• Title/Summary/Keyword: Low temperature degradation

검색결과 455건 처리시간 0.028초

백색 완두유묘의 IAA분해효소계에 미치는 저온의 영향 (Effects of low temperature on the IAA degradation system in etiolated pea(Pisum sativum L. var. Sparkle) seedlings)

  • 박노동;신용광;김광식;박창규
    • Applied Biological Chemistry
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    • 제33권2호
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    • pp.125-128
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    • 1990
  • 저온에서 완두유묘 줄기의 유리 IAA 수준과 그 전구체인 트립토판 수준이 저하하므로, IAA수준의 조절 메커니즘을 규명하기 위하여 IAA분해효소계에 미치는 저온의 영향을 조사하였다. $25^{\circ}C$에서 키운 백색 관두유표를 $5^{\circ}C$의 저온으로 옮기면 IAA oxidase와 peroxidase의 수준은 증가하였으며 catalase의 수준은 저하되었고 과산화수소는 축적되어, 전체적으로 IAA분해계가 저온에서 강화되었다. 저온에 놓였던 유묘를 상온으로 옮기면 IAA 분해계는 다시 대조구 수준으로 회복하였다.

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액체질소에서의 극저온 절연매질의 Warm-up/Cool-down 특성 (Warm-up and Cool-down Characteristics of Cryogenic Insulation Materials in Liquid Nitrogen)

  • 이상화;신우주;;오석호;성재규;이방욱
    • 한국전기전자재료학회:학술대회논문집
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    • 한국전기전자재료학회 2010년도 하계학술대회 논문집
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    • pp.119-119
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    • 2010
  • Among the various factors influencing the service life of the electric equipment, the performance of dielectric insulation materials has an important role to determine their whole service life. In order to determine the degradation of insulating materials immersed in extremely low temperature media such as liquid nitrogen, the abrupt temperature change from cryogenic to normal room temperature should be considered. But the assessments of low-temperature aging test method for the dielectric materials immersed in liquid nitrogen considering these conditions were not fully reported. Therefore, for the fundamental step to establish the suitable degradation test methods for cryogenic dielectric materials, we focused on the evaluation of ageing test methods for dielectric materials exposed to low temperature environments considering thermal shock by cool-down and warm up test.

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인가 전압이 Y-TZP의 저온열화에 미치는 영향 (Influence of Applied Electric Field on Low Temperature Degradation of Y-TZP)

  • 장주웅;이홍림;김대준;오남식;이득용
    • 한국세라믹학회지
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    • 제34권12호
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    • pp.1254-1260
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    • 1997
  • Influence of applied electric field on the low temperature degradation of 3 mol% YaO3 stabilized tetragonal zirconia polycrystals(3Y-TZP) was investigated using X-ray diffractometry of specimens aged under the dc field of 1.1 kV/mm in silicone oil both of 12$0^{\circ}C$-21$0^{\circ}C$. After the aging, the tetragonal to monoclinic phase transformation was observed only on the specimen surface of 3Y-TZP faced to the anode. This indicated that the surface was overcrowded with oxygen ions as a result of diffusion of oxygen vacancies toward the cathode-sided surface. To elucidate an influence of the applying time of the electric field on the extent of the degradation of 3Y-TZP in air, specimens were aged fore 0-2 hours under the electric field in the oil bath of 12$0^{\circ}C$ and then subsequently aged for 3h at 22$0^{\circ}C$ in air. The longer the specimens were aged under the field, the more extensive the transformation to the monoclinic phase was on the specimen surface faced to the cathode, probably originated from a high diffusion rate of oxygen ions due to a steep oxygen vacancy concentration gradient.

