• Title, Summary, Keyword: Glass transition temperature

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Study for Local Glass Transition of Bulk Metallic Glasses using Atomic Strain (원자변형률을 이용한 비정질 금속의 천이온도에 관한 연구)

  • Park, Jun-Young
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.10 no.5
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    • pp.104-109
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    • 2011
  • Bulk metallic glasses (BMG) have been greatly improved by the advance of synthesis process during last three decades. It was also found that the Glass Forming Ability (GFA) strongly depends on the glass transition temperature. When the temperature approaches to a critical value, the crystals nucleation from the supercooled liquid can be suppressed so that bulk glass formation possible. Egami and others found that the local glass transition temperature depends on the volumetric strain of each atom and suggested the critical transition temperature. In this paper, we explore the strain dependency of local glass transition temperature using the atomic strain defined by the deformation tensor for the Voronoi polyhedra.

Effects of Transition Temperature and Atomic Ratio on Glass Formation Tendency in the PbO-B$_2$O$_3$-TiO$_2$-BaO System (PbO-B$_2$O$_3$-TiO$_2$-BaO계의 유리화에 대한 전이온도 및 성분 원소비의 영향)

  • 이선우;심광보;오근호
    • Journal of the Korean Ceramic Society
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    • v.35 no.12
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    • pp.1274-1279
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    • 1998
  • The glass forming ability of the PbO-B2O3-TiO3-BaO system was investigated in relation to transitieon tem-peratures and the atomic ratio between constituents. Glass forming tendency was improved as the tem-peratures and the atomic ratio between constituents. Glass forming tendency was improved as the tem-perature differences between liquidus temperature and crystallization(or glass transition) temperature de-creased and the temperature difference between crystallization and glass transition temperature increases. The atomic ratio could be used as a criterion to deign glass systems. The interposition of B and Ba atoms between Pb and Ti atoms was one of important factors in glass formation.

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The Effect of DSC Analysis Condition on the Glass Transition Temperature of curred Epoxy This paper studies on the effect of DSC(Differential Scanning Calorimeter) analysis condition on the glass transition temperature of silica filled epoxy network polymer used for ultra-high voltage apparatus. The effects of temperature scanning rate specimen size and gas flow rate on measured glass transition temperature have been studied in order to select optimum thermal analysis condition. (에폭시 경화물 DSC에 의한 유리전이 온도 측정의 분석조건 의존성)

  • 오무원;권혁삼
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.30-33
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    • 1994
  • This paper studies on the effect of DSC(Differential Scanning Calorimeter) analysis condition on the glass transition temperature of silica filled epoxy network polymer used for ultra-high voltage apparatus. The effects of temperature scanning rate specimen size and gas flow rate on measured glass transition temperature have been studied in order to select optimum thermal analysis condition.

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Change of Glass Transition Temperature of PETG Containing Gas (가스를 포함하는 고분자 재료(PETG)의 유리전이온도 변화)

  • Cha, Seong-Un;Yun, Jae-Dong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.4
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    • pp.824-829
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    • 2000
  • The industries use polymer materials for many purposes because they have many merits. But these materials' costs take up too much proportion in overall cost of products that use these materials as their major material. So it is very economical for polymer industries to reduce these costs. Microcellular foaming process appeared in 1980's to solve this problem and it proved to be quite successful. This process uses inert gases such as CO2, N2. As these gases are dissolved into polymer matrices. many properties are changed. Glass transition temperature is one of these properties. DSC, DMA are devices that measures this temperature, but these are not sufficient to measure the temperature of polymer containing gas. In this paper, we devised a new tester that uses magnetism. We used this device to acquire data of the change of glass transition temperature and made Cha-Yoon model that can predict the change of glass transition temperature. Using this model, the change of this temperature can be estimated as a function of weight gain of gas. Cha-Yoon model proved that Chow's model is inappropriate to predict the change of glass transition temperature of polymer matrices containing gas.

A Change of Thermal Expansion Coefficient according to Li2O-added Porcelain for Dental Zirconia (치과용 지르코니아 도재의 Li2O 첨가에 따른 열팽창계수 변화)

  • Yoon, Han-Sok
    • The Journal of Korean Academy of Dental Technology
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    • v.31 no.4
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    • pp.25-30
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    • 2009
  • Zirconia($ZrO_2$) has attracted much attention in science and technology because of its high refractive index, high melting temperature, hardness, low thermal conductivity and corrosion barrier properties. And it is widely used as the dental restoration material because of its esthetic appearance. In this research, we analyzed the particle size and composition of the imported dental porcelain for zirconia. And the glass frit was produced. To decrease the glass transition temperature and softening temperature of the glass frit, $Li_2O$ was added into it and the effect of $Li_2O$ on the firing temperature was researched. Then the glass which contains leucite crystal with a high coefficient of thermal expansion(CTE) was manufactured and it was mixed with the glass frit to control the CTE. The phase composition were analyzed using the X-ray diffraction. The morphologies of the samples were observed by the scanning electron microscope. The 4wt% $Li_2O$-added glass frit has the optimal glass transition temperature and softening temperature. And 6 wt% leucite crystal was mixed with the glass frit to control the CTE. From the experimental results of crystallization, the crystal phase was found only leucite crystal.

