• Title/Summary/Keyword: phase change materials

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Hysteresis Behavior in Electric Resistance-hydrogen Concentration of Pd Thin Films (Pd 박막의 전기저항-수소농도 이력현상)

  • Lee, Eunsongyi;Lee, Jun Min;Jeon, Kye Jin;Lee, Wooyoung
    • Korean Journal of Metals and Materials
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    • v.47 no.6
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    • pp.372-377
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    • 2009
  • We report on hysteresis behavior in the electrical resistance-hydrogen concentration of Pd thin films. The variation of the electrical resistance has been investigated during the process of absorption and desorption of hydrogen gas ($H_{2}$) as a function of thickness of Pd thin films. The hysteresis behavior in the electrical resistance with $H_{2}$ concentration was found for Pd thin films and consists of $\alpha$ phase, ${\alpha}+{\beta}$ phase, and $\beta$ phase regions. The sensitivity of Pd thin films with $H_{2}$ concentration was found to follow Sieverts' law in the $\alpha$ phase region. However, the sensitivity was observed to increase abruptly with $H_{2}$ concentration in the ${\alpha}+{\beta}$ phase co-exist region. This is because Pd-H interaction is stronger in the $\beta$ phase than in the $\alpha$ phase and needs a higher concentration gradient as a driving force to desorb. The formation of the $\beta$ phase also was observed to cause the structural change because of the lattice expansion during absorption. The hysteresis height and the trace of structural change were affected by the thickness of the Pd film. As the film becomes thinner, the hysteresis height becomes lower and the amount of delamination on the surface becomes smaller. For films thinner than 20 nm in thickness, the delamination was not found but electrical resistance hysteresis was still observed.

Paraffin-Based Phase Change Materials for Solar Reflective Paints Applications (파라핀 기반 상변화 물질을 이용한 태양광 반사 페인트 개발에 관한 연구)

  • Adnin Raihana Jannat;Soumen Mandal;Lee, Han Seung
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2023.11a
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    • pp.67-68
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    • 2023
  • This paper reports on the synthesis of paraffin-based phase change materials (PCMs) designed for use in solar reflective paint (SRP) as a thermal energy storage (TES) medium. These PCMs are prepared using the sol-gel process and are encapsulated in silica. The focus of this research is to evaluate the suitability of these synthesized PCMs for efficient thermal energy storage within SRP applications. The obtained PCMs have nanometric dimensions, which make them well-suited for integration into paint formulations. The study also includes a thorough analysis of the chemical, thermal, and structural stabilities of these materials, confirming their applicability in solar reflective paint.

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Flexible Mold Production Process for Using the PCM (PCM을 활용한 가변형 몰드 제작 프로세스)

  • Kim, Taekoo;Lee, Donghoon;Kim, Sunkuk
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2014.05a
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    • pp.272-273
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    • 2014
  • Existing the free-form concrete segments (FCS) mold is produced by state of solid such as steel, wood, Styrofoam that can not be recycled. Using FCS mold result in delay on schedule and decrease of productivity because it consists of irregular curved variety and it requires more time than fixed mold. Thus, FCS mold should be developed which can reduce the costs and also it can be used as semipermanent. The aim of this study is to suggest of flexible mold production process for using the phase change materials(PCM). PCM is maintain that its solid state at low temperature but it changes phase to liquid state by heating. PCM is suitable material for flexible mold due to change of phase in relatively high temperature compare to other phase change materials such as water. Flexible mold is possible that reuse semi-permanently made by PCM. Thus, this study is proposed the process of flexible mold production for using the PCM. The study results will be used as the basic theory for studies on production and installation of FCS.

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Enhancement of Surface Hardness of Zirconia Ceramics by Hydroxyapatite Powder Bed Sintering (Hydroxyapatite 분위기 소결을 통한 지르코니아 표면 경도 강화)

  • Choi, Min-Geun;Lim, Ji-Ho;Kong, Kyu-Hwan;Jeong, Dae-Yong;Lee, Wonjoo;Li, Long-Hao;Kong, Young-Min
    • Korean Journal of Materials Research
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    • v.24 no.12
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    • pp.677-681
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    • 2014
  • To increase the mechanical property of zirconia, we have investigated the phase change and the resulting hardness of zirconia ceramics by hydroxyapatite (HA) powder bed sintering. It was observed using X-ray diffraction that the cubic zirconia phase, which has a higher hardness value than that of the tetragonal phase, was obtained at the surface of 3 mol% $Y_2O_3$ doped tetragonal zirconia polycrystal (3Y-TZP) ceramics during the sintering process; in our experimental conditions, the phase change at the surface increased as the sintering time increased. We believe that the observed crystalline phase change originated from the decomposition of HA and the diffusion of CaO, as follows. CaO, which was derived from the decomposition of HA at high temperature ($1400^{\circ}C$), diffused into the surface of 3Y-TZP and acted as a stabilizer. As a result, the Vickers hardness value of the treated specimens was higher than that of the non-treated specimen due to the formation of the cubic phase on the surface of 3Y-TZP.

Consideration on the T-history Method for Measuring Heat of Fusion of Phase Change Materials (PCM의 잠열측정을 위한 T-history법에 대한 고찰)

  • 박창현;최주환;홍희기
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.12
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    • pp.1223-1229
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    • 2001
  • Though conventional calorimetry methods such as differential scanning calorimetry (DSC) and differential thermal analysis (DTA) are used generally in measuring heat of fusion, T-history method has the advantages of a simple experimental apparatus and no requirements of sampling process, which is particularly useful for measuring thermal properties of inhomogeneous phase change materials (PCMs) in sealed tubes. However, random criteria (a degree of supercooling) used in selecting the range of latent heat release and neglecting sensible heat during the phase change process can cause significant errors in determining the heat of fusion. In the present study, it was shown that a 40% discrepancy exists between the original T-history and the present methods when analyzing the same experimental data. As a result, a reasonable modification to the original T-history method is proposed.

