Preparation And Characteristic Of Zirconia Based Composites For Thermal Insulation With Nano Pore

Owing to the unique nano porous structure and excellent thermal insulation performance,aerogel was listed as one of the top ten materials in the 21^st century.Researchers have theoretically predicted that zirconia aerogel has the lowest thermal conductivity among metal oxide aerogel due to its high melting point and low intrinsic thermal conductivity,which make zirconia aerogel have great potential in the field of highly efficient insulation.At present,the research on zirconia aerogel is not enough for rapid development of industrial application.Due to the high activity of the precursors commonly used in the sol-gel reaction of zirconia aerogel,the rate of hydrolysis-condensation is difficult to control,and the performance of the prepared zirconia aerogel still has a large space for improvement.Recently,polyacetylacetonatozirconium with low reactivity was chosen as precursor to prepare zirconia aerogel with uniform structure.But the acetyl acetone ligand in the wet gel affected the performance of zirconia aerogel.In this thesis,acetyl acetone group in wet gel was successfully removed by alkoxide soaking method,and zirconia aerogel composites were synthesized with the introduction of continuous quartz fiber wool as enforcement.The zirconia wet gels prepared by polyacetylacetonatozirconium were modified by a variety of alkoxide solutions.It was found that the methyl orthosilicate,ethyl orthosilicate,triethyl borate could effectively remove the acetyl acetone group in wet gel and enhance the mechanical strength of wet gel.Among the three kinds of alkoxides,it is found that the modification effect of methyl orthosilicate is the most obvious.The modified wet gels were dried by supercritical drying of ethanol and microwave drying respectively,which provided a new idea for low-cost drying of aerogel.The rheological properties of zirconia sol placed at ambient temperature for different time were investigated and it was found that the zirconia sol has excellent stability.Meanwhile,the silica-zirconium aerogel composites were prepared by using continuous quartz fiber wool with fiber diameter 1-3μm as reinforcement.The morphology,structure,and composition of the composites with different fiber volume ratio and aerogels with various density were analyzed.The microstructures of the composites were characterized by computed tomography technology.The fiber with different volume ratio（3.103%）,defect volume（1.415%）and fiber specific surface area（58.74 mm²）of the composite,which obtained by computed tomography,were compared with the theoretical value.The application of computed tomography provides a new idea for the microstructure characterization of thermal insulation composites.The prepared composites have excellent thermal insulation performance,whose thermal conductivity is as low as 0.036 W/（m·K）at 1000℃and 0.070 W/（m·K）at1200℃.A butane spray gun was used to heat one side of the composite with a thickness of 10 mm.After 20 minutes,the back side temperature of the composite stabilized at about 230℃.It has good mechanical properties and its compressive strength,flexural strength,bending strength and shear strength can reach 0.97 MPa,1.39 MPa,1.55 MPa,0.4 MPa,respectively.The aerogel composite has no shrinkage after 30 min heat treatment at 800℃in muffle furnace,which confirmed its good thermal stability.In previous studies,fiber needled felt and short fiber were generally used as the fiber reinforcement of aerogel composites.In this thesis,continuous fiber wool was innovatively used as the reinforcement to fabricate aerogel composites with low density,low coefficient of thermal conductivity,high strength,good stability,which provides a new idea for the study of aerogel insulation composites.