Controllable Preparation And Multifunctional Research Of ZrO₂-SiO₂ Aerogels Composites

ZrO₂-SiO₂ aerogels exhibit excellent thermal insulation due to their high specific surface area.However,the applications of ZrO₂-SiO₂ aerogels are limited by their low mechanical strength and poor temperature resistance.Hereof,the multi-scale mullite fibers were introduced to enhance the strength of ZrO₂-SiO₂ aerogels.Meanwhile,the high temperature stability of ZrO₂-SiO₂ aerogels were improved by Ca²⁺modifying,hexamethyl-disilazane（HMDS）modifying and solvent thermal treatment.With the help of hydrophobic modification by HMDS,the ZrO₂-SiO₂ aerogels composites were fabricated with high mechanical strength,excellent high temperature resistance and super-hydrophobicity,which exhibited enormous potential in the application of thermal insulation.The high mechanical strength and excellent thermal insulation of ZrO₂-SiO₂aerogels composites were prepared by introducing multi-scale mullite fibers such as short-cut mullite fibers,mullite fibers preform and ZrO₂ fibrofelt.The short-cut mullite fibers were homogeneously dispersed in the ZrO₂-SiO₂aerogels with the help of introducing epoxypropane to ensure rapid gel.The ZrO₂-SiO₂aerogels were enhanced with the help of“fiebrs-pull out”and“fibers-bridge”during the process of loading.Inspired by the bird’s nest in nature,the mullite fibers preform/ZrO₂-SiO₂aerogels composites were fabricated by using mullite fibers preform as skeleton and using ZrO₂-SiO₂aerogels as filler,which showed high mechanical strength of 1.35MPa because the bond inside the fiber perform.A large scale（180 mm×180 mm×25mm）and low density（0.302 g/cm³）of ZrO₂-SiO₂aerogels composites were obtained by enhanced with ZrO₂ fibrofelt.The introducing aerogels were useful to decrease the gas conductance because of its high porosity and mesoporous which were lower than that of air free path.The ZrO₂ fibrofelt/ZrO₂-SiO₂aerogels composites exhibited excellent thermal insulation of 0.0341-0.096 W·m^-1·K^-1 with the temperature from room temperature to 1100℃,which were lower than that of traditional fibrous materials and showed enormous POtential in the application of thermal insulation.In order to improve the thermal stability of ZrO₂-SiO₂ aerogels,inorganic ion Ca²⁺and HMDS were introduced to modify the surface of ZrO₂-SiO₂ aerogels without damaging the three-dimensional porous network.The hydroxy of ZrO₂-SiO₂ aerogels were replaced by the Ca²⁺and-Si（CH₃）₃ of HMDS,which were useful to decrease the unsaturated bond on the surface of ZrO₂-SiO₂ aerogels and reduce the surface activity of aerogels at the high temperature.The introduced Ca²⁺and Si obtained by the pyrolyzation of-Si（CH₃）₃ served as the“pinning”particles with dispersed distribute at ZrO₂ grain boundaries at high temperature,which were favor for inhibiting the phase transformation of ZrO₂ and improving the thermal stability of ZrO₂-SiO₂ aerogels.It could be found that the ZrO₂-SiO₂ aerogels exhibited high specific surface area of 223m²·g^-1 and 174.4 m²·g^-1 respectively after sintering at 1000℃,which were higher than that of pure ZrO₂-SiO₂ aerogels(105.8 m²·g^-1).Meanwhile,the solvothermal technology was introduced to modulate the microstructure of ZrO₂-SiO₂ aerogels at aging process,which was useful to promote the particles grow up and strengthen the network skeleton.Thus,the diffusion driving force of particles were increased,which were favor for improving the thermal stability of ZrO₂-SiO₂ aerogels.It exhibited high specific surface area of 130 m²·g^-1,high pore volume of 0.79 cm³/g and low shrink of 9.3%at 1000℃after dealing with solvothermal at 210℃.The ZrO₂-SiO₂ aerogels exhibited a super-hydrophobicity with the contact angle of 154°due to generated methyl siloxy groups on the surface and the formation of a nano-micro structure after modified by HMDS gas.Bacterial cellulose aerogels/silica aerogels（BCAs/SAs）were prepared using three-dimensional self-assembled BC skeleton as reinforcement and methyltriethoxysilane derived silica aerogels as filler,which showed a hierarchical porous structure.The BCAs/SAs could bear a compressive strain up to 80%and recovered their original shapes after the release of the stress.Meanwhile,the BCAs/SAs exhibited super-hydrophobicity with a contact angle of 152°and super-oleophilicity resulting from the methyl groups on the surface of silica aerogel filler.This endowed the BCAs/SAs outstanding oil absorbing capability with the quality factor Q from 8 to 14 for organic solvents and oils.Moreover,the absorbed oil could be retrieved by mechanically squeezed with a recovery of 88%related to the superelastic ability of the composites.In addition,the oil absorbing of BS/SAs could be well maintained with the quality factor Q about 11for gasoline after harsh conditional treatment down to-200℃and up to 300℃.Such outstanding elastic and oleophilic properties made the BC/SAs tremendous potential for applications of oil absorbing,recovery and oil-water separation.