• 한국세라믹학회지
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• 제27권1호
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• pp.48-54
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• 1990

YBa2Cu3O7-x(=YBCO) single crystals were grown by flux method and the growing process of crystals was investigated. YBCO and 3BaO-7CuO composition powders were mixed by the ratio of 25 : 75(wt%), and the mixtures were melted at 105$0^{\circ}C$ in a electric furnace with no temperature-gradient. Then the melt was cooled at a rate 2-1$0^{\circ}C$/h in the above furnace. YBCO single crystal plate with average size of $1.5\times$2.0$\times$0.1㎣ were obtained in the cavities between crucible and solidified ingot, and the single crystals were oriented to <001> direction. The ingots of flux parts were analyzed by XRD and EDS for the purpose of presuming the growing process of the crystals. It was assumed that the divorced eutectic reaction, by which YBCO crystals were grown first and then BaCuO2 and CuO crystals, occured in the case of cooling rate faster than 2$^{\circ}C$/h. When the cooling rate was 2$^{\circ}C$/h, it was assumed that quasi-equilibrium eutectic reaction occured, so that YBCO, BaCuO2 and CuO crystals were grown at the same time.

• 열처리공학회지
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• 제33권5호
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• pp.219-225
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• 2020

The objective of this study was to investigate the tensile properties and thermal conductivities of Mg9.3%Al alloy in as-cast state and heat-treated state consisting of fully discontinuous precipitates (DPs), respectively. The fully DPs microstructure was obtained by solution treatment at 405℃ for 24 h, followed by furnace cooling to RT. The as-cast alloy showed a partially divorced eutectic β(Mg₁₇Al₁₂) phase particles formed along the α-(Mg) cell boundaries. The DPs had various apparent (α+β) interlamellar spacings, which is related to different transformation temperatures during the furnace cooling. The DPs microstructure exhibited better tensile strength than the as-cast one, resulting from the higher value of elongation in response to its more homogeneous microstructure. It is noticeable that the DPs microstructure had 12.4% higher thermal conductivity in average than the as-cast one between RT and 200℃. The XRD analyses revealed that the lower Al concentration in the α-(Mg) matrix may well be responsible for the better thermal conductivity of the DPs microstructure.

• 한국기계가공학회지
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• 제13권2호
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• pp.124-130
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• 2014

In a mass manufacturing system of optical fibers, the sufficient cooling of glass fibers freshly drawn from a draw furnace is essential, asinadequately cooled glass fibers can lead to poor resin coating on the fiber surface and possibly fiber breakage during the process. In order to improve fiber cooling at a high drawing speed, it is common to use a helium injection into a glass fiber cooling unit in spite of the high cost of the helium supply. The present numerical analysis carried out three-dimensional thermo-fluid computations of the cooling gas flow and heat transfer on moving glass fiber to determine the cooling performance of glass fiber cooling depending on the method of helium injection. The results showed that afront injection of helium is most effective compared to a uniform or rear injection for reducing air entrainment into the unit and thus cooling the glass fibers at a high fiber drawing speed. However, above a certain amount of injected helium, there was no more increase of the cooling effect regardless of the helium injection method.

• 대한기계학회논문집A
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• 제20권7호
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• pp.2134-2140
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• 1996

This study was carried out to anlayze the heat-resistant characteristics of functionally gradient material(FGM) composed with ceramic and metal. The thermal fracture behavior of plasma-sprayed FGM and conventional coating material(NFGM) was exaimined by acoustic emession technique under heating and cooling. Furnace cooling and rapid cooling tests were used to examine the effect of temperature change under various conditions, respectively. At the high temperature above $800^{\circ}C$, it was shown that FGM gives higher thermal resistance compared to NFGM by AE signal and fracture surface analysis.

• 대한심미치과학회지
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• 제23권2호
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• pp.77-79
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• 2014

There are several factors affected fractures of full contour zirconia (FCZ) dental prosthesis in laboratory process. First, residual moisture can cause zirconia cracks. Complete dry is requisite before zirconia sintering to prevent zirconia cracks. Second, slow cooling rate is essential to prevent cracks during zirconia sintering process. Cracks in bridge pontic area, thick dental implant prosthesis can be prevented by slow cooling rate such as 3 degree Celsius per minute during zirconia sintering. Third, slow heating rate and slow cooling rate during staining and glazing procedure is necessary to inhibit thermal shock of sintered dental zirconia. Lower preheat temperature of porcelain furnace is recommended. Finally, using diamond disc to open embrasure can lead cracks.

• 콘크리트학회논문집
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• 제11권6호
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• pp.3-12
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• 1999

The larger, loftier and more highly strengthened the recent structures become, the greater attention is paid to the problem of thermal crack occurrence associate with hydration heat. As one of methods to solve the problem, a care has been taken to the improvement of construction such as the application of pre-cooling or pipe-cooling, adjustment of concrete block size, concrete placement timing, joint arrangement and so on. But it is expected that a proper selection of cement shall additionally contribute to the control of thermal cracks. In this study, thus, we selected 4 types of cements such as Type V for anti-sulphate, blast furnace cements (slag content of 45% and 65% respectively)and ternary blended low heat cement, and carried out mock-up tests. In every assigned time, temperatures and thermal stresses were measured and calculated from raw data. As a result of measurement, it was found that the magnitude of hydration heat is in order of blast furnace slag cement. Type V and ternary blended low heat cement. Results of thermal stresses were same as the order of temperature. In addition, thermal stresses calculated from the data of strain gauges showed almost similar to those measured from effective stress gauges only when strain values were adjusted properly in accordance with initial time of stress appearance. Theoretical results agreed well with the measured values comparatively, but showed slight differences. It is inferred that these differences shall be reduced if more tests capable of evaluating thermal characteristics of concrete are carried out.

