| Energy crisis has become increasingly severe since 1970s, which pick up the rise and development of the study of energy storage. Considering the principle of selecting energy storage materials, phase change materials(PCMs) have been widely studied. Particularly, the solid-solid phase materials are attached to increasing importance because of many advantages such as low temperature, high enthalpies, low supercooling degree and so on during the solid-solid phase transition. They also offer many other advantages of small change in volume and no phase separation, which make them suitable for heat storage. Alkylammonium tetrachlorometallates(H) (Cn^bn+i^MCLt (CnM) and their binary system have solid-solid phase transition and can be widely used in many heat storage areas. The article is divided into four parts to study and analyze CnM and their binary system.In the first part, a series of CnM were synthesized, element analysis and IR spectra were used to characterize them, differential scanning calorimetric(DSC) method was used to study the thermodynamic properties such as transition temperature, enthalpy, volatility, supercooling degree and the properties after times of heating-cooling cycles of CnM in phase transitions. The calorimetric results show that CnM are promising candidate materials for thermal energy storage.In the second part, several binary systems of CnM were prepared, the properties of thermal storage of binary system CioZn/C12Zn and and so on were studied by DSC method. The results showinthat binary system have good properties in heat storage such as high enthalpies, no volatility, low supercooling degree and wide range of phase transition tempertures. The last property makes them suitable for wide areas.In the third part, the experimental phase diagrams of binary system CioZn/C^Zn and CioZn/CigZn were established at room temperature by three techniques: DSC method, X-ray diffraction, and IR spectra at various temperatures. X-ray diffraction patterns are convenient for phase analysis, because the interplanar spacing d and relative intensify I arc intrinsic properties of substances, which can confirm the phase of different binary system. The infrared spectra in the range 4000-450cm~' were measured. In the temperature range corresponding to the solid-solid phase transition the characteristic absorption has a sudden change which can declare the mechanism of solid-solid phase transition. The results show that the phase diagrams of the above two systems are similar and are partial miscibility phase diagram with a stable compound being formed. This need think about the miscible degree of two compositions. For binary system phase diagram is determined by the different of two compositions. If their structure and size have little different, they often dissolve each other and form miscible system. Conversely, when they have much different, the miscible degree is limit.The last part of the article chiefly dealt with the calculation of two kinetic parameters(activation energy, Ea; reaction order, n) of C10Zn, C12Zn and C10oZn/C12Zn binary system by modeling the thermograms observed by DSC. The kinetic treatment methods-Kissingerivand Ozawa were used and came to the same conclusion. The conclusion is drawn that the reaction order of their solid-solid phase transition is one and the change of Ea has a rule: For pure compounds CnZn Ea raises with increasing chain length; For C10Zn/C12Zn binary system Ea decreases with increase of the mass concentration of C10Zn. Compared Ea of pure compounds with binary system, the later has a low Ea, which make binary system take place phase transition easily. |
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