• 폴리머
• /
• 제27권2호
• /
• pp.120-128
• /
• 2003

불포화 폴리에스터(UPE), 비닐에스터(VE) 및 그 블렌드의 경화 거동에 미치는 촉매 반응촉진제 그리고 블렌드 조성의 영향을 시차주사열량(DSC) 분석법을 이용하여 조사하였다. 이들 수지의 DSC 열분석도는 각 변수에 크게 의존하였다. 115$^{\circ}C$에서 나타나는 작은 발열 피크는 주로 UPE/VE 블렌드를 구성하고 있는 UPE 성분에 의한 것이며, 134~138$^{\circ}C$ 사이에서 나타나는 큰 피크는 주로 VE 성분에 기인한 것이다. 또한 각 블렌드를 고온 18$0^{\circ}C$와 수십초의 빠른 경화 조건에 노출시킨 후 측정한 DSC 열분석도 결과는 고속에서 블렌드의 열성형 공정을 이해하는데 유용한 정보를 제공하여 준다. UPE에 대한 이전의 연구 결과와 유사하게, 수지 흐름시간의 측정 결과는 UPE/VE 블렌드에서도 세 영역치 경화 단계가 존재하고 있음을 제시해주었다. 즉, 유도단계, 전이단계, 거대 젤 형성단계, 경화된 UPE의 열안정성과 굴곡 특성은 UPE에 VE측 블렌딩함으로써 조성비에 따라 두드러지게 향상되었다.

• 한국세라믹학회지
• /
• 제31권10호
• /
• pp.1218-1230
• /
• 1994

In manufacturing process of porous glass-ceramics by the filler method, the sintering behaviour of crystallizable glass powder mixed with various salts was studied and also the effects of precipitated crystal phases on the properties of porous glass-ceramics were investigated. Fine-grained crystallizable glass powder was homogeneously mixed with various slat having grain size 100~200 ${\mu}{\textrm}{m}$ and sintered for densification. After washing out the inorganic salt with distilled water, the porous sintered body was heat treated additionly for crystallization. The MgO-Al2O3-SiO2 base glass was used as crystallizable glass powder and the water soluble salts such as K2SO4 and MgSO4 were used as filler. When K2SO4 was used, leucite crystal phase was formed as a result of the ion exchange and porous glass-ceramics which exhibit high temperature resistance and high thermal expansion coefficient of 17$\times$10-6/$^{\circ}C$ could be obtained. On the contrary, when MgSO4 was used, only slight ion exchange is observed and $\mu$-cordierite and $\alpha$-cordierite crystal phases were formed and porous glass-ceramics which exhibit low thermal expansion coefficient schedule were determined with the results of DTA curves, thermal shrinkage curves and XRD patterns analysis. From DTA curves and thermal shrinkage curves, it was found that the sintering densification have been completed at the temperature range of exothermic peak for crystallization. The pore size distributions and pore diameters were measured by mercury porosimeter. The pore diameter of porous glass-ceramics was 10~15 ${\mu}{\textrm}{m}$ when 100~200${\mu}{\textrm}{m}$ grain size of K2SO4 was used and it was 25~30 ${\mu}{\textrm}{m}$ when the same grain size of MgSO4 was used. The porous glass-ceramics K2SO4 used shows bimodal pore size distribution and its porous skeleton structure was ascertained by SEM observation.

• Tribology and Lubricants
• /
• 제15권1호
• /
• pp.77-82
• /
• 1999

The processing conditions fur the synthesis of platelet W $S_2$ lubricant powder through a solid-gas reaction were optimized. The mixture of tungsten and sulfur powders were sealed in a vacuum of 10$^{-6}$ torr, prior to heat-treating at 85$0^{\circ}C$ fur 8 days. The reaction product showed a well-developed platelet W $S_2$ powder with an average size of 3.8 ${\mu}{\textrm}{m}$. The TGA/DTA analysis of the synthesized W $S_2$ powder was performed up to 120$0^{\circ}C$ at a rate of 1$0^{\circ}C$/min in flowing air (100 ${\mu}{\textrm}{m}$/min) atmosphere. The weight loss was about 6% up to 120$0^{\circ}C$ compared to the original weight. A rapid weight loss of about 5% occurred in the temperature range of 44$0^{\circ}C$ to 66$0^{\circ}C$ and an exothermic peak observed due to the transition of W $S_2$ to W $O_3$. The synthesized W $S_2$powder was coated on the commercial deep grooved ball bearing (No. 6203) to examine the effect of W $S_2$, coating layer on the noise and endurance of the ball bearing. The level of noise obtained from W $S_2$, coated-ball bearing (56 ㏈) was higher. than the value (32 ㏈) occurred in the case of greece lubrication. The endurance of the ball-bearing assembled after the coating of W $S_2$ powder onto each part increased 50 times compared to the non-coated ball-bearing..

