• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.202.2-202.2
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• 2013

Ti2O3 is known as a typical Mott insulator with a transition temperature of near $200^{\circ}C$. Unlike VO2, Ti2O3 does not have a structural phase transition near the metal-insulator-transition (MIT) temperature. We investigated the temperature-dependent thermal vibration change using temperature-dependent x-ray absorption fine structure (XAFS) at Ti K-edge in the temperature range of 300~600 K. Ti2O3 powder and films were synthesized using thermal chemical vapor deposition (CVD) at $800{\sim}900^{\circ}C$. X-ray diffraction measurements show a single phased Ti2O3 at room temperature. XAFS confirmed no structural phase transition in the temperature of 300~600 K. A small but distinguishable structural disorder change was observed near the transition temperature. We will discuss the MIT behavior with the change of structural disorder.

• BMB Reports
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• 제39권2호
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• pp.167-170
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• 2006

Bovine adenosine deaminase undergoes a nondenaturational conformational change at $29^{\circ}C$ upon heating which is characterized by a large increase in heat capacity. We have determined the transition state thermodynamics of the conformational change using a novel application of differential scanning calorimetry (DSC) which employs very slow scan rates. DSC scans at the conventional, and arbitrary, scan rate of $1^{\circ}C/min$ show no evidence of the transition. Scan rates from 0.030 to $0.20^{\circ}C/min$ reveal the transition indicating it is under kinetic control. The transition temperature $T_t$ and the transition temperature interval ${\Delta}T$ increase with scan rate. A first order rate constant $k_1$ is calculated at each $T_t$ from $k_1\;=\;r_{scan}/{\Delta}T$, where $r_{scan}$ is the scan rate, and an Arrhenius plot is constructed. Standard transition state analysis reveals an activation free energy ${\Delta}G^{\neq}$ of 88.1 kJ/mole and suggests that the conformational change has an unfolding quality that appears to be on the direct path to the physiological-temperature conformer.

• Journal of the Korean Physical Society
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• 제73권11호
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• pp.1729-1734
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• 2018

Organic-inorganic halide perovskite single crystals undergo phase transition of being cubic, tetragonal, or orthorhombic depending on the temperature. We investigated the $CH_3NH_3PbBr_{3-x}I_x$ single crystals grown by the inverse temperature crystallization method with temperature-dependent UV-Vis absorption and photoluminescence. From the temperature-dependent absorption measurement, the optical band gap is extracted by derivation of absorption spectrum fitting and Tauc plot. In our results, $CH_3NH_3PbBr_{3-x}I_x$ single crystals show that an abrupt change in optical band gap, PL peak position and intensity appears around 120 K - 170 K regions, indicating the phase transition temperature.

• 전기의세계
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• 제30권7호
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• pp.441-447
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• 1981

As a preceeding work for the study on dielectric characterstics of a kind of low density polyethylene introduced morphological change by mechanical method, glass transition temperature which is regarded as a macroscopic aspect for relaxation of molecular chain segments has been observed by means of temperature dependent dilatometric measurement. The origina specimen clearly shows two knees which correspond to two peaks (.gamma. and .betha. peak) in the intenal friction measurement, suggesting the existence of separated glass transition temperatures at 150.deg.k and 260.deg.k respectively. On the specimen irradiated to 100 Mrad both glass transition temperatures tend to shift towards high temperature sides because of crosslinking by irradiation. furthemore an evidence can be seen that radiation effect, even in amorphous phase, is also slelctive depending on slight morphological differences. The specimen extended to four times in length shows a peculiar nature such as negative linear thermal expansion coefficient increasing with temperature between 220.deg.k and ambient temperature and that this fact is interpreted by considering that c axis of the lattice aligns along the extended direction by drawing, further c axis inherently possesses the characteristics of negative linear thermal expansion coefficient. For the observations that the relatively small positive linear expansion on the specimen extended to ca. two times as well as the part below 220.deg.k of the specimen extended to four times, it is considered for the reason of the facts that the incompletely oriented region indicated as the middle part of Peterlin's model tends to restore partially to orginal arrangement-a kind of phase transition-as increasing with temperature.

