Y_2(CO_3)_3的沉淀结晶过程与晶粒大小控制

Precipitation Crystallization Process of Yttrium Carbonate and Size Controlling Synthesis of Ytterium Oxide Particles

研究了NH_4HCO_3与Y(NO3)3反应形成的Y_2(CO_3)_3沉淀在陈化过程中的结晶生长机制及其晶粒大小控制方法。结果表明:在陈化过程中发生了由无定型沉淀向水菱钇型结晶Y_2(CO_3)_3的相态转变,其外观形貌也相应地由纳米球形颗粒转变为哑铃状、鸟巢状和球状结晶聚集体。首先是晶型核在颗粒表面的形成,随即进入晶体生长阶段,促进无定型沉淀的快速溶解并在晶核表面生长,表现出以沿晶胞c轴方向的一维生长特征,形成针状细小结晶;由于结晶速度快,针状结晶演变为枝状,并相互连生聚集成哑铃型、巢型和球形聚集体。提高陈化温度可以加速相态转变和形貌演变过程,在短时间内获得大颗粒结晶聚集体。据此,提出了通过沉淀结晶过程和条件的控制来合成不同大小和形貌的Y_2(CO_3)_3和Y_2O_3粒子的基本方法,并分别制备了中心粒径D50在600 nm左右和35μm左右的Y_2O_3产品。

The crystallization growth characterization of yttrium carbonate formed via the precipitation reaction of yttrium nitrate with ammonium bicarbonate was investigated by means of scanning electron microscopy（ SEM）,X-ray diffraction（ XRD） and laser particle size analyzer（ LPSA）. The results showed that during the aging process,the initially formed spherical nano amorphous precipitates were successively transformed into dumbbell,nest and spherical shaped aggregates of tengerite type yttrium carbonate crystals. This morphology evolution and size enlargement meant that the aging process was experienced a nucleation and Ostwald ripening in which the amorphous particles dissolved and grew onto the crystalline particle surface. It was found that the nucleation and crystal growth of yttrium carbonate showed characteristics of one dimension growth along the c direction,resulted in the formation of fine acicular crystal. These acicular crystals then evoluted to dendrite crystals which assembled to dumbbell,nest type and spherical aggregates by linked each other. Increasing aging temperature could accelerate the phase transformation and structure evolution,and form large particles of crystalline aggregates in a short period of time. Therefore,a method to synthesis yttrium carbonate particles with large size（ D50） over 40 micrometers or small size below 1micrometer was proposed. With this method,yttrium oxides with medium size ranging from 600 nm to 35 μm could be obtained by simple controlling the precipitation and crystallization process of yttrium carbonates.