• 한국미생물·생명공학회지
• /
• 제41권1호
• /
• pp.60-69
• /
• 2013

Purified melanin pigment from Klebsiella sp. GSK was characterized by thermogravimetric, differential thermal, X-ray diffraction and elemental analysis. This melanin pigment is structurally amorphous in nature. It is thermally stable up to $300^{\circ}C$ and emits a strong exothermic peak at $700^{\circ}C$. Its carbon, hydrogen and nitrogen composition is 47.9%, 6.9% and 12.0%, respectively. It was used to scavenge metal ions and free radicals. After immobilizing the pigment and using it to adsorb copper and lead ions, the metal ion adsorption capacity was evaluated by atomic absorption spectroscopy (AAS) and the identity of melanin functional groups involved in the binding of metal ions was determined by Fourier transform infrared (FT-IR) spectroscopy. Batch adsorption studies showed that 169 mg/g of copper and 280 mg/g of lead were adsorbed onto melanin-alginate beads. The metal ion adsorption capacity of the melanin-alginate beads was relatively significant compared to alginate beads. The metal ion desorption capacity of HCl was greater (81.5% and 99% for copper and lead, respectively) than that of EDTA (80% and 71% for copper and lead, respectively). The ability of the melanin pigment to scavenge free radicals was evaluated by inhibition of the oxidation of 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and was shown to be about 74% and 98%, respectively, compared with standard antioxidants.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
• /
• pp.162-162
• /
• 2011

Nanometer-sized noble metals can trap and guide sunlight for enhanced absorption of light based on surface plasmon that is beneficial for generation of hot electron flows. A pulse of high kinetic energy electrons (1-3 eV), or hot electrons, in metals can be generated after surface exposure to external energy, such as in the absorption of light or in exothermic chemical processes. These energetic electrons are not at thermal equilibrium with the metal atoms. It is highly probable that the correlation between hot electron generation and surface plasmon can offer a new guide for energy conversion systems [1-3]. We show that hot electron flow is generated on the modified gold thin film (<10 nm) of metal-semiconductor (TiO2) Schottky diodes by photon absorption, which is amplified by localized surface plasmon resonance. The short-circuit photocurrent obtained with low energy photons (lower than bandgap of TiO2, ~3.1-3.2 eV) is consistent with Fowler's law, confirming the presence of hot electron flows. The morphology of the metal thin film was modified to a connected gold island structure after heating to 120, 160, 200, and 240$^{\circ}C$. These connected island structures exhibit both a significant increase in hot electron flow and a localized surface plasmon with the peak energy at 550-570 nm, which was separately characterized with UV-Vis [4]. The result indicates a strong correlation between the hot electron flow and localized surface plasmon resonance with possible application in hot electron based solar cells and photodetectors.

• 한국세라믹학회지
• /
• 제41권1호
• /
• pp.76-80
• /
• 2004

분무연소합성법을 이용하여 나노 크기의 산화아연(ZnO) 콜로이드를 제조하였다. 연소반응을 위한 산화제로서 $Zn(NO_3)_2{\cdot}6H_2O$와 환원제(연료)로서 $CH_6N_4O$를 사용하였다. DTA/TGA를 이용하여 열분석을 행한 결과 $230^{\circ}C$에서 전구체 혼합물의 착화(ignition)에 의한 연소반응으로 생각되는 발열피크가 나타났다. 그러나 분무 연소 반응의 경우 ${\mu}m$ 크기의 액적들로 인해 착화를위한 분자 또는 기들의 함량이 상대적으로 적기 때문에 분무된 액적들의 착화를 위해 연소반응기의 온도를 $500^{\circ}C$로 유지하였다. 응집체의 형성을 억제하기 위하여 여과매체를 사용하여 액적의 개수 농도를 감소시켰으며, 에어로졸 입자의 체류시간을 2.5초로 조절하여 열 유체의 흐름을 층류로 유도하였다. 제조된 입자들의 모양은 모두 구형이었으며, 평균 입자 크기는 180nm이었다. XRD와 TEM 분석 결과 각각의 콜로이드들은 ZnO 고유의 결정성을 나타내고 있었으며, hexagonal 구조를 가지는 것으로 확인되었다.