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Improvement of the T-history Method to Measure Heat of Fusion for Phase Change Materials

  • Hong, Hi-Ki;Park, Chang-Hyun;Choi, Ju-Hwan;Peek, Jong-Hyeon
    • International Journal of Air-Conditioning and Refrigeration
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    • v.11 no.1
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    • pp.32-39
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    • 2003
  • Though conventional calorimetry methods such as differential scanning calorimetry and differential thermal analysis are used generally in measuring heat of fusion, T-history method has advantages of a simple experimental apparatus and no requirements of sampling process, which is particularly useful for measuring thermophyical properties of in-homogeneous phase change materials in sealed tubes. However, the degree of supercooling used in selecting a range of latent heat release and neglecting sensible heat during the phase change process can cause significant errors in determining the heat of fusion. In the present study, it was shown that a 40% discrepancy exists between the original T-history and the present methods when analyzing the same experimental data. As a result, a reasonable modification to the original T-history method is proposed.

Surface acoustic wave gas sensors by utilizing the phase change (위상변화를 이용한 표면탄성파 가스센서)

  • Kim, Jin-Sang;Jung, Yong-Chul;Kang, Chong-Yun;Kim, Dal-Young;Nam, Chang-Woo;Yoon, Seok-Jin
    • Journal of Sensor Science and Technology
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    • v.14 no.3
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    • pp.186-190
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    • 2005
  • This paper describes the development of a surface acoustic wave gas sensor that is designed to detect volatile gas by monitering phase change of output signal as a function of time. The sensor consists of SAW oscillators with a center frequency of 100 MHz fabricated on $128^{\circ}$ Y-Z $LiNbO_{3}$ substrates. Experimental results, which show the phase change of output signal under the absorption of volatile gas onto sensors, are presented. The proposed sensor has the properties of high sensitivity compare to the conventional SAW gas sensor and chemical selectivity. Thus, it is thought these results are applicable for use in sensor array of an high performance electronic nose system.

Rapid Manufacturing of 3D Micro-products using UV Laser Ablation and Phase-change Filling

  • Shin Bo-Sung;Kim Jae-Gu;Chang Won-Suk;Whang Kyung-Hyun
    • International Journal of Precision Engineering and Manufacturing
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    • v.7 no.3
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    • pp.56-59
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    • 2006
  • UV laser micromachining is generally used to create microstructures for micro-products through a sequence of lithography-based photo-patterning steps. However, the micromachining process is not suitable for rapid realization of complex 3D micro-products because it depends on worker experience. In addition, the cost and time required to make many masks are excessive. In this paper, a more effective and rapid micro-manufacturing process, which was developed based on laser micromachining, is proposed for fabricating micro-products directly using UV laser ablation and phase-change filling. The filling process is useful for holding the micro-products during the ablation step. The proposed rapid micro-manufacturing process was demonstrated experimentally by fabricating 3D micro-products from functional UV-sensitive polymers using 3D CAD data.

An Experimental Study on Electrical Energy Generation Based on Phase Change Materials for Application of Underwater Unmanned Vehicles (수중 무인 이동체 적용을 위한 상변화물질 기반의 전기 에너지 생성에 대한 실험적 연구)

  • Yeon-Chul Ha
    • Journal of the Institute of Convergence Signal Processing
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    • v.23 no.4
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    • pp.228-233
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    • 2022
  • This study is an experimental study on how to use phase change materials(PCM) to generate electrical energy for long-term operation of underwater unmanned vehicles. The electrical energy generation method is a volume change and a pressure change that occur as a phase change material changes to a solid or liquid state according to temperature, and the change in pressure creates a flow of fluid to create electrical energy. Polyethylene glycol was used as a phase change material considering the temperature of the ocean. In addition, an electrical energy generating device that converts volume change into pressure at low temperature (1℃~2℃) in solid state and high temperature (21℃~25℃) in liquid state was fabricated. As a result of the experiment, the pressure change according to the phase change rapidly changed between 1 hour and 2 hours, and maintained a pressure of about 24MPa after 4 hours. Through this, it was confirmed that it can be used as a power source for underwater unmanned vehicles using phase change materials and temperature differences. In addition, it was found that a more improved design should be made in order to apply the phase change material to an underwater unmanned vehicle.

Shape-Stabilized Phase Change Materials: Preparation and Properties of Frozen Gels from Polypropylene and n-Eicosane for Latent Heat Storage (형태안정성 PCM: 잠열저장을 위한 Polypropylene과 n-Eicosane으로 구성된 고화젤의 제조 및 특성)

  • Son, Tae-Won;Lim, Hak-Sang;Kim, Tae-Hun;Ko, Jae-Wang
    • Polymer(Korea)
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    • v.34 no.3
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    • pp.261-268
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    • 2010
  • Phase change materials based on polypropylene blended with n-eicosane were studied in this paper. In addition, this paper reviews recent studies on the preparation of shape stabilized phase change materials (SSPCM), such as SSPCM from polypropylenes and n-eicosane, their basic properties and possible applications to latent heat storage. The preparation methods used were the melting method and absorption methods. Shape stabilized PCM(SSPCM) prepared for DSC, WAXD, FTIR spectroscopy, ARES, results of the analysis of shape stability heat capacity to improve were identified.