Study On The Rare Earth Oxide And The Polishing Powder Prepared By Pyrolysis Of Cerium Chloride

The pollution is a severe problem in the process of rare earths oxide preparation.In this article,cerium chloride solution was used to prepare cerium oxide powder via spray pyrolysis,and rare earth polishing powder was made from the crystal cerium chloride through static roasting.The thermodynamics and the kinetics in the preparation process were studied.The CeO2 conversion rate and influencing factors on organizational structure were analyzed.The differential thermal analysis and thermodynamic study of cerium chloride thermal decomposition process showed that the first step was dehydration.With temperature increasing,cerium oxide was generated.The theoretical starting temperature of cerium oxide formation reaction was603K.The kinetics study was also carried out.The pyrolysis process of CeCl3 can be regarded as a gas-solid reaction and it was controlled by diffusion process.Kinetic equation was 1-2/3?(1-?)2/3 = 0.646exp(22.431/RT)t.Combined with Arrhenius equation,the apparent activation energy and pre exponential factor can be respectively calculated as 22.43 1kJ/mol and 0.646.Cerium chloride solution spray roasting system and monitor system wereset up.By combining the mathematical model of temperature and pressure and self-designed monitor system,the real-time monitoring of the temperature and pressure of the spray roasting process was achieved.The control and collection methods for gas flow and liquid flow were explained.A relationship between analog voltage and communication control and Gas mass flow controller or peristaltic pump was set up.The problems of interference fluctuation encountered during signal acquisition were solved via filter methods.The main operating interface and important attached window interfaces were designed.The effects of pyrolysis process conditions were studied.The results showed that the conversion rate of CeO2 reached 99.56%with roasting temperature of 860?,feed concentration of 200g/L and spray rate of 0.3mL/s.Under the same conditions,the Cl%in the products was 0.15%.CeOCl existed when the conversion rate was lower than 88%.With the rate increasing,CeOCl was gradually turned into CeO2.Moreover,the diffraction peak of CeO2 became more sharp and smooth.Lattice structure was becoming more and more orderly and lattice defects decreased.Seen from the SEMand HRTEM images,the cerium oxide powder was hollow sphere or sheet or hemispherical grain.The grain and sub grain boundary was clear.The crystal lattice structure was neat and the crystalline state was good.Small crystal grain fluoride-free polishing powders were prepared by spray pyrolysis.The cutting force was increased with increasing of polishing time.The polishing powders had good performance which prepared at 1100?.The study of solid cerium oxide preparation with citric acid was conducted.With roasting temperature of 600?,cerium chloride concentration of 150g/L and citric acid concentration of 0.029mL/s,cerium oxide of high crystallinity and good sphericity can be obtained.In addition,the citric acid had little effect on the conversion rate of CeO2.The study on the preparation of rare earth polishing powders was carried out.The results showed that the granular morphology of the calcined product interweaved into a network.Larger grain can be got with higher roasting temperature.With the roasting temperature of 800?,roasting time of 3.5 hours and CeCl3:NH4Cl of 1:1,the main constitutes of the generated cerium oxide were:Cl 0.042%,F 5.50%,CeF3 17%,CeO2 83%.The XRD pattern showed that CeF3 and CeO2 existed.The particles were woven mesh structure and small and large particles coexisted.The two phses uniformly mixed,which was beneficial for the effects on the surface of glass in the polishing process.The cutting force remained stable as time went on and it always maintain at a high level of approximate 0.12 mg/min·cm2.