCH), benzilmonohydrazone (BMH)/diacetylmonohydrazone (DMH) and carbon disulphide, M = $UO_2$ (VI), Th(IV) and ZrO(IV), n = 2, 4, m = 2, 3, have been synthesized via metal ion template methods. The complexes are characterized on the basis of elemental analysis, thermal analysis, molar conductivity, magnetic moment, electronic, infrared and $^1H$-NMR spectral studies. The ESR and cyclic voltammetry studies of the vanadyl complexes have been carried out. The results indicate that the VO(IV) ion is penta-coordinated yielding paramagnetic complexes; $UO_2$(VI) and ZrO(IV) ions are hexacoordinated where as Th(IV) ion is octa-coordinated yielding diamagnetic complexes of above composition.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2012.05a
• /
• pp.83-83
• /
• 2012

금속 실리사이드는 낮은 비저항, 실리콘과의 좋은 호환성 등으로 배선 contact 물질로 널리 연구되고 있다. 특히 $CoSi_2$는 선폭의 축소와 관계없이 일정하고 낮은 비저항과 열적 안정성이 우수한 특성 등으로 배선 contact 물질로 활발히 연구되고 있다. 금속 실리사이드를 실리콘 평면기판에 형성시키는 방법으로는 열처리를 통한 금속박막과 실리콘 기판 사이에 확산작용을 이용한 SALICIDE (self-algined silicide) 기술이 대표적이며 CoSi2도 이와 같은 방법으로 형성할 수 있다. Co 박막을 증착하는 방법에는 물리적 기상증착법 (PVD)과 유기금속 화학 증착법 등이 보고되어있지만 최근 급격하게 진행 중인 소자구조의 나노화 및 고 단차화에 따라 기존의 증착 기술은 낮은 단차 피복성으로 인하여 한계에 부딪힐 것으로 예상되고 있다. ALD(atomic layer deposition)는 뛰어난 단차 피복성을 가지고 원자단위 두께조절이 용이하여 나노 영역에서의 증착 방법으로 지대한 관심을 받고 있다. 앞선 연구에서 본 연구진은 CoCp2 전구체과 $NH_3$ plasma를 사용하여 Plasma enhanced ALD (PE-ALD)를 이용한 고 순도 저 저항 Co 박막 증착 공정을 개발 하고 이를 SALICIDE 공정에 적용하여 $CoSi_2$ 형성 연구를 보고한 바 있다. 하지만 이 연구에서 PE-ALD Co 박막은 플라즈마 고유의 성질로 인하여 단차 피복성의 한계를 보였다. 이번 연구에서 본 연구진은 Co(AMD)2 전구체와 $NH_3$, $H_2$, $NH_3$ plasma를 반응 기체로 사용하여 Thermal ALD(Th-ALD) Co 및 PE-ALD Co 박막을 증착 하였다. 고 단차 Co 박막의 증착을 위하여 Th-ALD 공정에 초점을 맞추어 Co 박막의 특성을 분석하였으며, Th-ALD 및 PE-ALD 공정으로 증착된 Co 박막의 단차를 비교하였다. 연구 결과 Th-ALD Co 박막은 95% 이상의 높은 단차 피복성을 가져 PE-ALD Co 박막의 단차 피복성에 비해 크게 향상되었음을 확인하였다. 추가적으로, Th-ALD Co 박막에 고 단차 박막의 증착이 가능한 Th-ALD Ru을 capping layer로 이용하여 CoSi2 형성을 확인하였고, 기존의 PVD Ti capping layer와 비교하였다. 이번 연구에서 Co 박막 및 $CoSi_2$ 의 특성 분석을 위하여 X선 반사율 분석법 (XRR), X선 광전자 분광법 (XPS), X선 회절 분석법 (XRD), 주사 전자 현미경 (SEM), 주사 투과 전자 현미경 (STEM) 등을 사용하였다.

• Polymer(Korea)
• /
• v.27 no.5
• /
• pp.470-476
• /
• 2003

In order to obtain high refractive plastic materials, 1,2 -ethylenedisulfanylbis(2-mercaptomethyl-1-ethanthiol) (ESTT) was newly prepared in good yield by the reaction of 1,2-ethylenedisulfanylbis(2-bromomethyl-1-ethanthiol) (ESTB) with thiourea followed by hydrolysis using an aqueous ammonia solution and characterized by $^1$H-NMR (-SH at 1.7 ppm), $\^$13/C-NMR(-CH$_2$SH at 28.4 ppm) and FT-IR (-SH at 2540 cm$\^$-1/) spectroscopy, etc. Polythiourethanes (PTU) were obtained from the combinations of ESTT with each of 4,4＇-methylenebis(phenylisocyanate) (MDI), tolyene 2,4-diisocyanate (TDI), isophorone diisocyanate (IPDI), mxylene diisocyanate (XDI), and 1,6-diisocyanatohexane (HMDI) in the presence of dibutyltin dilaurylate as a catalyst, in a casting mold, and characterized by FT-IR (existence of N=C=O) spectroscopy and elemental analyzer (sulfur content). Accordingly, their thermal, mechanical and optical properties were investigated by using DSC, TGA, hardness tester and refractometer: both the melting point on DSC and crystallinity on X -ray diffraction (XRD) for specimens of PTUs were not observed. PTUs with T$\_$g/s above 110 $^{\circ}C$ showed good hardness (Shore D) in the range of 86 to 89. Thermal stabilities of PTUs obtained by using ESTT and each of diisocyanates containing aromatic rings were especially good. Also, the optical transmittances of amorphous PTUs through UV-visible source in the range of 400 to 600 nm were good. PTUs showed refractive indexes above 1.60, and their refractive indexes gradually increased with increase of sulfur contents.

