• 비파괴검사학회지
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• 제20권1호
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• pp.18-26
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• 2000

화력발전소 보일러 고온배관인 주증기관, 헤드 및 증기드럼 등의 설비들은 장시간동안 고온고압의 가혹한 조건으로 운전됨에 따라 크리프손상에 의해 열화되고 있다. 이들 설비의 크리프손상측정에 적용되는 종래의 비파괴기법인 레프리카법, 전기저항법 및 경도법 등은 복잡한 측정절차 및 접근성, 검사결과의 신뢰도 및 측정정도 등 여러가지면에서 단점이 많다. 따라서 본 논문에서는 화력발전소 주요 고온배관에서 발생되는 경년열화인 크리프손상에 대한초음파 측정연구를 수행한 결과로서, 고온배관재료인 Cr-Mo강의 크리프 인공열화재를 대상으로 이들에 대한 크리프손상 상태별 초음과 음속(sound velocity) 및 감쇠(attenuation)의 초음파 신호특성을 평가하였다.

• Current Research on Agriculture and Life Sciences
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• 제5권
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• pp.33-39
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• 1987

제초제(除草劑) propanil 이 용액(溶液) 내(內)에서 분해(分解)되는 양상(樣相)을 구명(究明)하기 위하여 propanil의 분해(分解)에 관여(關與)하는 온도(溫度), pH 및 자외선(紫外線) 조사(照射) 등(等) 환경요인(環境要因)의 영향(影響)을 조사(調査)한 결과(結果)는 다음과 같다. 온도(溫度)가 높을수록 propanil의 분해(分解)가 빨랐으며, 원제(原劑)보다 제품(製品)의 분해(分解)가 다소 빨랐다. 띠라서 분해산물(分解産物)인 DCA의 생성량(生成量)은 온도(溫度)가 높을수록 증(增)가하였으며, 증가(增加)된 DCA는 일정기간(一定其間) 후(後) TCAB로 축합(縮合)되었기 때문에 오히려 감소(減少)하였다. 그러나, 축합(縮合)된 TCAB는 증가(增加) 후(後) 더 이상 분해(分解)되지 않고 일정량(一定量)을 유지(維持)하였다. Propanil은 알칼리성(性) 용액(溶液)에서 빨리 가수분해(加水分解)되었으며, 또한 강산(强酸)에서도 빨리 분해(分解)되었다. 그러므로 분해산물(分解産物)인 DCA는 강산(强酸)이나 강(强)알칼리 조건(條件)에서 그 생성(生成)이 빨랐고, TCAB로도 빨리 축합(縮合)되었다. 자외선(紫外線) 조사(照射)에 의(依)하여 20분(分) 이내(以內)에 90%이상(以上)의 propanil이 분해(分解)되었으며, 10분(分) 후(後)에는 0.3 ppm의 DCA가 생성(生成)되어 조사시간(照射時間)을 통(通)하여 거의 일정(一定)한 양(量)을 나타냈다.

• 한국신뢰성학회지:신뢰성응용연구
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• 제14권3호
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• pp.203-207
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• 2014

Electrodeless lamp is famous for its long life. But its reliability is dependent not only on electrodes but also on materials and structures. To evaluate end product's reliability, we studied high temperature durability by $60^{\circ}C$, $75^{\circ}C$ and $90^{\circ}C$ temperature tests, and predicted failure times by an exponential model through regression analysis. However, the test showed that temperature does not affect degradation of electrodeless lamps. Their luminous outputs degrade during the early time of the test (till 250 hours) and then converge to a saturation points. Also, '410nm ~ 530nm' spectrum degrades more than other spectra.

