Study On The Microstructure Regulations And Thermal Insulation Properties Study Of ZrO₂ Aerogel

Due to its low intrinsic room temperature thermal conductivity??2.4 W/?mK??,extremely low density and high porosity as mesoporous materials,ZrO₂ aerogel is considered to be the next generation effective thermal insulation materials.However,traditional ZrO₂ aerogel which is built up by the aggregating of nanoparticles of 3-5 nm in diameter exhibits monotonous microstructure,scattering pore size distribution and untenable pore structure.Therefore,properties such as thermal conductivity of ZrO₂ aerogel are hard to optimize by designing its microstructure,which limits the application of ZrO₂ aerogel.To solve the above problem,this research further optimizes the sol-gel technology from the point of microstructure designing and pore structure tuning.On the one hand,by introducing the inducer into the sol-gel system to induce the formation of nanofiber,ZrO₂ aerogel composed of nanofiber subunits-was prepared.On the other hand,ZrO₂ aerogel composed of various types of subunits such as submicron spheres and one-dimension nanofibers was developed by combining phase separation method with sol-gel technology.Such progress provides new thoughts and experiences for designing new types of ZrO₂ aerogel.Based on our research,by analyzing the microstructure and pore structure of the samples,and combing with the heat transfer mechanism,the influence factors to thermal conductivity such as density and pore size distribution is studied.In addition,by tuning the density and pore structure of such materials,ZrO₂ aerogel with very low thermal conductivity was prepared.The main research contents can be summarized as below:1.By optimizing sol-gel technology,H₂O₂ was used as nucleation inducer before the gelation reaction to induce the nanoparticles in the sol to form nanofiber subunits.Then rapid gelation reaction was initiated to maintain the nanofiber microstructure and ZrO₂ aerogel composed of nanofiber subunits was obtained.Characterization of microstructure showed that the interconnected network of such aerogel sample is built up by nanofiber bundles which are aggregated by nanofiber of 10 nm long and 1-2 nm in diameter.ZrO₂ aerogel with low density?0.083-0.116 g/cm3?,high specific surface area?506 m2/g?,low room temperature thermal conductivity?0.0238 W/mK?can be obtained by optimizing the preparation parameter.It is worth noting that the as-prepared ZrO₂ aerogel has the tunable pore size distribution?The pore size distribution is tunable at the range of 19.5 nm-33.0 nm?and the thermal conductivity decreases with the increase of nanopore volume.2.By optimizing sol-gel technology,combining with phase separation method and additive,ZrO₂ aerogel composed of various microstructure subunits such as submicron sphere,one-dimensional nanofiber can be obtained.Microstructure and properties characterization were used to study the formation mechanism of such various microstructures,meanwhile the samples with one-dimensional nanofiber subunits were found to have lower thermal conductivity.ZrO₂ aerogel with low density?0.066 g/cm3?,high specific surface area?505.5 m2/g?,low room temperature thermal conductivity?0.0243 W/mK?and tunable pore size distribution?pore size distribution is tunable at the range of 14.3 nm-51.9 nm?can be obtained by optimizing the preparation parameter.'The relationship between thermal conductivity and pore structure was also studied.3.The influence factor to the thermal conductivity such as density,pore structure of the aerogel samples were studied based on the research data and thermal insulation principle.By adjusting the preparation parameter,the nanopores?particular nanopores with the diameter under 70 nm?volume of the samples could be increased.In this way,the room temperature thermal conductivity of the samples could be significantly reduced.