Preparation And Properties Of Lanthanum Oxide Aerogel And Its Doped Zirconium Aerogel

Aerogel is a solid material with a special three-dimensional nanoporous structure and filled with air medium.The special structure gives it excellent properties such as low density,high porosity,and high specific surface area.It has excellent performance in the fields of thermal insulation,catalysis,adsorption,etc.Rare earth lanthanum possesses fantastic properties due to the inherent electronic structure,making them find wide applications in the field of magnetism,optics,catalysis,etc.In theory,rare earth aerogels have the common properties of both aerogels and rare earth compounds.For aerogels,rare earth aerogels are a relatively new field.Insufficient preparation techniques limit the development of their properties and applications.Therefore,researching preparation techniques to obtain lanthanum-based aerogels has important practical value.In this thesis,the preparation of lanthanum oxide aerogel by sol-gel method was systematically studied,and the improvement technology and process of chlorine reduction were proposed for the problem of chlorine residue.Finally,lanthanum and zirconium aerogels were combined to prepare lanthanum-zirconium composite aerogels,and their microstructure and properties were studied.Firstly,Lanthanum chloride was chosen as the precursor and propylene oxide was chosen as the gel initiator.The optimal parameter ratio was determined as n（La）:n（Et OH）:n（PO）=1:36:8.The prepared lanthanum oxide aerogel had good blocking properties.The macroscopic appearance was white and opaque,and the microstructure presented a nanoporous network structure formed by overlapping nanorods.The specific surface area of aerogel was as high as 131 m²/g.After heat treatment at 600-1000℃,the crystal phase changed from h-La（OH）₃ to h-La OCl,the linear shrinkage increased from 12%to 36%,and the crystallinity increased.After heat treatment at 1200℃,the crystal phase changed from h-La OCl transform into stable t-La₂O₃.Secondly,a chlorine reduction technology for synthesizing rare earth lanthanum-based aerogels had been developed,ethanediamine were added into the sol solution to form ethylenediamine hydrochloride precipitates,while acetylacetone was introduced to coordinate La³⁺ions to avoid the further loss of the metal precursor.This method can effectively reduce the Cl^-content in the aerogel.Experiments have determined that the optimal n（La）:n（Hacac）=1:1,the prepared lanthanum oxide aerogel had a macroscopic appearance of white and opaque,and good agglomeration.The microstructure was composed of a nanoporous structure composed of h-La（OH）₃ nanorods and h-La₂O₂CO₃nanosheets.With the increase of PO,La₂O₂CO₃ is gradually replaced by La（OH）₃,and the crystallized lanthanum oxide aerogel still had a high specific surface area up to 74.5m²/g.EDS and IC proved that the chlorine content decreased with the increase of PO,and the lowest was 0.371 wt%.Finally,Zirconium oxychloride was chosen as the zirconium source and lanthanum chloride was chosen as the lanthanum source.The lanthanum-zirconium composite aerogel was successfully prepared by the gel-sol method combined with the supercritical drying.The aerogels with different molar ratios of lanthanum to zirconium were characterized,and the effect of lanthanum doping on zirconia aerogels was researched.The composite aerogel still maintained its original morphology after heat treatment at1000°C,the linear shrinkage was only 25%,the specific surface area remained at 107m²/g,and the grain size was 8.6 nm,which are better than pure zirconia aerogels.It was still t-Zr O₂ after heat treatment at 1200℃,and not changed to m-Zr O₂.Lanthanum doping can effectively inhibit the crystallization,growth and transformation of zirconia particles,and enhance the thermal stability of aerogels.