Synthesis and Size Control for Calcium Fluoride Powders by Precipitation Method

Synthesis and size control of the CaF_2 powders in the sub-micron and nano-meter ranges were investigated by precipitation method in the pure water solvent and ethanol/water mixed solvents.The particle size and morphology of CaF_2 powders were characterized by transmission electron microscopy(TEM) and X-ray diffractometry(XRD).The results indicate that in the aqueous solvent,CaF_2 powders with the average particle sizes of 242nm,79nm and 51nm were obtained through controlling the ratio of nucleation to grain growth by means of changing the adding speed and the concentration of the reactants.In the mixed solvents with the volume ratios of water to ethanol 1∶1,1∶4 and pure ethanol solvent,CaF_2 powders with the average size of 34nm,20nm and 12nm were prepared successfully,and the linear relationship between the reciprocal of CaF_2 particle size and the reciprocal of dielectric constant of mixed solvents is demonstrated.In conclusion,combining the means of controlling the ratio of nucleation to grain growth in the aqueous solvent,which is suitable for synthesizing larger precipitate powders,with the way changing the volume ratio of water to ethanol in the mixed solvents,which is effective to control the size of the nano-meter precipitates,can be utilized to control the particle size in the large range from submicron to nanometer.