Preparation And Performance Of Ceramic Matrix Composites Infiltrated Phase Change Materials As Thermal Insulations

Phase change materials (PCMs) have the function of energy storage andtemperature control, because it can absorb a large amount of heat in an approximateisothermal process. Thus PCMs can be introduced into the high-speed aircraftthermal protection system (TPS) to improve the performanee of TPS. This workadopt paraffin wax, stearic acid, erythritol, mannitol as phase change materials andporous silicon nitride ceramic serves as the framework, and prepare form-stablephase change materials by the technology of spontaneous molten infiltration. theeffect of the parameters in infiltration process including infiltration temperature andtime on the mass fraction of PCMs in the composite, then the microstructure ofcomposite, the compatibility of phase change materials and the matrix, thermalstability and thermal control properties of the composites were characterized.The properties of porous silicon nitride and the phase change materialsarecharacterized by a series of test means, such as mercury intrusion porosimetry,SEM and DSC etc. The results indicate that the porous silicon nitride have athree-dimensional network of interconnected pore structure, and the phase changematerials of paraffin, stearic acid, erythritol and mannitol has a high latent heatstorage capacit。The infiltration process is researched by considering infiltration temperatureand time, the result shows that under the best infiltrating conditions which are70℃,80℃,150℃,200℃for paraffin wax, stearic acid, erythritol, mannitol,30min,PCMs reach infiltrating saturation. the mass fraction of the PCMs in the compositeis respectively41.46%、43.55%、50.32%、53.14%, it indicates that the porous matrixhas a strong adsorption capacity and good wetting to the liquid.of PCMs.There is noreaction among the PCM-porous silicon nitride ceramic composite according thechemical and phase analysis with FTIR,XRD, and no produce new substance. Thematerial phase change temperature and enthalpy of the four kinds of phase changecomposite are:53.17℃,54.12J/g;48.66℃,77.29J/g;118.08℃,191.13J/g;165.21℃,213.15J/g. In addition,the dielectric constant of paraffin and stearic acid compositephase change material are approximately2.8and3.2, the values of their loss tangentare in the range1.04~3.51×10-2and1.12~1.43×10-2range, basically meet therequirements of wave-transparent materials.The experiment are proposed to investigate the thermal absorb characteristicsof porous silicon nitride infiltrated with PCMs for thermal protectionapplications.,the result shows that there is a significant temperature platform in the temperature-time curves of three kinds of stearic acid,erythritol,mannitolcomposite phase change materials, the duration of the temperature platform are:80s,360s,600s.having a positive correlation with the phase change latent heat. Itindicates that PCMs acts as thermal absorb material limiting the temperatureabruptly rising.The result of thermal stability test shows that the decompositiontemperature ranges of paraffin wax, stearic acid, erythritol and mannitol are:180℃~350℃;140℃~260℃;170℃~291℃;250℃~360℃; The result of thermal cycleexperiment shows that phase change composites have little weight loss, of whichthe stearic acid composite has the highest weightlessness rate which is2.1%, theweightlessness rate of paraffin, erythritol, mannitol composite phase changematerial are0.66%,0.15%,0.20%.