Tuning The Phase And Particle Characterization Of Rare Earth Doped Zirconia Powders And Their Applications

Due to the unique physical and chemical properties, rare earth doped zirconiahave found wide applications in ceramics, catalytic, solid electrolytes and adsorptionmaterials. Moreover, it is found that their crystal structure and particle characteristicsdepend on their synthesis methods, and show a substantial influence on theirperformance in industrial applications. This study focuses on the relationship of theparticle characteristics and phase structure of rare earth doped zirconia with theirsynthesis methods with sodium chloride as addictive or not. And the applicationproperties of rare earth doped zirconia as ceramics and contamination adsorption areevaluated. The detailed contents are as following.(1) Partially stabilized yttria and ceria co-doped zirconia nanocrystals(PS-YCZ-NCs) were successfully synthesized using a sol-gel method with sodiumchloride as an additive. The phase composition of PS-YCZ-NCs was dependent onthe dosage of sodium chloride added during the sol-gel process as well as thecalcination conditions. Therefore, the percentage of the tetragonal phase was easilytuned by the dosage of sodium chloride and the calcinations conditions. By increasingthe dosage of sodium chloride and the calcination temperature, the content of thetetragonal phase in the PS-YCZ-NCs decreased from100%to10.9%. PS-YCZ-NCscontaining the pure tetragonal phase (100%) have been prepared using this method byemploying calcination temperatures of less than600℃.According to these results,method of controllably synthesizing PS-YCZ-NCs with different tetragonal andmonoclinic content is proposed. The role of NaCl in tuning the phase compositionand particle characteristics was discussed.(2) Yttria and ceria co-doped zirconia (3YxCe-ZrO2) were prepared via solutioncombustion method. It is found that the phase and morphology of synthesized3YxCe-ZrO2powders using ethylene glycol as fuel NaCl as additive were dependenton the dosage of sodium chloride and calcination temperature. By increasing thedosage of sodium chloride, the monoclinic phase content in3Y1Ce-ZrO2increased.When the ratio of ethylene glycol (EG) to NO3-assuming from1:2to3:2, the 3Y1Ce-ZrO2obtained by combustion synthesis with NaCl dosage ranging from5%to20%, washing NaCl with water and calcination at800℃show well-dispersedspherical particles with size around0.1μm. Increasing the dosage of NaCl in thecombustion process or without washing the remaining NaCl before calcining, themonoclinic phase content of synthesized3Y1Ce-ZrO2increased and the particleagglomeratiom became more serious. Meanwhile,3YxCe-ZrO2powders were alsosynthesized using citric acid as fuel, ethylene glycol as additive. It is found that thephase composition of products is dependent on the dosage of co-doped ceria andcalcination temperature. By increasing the calcination temperature from400℃to1400℃, the content of the tetragonal phase in the3Y1Ce-ZrO2decreased from100%to35.8%. At calcining temperature800℃, the phase composition of obtained3YxCe-ZrO2were determined to be tetragonal-monoclinic phase for x=1, puretetragonal phase for x=5,9and cubic-monoclinic phase for x=11,13,15.(3) Spherical granulation powders with particle size around5μm were preparedby a method employing co-precipitation, spray drying and calcination. The phasecomposition of3YxCe-ZrO2was found to be controlled by the calcinationtemperature and ceria content. At the same calcination temperature, the content of thetetragonal phase in the3YxCe-ZrO2increased with the ceria content increasing.When the calcination temperature increasing from400℃to1400℃, the tetragonalphase content of3YxCe-ZrO2were decreased sharply for x=1-3and slightly forx=5-7. Therefore, the phase composition of3YxCe-ZrO2can be easily tuned bychanging the content of ceria or calcination temperature.(4)3Y-ZrO2and its mixture with multi-walled carbon nanotube (MWCNTs) orgraphene or graphite were conducted to milling, spray drying granulation, isostaticpressing and sintering, a series of composite ceramics materials were prepared. Theeffects of sintering atmosphere and temperature on their Vickers hardness, bendingstrength, morphology, and the phase composition are investigated. The Raman spectrademonstrated the main phase of the as-prepared composite ceramics is tetragonal. Theceramics prepared by calcination at1450and1500℃are compactness and show highVickers hardness of1271.4~1672.6. Correspondingly, the maximum bending strengthof composite ceramics prepared taking0.1wt%MWCNTs, graphene graphite as additive and without additive were determined to be553.50,572.95,517.12and535.13MPa respectively, indicating that MWCNTs and graphene have positive effectsto strengthen3Y-ZrO2ceramics.(5) MWCNTs/3Y-ZrO2composed powders were prepared by ball-milling andspray drying, and used as adsorbent for methylene blue. It is found that theiradsorption process fits well to Langmuir and Freundlich models. The maximumadsorption capacity calculated by Langmuir model is69.5mg/g at308K.Thermodynamic data calculated based on the adsorption data at differenttemperatures show the adsorption process is spontaneous (negative△Gθ) andendothermic (positive△Hθ).3Y-ZrO2powders prepared by precipitation, ball-millingand spray drying methods also exhibit adsorption ability toward methylene blue, theiradsorption process fits well with Langmuir isotherm model and pseudo-second-orderkinetic model. However, the negative values of△Gθand△Hθindicated theadsorption process is a spontaneous exothermic process. The calculated maximumadsorption capacity based on Langmuir model is only43.99mg/g.