Preparation And Properties Of MnO₂ Composite Phase Change Materials With Different Crystal Forms And Different Morphologies

Phase change materials(PCMs)have been commonly used in latent heat storage systems.However,most phase change materials have constraints in real-world applications,one of which is poor thermal conductivity.The crystal structure and morphology of manganese dioxide play a certain role in its performance.Different synthesis methods can obtain products of different crystal forms and different morphologies,which directly affects the performance of manganese dioxide.Natural manganese dioxide resources are not lacking,but the purity of natural manganese dioxide is not high,and the purification process is very cumbersome and cannot be directly used as a raw material.Although electrolytic manganese dioxide has excellent chemical properties,it has disadvantages such as high cost,high power consumption,large investment,and large particles.Therefore,the selection of a suitable synthesis method to prepare a comprehensive performance is better,especially manganese dioxide can be used as a composite phase change material carrier has a greater significance.At the same time,the manganese dioxide composite phase change materials with different crystal forms and different morphologies are studied,and its thermal conductivity is better than that of phase change materials.In the experiment,the main equipment used was SEM,XRD,DSC,TGA and thermal conductivity analyzer.The morphological characterization and performance tests were carried out on samples with different crystal forms,different morphologies of manganese dioxide and their composite phase change materials.The potential application of these different crystalline manganese dioxides in thermochemistry was also analyzed.In this paper,potassium permanganate,manganese sulfate monohydrate,ammonium persulfate and other raw materials,by hydrothermal method,redox precipitation method,control reaction temperature,reaction time,raw material ratio and other factors to prepare without crystal form,different morphology Manganese dioxide.The crystal form of the sample was determined by XRD pattern,and the morphology of the sample was determined by SEM image.The raw material samples were prepared for subsequent experiments,and the effects of reaction temperature and time on the manganese dioxide product were also explored.Secondly,the synthesized ?,?,?,?,?-type manganese dioxide and the phase change material are composited by vacuum impregnation,wherein the phase change materials include organic fatty acids,paraffin wax and polyethylene glycol 1500.The composited samples were characterized.The SEM observation shows that a large amount of fatty acids are adsorbed on the surface of manganese dioxide nanowires,nanorods and nanospheres.The results obtained by DSC show that the composite phase change materials have a high latent heat value,ie 121J·g-1.It also shows that the manganese dioxide crystal form has little to do with the amount of phase change material adsorbed,and the decisive factor is still the morphology of manganese dioxide;in addition,after 500 cycles of cold and heat cycles without interruption,the thermal enthalpy value in the composite phase change material decreased by 10.4 J·g-1,which again indicates that the nanocomposite phase change material has stability;and the adsorption of organic fatty acid by manganese dioxide increases with the molecular weight of the fatty acid.Through the TGA test,the nanocomposite phase change material does not exhibit thermal decomposition below 350?,indicating that it has excellent thermal stability;through thermal conductivity experiments,its thermal conductivity is between 0.4158 W·m-1·K-1 and 0.8297 W·m-1·K-1,it is indicated that the manganese dioxide nanotubes and nanospheres can improve the thermal conductivity of the phase change material,and also indicate that the manganese dioxide nanotubes and nanospheres are in the phase change material with large value.