• 한국분말재료학회지
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• 제27권3호
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• pp.226-232
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• 2020

Bismuth vanadate (BiVO₄) is considered a potentially attractive candidate for the visible-light-driven photodegradation of organic pollutants. In an effort to enhance their photocatalytic activities, BiVO₄ nanofibers with controlled microstructures, grain sizes, and crystallinities are successfully prepared by electrospinning followed by a precisely controlled heat treatment. The structural features, morphologies, and photo-absorption performances of the asprepared samples are systematically investigated and can be readily controlled by varying the calcination temperature. From the physicochemical analysis results of the synthesized nanofiber, it is found that the nanofiber calcines at a lower temperature, shows a smaller crystallite size, and lower crystallinity. The photocatalytic degradation of rhodamine-B (RhB) reveals that the photocatalytic activity of the BiVO₄ nanofibers can be improved by a thermal treatment at a relatively low temperature because of the optimization of the conflicting characteristics, crystallinity, crystallite size, and microstructure. The photocatalytic activity of the nanofiber calcined at 350℃ for the degradation of RhB under visible-light irradiation exhibits a greater photocatalytic activity than the nanofibers synthesized at 400℃ and 450℃.

• 보존과학회지
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• 제33권6호
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• pp.467-483
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• 2017

본 연구에서는 문화재 복원용 속(速)경화형 Epoxy계 수지인 $Araldite^{(R)}$ rapid의 온도 스트레스에 의한 열화 특성을 분석하였다. 인장강도 및 접착강도는 $40{\sim}60^{\circ}C$에서 12,624시간까지 감소하여 내구성 및 접착특성의 미약한 열화가 발생하였다. 외부 응력 및 온도에 대한 안정성은 속(速)경화형에 비해 일반 경화형 Epoxy계 수지가 우수하여, 복원부의 강도 특성 및 응력 상태를 고려한 복원재료의 적절한 선택과 적용이 요구된다. $40{\sim}60^{\circ}C$에서 12,624시간까지 색차의 증가와 광택도의 감소 등 색상 및 광택 안정성은 취약하여, 향후 광학특성의 개선을 위한 안정성 향상 연구가 필요하다. 특히 접착제의 열적 특성(중량감소량, 열분해온도, 유리전이온도)은 기계적 물성 변화에 부분적으로 관여하였고, 피착재의 계면 특성 및 접착제의 기체투과특성(수분투과도)은 접착성능의 중요인자로 작용하였다. 따라서 도자기, 벽돌 및 석재와 같은 다공성 재질의 경우 항온항습에 의한 보존환경 관리가 중요하며, 옥외 전시유물의 경우 노출환경에 의한 물성 변화를 최소화할 수 있는 보존대책의 수립이 절실하다. 향후 이러한 결과는 문화재에 사용된 Epoxy계 수지의 열화속도 및 수명예측 자료로 활용될 것으로 기대된다.

• Journal of the Korean Wood Science and Technology
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• 제39권4호
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• pp.303-310
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• 2011

본 연구에서는 압체온도와 시간에 따른 열압밀화 라디에타 소나무재의 역학적 특성을 조사하였다. 종압축강도와 휨강도는 압체온도와 시간의 증가와 함께 증가하였다. 그러나 압체온도 $220^{\circ}C$에서는 열화로 인해 오히려 감소된 값을 나타내었다. 표면경도는 압체온도의 증가와 함께 증가하였으며, 압체시간이 표면경도에 미치는 영향은 미약하였다. 못뽑기저항의 경우 접선단면의 저항력이 가장 높았으며, 압체온도와 시간에 의한 영향은 거의 나타나지 않았다.

• Computers and Concrete
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• 제20권5호
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• pp.529-537
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• 2017

Excessively elevated temperature can lead to cracks in prestressed concrete (PC) continuous bridge with box girder on the pier top at cement hydration age. This paper presents a case study for evaluating the behavior of PC box girder during the early hydration age using a two-stage computational model, in the form of computer program ANSYS, namely, 3-D temperature evaluation and determination of mechanical response in PC box girders. A numerical model considering time-dependent wind speed and ambient temperature in ANSYS for tracing the thermal and mechanical response of box girder is developed. The predicted results were compared to show good agreement with the measured data from the PC box girder of the Zhaoshi Bridge in China. Then, based on the validated numerical model three parameters were incorporated to analyze the evolution of the temperature and stress within box girder caused by cement hydration heat. The results of case study indicate that the wind speed can change the degradation history of temperature and stress and reduce peak value of them. The initial casting temperature of concrete is the most significant parameter which controls cracking of PC box girder on pier top at cement hydration age. Increasing the curing temperature is detrimental to prevent cracking.

• 폴리머
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• 제38권4호
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• pp.484-490
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• 2014

Reduced graphene oxide (RGO) was fabricated using gelatin as a reductant, and it could be stably dispersed in gelatin solution without aggregation. A series of RGO/gelatin composite films with various RGO contents were prepared by a solution-casting method. The structure and thermal properties of the RGO/gelatin composite films were characterized by UV-vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and thermal gravimetric analysis (TGA). The addition of RGO enhances the degree of crosslinking of gelatin films and decreases the swelling ability of the gelatin films in water, indicating that RGO/gelatin composite films have a better wet stability than gelatin films. The glass transition temperature ($T_g$) of gelatin films is also increased with the incorporation of RGO. The presence of RGO slightly increases the degradation temperature of gelatin films due to the very low content of RGO in the composite films. Since gelatin is a natural and nontoxic biomacromolecule, the RGO/gelatin composite films are expected to have potential applications in the biomedical field.