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Hot-press법으로 제조된 $Y_2O_3$$Nb_2O_5$가 첨가된 정방정 ZrO2의 고온열화 (High-Temperature Degradation of Hot-Pressed $t-ZrO_2$ Co-doped with $Y_2O_3$ and $Nb_2O_5$)

  • 이득용;김대준;조경식
    • 한국세라믹학회지
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    • 제34권9호
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    • pp.915-920
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    • 1997
  • Tetragonal ZrO2 polycrystal (TZP), consisted of 90.24 mol% ZrO2-5.31 mol% Y2O3-4.45 mol% Nb2O5, were prepared using hot-press and mechanical properties and high-temperature degradation were investigated. The specimen, hot-pressed for 1 h at 140$0^{\circ}C$ in Ar atmosphere, exhibited flexural strength of 1010 MPa and fracture toughness of 7.5 MPam1/2 and experienced no low-temperature degradation below 40$0^{\circ}C$. However, as aged for 100h at temperatures higher than 40$0^{\circ}C$, TZP was suffered by high-temperature degradation due to an extensive cavitation caused by the oxidation of carbon. XPS observation revealed that the carbon incorporated in TZPs during hot-pressing exists as either an ether-type CO or a carbonyl-type C=O. Despite of the high-temperature degradation of t-ZrO2 co-doped with Y2O3 and Nb2O5, its flexural strength and fracture toughness were superior to those of the commercial 3 mol% Y2O3-TZP hot-pressed under the identical condition as determined before and after the aging treatments.

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Comparison of Degradation Phenomenon in the Low-Temperature Polysilicon Thin-Film Transistors with Different Lightly Doped Drain Structures

  • Lee, Seok-Woo;Kang, Ho-Chul;Nam, Dae-Hyun;Yang, Joon-Young;Kim, Eu-Gene;Kim, Sang-Hyun;Lim, Kyoung-Moon;Kim, Chang-Dong;Chung, In-Jae
    • 한국정보디스플레이학회:학술대회논문집
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    • 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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    • pp.1258-1261
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    • 2004
  • Degradation phenomenon in the low-temperature polysilicon (LTPS) thin-film transistors (TFTs) with different junction structures was investigated. A gate-overlapped lightly doped drain (GOLDD) structure showed better hot-carrier stress (HCS) stability than a conventional LDD one. On the other hand, high drain current stress (HDCS) at $V_{gs}$ = $V_{ds}$ conditions caused much severe device degradation in the GOLDD structure because of its higher current level resulting in the higher applied power. It is suggested that self-heating-induced mobility degradation in the GOLDD TFFs be suppressed for using this structure in short-channel devices.

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Y-TZP에서 표면 처리에 따른 저온열화 거동의 직접적 관찰 (Direct Observation on the Low Temperature Degradation Due to Surface Treatment in Y-TZP)

  • 정태주;김혜성
    • 한국분말재료학회지
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    • 제17권3호
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    • pp.197-202
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    • 2010
  • Low temperature degradation behavior in yttria stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics was microscopically observed from the phase contrast between monoclinic surface and tetragonal matrix. The degradation behavior was dependent on the surface treatment of sintered Y-TZP, even if the sintering history is same. In the mirror polished specimen, the monoclinic layer appeared in a uniform thickness from the surface. On the contrary, for the specimen with coarse scratch, the thickness of degraded surface was more than double especially from the coarse scratch. Since the scratch results in local deformation, the residual stress should be induced around the scratch. With the transformation from tetragonal to monoclinic, the volume expansion exerts a stress on a neighboring grains and promotes a successive phase transformation. Such a autocatalytic effect can be triggered from the part of coarse scratch.

$Ta_2O_5$ 첨가가 3 mol% Y-TZP의 저온열화에 미치는 영향 (Effect of $Ta_2O_5$ Alloying on Low Temperature Degradation of 3 mol% Y-TZP)

  • 김대준;최두진
    • 한국세라믹학회지
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    • 제29권8호
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    • pp.630-638
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    • 1992
  • Ta2O5 alloying into 3 mol% Y2O3-stabilized tetragonal ZrO2 polycrystals (3Y-TZP) increased the degradation during aging at 265℃ and the fracture toughness; both are determined by the amount of transformed m-ZrO2. It was proposed that the mechanism underlying the t→m transformation when aged at low temperatures is attributed to the reorientation of (Zzr'V ). complexes parallel to [111] lattice direction, which is accompanied by a relaxation of TZP lattice during annealing at low temperature. A small strain which results from the reorientation gives rise to a localized mechanical instability, thus lowering the nucleation barrier so that the t→m phase transformation (degradation) proceeds. The amount of transformed m-ZrO2 during aging becomes greater as the chemical free energy change related to the transformation, ΔGo, increases with increasing the Ta2O5 alloying content.

