Preparation Of Porous Zirconia Based Monoliths Through Sol-gel Process Accompanied By Phase Separation

Porous zirconia matrix materials have both properties of zirconia matrix materials and porous materials, such as low thermal conductivity, good chemical stability, high specific surface area, excellent heat-shielding and adsorptive performance. They have broad application prospects in catalysis, heat insulation and separation. The research status of yttria stabilized zirconia, La2Zr2O7 and BaZrO3 are firstly introduced, followed by the sol-gel process accompanied by phase separation. This research is focused on the preparation of yttria stabilized zirconia, La2Zr2O7 and BaZrO3, such as the impacts of phase separation inducer, gelation agent, solvent compositions and heat treatments on porous structures. Specific research contents and conclusions are as follows:(1)The inexpensive ZrOCl2·8H2O and YCl3·6H2O are used as precursors, mixture of ethanol and distilled water as solvent, poly(ethylene oxide) as phase separation inducer, propylene oxide as gelation agent, glycol as chelating agent, formamide as drying control chemical additive. Yttria stabilized zirconia monoliths with co-continuous skeletons and porosities as high as more than 60% can be prepared with appropriate compositions of the starting materials and proper gelation temperature. PEO is preferentially distributed into the liquid phase after phase separation and the decrease of entropy is the driving force of phase separation. The doping amounts of yttrium does not have a great influence on the micromorphology of as-dried gels. tetragonal phase of ZrO2 can be obtained after being heat-treated at 800℃ which can be attributed to the stabilization effect of yttrium. Mean marcopore size decrease from 1.7 to 0.7μm and BET surface area decrease from 287 to 34 m2·g-1,respectively, after heat treatment.(2)The low-cost ZrOCl2·8H2O and LaCl3·7H2O are used as precursors, mixture of ethanol and distilled water as solvent, poly(ethylene oxide) as phase separation inducer, propylene oxide as gelation agent, glycol as chelating agent, formamide as drying control chemical additive. Optimal compositions of the starting materials can lead to La2Zr2O7 monoliths with co-continuous skeletons after atmospheric pressure drying. Fluorite structure of La2Zr2O7 can be obtained after heat treatment at 1100℃, and the fluorite structure evolves to pyrochlore structure when increase the heat treatment temperature, what’s more, few zirconia exists in the final products. The prepared La2Zr2O7 has a high porosity but the BET surface area of La2Zr2O7 is relatively low.(3)The cheap ZrOCl2·8H2O and BaCl2·2H2O are used as precursors, mixture of ethanol and distilled water as solvent, poly(ethylene oxide) as phase separation inducer, propylene oxide as gelation agent, glycol as chelating agent, formamide as drying control chemical additive. BaZrO3 monolith, which mean marcopore size is 1.8μm and porosities is as high as 63%, can be fabricated with suitable compositions of the starting materials. Perovskite BaZrO3 can be obtained after being calcinated at 1100℃, and zirconia exists in the final products as well. Mean marcopore size slightly decrease to 1.5 μm and BET surface area dramatically decrease from 188 to 0.8 m2·g-1 after heat treatment.