太陽能基於其取之不盡用之不竭的特性，已被視為現今最可靠的能源形式之一。太陽能發電之技術目前可分為兩大類，分別為太陽能光伏發電以及太陽熱能發電。與太陽能光伏發電系統相較之下，太陽熱能的發電形式可得到更高的能量轉換效率，最高可達到接近50%。為了增加太陽熱能系統中儲熱流體的儲熱能力，在儲熱之工作流體中添加相變化材料，已被證明是一種很有效的方式，然而在相變化材料發揮作用的過程中，一種被稱為材料過冷的現象普遍會隨之發生，這種現象對材料的儲熱表現有害。
　　在本研究中，純鋅微米粒子被選為相變化材料，並在表面包覆二氧化鈦及氧化鋁作為保護性的殼層結構。合成完成後之材料，將以掃瞄式電子顯微鏡（SEM）、X光繞射分析（XRD）、能量色散X-射線光譜（EDS）以及差示掃瞄量熱法（DSC）進行分析。合成後之微粒表面形貌以SEM進行觀測，元素定性分析由XRD及EDS進行。DSC則用以分析鋅微米粒子在不同氧化物殼層的包覆下，其相變化行為間的差異。分析結果顯示鋅微米粒子無論是在二氧化鈦或氧化鋁殼層的包覆下，經過40個吸熱及放熱的循環測試後，都依然維持相當高的熱穩定性。然而由於不同殼層材料其熱傳導性質不同，以及不同製程下殼層的厚度亦不相同，最終材料在使用過程發生的過冷現象，也有不同的嚴重程度。具有較高熱傳導係數之氧化鋁殼層，可使最後的核殼結構鋅微米粒子具有較低的過冷度，同時其殼層厚度亦可透過調整包覆反應時間進行控制。
　　總結而言，本研究提供材料設計上在選擇材料時的參考準則。藉由揀選具高熱傳導係數之材料作為殼層，並控制適當之殼層厚度，由殼層結構所造成的核心材料過冷度可被改善。

　　Solar energy has been considered as one of the most promising energy source because of its inexhaustible feature. The techniques to generate electrical power from solar energy can be divided into two categories nowadays, solar photovoltaic (PV) and solar thermal. Compared to solar photovoltaic systems, solar thermal systems have much higher energy conversion efficiency reach up to 50%. In order to increase the heat storage ability of working fluid used in solar thermal systems, the addition of phase change materials (PCMs) into working fluid have been demonstrated to be an effective method. However, during the operation of PCMs, an unfavorable phenomenon called supercooling is widely observed.
　　In this study, Zn microparticles have been chose to be PCM and coated with TiO2 and Al2O3 as shell layer. The as-synthesized materials are analyzed by SEM, XRD, EDS, and DSC. The difference in surface morphologies was examined by SEM. Elemental analysis was performed by XRD and EDS. And the DSC measurement was used to investigate the phase change behavior of Zn with different oxide coatings. The results show that both of the Zn particles coated with TiO2 and Al2O3 possessed high durability and the performance remained stable under 40 cycles thermal test. However, due to the difference in thermal conductivity and shell thickness, various extent of supercooling will be induced. Al2O3 shell with higher thermal conductivity was able to make the final encapsulated Zn particles possess lower degree of supercooling, and the shell thickness can be controlled easily.
　　In summary, this study provides a guideline for material selection. By choosing the material with high thermal conductivity as shell layer and controlling the appropriate shell thickness, the supercooling raised by shell structure can be less.

1. Abas, N., A. Kalair, and N. Khan, Review of fossil fuels and future energy technologies. Futures, 2015. 69: p. 31-49.
2. Doig, A. Renewable Energy: Climate Change and Carbon Funding. 2007.
3. McIntyre, J., et al., Comparison of Lifecycle Greenhouse Gas Emissions of Various Electricity Generation Sources. 2011, World Nuclear Association.
4. Joseph Byrne, et al. Global Trends in Renewable Energy Investment 2016. 2016.
5. REN21 The Renewables 2016 Global Status Report. 2016.
6. Schleicher-Tappeser, R., How renewables will change electricity markets in the next five years. Energy policy, 2012. 48: p. 64-75.
7. Laboratory, L.L.N., 2015 U.S. Energy Flow Chart. 2016.
8. Laboratory, L.L.N., 2014 U.S. Energy Flow Chart. 2015.
9. Teng, H., G. Regner, and C. Cowland, Waste heat recovery of heavy-duty diesel engines by organic Rankine cycle part I: hybrid energy system of diesel and Rankine engines. 2007, SAE Technical Paper.
