Synthesis And Dispersion Property Of CeO₂ Nanoparticles By Precipitation Method

Because of having lots of functional characters,CeO2 nanoparticles have been applied widely in the fields of high technology, such as oxygen tolerance materials,SOFC,radiation resistant glass, luminescent materials and purification of automobile exhaust gases.Recent investigation shows that CeC>2 nanoparticles can be used as CMP slurry to polish IC chip. As abrasive particles for silicon wafer and silica dielectric layer in CMP process, CeO2 nanoparticles have more advantages of higher smoothness,higher velocity and better selectivity than SiO2 nanoparticles.CeO2 nanoparticles are synthesized by liquid precipitation with a little surfactant added.In this reaction,Ce(NO3)36H2O is used as raw materials and (NH4)2CO3.H2O is used as precipitator. Reaction time,reaction temperature,stirring velocity,surfactant and condition of thermal treatment condition are investigated systematically, and finally the optimum technological conditions are obtained. 0.lmol/L (NH4)2CO3.H2O aqueous solution is added quickly into 0.lmol/L Ce(NO3)3-6H2O aqueous solution with 4.0g/L PEG4000, reacting for 10min at 40 under stirring velocity of 800r/min according to 3:2(ratio of mol of (NH4)2CO3-H2O and Ce(NO3)3-6H2O), then the precursor of Ce2(CO3)3-H2O is obtained.After Ce2(CO3)3-H2O is calcined for Ih at 300,CeO2 nanoparticles with high purity are obtained successfully . CeO2 nanoparticles size is smaller than90nm ,crystal size is 5.41nm,specific surface area is 140.61m2 /g,purity is not lower than 99.97%. The result shows that cost is low,the equipment and the process are simple, pollution is low, impurity can be removed effectively and dispersion property is good by this method, which has bright prospect in industry.Heat treatment process has an important effect on the structure and property of nanoparticles.In this paper,the behavior during the growth of CeO2 nanocrystalline is studied in detail and the effect of calcination temperature and time on the crystal size,degree of lattice distortion,lattice parameter and density of CeO2 are also investigated.With increasing calcination temperature,crystal size and density of CeO2 grow larger evidently,while lattice parameter and the degree of lattice distortion of CeO2 grow smaller.At 300, calcination time has no evident effect on the crystal size of CeO2.However, with increasing time, crystal size of CeO2 becames larger at 700 癈 ,during which growth of the crystal is found to be fast at first, and then slow gradually. At the same time, lattice parameter increases, while density and the degree of lattice distortion decrease. Growing index of CeO2 is 5, agreeing with equation that index is 5 and constant of growing velocity of CeO2 is 6.46 105nm5/h at 700.Activation energy of growth of CeO2 is 34.315kJ/mol in the range of 300~400and 89.376kJ/mol in the rang of 400~1000. In the process of growth, disffusion growth plays a leading role.In CMP technology,abrasive particles which disperse fully in the liquid is the premise to ensure the quality of CMP.In this paper, wettability, surface charge potential and dispersion property of CeO2 nanoparticles in the water under different conditions are researched furtherly.It shows that pH value has an important effect on the wettability of CeO2 nanoparticles , CeO2 nanoparticles have good wettability at pH 11 or so and bad wettability at pH 6.7 or so. In the acidic water,surface of CeO2 nanoparticles has positive charge and Zeta potential is most at pH 4 or so.While in the alkalescent water,surface of CeO2 nanoparticles has negative charge ,and absolute value of Zeta potential is most at pH 11 or so,pHIEP of CeO2 is about 6.7. Dispersion method by ultrasonic is better than mechanical agitation method.When 225mg/L (NaPOa)6 is added into CeO2 suspension,the CeO2 has good dispersion in wide pH value.