Preparation And Characterization Of Low-temperature Of Apatite-type Ionic Conductor

When the environment and energy issue become more and more serious, solid oxide fuelcells as a new and high-performanced energy using technology, has been attracting greatattention in many countries. Commercial yttria stabilized zirconia (YSZ) has considerableconductivity only at high temperature, which would bring many problems because of itshigh-temperature operation. Therefore, to prepare a sort of electrolyte with great conductivityat intermediate-temperature means a great lot to speed up the industrialization course of theSOFC because it not only can enhance the energetics efficiency, but also decrease the costgreatlyand work out the encapsulation problem.Oxyapatite-type lanthanum silicate is an intermediate-temperature ceramics electrolytematerial with great exploitation potential. This new familyof material become the focus in theresearch of the new-style oxygen ionic conductor due to its higher conductivity than YSZ atrelatively low temperature (below 600℃), lower electron conduction under wide-rangeoxygen partial pressure, lower heat swell and lower cost.In this thesis, using TEOS (tetraethyl orthosilicate 99.9%) and hydrate nitrates (>99%) asraw materials, a series of apatite-type lanthanum silicate powders were prepared by sol-gelmethod. Compared to solid state synthesis, the sol-gel method has the advantages of lowtemperatures and short time. In addition, the resulting products have high conductivities. Thestructure and surface properties of the materials were studied by XRD and SEM. The thermaldecomposition process of the complex precursors and the apatite-structure formationprocesses were characterized byFTIR together withTG-DSC techniques.The dependence of transport number of oxygen ion and electrical conductivity onoxygen partial perssuer indicates that the charge carriers of the silicate oxypatite are oxygenions. Ceramics with larger densiy have higher conductivity. The conductivities were mostlyinfluenced by the La-doping, the amount of inerstisial oxygen, the amount of cation vacanciesand oinic radius et al.