• 한국인쇄학회지
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• 제14권1호
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• pp.17-29
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• 1996

N-substituted acrylamide hydrogel is reported to have the feature of bing transparent and sensitive enough to response to a temperature stimulus below the temperature of phase transition. Especially at the near of 35 C it becomes shrunk and opaque very quickly. It has also the characteristic of reversing swelling and shrinking. The experiment showed that it is possible to produce a functional gel of super water absorption with the process of free radical polymerizing PVA(polyvinylalcohol) and PAA(polyacrylamide), and crosslinking. The ratio of shrinking and swelling caused by copolymerization rises 10% to 80% at the each temperature of 20 C, 30 C, 40 C, respectively. Phase transition temperature of this gel by copolymerization is50 C while that of ordinary N-substituted acrylamides is between 32~35 C. This temperature reaches the rearing limit of animals and plants so that volumetric transition polymer gel can be ulilized in varying fields such as agriculture/gardening which are water-using field, on-off switch sensing temperature and volumetric variation, processing of liquid wastes and civil engineering works, architecture and electronics. We have no doubt that this material will be the high-functional resin in the hi-tech age of the near future.

• Bulletin of the Korean Chemical Society
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• 제23권3호
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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.

• 한국세라믹학회지
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• 제35권12호
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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.

• Archives of Pharmacal Research
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• 제7권1호
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• pp.47-52
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• 1984

Four polymorphic forms (I, II, III and IV) of hydrochlorothiazide have been characterized on the basis of x-ray diffractometry and differential thermal analysis. Form I was obtained by crystallization from N, N-dimethylformamide and Form II was crystallized from hot methanol. Form III was precipitated from sodium hydroxide aqueous solution by treatment with hydrochloric acid and Form IV was crystallized from 50% methanol. The metastable form I was a most stable form among four polymorphs, which was stable more than ten months at room temperature. The thermodynamic parameters such as heat of solution, enthalpy, entropy, free energy difference and transition temperature were determined by the measurement of intrinsic dissolution rate. The transition temperature and the heat of transition between the metastable Form I an Form II were determined to be $299.15^{\circ}$K and 5.03 Kcal/mole, respectively and free energy difference ($\delta$ F) was 302. 13 cal/mole. Diuretic action of these four polymorphic forms was also evaluated by monitoring the difference in urinary excretion of sodium, potassium and magnesium in rats.

• 한국세라믹학회지
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• 제29권12호
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• pp.981-989
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• 1992

This is a study on the effects of cristobalite transition of quartz in semi-vitrious whiteware body, as addition of alkali and alkali earth oxides, prepared by pottery stone, feldspar, kaolin and clay minerals. The amounts of ${\alpha}$-quartz to ${\alpha}$-cristobalite transition, F.O.C. (fraction of cristobalite), were increased with firing temperature. In MgO added body, ${\alpha}$-quartz was decreased and the formation of cristobalite was increased. Effects of K2O addition was remarkably decreased the formation of cristobalite. Additive effects of MgO and K2O were confirmed that it was very different to variation of transition temperature of metakaolinite to Si-Al spinel structure in thermal reaction of kaolinite minerals. Result CaO addition was ineffective to transition temperature, and the transition temperature in Na2O added body was decreased, but relative intensity of quartz and cristobalite crystal in XRD results was decreased. This was characterized by the effects on the formation of liquid phase much more.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.579-584
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• 2001

As the huge energy transfer systems like as nuclear power plant and steam power plant are operated for a long time, mechanical properties are changed and ductile-brittle transition temperature is raised by degradation. So it is required to estimate degradation in order to assess the safety, remaining life, and further operation parameters. The sub-sized specimen test method using surveillance specimen was developed for evaluating the integrity of metallic components. In this study, we would like to present the evaluation technique of the ductile-brittle transition temperature by the sub-sired specimen test. The four classes of the thermally aged 1Cr-1Mo-0.25V specimens were prepared using an artificially accelerated aging method. The tensile test and fracture toughness test were performed. The results of the fracture toughness tests using the sub-sized specimens were compared with the evaluation technique of the ductile-brittle transition temperature.