• Applied Chemistry for Engineering
• /
• v.7 no.3
• /
• pp.597-604
• /
• 1996

Resin-type neutron shielding materials, KNS-115A, 115B and 115C have been fabricated to be used for spent fuel shipping cask. The base material is epoxy resin, and polypropylene, aluminium hydroxide and boron carbide are added. These shielding materials offer good fluidity at processing, which makes it possible to apply this resin shield to complicated geometric shapes such as shipping cask. Several measurements were made for the shielding materials to evaluate the shielding property, combustion characteristics, fire resistance, thermal and mechanical properties. The neutron shielding ability of the shielding materials is estimated to be better than that of foreign's shielding material, NS-4-FR, due to higher hydrogen atomic density. Other properties of the shielding materials are as follows: Onset temperatures; $267{\sim}270^{\circ}C$, thermal conductivities; $0.62{\sim}0.72W/m{\cdot}K$, combustion characteristics; <$800^{\circ}C$, ATB(average time of burning); <5sec, AEB(average extent of burning) ; <5mm, tensile strengths; $2.3{\sim}3.0kg/mm^2$, compressive strengths; $5.3{\sim}13.3kg/mm^2$, flexural strengths; $4.4{\sim}5.4kg/mm^2$.

• Clean Technology
• /
• v.28 no.4
• /
• pp.293-300
• /
• 2022

The remarkable mechanical, electrical, and thermal properties of graphene have recently sparked tremendous interest in various research fields. One of the most promising methods to produce large quantities of graphene dispersion is liquid-phase exfoliation (LPE) which utilizes ultrasonic waves or shear stresses to exfoliate bulk graphite into graphene flakes that are a few layers thick. Graphene dispersion produced via LPE can be transformed into graphene ink to further boost graphene's applications, but producing high-quality graphene more economically remains a challenge. To overcome this shortcoming, an advanced LPE process should be developed that uses relatively cheap natural graphite as a graphene source. In this study, a flow-LPE process was used to exfoliate natural graphite to produce graphene that was three times cheaper and seven times larger than synthetic graphite. The optimal exfoliation conditions in the flow-LPE process were determined in order to produce high-quality graphene flakes. In addition, the structural and electrical properties of the flakes were characterized. The electrical properties of the exfoliated graphene were investigated by carrying out an ink formulation process to prepare graphene ink suitable for inkjet printing, and fabricating a printed graphene pattern. By utilizing natural graphite, this study offers a potential protocol for graphene production, ink formulation, and printed graphene devices in a more industrial-comparable manner.

• Journal of the Korean Magnetics Society
• /
• v.15 no.3
• /
• pp.167-171
• /
• 2005

Detailed aspects of the charge disproportionation (CD) transition for a polycrystalline $La_{1/3}Sr_{2/3}FeO_{2.96}$ were studied with the X-ray diffraction, $M\ddot{o}ssbauer$ spectroscopy, and SQUID magnetometer. The crystal structure was found to be rhombohedral with a space group R/3c. The lattice parameters were $a_R=5.4874\;\AA,\;and\;a_R=60.07^{\circ}$, respectively. $M\ddot{o}ssbauer$ spectra were taken within a wide range of temperature from 4.2 K up to room temperature. In the low temperature region, the spectra were comprised of two superimposed sextets which originated from $Fe^{3+}\;and\;Fe^{5+}$, respectively. This was the antiferromagnetic mixed valence state produced by the charges disproportionated into two different species. In the high temperature region, however, only a singlet from $Fe^{3.6+}$ was observed, indicating that it was a paramagnetic averaged valence state. The CD transition occurred in the temperature range from 175 K to 200 K, in which the two phases coexisted. The origin for the CD transition was explained by the thermally generated fast hopping of electrons. Hysteresis loop showed that there existed a strong antiferromagnetic interaction among magnetic ions. As the temperature increased thru the CD transition temperature, it was very likely that the interaction between $Fe^{3+}\;and\;Fe^{5+}$ was replaced by a more stronger one.

• Journal of the Korean Ceramic Society
• /
• v.34 no.1
• /
• pp.102-108
• /
• 1997

ZrO2 powders stabilized with Y2O3 and CeO2 of various compositions were prepared by the coprecipitation of water-soluble ZrOCl2.8H2O, YCl3.6H2O and Ce(NO3)3.6H2O, and their compacts were pressurelessly sintered at 1400 and 150$0^{\circ}C$ for 2hrs in air. 2mol% Y2O3-ZrO3 showed the most superior strength (1003MPa) and microhardness (12.6GPa), while 10 mol%CeO2-ZrO2 had the hightest toughness (13.3 MPa.m1/2) after sintering at 140$0^{\circ}C$. The addition of Y2O3 into Y2O3-ZrO3 decreased mean grain size and increased strength and hardness but decrease toughness. On the other hand, the addition of CeO2 into Y2O3-ZrO2 enhanced the stability of tetragonal phase during low-temperature aging for a long time under hydrothermal atmosphere.