Crystal structures and thermodynamic properties on phase change materials n-C_nH_2n+1NH₃路H₂PO₄(s) (n=8, 9 and 10)

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• 作者：Li-Jun Zhang^a ; You-Ying Di^a ; ^{diyouying@126.com} ; ^{diyouying@lcu.edu.cn} ; Zhi-Cheng Tan^b ; Jian-Min Dou^a
• 关键词：n-CnH2n+1NH3· ; H2PO4(s) (n=8 ; 9 and 10) ; Crystal structure ; Adiabatic calorimetry ; Low-temperature heat capacity ; Solid&ndash ; solid phase transition ; Thermodynamic functions
• 刊名：Solar Energy Materials and Solar Cells
• 出版年：2012
• 期刊代码：81_09270248
• 类别：ce
• 出版时间：June, 2012
• 卷：101
• 期：Complete
• 页码：79-86
• 文件大小：702 K

摘要

Crystal structures of three long-chain n-alkylammonium dihydrogen phosphates n-C_nH_2n+1NH₃路H₂PO₄(s) (n=8, 9 and 10) (abbreviated as C₈P, C₉P and C₁₀P), which may be used as the phase change materials in storage and utilization of solar energy, were determined in layered structures by X-ray crystallography, and the same hydrogen bonding network is observed for these long carbon chain compounds. Low-temperature heat capacities of the compounds were measured by a precision adiabatic calorimeter over the temperature range from 78 to 380 K. Two solid-solid phase transitions were observed for C₈P and C₉P, but only one solid-solid phase transition was observed for C₁₀P. The temperatures, molar enthalpies and entropies of the phase transitions were determined based on the analysis of heat capacity curves. Experimental heat capacities for each compound were fitted to two polynomial equations. The smoothed heat capacities and thermodynamic functions and of the three compounds were calculated with an interval of 10 K in terms of the polynomial equations.