| As the motive force of human life,energy is closely related to the development of modern society and economic prosperity.Today,the energy has entered a new period of change,and the problem of energy shortage has emerged all over the world.Phase change materials will absorb or release a large amount of latent heat in the process of phase change,and can exchange energy with the environment,so as to achieve the purpose of controlling environmental temperature and energy storage,which are playing an eye-catching role for easing the energy crisis in recent years.This thesis mainly studied from the following aspects: paraffin/calcium carbonate microencapsulated phase change materials and paraffin/silica microencapsulated phase change materials were prepared by in-situ polymerization and sol-gel method with paraffin as the core material,calcium carbonate and silica as the shell materials,respectively.The effects of different inorganic shell materials on the thermal properties and infrared stealth property of phase change materials were studied.Then,stearic acid and decanoic acid were used as the composite core materials,and calcium carbonate as the shell material to prepare stearic acid/decanoic acid composite microencapsulated phase change materials by in-situ polymerization.The phase transition temperature range of the microcapsules was adjusted by changing the proportion of the core materials.Finally,the microcapsules were modified by nano iron powder,and the effects of the doping amount of nano iron on the thermal properties,infrared stealth performance and magnetic properties of the microcapsules were studied.The results show that the coating of paraffin by calcium carbonate or silicon is a physical process.It was found that the paraffin/calcium carbonate microencapsulated phase change material have better phase change performance and thermal stability.When the amount of emulsifier sodium dodecylbenzene sulfonate is 8% of the core material and the mass ratio of paraffin to calcium carbonate is 3: 2,the prepared microcapsule has the best thermal properties:the melting temperature and solidification temperature are 53.90°C and 50.88°C,respectively,the melting enthalpy and solidification enthalpy are 115.86 J/g and 114.04 J/g,respectively,and the heat storage efficiency is 97.27%.The heat weight loss temperature is in the area of172.37-398°C,which the initial and termination heat weight loss temperature are delayed about50°C and 127°C,respectively compared with paraffin.The thermal conductivity is 0.856 W/(m K),which is increased by 6.8 times compared with paraffin.It has the best infrared stealth performance when it acts around the phase transition temperature.With the change of the proportion of composite core materials,the melting temperature range is 24-53°C.After encapsulated by calcium carbonate,the melting temperature and solidification temperature range of stearic acid/decanoic acid composite microencapsulated phase change material are 31.73-62.49°C and 24.87-54.53°C,respectively.The thermal stability and thermal conductivity of microcapsules are not affected by the proportion of the core materials.In addition,by changing the proportion of the core materials in microcapsules,it can be applied to the targets with different temperature to achieve the best infrared stealth performance.After doping with nano iron,the phase transition temperatures of microcapsules increased,but the phase transition enthalpy decreased.The microcapsules modified with nano iron have excellent thermal stability and packaging performance in the range of 20-450°C.With the mass ratio of nano iron to the core materials increasing from 0% to 10%,the thermal conductivity increased from 0.755 W/(m K)to 2.538 W/(m K),which increased about 2.4 times;and the infrared emissivity decreased from 0.89 to 0.38,which decreased about 57.3%.The thermal conductivity and infrared stealth performance of the microcapsules modified with nano iron were greatly enhanced,and the microcapsules have typical superparamagnetism. |
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