• Journal of the Korean Wood Science and Technology
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• 제22권1호
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• pp.66-71
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• 1994

To increase drying rate and reduce drying degradation, pretreatments such as prefreezing and presteaming have been widely used in wood industries. Presteaming lumbers prior to kiln drying is known positively to improve its permeability, to increase diffusion coefficient and to reduce discoloration, but negatively to increase collapse. Prefreezing lumbers prior to kiln drying is also known to reduce significantly its drying defects and its shrinkages. Thus it is no doubt that the pretreated lumbers shrink diversely from the untreated. In this study the shrinkage behaviors of the pretreated specimens are investigated by drying two tropical hardwoods (Apitong and Taun) in three different dying conditions: high temperature and slow drying rate (drying in a closed cylinder), high temperature and rapid drying rate (drying in an oven) and low temperature and slow drying rate(drying at room temperature). The prefrozen specimens show the least volumetric shrinkages in most drying conditions. The specimens dried in cylinders shrink most among all drying conditions. In general the pretreated specimens reached the 30 % moisture content faster than the untreated by about 30 %.

• 전자공학회논문지D
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• 제35D권4호
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• pp.71-77
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• 1998

In this paper, algeration of electical characteristics is analyzed when the operating temperature of MOSFET, BJT and CMOS/BiCMOS inverter is lowered from 300K to 77K. As the operating temperature is lowered, electric characteristics of MOSFET are enhanced generally but, those of bipolar transistor are degraded because current gain is reduced by BGN(Band Gap Narrowing) effect. For the inverter considered in this work, switching characteristics of PSA-BiCMOS inverter are enhanced by the electrical characteristics enhancement of MOSFET when the operating temperature is reduced to 200K, while under 200K, those of PSA-BiCMOS inverter are degraded because the degradation of BJT impacts on the inverter circuit.

• 한국세라믹학회지
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• 제53권5호
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• pp.469-477
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• 2016

The application of nanomaterials for electrodes of intermediate temperature solid oxide fuel cells (SOFC) is introduced. In conventional SOFCs, the operating temperature is higher than 1073 K, and so application of nanomaterials is not suitable because of the high degradation rate that results from sintering, aggregation, or reactions. However, by allowing a decrease of the operating temperature, nanomaterials are attracting much interest. In this review, nanocomposite films with columnar morphology, called double columnar or vertically aligned nanocomposites and prepared by pulsed laser ablation method, are introduced. For anodes, metal nano particles prepared by exsolution from perovskite lattice are also applied. By using dissolution and exsolution into and from the perovskite matrix, performed by changing $P_{O2}$ in the gas phase at each interval, recovery of the power density can be achieved by keeping the metal particle size small. Therefore, it is expected that the application of nanomaterials will become more popular in future SOFC development.

• 치위생과학회지
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• 제14권1호
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• pp.29-34
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• 2014

본 연구는 최근 심미보철물 제작에 널리 사용되는 지르코니아의 저온열화가 수복물의 안정성 및 내구성에 영향을 미치는 여부를 확인하기 위하여 전단결합강도를 측정하였다. 디스크 형태의 시편을 각각 7개씩 제작한 후 전장도재를 축성하여, ISO 13356 규격에 의거한 조건으로 고압증기 멸균기에 저온열화의 정도를 조절하기 위하여 3, 5, 10시간 동안 수열처리를 진행하였다. 제한된 조건하에 시행된 실험을 통해 전단결합강도를 확인하였으며, 측정 후 파절양상을 관찰 하였다. 저온열화 처리 전후의 시편에 대한 전단결합강도의 변화는 각 실험군별 유의한 차이가 있었다(p<0.05). 10시간을 저온열화 처리한 시편이 가장 낮은 전단결합강도로 나타났으며, 처리시간이 길어질수록 전단결합강도가 낮아지는 경향을 보였다. 파절 양상으로 저온열화 처리를 하지 않은 시편에서 응집성 파절을 보였으며, 저온열화 처리가 길어질수록 혼합형 파절 경향으로 전환되었다. 결론적으로 본 연구는 저온열화 현상이 진행될수록 지르코니아 코어와 전장도재 간의 결합강도가 낮아지는 경향을 확인하였다. 본 실험결과를 토대로 치과용 지르코니아를 이용한 보철물 제작과정과 환자에게 장착 후 안정적인 사용을 위하여 저온열화 현상에 대한 주의가 필요할 것으로 생각된다.