10. Burch, S.D., et al., Reducing cold-start emissions by catalytic converter thermal management. 1995, National Renewable Energy Laboratory.
11. Burch, S.D., et al. Applications and benefits of catalytic converter thermal management. in Presented at SAE Fuels & Lubricants Spring Meeting (Dearborn, MI). 1996.
12. IEA, 2015 Key World Energy Statistics. 2016: International Energy Agency.
13. Bolton, J.R., S.J. Strickler, and J.S. Connolly, Limiting and realizable efficiencies of solar photolysis of water. Nature, 1985. 316: p. 495.
14. Green, M.A., et al., Solar cell efficiency tables (Version 45). Progress in photovoltaics: research and applications, 2015. 23(1): p. 1-9.
15. Forsberg, C.W., P.F. Peterson, and H. Zhao, High-temperature liquid-fluoride-salt closed-Brayton-cycle solar power towers. Journal of Solar Energy Engineering, 2007. 129(2): p. 141-146.
16. Denholm, P. and M. Mehos, Enabling Greater Penetration of Solar Power via the Use of CSP with Thermal Energy Storage 2011: National Renewable Energy Laboratory.
17. Lee, K.-H., M.-C. Joo, and N.-C. Baek, Experimental Evaluation of Simple Thermal Storage Control Strategies in Low-Energy Solar Houses to Reduce Electricity Consumption during Grid On-Peak Periods. Energies, 2015. 8(9): p. 9344-9364.
18. Poullikkas, A., Economic analysis of power generation from parabolic trough solar thermal plants for the Mediterranean region—A case study for the island of Cyprus. Renewable and Sustainable Energy Reviews, 2009. 13(9): p. 2474-2484.
19. Salazar, C.M., An overview of csp in europe, north africa and the middle east. CSP Today, 2008.
20. Gielen, D., Renewable Energy Technologies Cost Analysis Series: Concentrating Solar Power. IRENA WORKING PAPER, 2012. 1(2/5).
21. Torresol Energy Commissions 19.9MW Gemasolar Power Plant in Spain. 2011: Torresol Energy.
22. Pavlović, T.M., et al., A review of concentrating solar power plants in the world and their potential use in Serbia. Renewable and Sustainable Energy Reviews, 2012. 16(6): p. 3891-3902.
23. Amadei, C., et al., Simulation of GEMASOLAR-based solar tower plants for the Chinese energy market: Influence of plant downsizing and location change. Renewable energy, 2013. 55: p. 366-373.
24. Behar, O., A. Khellaf, and K. Mohammedi, A review of studies on central receiver solar thermal power plants. Renewable and sustainable energy reviews, 2013. 23: p. 12-39.
25. Dunn, R.I., P.J. Hearps, and M.N. Wright, Molten-salt power towers: newly commercial concentrating solar storage. Proceedings of the IEEE, 2012. 100(2): p. 504-515.
26. Tian, Y. and C.-Y. Zhao, A review of solar collectors and thermal energy storage in solar thermal applications. Applied Energy, 2013. 104: p. 538-553.
27. Zhang, H., et al., Concentrated solar power plants: review and design methodology. Renewable and Sustainable Energy Reviews, 2013. 22: p. 466-481.
28. Philibert, C., Technology roadmap: concentrating solar power. 2010: OECD/IEA.
29. Agency, I.E., Energy Technology Perspectives 2010-Scenarios & Strategies to 2050. 2010: OECD/IEA.
30. Peng, Q., et al., Design of new molten salt thermal energy storage material for solar thermal power plant. Applied Energy, 2013. 112: p. 682-689.
31. Scarlat, R.O. and P.F. Peterson, The current status of fluoride salt cooled high temperature reactor (FHR) technology and its overlap with HIF target chamber concepts. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2014. 733: p. 57-64.
32. Kenisarin, M.M., High-temperature phase change materials for thermal energy storage. Renewable and Sustainable Energy Reviews, 2010. 14(3): p. 955-970.
33. Delpech, S., et al., Molten fluorides for nuclear applications. Materials Today, 2010. 13(12): p. 34-41.
34. Shin, B.C., S.D. Kim, and W.-H. Park, Ternary carbonate eutectic (lithium, sodium and potassium carbonates) for latent heat storage medium. Solar energy materials, 1990. 21(1): p. 81-90.
35. Kearney, D., et al., Assessment of a molten salt heat transfer fluid in a parabolic trough solar field. Journal of solar energy engineering, 2003. 125(2): p. 170-176.
