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Investigation On The Properties And Application Of Cerium Based Rare Earth Compounds

Posted on:2009-01-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:M LiFull Text:PDF
GTID:1101360245474836Subject:Materials science
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The rare earth extraction and separation techniques in China rank the advanced world level with the decade's efforts contributed by Chinese scientists.However the control of the particle properties of rare earth oxide powder is still not fully understand,so the most exported rare earth products from China are still raw materials.This not only inhibits the application of rare earth materials in high technology areas,but also the transformation of the resource advantage into the economic advantage of rare earth elements in China.Baiyunebo rare earth element district is the world's largest deposit of rare earth elements.98%of the deposit is light rare earth elements including those rare earth elements located before neodymium in the periodic table,and 50%of it is cerium oxide.However, the market has a majority demands for neodymium and praseodymium products.Moreover,the produce of cerium is accumulated with the increasing of exploitation of iron,and the application of cerium products is not fully discovered,this induced severe accumulation of cerium raw materials in Baiyunebo.The value of rare earth elements products is not fully fulfilled in China.This work investigated the synthesis of rare earth oxide powder and the control of their properties based on oxalate deposit system.At the same time,we studied the synthesis of the small and large particles of different system and rare earth oxide with high specific surface area according to the industry market demands.The potential applications of such rare earth oxide particle were also investigated in this work.1.The investigation of the liquid synthesis techniqueThe precursors of CeO2 nanoparticle,Ce2(C2O4)3 particles were prepared using continuous precipitation method.The effects of the precipitation conditions on the kinetic of crystallization were investigated. For example,the effects of the feeding position of reactants,the micro-mixing effects,the feeding speed of reactants and the concentration of reactants on the speed of nucleation and crystal growth were monitored in the process of crystallization.The speed of nucleation and crystal growth as a function of the degree of supersaturation of solution was obtained based on theoretic and experiment data.It can be described as: B=3.01×108Δc1.65,R2=0.91;G=5.17×10-6ΔC1.82,.R2=0.97On the other hand,the effects of the conditions of nucleation and crystal growth on particle size,aggregation and the size of aggregation were investigated in details.The mathematical model was built up based on our results:Lmean=[K1ε1/2-K2ε]∫0(At-B)2.15dt 2.The preparation and application of small CeO2 particlesThe best cerium oxide nanoparticle preparation procedure was obtained after investigated the effects of all precipitation conditions on the particle size.The thermo decomposition of the precursor of cerium oxide was monitored by DTA/TG.The effects of the calcination temperature on the particle size and specific surface area were examined. The best calcination temperature of preparation of cerium oxide nanoparticles was determined.The small CeO2 particles prepared based on carbonate precipitation method can be used as the additive addition of rubber.The effects of the particle size,filling quantity and property modified surface on the properties of rubber were investigated.The results show that the sulfuration and scorch time decreases by adding cerium oxides while the tensile strength at break,modulus at 200%,abrasion resistance,tear strength and the ageing property were improved.The explanation of all improved effects of surface modified cerium oxide particles on rubber is that the hydrophobic organic layer on the surface modified cerium oxide particles enhanced the interaction between particle and the surface of rubber resulted in the increases of dispersity of cerium oxide nanoparticle. So the physical mechanic property of rubber was improved by adding the surface modified cerium oxide nanoparticles.Additionally we invented the ammonia-oxalic acid deposition method to prepare fine cerium oxide particle by modified the oxalate precipitation method.The pH effect of reaction solution on Zeta potential of the precipitants was studied,and pH of final adding point of ammonia and oxalic acid to completely precipitate reactant was determined.The thermo decomposition of the precursor of cerium oxide was examined by DTA/TG and XRD.The effect of the calcination temperature and holding time on the particle size and specific surface area of cerium oxide particles was also studied.The best calcinations conditions to prepare cerium oxide nanoparticles were determined.The result indicates that cerium oxide nanoparticlcs prepared by ammonia-oxalic acid deposition method can be used as high quality polishing powder.The effects of particle size,calcinations temperature,and holding time on the polishing results were also investigated.3.The preparation and application of large CeO2 particles.The effects of preparation conditions on the particle size and loose density by oxalate and bicarbonate precipitation methods were investigated.Finally the best preparation conditions of large rare earth oxide particle with high loose density were discovered.We also investigated the effects of calcinations temperature on the particle size and specific surface area.The application studies show that large CeO2 particles prepared by these two methods have obvious advantage on the polishing application. The particles prepared by oxalate method have six cylinder morphology and higher loose density comparing the particles prepared by carbonate method.They are good materials for polishing the hard surface.The morphology of the CeO2 particles prepared by carbonate method is cauliflower like;they are good materials for polishing the lower hardness surface.On the other hand,both particles can be used as glass decoloring and clarifying reagent instead of the traditional compounds such as As2O3 and Na2SO4·10H2O,which are toxicant and pollutant to the environment. Using rare earth oxide instead of As2O3 and Na2SO4·10H2O can eliminate the pollution and improve the transparent degree of glass.4.The properties and application of cerium oxide particles with high specific area.The effects of different preparation methods on the properties of cerium compounds were studied.The best preparation conditions were determined based on the investigation of the effects of the precipitation method,metal ions' concentration,the molar ratio of metal ions, precipitator's concentration,stirring speed,the reaction temperature and pH of solution on the properties of cerium compounds.Additionally, cerium compound coated with Al2O3 and SiO2 was prepared,the result show that the specific surface area of cerium compound dramatically increased as well as thermo stability,however the oxygen storage capacity decreased.The effects of doping elements on the properties of cerium compound were studied.It turns out that doping a small amount of yttrium can enhance the specific surface area and thermo stability of Ce-Zr compound as well as doping a small amount of lanthanum.We found that doping large amount of yttrium and lanthanum decreased the specific surface area and thermo stability.LaCePrZr and LaCePrYZr compounds were prepared using LaCePr rich by-products from the extraction and separation of neodymium.It tums out that LaCePrZr and LaCePrYZr compounds have high specific surface area and thermo stability.The catalysis evaluations show that these cerium compounds can be used as the motorcar tail gas purification catalyst.
Keywords/Search Tags:Rare earth element, Cerium, precipitation, nucleation, crystal growth, Small particles, Large particles, High specific surface area, Glass, Rubber, Polish, Catalyst
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