• 한국산학기술학회논문지
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• 제13권2호
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• pp.808-816
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• 2012

본 논문은 열 해석 시뮬레이션과 주조로의 구조 변경을 통한 실리콘 잉곳의 방향성 응고에 대한 연구이다. 열 해석 시뮬레이션에 의한 결과, 용융은 유지 시간이 80분일 때 실리콘이 전체적으로 고르게 용융 온도에 도달하였고 냉각은 상부 냉각 온도가 $1,400^{\circ}C$와 60분 냉각 시 가장 좋은 결과 값을 나타내었다. 제작된 웨이퍼가 기존의 상용웨이퍼보다 결정립계에서의 에칭이 훨씬 적게 이루어졌다. FTIR 측정결과 산소와 탄소 모두 모두 임계값 이하의 불순물로 존재함을 확인하였다. NAA 분석 결과 총 18가지 금속 불순물이 검출 되었지만, 농도 분포는 같은 위치에서 위와 아래의 차이는 크게 나지 않고, 어떤 특정한 위치에서 한쪽으로 집중되거나 어떤 경향성 없이 전체의 샘플의 모든 부분에서 농도가 거의 일정하게 분포를 나타냈다.

• 한국재료학회지
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• 제22권12호
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• pp.650-657
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• 2012

For the purpose of improving the durability problem, translucent opal glass was fabricated as a substitute for the polycarbonate diffuser of LED lighting. Calcium phosphate was used as an opacifier of opal glass and melted in an electric furnace. The opaque effect was identified according to the change of the cooling procedure. As results, translucent opal glass was obtained by the melting of a batch with a composition of 3.8% calcium phosphate at $1550^{\circ}C$ for 2 hrs and then the cooling of the material in the furnace. For the cooling condition of the glass sample, HTCG (High Temperature Cooled Glass) was found to have better optical properties than LTAG (Low Temperature Annealed Glass). It had excellent optical properties for a diffuser of LED lighting, with no dazzling from direct light due to its high haze value of over 99% and low parallel transmittance value of under 1%. For the thermal properties, it had an expressed thermal expansion coefficient of $5.7{\times}10^{-6}/^{\circ}C$ and a softening point of $876^{\circ}C$; it also had good thermal properties such as good thermal shock resistance and was easy to apply to the general manufacturing process in the forming of glass tubes and bulbs. Therefore, it is concluded that this translucent opal glass can be used as a glass diffuser material for LED lighting with high heat resistance and high durability; this material is suitable as a substitute for polycarbonate diffusers.

• 열처리공학회지
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• 제16권6호
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• pp.320-328
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• 2003

A specimen of Cu-35%Sn alloy has been subjected to the unidirectional heat treatment in an attempt to examine the evolution of microstructures under varying thermal conditions. The specimen was cast in the form of a cylinder 10 mm in diameter and 200 mm in length, which was then installed in the temperature gradient field established inside a vertical tube furnace. The furnace temperature was adjusted to make the upper part at $750^{\circ}C$ and bottom end part at $300^{\circ}C$ of the specimen. The experiment was terminated by dropping it into water after the 30 minutes holding at given temperature. By the rapid cooling, the high temperature phases, ${\gamma}$ and ${\zeta}$, were retained at ambient temperature with some of ${\gamma}$ phase transformed to ${\varepsilon}$ phase, especially at the grain boundaries of ${\gamma}$ phase. The presence of ${\varepsilon}$ phase was found to determine the nature of phase transformations of the ${\zeta}$ phase undergoes upon cooling. In the close area of the ${\varepsilon}$ phase, ${\varepsilon}$ phase grew separately out of ${\zeta}$, and adds to the preexisting ${\varepsilon}$ whereas in areas away from ${\varepsilon}$, both ${\delta}$ and ${\varepsilon}$ grew simultaneously out of ${\zeta}$, and formed a lamella eutectoid structure. The transformation to ${\delta}$ was found to occur only in slow cooling. The hardness on each phase showed that the retained phases, ${\gamma}$ and ${\zeta}$, could be plastically deformed without brittle fracture while the phases, ${\varepsilon}$ and ${\delta}$, were too brittle to be deformed.

• Corrosion Science and Technology
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• 제23권2호
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• pp.104-112
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• 2024

Al-Zn-Mg-Si alloy coatings have been developed to inhibit corrosion of cold rolled steel sheets, and an understanding of the alloy system helps prevent coating defects. We used a Bridgman furnace to characterise the nature and formation mechanisms of the phases present in the quaternary system with 0.4 wt% Fe. In the directional solidification experiments we imposed steep temperature gradients and varied the pull rate. After the samples were quenched in the furnace, detailed characterization of the samples was carried out by electron microscopy (SEM/EDS). From the dT/dt vs T plots of the cooling curves of the alloys, the solidification path was determined to be $Liquid{\longrightarrow[80]^{544-558}}{\alpha}-Al{\longrightarrow[80]^{453-459}}Al/Mg_2Si{\longrightarrow[80]^{371-374}}Al/Zn{\longrightarrow[80]^{331-333}}Zn/mgZn_2$. The formation mechanisms of the Mg and Zn containing phases and their morphology was discussed together with the effects of the cooling rate. Key findings include the lengthening of the mushy zone in directionally solidified samples remelted against a positive temperature gradient, as well as an enrichening of the α-Al phase by Zn through remelting. Mg₂Si and other Si based phases were observed to adopt a much finer faceted microstructure in favour of a script-like microstructure when exposed to the higher cooling rate of coolant quenching.