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The Effect of Gas Absorption Induced a Change of Glass Transition Temperature in Microcellular Foamed Plastics (초미세 발포 플라스틱의 유리전이온도를 변화시키는 가스 용해량의 영향)

  • Hwang, Yun-Dong;Cha, Seong-Un
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.5
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    • pp.816-822
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    • 2001
  • The thermoforming process is widely used in the plastics industry to produce articles for the packaging, automotive, domestic construction and leisure industries. The microcellular foaming process appeared at M.I.T. in 1980s to save a quantity of polymer materials and increase their mechanical properties. The glass transition temperature of polymer materials is one of many important process variables in appling the microcellular foaming process to the conventional thermoforming process. The goal of this research is to evaluate the relation between gas absorption and glass transition temperature in batch process using microcellular foaming process. The weight gain ratio of polymer materials has a conception of gas absorption. Polymers such as acrylonitrile-butadiene-styrene(ABS), polystyrene(PS) have been used in this experiment. According to conventional Chows model and Cha-Yoon model, it was estimated with real experimental result to predict a change of glass transition temperature as a function of the weight gain ratio of polymer materials in batch process to gain microcellular foamed plastic products.

Dielectric Relaxation of Siloxane-Epoxy Copolymers

  • Kim, Chy-Hyung;Shin, Jae-Sup
    • Bulletin of the Korean Chemical Society
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    • v.23 no.3
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    • pp.413-416
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    • 2002
  • The dielectric responses of 10 and 40 wt% siloxane-epoxy copolymers were investigated in temperature range near the glass transition of polydimethylsiloxane at which the dielectric transitions were also observed. On the other hand, the pure epoxy did not show any dielectric transition in measurement temperature range -90 to 150 $^{\circ}C.$ The experimental data showed that for the copolymer investigated, the temperature-frequency super-position principle could be applied to the dielectric response. From the Cole-Cole equation, the dielectric relaxation of the 10 wt% siloxane near the glass transition temperature resulted in a broad distribution with ${\beta}=$ 0.19 and the relaxation time at -70 $^{\circ}C$ was 5.3 ${\times}$ $10^{-2}$s. The glass transition temperature, 188 K, was estimated by using WLF relation, which was consistent with the data presented in experiment.

Effect of Thermal Aging Temperature on Weight Loss and Glass Transition Temperature of Epoxy Adhesives (열화 온도가 에폭시 접착제의 질량변화 및 유리전이온도에 미치는 영향)

  • Park, Soo-Jin;Kim, Jong-Hak;Joo, Hyeok-Jong;Kim, Joon-Hyung;Jin, Fan-Long
    • Elastomers and Composites
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    • v.41 no.1
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    • pp.19-26
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    • 2006
  • In this study, the effect of thermal aging temperature on the weight loss, glass transition temperature, and morphology of epoxy adhesives cured with amine (D-230), amide (G-5022), and anhydride (HN-2200) was investigated. As a result, the weight loss of three specimens was increased with increasing the thermal aging temperature. The result was attributed to the thermal aging which was occurred at the surface of adhesive specimens at high aging temperature, resulting in increasing the weight loss of the specimens. According to the DSC result, the glass transition temperature of DGEBA/D-230 and DGEBA/G-5022 samples war increased as the aging temperature increased, whereas the glass transition temperature of DGEBA/HN-2200 samples was constant above aging temperature of $150^{\circ}C$ and aging tine of 7 days. The SEM result indicated that the surface of DGEBA/G-5022 specimen showed more rough topography than that of DGEBA/D-230 or DGEBA/HN-2200 specimen after thermal aging. This could be correlated with the result of weight loss.

Characteristics of Thermal Degradation for Carbon Fiber/Epoxy Composite using Strand Specimen (스트랜드 인장시편을 적용한 탄소섬유/에폭시 복합재의 열화특성 연구)

  • Oh, Jin-Oh;Kil, Hyung-Bae;Yoon, Sung-Ho
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.408-410
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    • 2012
  • In this study, High temperature properties of carbon fiber reinforced composites is performed using strand specimens and resin specimens. As for the tensile test at the different temperature, the tensile modulus of resin specimens decreases slightly until the temperature reaches the glass transition temperature. but the tensile modulus of strand specimens maintains tensile modulus at the room temperature. The tensile strength of resin and strand specimens decreases rapidly until the temperature reaches the glass transition temperature.

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Glass Transition Behavior of Dendritic Polymers Containing Mobile Aliphatic Polyether Cores and Glassy Peripheral Polystyrenes

  • Song, Jie;Cho, Byoung-Ki
    • Bulletin of the Korean Chemical Society
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    • v.29 no.6
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    • pp.1167-1172
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    • 2008
  • We investigated the glass transition temperatures ($T_g$) of dendrons consisting of conformationally mobile aliphatic polyether dendritic cores plus glassy peripheral polystyrenes (PSs), and linear PSs in the molecular weight range of 1000-8500 g/mol. We compared their $T_g$ behavior depending on their polymeric architecture. The linear PSs show a typical growth of $T_g$ up to 92.5 ${^{\circ}C}$ as the molecular weight increases to 8300 g/mol, while the dendrons display nearly constant $T_g$ values of 58-61 ${^{\circ}C}$, despite the increase of molecular weight with each generation. The striking contrast of Tg behavior would be mainly attributed to the fact that the dendrons keep the ratio of $N_e$/M ($N_e$: number of peripheral chain ends, M: molecular weight) over all the generations. Additionally, for the influence of dendritic spacers on glass transition temperature we prepared dimeric PSs with different linkage groups such as aliphatic ether, ester and amide bonds. We found that the dimer with the ether spacer exhibited the lowest glass transition at 55.4 ${^{\circ}C}$, while the amide linked dimer showed the highest glass transition temperature at 74.2 ${^{\circ}C}$. This indicates that the peripheral PS chains are effectively decoupled by the conformationally flexible ether spacer. The results from this study demonstrated that polymeric architecture and dendritic core structures play a crucial role in the determination of glass transition behavior, providing a strategy for the systematic engineering of polymer chain mobility.