Preparation Of Compound Pec/silica Phase Change Material By Sol-gel And Ultrasonic On-line Monitoring

In recent years, phase change materials (PCM) become hot in the research of energy conservation, temperature controlling, infrared stealth and so on because of its energy storage ability. Common phase change materials become to liquid in the solid-liquid phase transfer, while causing inconvenience to use, but compound phase change materials can overcome the shortcoming effectively, improve the application effect and expand application scope. For example, organic phase change materials can overcome undercooling and phase separation, with large latent heat; the silicon sol-gel can support dispersible phase change material, improve heat and mass transfer and own good chemical and thermal stability. The sol-gel reaction of ethyl-orthosilicate (TEOS) is commonly applied when produce the compound material with silicon gel, so it is crucial to research its sol-gel action change. In this thesis, polyethylene glycol (PEG) is modified by the porous sol network structure of silica (SiO2) gel through the Sol-Gel approach in the preparation of compound phase change material, and the thermal performance of material is researched. It simultaneously attempts to use ultrasonic on-line monitoring method and make the real-time feedback to sol-gel internal information (gel generation process, phase separating degree and so on), inquire into the dynamical mechanism of materials preparation by the analysis and tests verification.The main results include:1. It has studied the sol-gel system preparation with TEOS as the forerunner, with ethanol for solvent and diluted hydrochloric acid as catalyst ( the pH of mixture is about 1.4), mainly inspected the temperature change and different mole ratios of water and silicon combined with ultrasonic on-line testing. Results indicate that, the higher temperature favor the condensation, the response effectiveness is better when mole ratio of water and silicon is 8:1 under same temperature. The ultrasonic signal attenuation change is obviously consistent with the reaction degree and change trend of particle size, and the experience model is put forward about TEOS sol-gel process by fitting ultrasonic data.2. In the foundation of above system, it studies the method of compound phase change material preparation through PEG being modified by SiO2 and the thermal performance of materials. The sol-gel reaction is carried through with different molecular weight PEG (1000, 2000, 4000, 6000, 10000) for phase medium. In the compound materials, the biggest quality content of PEG achieves 80% to 90% and no PEG exudate is observed. The DSC analysis indicate that, The phase change enthalpy is 62.57J/g- 48.73J/g, and phase change temperature is 25.8℃- 61.77℃in the compound materials with different PEG molecular weight. The phase change enthalpy is 54.97J/g-146.4J/g, and phase change temperature is 55.4℃- 60.5℃in the compound materials with different mass content of PEG4000. The maximum difference of compound material phase change temperature is less than 8% compared with PEG4000, and the phase change enthalpy of 70% compound material only decreases 24%. So the phase change materials still have good thermal performance after modification. The step cold curves analysis may know, the maintenance temperature is 31℃- 45℃, the maintenance time is approximately 6-10 minutes.3. It discussed the influence factors to thermal properties of compound materials. The DSC analysis show that, the phase change temperature and enthalpy increase along with the PEG molecular weight increases, but the change is not obvious even less when the PEG molecular weight is bigger than 4000 or the content is bigger than 70%, and is consistent with the gelatin time change. The IR analysis indicate that, PEG and SiO2 are mechanical compound in the preparation process, not producing new substance. Through DSC and XRD analysis, it indicates the PEG molecular chains are fixed and restricted in the silicon gel network to cause the degree of crystallization to drop, and the phase change temperature and enthalpy depression.It has researched the thermal properties of compound phase change materials and the phase change behavior of PEG, and carried on the inspection and confirmation by ultrasonic on-line monitoring technology. It has provided a reference for the synthesis experiment of compound materials by the sol-gel approach and the innovative thinking to innovate in a means of detection in the material preparation research.