• Computers and Concrete
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• 제33권5호
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• pp.605-619
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• 2024

The increase of reclaimed asphalt pavement (RAP) content in recycled asphalt concrete (RAC) is accompanied by the degradation of low-temperature cracking resistance, which has become an obstacle to the development of RAC. This paper aims to reveal the meso-scale mechanisms of the low-temperature fracture behavior of RAC and provide a theoretical basis for the economical recycling of RAP. For this purpose, micromechanical heterogeneous peridynamic model of RAC was established and validated by comparing three-point bending (TPB) test results against corresponding numerical simulation results of RAC with 50% RAP content. Furthermore, the models with different aggregate shapes (i.e., average aggregates circularity (${\bar{C_r}}=1.00$, 0.75, and 0.50) and RAP content (i.e., 0%, 15%, 30%, 50%, 75%, and 100%) were constructed to investigate the effect of aggregate shape and RAP content on the low-temperature cracking resistance. The results show that peridynamic models can accurately simulate the low-temperature fracture behavior of RAC, with only 2.9% and 13.9% differences from the TPB test in flexural strength and failure strain, respectively. On the meso-scale, the damage in the RAC is mainly controlled by horizontal tensile stress and the stress concentration appears in the interface transition zone (ITZ). Aggregate shape has a significant effect on the low-temperature fracture resistance, i.e., higher aggregate circularity leads to better low-temperature performance. The large number of microcracks generated during the damage evolution process for the peridynamic model with circular aggregates contributes to slowing down the fracture, whereas the severe stress concentration at the corners leads to the fracture of the aggregates with low circularity under lower stress levels. The effect of RAP content below 30% or above 50% is not significant, but a substantial reduction (16.9% in flexural strength and 16.4% in failure strain) is observed between the RAP content of 30% and 50%. This reduction is mainly attributed to the fact that the damage in the ITZ region transfers significantly to the aggregates, especially the RAP aggregates, when the RAP content ranges from 30% to 50%.

• Journal of the Korean Wood Science and Technology
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• 제38권3호
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• pp.205-212
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• 2010

본 연구는 홀로셀룰로오스를 이용하여 제조한 에어로겔과 에어로겔의 열적특성 및 다공성에 대해서 검토하였다. 홀로셀룰로오스는 alkali hydroxide-urea 용액으로 용해 및 겔화시켜 동결건조로 에어로겔을 제조하였다. 홀로셀룰로오스 에어로겔은 그물모양 또는 스폰지와 같은 다공성구조로 이루어졌다. 밀도는 0.04g/$cm^3$이었고, 비표면적은 145.3 $m^2$/g이었다. 에어로겔의 열분해는 $210{\sim}350^{\circ}C$의 온도범위에서 일어났으나,저속의 승온조건일수록 열분해가 보다 낮은 온도에서 일어났다. 홀로셀룰로오스 에어로겔은 승온조건이 저속일수록 micro pore체적이 증가하였다. 홀로셀룰로오스 에어로겔 탄화물의 비표면적은$0.5^{\circ}C$/min의 승온조건이 656.7 $m^2$/g로 가장 높았다. 탄화물들은 에어로겔의 구조가 열에 의해 섬유의 배열이 변형되어 불규칙적 구조로 변화된 것이 주사전자현미경에 의해 관찰되었다.

• 열처리공학회지
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• 제17권1호
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• pp.29-35
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• 2004

The effect of low tempering in a temperature range of $150{\sim}400^{\circ}C$ on corrosion resistance in 420J2 stainless steel austenitized at $1000^{\circ}C$ was investigated by the application of salt spray test, electrochemical pitting test in 3.5% NaCl solution and DL-EPR test for intergranular corrosion in 0.5M $H_2SO_4$+0.01M KSCN solution. In salt spray test, good corrosion resistance was obtained in a tempering temperature range of $150{\sim}250^{\circ}C$. Pitting potential was increased to the tempering temperature of $250^{\circ}C$, but decreased with the increase of temperature up to $400^{\circ}C$ And it was thought that the degradation of pitting corrosion resistance showed at the tempering temperature of around $400^{\circ}C$ was due to the precipitation of $Cr_7C_3$ of $M_7C_3$ type. The degree of sensitization showed increasing tendency with the increase of tempering temperature, and also Cr depletion phenomena were observed in the vicinity of grain boundary.