• Transactions on Electrical and Electronic Materials
• /
• 제8권6호
• /
• pp.241-245
• /
• 2007

[ $(Ba_{0.9-x}Sr_xCa_{0.10})TiO_3$ ] (x=0.33, 0.36) powders were prepared by sol-gel method. $(Ba,Sr,Ca)TiO_3$(BSCT) thick films, undoped and doped with $MnCO_3$ and $Yb_2O_3(0.1{\sim}0.7mol%)$, were fabricated by the screen printing method on the alumina substrate. The coating and drying procedure was repeated 6-times. The Pt bottom electrode was screen printing method on the alumina substrate. These BSCT thick films were annealed at $1420^{\circ}C$ for 2 hr in atmosphere. The upper electrodes were fabricated by screen printing the Ag paste and then firing at $590^{\circ}C$ for 10 min. And then the structured and dielectric properties as a function of the doping amount of $Yb_2O_3$ were studied. As a result of the TG-DTA, exothermic peak was observed at around $670^{\circ}C$ due to the formation of the polycrystalline perovskite phase. All BSCT thick films showed XRD patterns of typical cubic peroveskite structure. The average thickness of BSCT thick films was about $70^{\mu}m$. The curie temperature and the dielectric constant decreased with increasing $Yb_2O_3$ doped content and the relative dielectric constant of the specimen, doped with 0.5 mol% $Yb_2O_3$ at BSCT(54/36/10), showed a best value of 5018 at curie temperature.

• 폴리머
• /
• 제25권2호
• /
• pp.177-185
• /
• 2001

본 연구에서는 이관능성 에폭시인 diglycidylether of bisphenol A (DGEBA)/polysulfone (PSF) 블렌드를 시차 열분석기와 레오미터를 이용하여 경화 동력학과 유변학적 특성에 대해 연구하였다. DSC 측정 결과, 최대 발열 피크와 half-width 방법을 사용하여 구한 경화 활성화 에너지 (E$_{a}$ )는 PSF의 함량이 30wt%까지는 증가하였으나, 그 이상의 첨가에서는 감소하였다. 그리고, 전화량($\alpha$)과 전환 속도(d$\alpha$/dt)는 PSF의 함량이 증가함에 따라 감소함을 보였다. 본 연구에서의 유변학적 특성은 레오미터를 이용하여 등온 조건하에서 검토하였고, 겔화 시간과 경화 온도를 이용한 Arrhenius 방정식을 적용하여 가교 활성화 에너지 (E$_{c}$)를 검토한 결과, E$_{a}$ 와 유사한 경향을 나타내었다. 이는 높은 점도를 지닌 PSF의 첨가로 인한 DGEBA와 PSF의 상분리 현상 때문이라 사료된다.다.

• Bulletin of the Korean Chemical Society
• /
• 제30권4호
• /
• pp.783-786
• /
• 2009

Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and ion chromatography(IC) were employed to analyze the thermal behavior of $Li_xCoO_2$ cathode material of lithium ion battery. The mass loss peaks appearing between 60 and 125 ${^{\circ}C}$ in TGA and the exothermic peaks with 4.9 and 7.0 J/g in DSC around 75 and 85 ${^{\circ}C}$ for the $Li_xCoO_2$ cathodes of 4.20 and 4.35 V cells are explained based on disruption of solid electrolyte interphase (SEI) film. Low temperature induced HF formation through weak interaction between organic electrolyte and LiF is supposed to cause carbonate film disruption reaction, $Li_2CO_3\;+\;2HF{\rightarrow}\;2LiF\;+\;CO_2\;+\;H_2O$. The different spectral DSC/TGA pattern for the cathode of 4.5 V cell has also been explained. Presence of ionic carbonate in the cathode has been identified by ion chromatography and LiF reported by early researchers has been used for explaining the film SEI disruption process. The absence of mass loss peak for the cathode washed with dimethyl carbonate (DMC) implies ionic nature of the film. The thermal behavior above 150 ${^{\circ}C}$ has also been analyzed and presented.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2007년도 제38회 하계학술대회
• /
• pp.1283-1284
• /
• 2007

The barium strontium calcium titanate((Ba,Sr,Ca)$TiO_3$) powders prepared by the sol-gel method and $MnCO_3$ as acceptor were mixed oxide method. The microstructure was investigated with variation of $Pr_{2}O_{3}$ amount. The BSCT powder and $Pr_{2}O_{3}$ were mixed with organic vehicle(Ferro. B75001). BSCT thick films were fabricated by the screen-printing method on alumina substrates. The bottom electrode was Pt and upper electrode was Ag, respectively. All BSCT thick films were sintered at $1420^{\circ}C$, for 2h. The result of the differential thermal analysis(DTA), exothermic peak at around $654^{\circ}C$ due to the formation of the polycrystalline perovskite phase. In the X-ray diffraction(XRD) patterns, all BSCT thick films showed the typical perovskite polycrystalline structure and no pyrochlore phase was dbserved. The microstructure investigated by scanning electron microscope(SEM). Pore and grain size of BSCT thick films were decreased with increasing amount of $Pr_{2}O_{3}$ dopant. And the average grain size and thickness of BSCT thick films doped with 0.1 mol% $Pr_{2}O_{3}$ was $3.09{\mu}m$, $60{\mu}m$, respectively. The relative dielectric constant decreased and dielectric loss decreased with increasing amount of $Pr_{2}O_{3}$ dopant, the values of the BSCT thick films no doped with $Pr_{2}O_{3}$ were 7443 and 4 % at 1 kHz, respectively.