36. Bradshaw, R.W. and N.P. Siegel, Development of molten nitrate salt mixtures for concentrating solar power systems. SolarPACES, Berlin, 2009.
37. Raade, J.W. and D. Padowitz, Development of molten salt heat transfer fluid with low melting point and high thermal stability. Journal of Solar Energy Engineering, 2011. 133(3): p. 031013.
38. Hong, Y., et al., Enhancing heat capacity of colloidal suspension using nanoscale encapsulated phase-change materials for heat transfer. ACS applied materials & interfaces, 2010. 2(6): p. 1685-1691.
39. Lai, C.-C., et al., A solar-thermal energy harvesting scheme: enhanced heat capacity of molten HITEC salt mixed with Sn/SiO x core–shell nanoparticles. Nanoscale, 2014. 6(9): p. 4555-4559.
40. Lai, C.-C., et al., Tunable endothermic plateau for enhancing thermal energy storage obtained using binary metal alloy particles. Nano Energy, 2016. 25: p. 218-224.
41. Liu, M., et al., Review on concentrating solar power plants and new developments in high temperature thermal energy storage technologies. Renewable and Sustainable Energy Reviews, 2016. 53: p. 1411-1432.
42. Sharma, S.D., H. Kitano, and K. Sagara, Phase change materials for low temperature solar thermal applications. Res. Rep. Fac. Eng. Mie Univ, 2004. 29(1).
43. Xi, P., et al., Preparation and performance of a novel thermoplastics polyurethane solid–solid phase change materials for energy storage. Solar Energy Materials and Solar Cells, 2012. 102: p. 36-43.
44. Sharma, A., et al., Review on thermal energy storage with phase change materials and applications. Renewable and Sustainable energy reviews, 2009. 13(2): p. 318-345.
45. Su, W., J. Darkwa, and G. Kokogiannakis, Review of solid–liquid phase change materials and their encapsulation technologies. Renewable and Sustainable Energy Reviews, 2015. 48: p. 373-391.
46. Cingarapu, S., et al., Nanofluids with encapsulated tin nanoparticles for advanced heat transfer and thermal energy storage. International Journal of Energy Research, 2014. 38(1): p. 51-59.
47. Nomura, T., et al., Microencapsulation of metal-based phase change material for high-temperature thermal energy storage. Scientific reports, 2015. 5.
48. Dao, T.D. and H.M. Jeong, Novel stearic acid/graphene core–shell composite microcapsule as a phase change material exhibiting high shape stability and performance. Solar Energy Materials and Solar Cells, 2015. 137: p. 227-234.
49. Tang, X., et al., Fabrication, characterization, and supercooling suppression of nanoencapsulated n-octadecane with methyl methacrylate–octadecyl methacrylate copolymer shell. Colloid and Polymer Science, 2013. 291(7): p. 1705-1712.
50. Yamagishi, Y., et al. An evaluation of microencapsulated PCM for use in cold energy transportation medium. in Energy Conversion Engineering Conference, 1996. IECEC 96., Proceedings of the 31st Intersociety. 1996. IEEE.
51. Hong, Y., et al., Controlling supercooling of encapsulated phase change nanoparticles for enhanced heat transfer. Chemical Physics Letters, 2011. 504(4): p. 180-184.
52. Kano, M., Supercooling and its thermal hysteresis of pure metal liquids. 熱測定, 1991. 18(2): p. 64-70.
53. Lin, C., Y. Lai, and S. Liu, Effect of the surface roughness of sulfuric acid-anodized aluminum mold on the interfacial crystallization behavior of isotactic polypropylene. Journal of adhesion science and technology, 2001. 15(8): p. 929-944.
54. Camacho, E.F. and M. Berenguel, Control of solar energy systems. IFAC Proceedings Volumes, 2012. 45(15): p. 848-855.
55. Sakka, S., Handbook of sol-gel science and technology. 1. Sol-gel processing. Vol. 1. 2005: Springer Science & Business Media.
56. Battisti, D., et al., Vibrational studies of lithium perchlorate in propylene carbonate solutions. The Journal of Physical Chemistry, 1993. 97(22): p. 5826-5830.
57. Klimenkov, M., R. Lindau, and A. Möslang, New insights into the structure of ODS particles in the ODS-Eurofer alloy. Journal of Nuclear Materials, 2009. 386: p. 553-556.
58. Goldstein, J., et al., Scanning electron microscopy and X-ray microanalysis: a text for biologists, materials scientists, and geologists. 2012: Springer Science & Business Media.
