Precipitation And Crystallization Of Rare Earth Carbonates Or Phosphates And Their Particle Characterization Tunning

Particle characteristics of rare earth compound nano/micromaterials has been considered to be the key factors affecting on their functional properties. Therefore, to realize the controlled synthesis on the morphology, structure, size is a necessary way to reveal new material properties and strengthen material functional properties. In this research, precipitation formation and crystal growth characteristics of rare earth carbonates and phosphates as well as the particle growth and aggregation mechanism are comparatively studied, and some concrete method for controlled synthesis of rare earth materials with different required particles chracterizations are proposed.The XRD, SEM and particle size analysis data of yttrium carbonate precipitate and crystals synthesized at different temperature and aging times using yttrium nitrate as raw materials and ammonium bicarbonate as precipitant showed a phase transfer from amorphous to tengerite type yttrium carbonate. Correspondingly, the particle mophorlogy and size changed in the aging process after precipitation, from spherical nano particles into dumbbell shaped and nest like large particle and finally to large spherical aggregates. After calcination, the medium particle size D50 of yttrium oxide increased from 600 nm to 35μm with prolonging of aging time. Furthermore, the precipitation and crystallization mechanism are discussed. And some simple methods to prepare yttrium oxides with different particle sizes by controlling the precipitation and crystallization process are proposed. With these methods, some Eu3+ doped yttrium oxides with different sizes and mophorlogies were prepared and their fluorescent intensities show great dependance on their morphology and size.The crystallization growth behaviour of rare earth phosphate precipitate formed at different p H values using lanthanum cerium terbium chloride as raw material and phosphoric acid or phosphate as precipitant during the aging process was investigated by means of XRD, SEM and particle size analysis. It was found that under acidic conditions,the formed precipitation shows one-dimensional crystal growth characterization. With the rise of p H, the one-dimensional growth will be limited which result in the formation of spherical particles.Therefore, La PO4:Ce,Tb particles with small size and spherical mophology can be easily synthesized by adjusting the solution p H and aging time. With this method, La PO4:Ce,Tb spherical phosphor with excellent properties and size around 1 micrometer was obtained after calcining La PO4:Ce, Tb precursor at high temperature in a reducing atmosphere. Finally,we comparative study the fluorescence properties of the spherical and rod morphology of La PO4:Ce and the effects of solvent on the fluorescence properties.Using yttrium nitrate as raw material, mixed solution of different molar ratios of oxalic acid to ammonium bicarbonate as precipitant, a series of yttrium carbonate oxalates were prepared under different conditions such feeding molar ratios, aging time and temperature. Their composition and phase state as well as mophology and particle size were characterized by XRD, SEM and particle size analysis. The results showed that under condition of no excessive ammonium bicarbonate, the composition and crystall phase of formed precipitates varied from carbonate to carbonate oxalate and finally to oxalate when using pure solution of ammonium bicarbonate, mixed solution of ammonium bicarbonate and oxalate acid, pure oxalate acid as precipitant respectively.Correspondingly, the particle morphology transferred from strip to ellipsoidal and finally to irregular massive. Under the condition of excessive ammonium bicarbonate, the formed products are typical crystalline ammonium yttrium double carbonate. The addition of oxalic acid can change the mophorlogy from rhombus to hexagonal tabular crystal at first, and then further transfer to six prism crystal by the accumulation of thin hexagonal tabular slice during the aging process. With these six prism crystals as seeds and continue synchronous feeding reaction, folds like spherical large particles were formed. Therefore, a simple method was proposed to prepare flaky, columnar and flower shaped yttrium oxide by controlling the crystallization process of ammonium yttrium carbonate complexes using oxalate acid as co-precipitant.