Preparation And Morphology Control Of Submicron Spherical Yttrium Fluoride Oxide

Fluorine yttrium oxide（YOF）is a good rare earth doped matrix,which can improve the luminescence,heat resistance and corrosion resistance of materials,and is widely used in semiconductor materials,thermal barrier materials,thermal spraying materials and other fields.In view of the existing preparation method is difficult to obtain submicron spherical YOF problem,based on scanning electron microscopy,energy dispersive spectrometer,laser granularity instrument,X-ray diffraction analysis,thermal analyzer and infrared spectrum for characterization methods,submicron spherical yttrium fluoride oxide powder was prepared by yttrium hydroxide spray granulation-fluorination-roasting and urea homogeneous precipitation-fluorination-roasting.The YOF preparation and morphology control technology and the thermal decomposition kinetics of fluorinated precursor obtained by urea homogeneous precipitation-fluorination were studied.The main research contents and results are as follows:（1）The effects of spray granulation conditions on the morphology and particle size distribution of the precursor were investigated.The spherical precursor with D₅₀of 12.4μm was obtained under the conditions of slurry concentration of 5 g/L,feeding speed of 15 rpm and nozzle frequency of 200 Hz.The effects of fluorination temperature,addition amount of HCl,YCl₃,NH₄F and other factors on the morphology and elemental composition of the fluorinated precursor were investigated.The spherical fluorinated precursor with 100～500 nm was obtained at Y（OH）₃:YCl₃:HCl:NH₄F=1:0.6:0.9:3.3,liquid-solid ratio 50:1 and fluorination for 5 min.The thermal decomposition of fluorinated precursor and the effects of calcination temperature and time on the phase composition,particle size and morphology of fluorine yttrium oxide were analyzed.YOF powder was obtained by calcination of fluorinated precursor for 2 h at 800℃.However,it was difficult to obtain spherical YOF by this preparation method because of melting and sintering of the powder during calcination.（2）The influence of the conditions for preparing the precursor by homogeneous precipitation method of urea on the morphology and particle size of the powder was analyzed,and the phase composition of the precursor was determined.Spherica Y（OH）CO₃·n H₂O with particle size distribution range of 300～400 nm was obtained under the conditions of urea concentration of 1mol/L,yttrium chloride concentration of 0.01 mol/L,initial solution p H 4,reaction time of 2 h,temperature of 85℃,ice water quenching and air blast drying.The preparation conditions of YOF from fluorinated precursor by roasting were studied.The results show that the spherical morphology of the powder can be inherited after the fluorination process.The spherical YOF with particle size range of 150～300 nm can be obtained by roasting the fluorinated precursor at 800℃for 2 h,and the roasting time should not exceed 2 h.The formation kinetics of yttrium fluoride oxide was studied by Flynm-wall-ozawa method and Coats-Redfem method.The apparent activation energy of the first stage of the thermal decomposition reaction of fluorinated precursor was 65.46 KJ·mol^-1,and the apparent activation energy of the second stage was 153.60 KJ·mol^-1.The pre-exponential factor is 2.37×10⁹,and the reaction order is 4.