59. O'neill Michael, J., Differential microcalorimeter. 1966, Google Patents.
60. Steinmann, W., et al., Thermal analysis of phase transitions and crystallization in polymeric fibers. 2013: INTECH Open Access Publisher.
61. Thomas, L.C., Use Of Quasi-isothermal Mode for Improved Understanding of Structure Change. 2005, TA Instruments.
62. ASTM, Standard Test Method for Determining Specific Heat Capacity by Differential Scanning Calorimetry. 2011, ASTM International, West Conshohocken, PA, 2011.
63. Myung, S.-T., et al., Functionality of oxide coating for Li [Li0. 05Ni0. 4Co0. 15Mn0. 4] O2 as positive electrode materials for lithium-ion secondary batteries. The Journal of Physical Chemistry C, 2007. 111(10): p. 4061-4067.
64. Liu, P., Y. Zhu, and S. Zhang, Hydrophilicity characterization of Al 2 O 3-coated MoS 2 particles by using thin layer wicking and sessile drop method. Powder Technology, 2015. 281: p. 83-90.
65. ZHAO, S.-X., et al., Structure and electrochemical performance of LiFePO4/C cathode materials coated with nano Al2O3 for lithium-ion battery. 无机材料学报, 2013. 28(11).
66. Liu, W., et al., Improvement of the high-temperature, high-voltage cycling performance of LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathode with TiO 2 coating. Journal of Alloys and Compounds, 2012. 543: p. 181-188.
67. Li, Y., et al., Core-shell VO2@ TiO2 nanorods that combine thermochromic and photocatalytic properties for application as energy-saving smart coatings. Scientific reports, 2013. 3.
68. El-Shereafy, E., et al., Mechanism of thermal decomposition and γ-pyrolysis of aluminum nitrate nonahydrate [Al (NO3) 3· 9H2O]. Journal of radioanalytical and nuclear chemistry, 1998. 237(1-2): p. 183-186.
69. Song, J.M. and K.L. Lin, Behavior of intermetallics in liquid Sn–Zn–Ag solder alloys. Journal of materials research, 2003. 18(09): p. 2060-2067.
70. Nie, X., et al., Doping of TiO2 polymorphs for altered optical and photocatalytic properties. International Journal of Photoenergy, 2009. 2009.
71. Tilsch, M., V. Scheuer, and T.T. Tschudi. Effects of thermal annealing on ion-beam-sputtered SiO2 and TiO2 optical thin films. in Optical Science, Engineering and Instrumentation'97. 1997. International Society for Optics and Photonics.
72. Yang, T.e., et al., Effects of nano-Al2O3 and nano-ZrO2 on the microstructure, behavior and abrasive wear resistance of WC-8Co cemented carbide. Rare Metals, 2011. 30(5): p. 533-538.
73. Cingarapu, S., et al., Use of encapsulated zinc particles in a eutectic chloride salt to enhance thermal energy storage capacity for concentrated solar power. Renewable Energy, 2015. 80: p. 508-516.
74. Hoffman, J.D. and J.J. Weeks, Melting process and the equilibrium melting temperature of polychlorotrifluoroethylene. J Res Natl Bur Stand A, 1962. 66(1): p. 13-28.
75. Wunderlich, B., Thermal analysis of polymeric materials. 2005: Springer Science & Business Media.
76. Black, J.K., et al., Phase transitions of hexadecane in poly (alkyl methacrylate) core− shell microcapsules. The Journal of Physical Chemistry B, 2010. 114(12): p. 4130-4137.
77. Ho, C.Y. and R.E. Taylor, Thermal expansion of solids. Vol. 4. 1998: ASM international.
78. Properties: Titanium Dioxide - Titania ( TiO2). 2002; Available from: CERAM Research Ltd.
79. Alumina - Aluminium Oxide - Al2O3 - A Refractory Ceramic Oxide. 2001; Available from: Lucideon.
80. Properties: Silica - Silicon Dioxide (SiO2). 2001; Available from: Lucideon.
81. Gunawan, L. and G. Johari, Specific heat, melting, crystallization, and oxidation of zinc nanoparticles and their transmission electron microscopy studies. The Journal of Physical Chemistry C, 2008. 112(51): p. 20159-20166.
82. Zhong, J., Z. Jin, and K. Lu, Melting, superheating and freezing behaviour of indium interpreted using a nucleation-and-growth model. Journal of Physics: Condensed Matter, 2001. 13(50): p. 11443.