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원전 저압케이블 열화도 평가를 위한 초음파 음속계측에 관한 연구 (A Study on the Measurement of Ultrasound Velocity to Evaluate Degradation of Low Voltage Cables for Nuclear Power Plants)

  • 김경조;강석철;구철수;김진호;박재석;주금종;박치승
    • 비파괴검사학회지
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    • 제24권4호
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    • pp.325-330
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    • 2004
  • 원자력발전소에는 여러 종류의 케이블이 전력공급, 감시 및 제어신호의 전달을 위해 열악한 환경하에서 이용되고 있다. 발전소의 안전한 운전을 위해서 이 케이블이 어느 정도 열화 되었는지 확인할 필요가 있다. 특히, 원자력발전소의 수명 연장과 더불어 저압 케이블을 장기간 사용함에 따라서 저압케이블의 열화를 평가하기 위한 방법이 필요하게 되었다 저압케이블의 열화를 측정하는 파라미터로는 주변 온도, 절연재질의 경도, 파단시 연신률(EAB, Elongation At Breaking Point) 등이 있다. 그러나, 온도나 경도를 계측하는 검사는 정량적인 판단기준의 설정이 곤란하고 진단의 정밀도가 낮으며, 부분적으로 샘플링하는 방법은 샘플링되는 케이블에 연결된 부하를 정전시켜야 하고 장소와 시간적인 제약이 있으며, 전기적 측정법은 노화 초기부터 중기까지의 열화정도를 확인하기 어렵다. 본 연구에서는 재료의 열화에 따라서 초음파의 음속이 변화한다는 이론적인 배경(1,2)을 바탕으로 저압 케이블 재료의 열화에 따른 초음파의 음속을 측정하였다. 이를 위해, 원자력발전소에서 사용되는 저압케이블을 가속 열화시켰으며, 저압케이블의 피복재에서 초음파의 음속을 측정할 수 있는 장비를 개발하여, 초음파의 음속측정 후 인장시험을 통해 파단시 연신률을 측정하였다. 파단시 연신률이 증가함에 따라서 음속이 선형적으로 감소하였으며, 초음파의 음속은 열화의 정량적 평가 파라미터로서의 사용 가능성을 확인할 수 있었다.

Thermal Stability of $MnOx-WO_3-TiO_2$ Catalysts Prepared by the Sol-gel Method for Low-temperature Selective Catalytic Reduction

  • 신병길;이희수
    • 한국재료학회:학술대회논문집
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    • 한국재료학회 2011년도 추계학술발표대회
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    • pp.28.2-28.2
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    • 2011
  • The selective catalytic reduction (SCR) of NOx by $NH_3$ is well known as one of the most convenient, efficient, and economical method to prevent NOx emission in flue gas from stationary sources. The degradation of the reactivity is the obstacle for its real application, since high concentrations of sulfur dioxide and thermal factor would deactivate the catalyst. It is necessary to develop high stability of catalysts for low-temperature SCR. Among the transition metal oxides, $WO_3$ is known to exhibit high SCR activity and good thermal stability. The $MnOx-WO_3-TiO_2$ catalysts prepared by sol-gel method with various $WO_3$ contents were investigated for low-temperature SCR. These catalysts were observed in terms of micro-structure and spectroscopy analyses. The $WO_3$ catalyst as a promoter is used to enhance the thermal stability of catalyst since it increases the phase transition temperature of $TiO_2$ support. It was found that the addition of tungsten oxides not only maintained the temperature window of NO conversion but also increased the acid sites of catalyst.

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