• Transactions on Electrical and Electronic Materials
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• 제12권3호
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• pp.89-92
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• 2011

Hydrogenated amorphous carbon (a-C:H) films were deposited by plasma enhanced chemical vapor deposition on silicon substrates. a-C:H thin film was irradiated to a typical He-Cd laser to study its emitting properties. The photoluminescence (PL) intensity during the irradiation achieved a maximum value when 2,000 seconds elapsed. Fourier transform infrared measurement revealed a-C:H thin film suffered transformation from a polymer-like to graphite-like phase during laser irradiation. Thermal annealing was done at various temperatures, ranging from room temperature to $400^{\circ}C$ in the atmosphere, to investigate structural changes in a-C:H film by heat generation during the emission. PL intensity of a-C:H thin film increased 1.5 times without apparent structural change, as annealing temperature increased up to $200^{\circ}C$. However, a-C:H film above $200^{\circ}C$ exhibited significant decrease of PL accompanying dehydrogenation. This led to a red shift of the PL peak.

• Bulletin of the Korean Chemical Society
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• 제24권9호
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• pp.1276-1280
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• 2003

Thermal behavior of bromphenols was investigated by direct pyrolysis at high temperature. The thermal degradation products formed by the pyrolysis of mono-bromophenols (o-, m-, and p-) were identified by gas chromatography-mass spectrometry. During the pyrolysis reactions, several kinds of dioxins and furans were produced, and the relative ratio of pyro-products was dependent on the substituted position of bromine in phenolic structure due to the effect of symmetry and steric hindrance. The formation of dioxins can be explained by the phenoxy radical addition and Br atom elimination at an ortho-carbon site on phenolic structure. On the other hand, the formation of furans can be explained by the ortho-ortho carbon coupling of phenoxy radicals at unsubstituted sites to form o, o'-dihydroxydiphenyl intermediate via its keto-tautomer, followed by $H_2O$ elimination. The pyrolysis temperature has also a substantial effect on the dimerized products quantities but little effect on the type of pyro-products. Moreover, the formation mechanism of pyro-products was suggested on the basis of products identified.

• Journal of the Optical Society of Korea
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• 제20권1호
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• pp.130-134
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• 2016

The influence of Au/Ni-based contact formed on a lightly-doped (7.3×1017cm−3, Zn-doped) InGaAsP layer for electrical compensation of surface plasmon polariton (SPP) propagation under various rapid thermal annealing (RTA) conditions has been studied. The active control of SPP propagation is realized by electrically pumping the InGaAsP multiple quantum wells (MQWs) beneath the metal planar waveguide. The metal planar film acts as the electric contact layer and SPP waveguide, simultaneously. The RTA process can lower the metal-semiconductor electric contact resistance. Nevertheless, it inevitably increases the contact interface morphological roughness, which is detrimental to SPP propagation. Based on this dilemma, in this work we focus on studying the influence of RTA conditions on electrical control of SPPs. The experimental results indicate that there is obvious degradation of electrical pumping compensation for SPP propagation loss in the devices annealed at 400℃ compared to those with no annealing treatment. With increasing annealing duration time, more significant degradation of the active performance is observed even under sufficient current injection. When the annealing temperature is set at 400℃ and the duration time approaches 60s, the SPP propagation is nearly no longer supported as the waveguide surface morphology is severely changed. It seems that eutectic mixture stemming from the RTA process significantly increases the metal film roughness and interferes with the SPP signal propagation.

• Elastomers and Composites
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• 제49권2호
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• pp.144-148
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• 2014

자동차 엔진 부품용으로 많이 사용되는 ACM 고무 샘플에 대하여 $150^{\circ}C$, $160^{\circ}C$, $170^{\circ}C$, 및 $180^{\circ}C$의 등온상태에서 시간에 따른 압축영구줄음율(CS)과 열중량감소율을 측정하여 상관관계를 구하고, 이를 비등온 TGA를 이용하는 Toop의 해석방법에 이용하여 사용온도에서의 수명을 예측하고자 하였다. 노화촉진시험으로부터 측정된 중량감소율는 CS에 대하여 선형적으로 변화하는 것이 관찰되었으며, 이로부터 CS 40%에 이르는 시간을 재료의 수명시간으로 했을 때 중량감소에 의한 전환율은 4.2%로 나타났다. TGA 곡선으로부터 Flynn-Wall-Ozawa법에 의하여 전환율 4.2%에서의 활성화에너지는 120.2 kJ/mol로 계산되었으며, 이를 Toop의 해석법에 적용하였을 때의 예측수명은 사용온도 $120^{\circ}C$에서 약 9,700 시간으로 계산되었다.

• 한국전기전자재료학회논문지
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• 제28권7호
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• pp.456-461
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• 2015

In this study, the frequency properties of electrostatic capacity and dielectric loss for the samples with different types of filler has been measured in through the applied frequency range of 7 kHz ~3,000 kHz at temperature of $80^{\circ}C$, $110^{\circ}C$, $140^{\circ}C$, $170^{\circ}C$. The results of this study are as follows. When the sample is degradated at the temperature of $80^{\circ}C$, $110^{\circ}C$, $140^{\circ}C$, $170^{\circ}C$ and the frequency range of 7 kHz ~3,000 kHz is applied, It found that the electrostatic capacity of the sample with Polyimide film is larger than the sample with Grass fiber. It found that the dielectric loss for the sample with Polyimide film is larger than the sample with Grass fiber with increasing frequency and temperature in the $80^{\circ}C$, $110^{\circ}C$, $140^{\circ}C$, $170^{\circ}C$ range. Also, the dielectric loss decreased with increasing frequency. In case of the sample with Polyimide film, It found that the electrostatic capacity decreased with increasing temperature, and the dielectric loss gradually decreased with increasing frequency.