仲钨酸铵晶体生长机理及形态研究

STUDIES ON THE GROWTH MECHANISM OF AMMONIUM PARATUNGSTATE (APT) CRYSTAL AND ITS TOPOGRAPHY

研究了掺入NH4Cl下仲钨酸铵（APT）的晶形变化，探讨了生长机理与晶体生长速率（LN）的关系在计算LN值时采用了将最终产品位度组成与生长质量速率结合的方法．结果表明：NH3·H2O－H2O系APT按二维核或位错机理生长，晶体表面光滑，层状结构明显，部分小晶体具有螺卷状结构．NH4Cl-NH3·H2O－H2O系APT生长则为二维成核或以最微小粒子集聚的连续生长机制．大颗粒晶体表面粗糙多孔，晶面界限不明，呈现生长丘形态．均相成核期内晶核长大到一定尺寸时开始生成大小不一的由复合贯穿和复合接触孪晶构成的连生体．NH4Cl掺入促进连生体形成．表面粗糙及连生体多的APT松装比重下降、流动性差．

In this paper, the variation in the crystal morphology of ammonium paratungstate (APT) were studied by adding NH4Cl (ammonium chloride) to the system and the relation between the mechanism of crystal growth and the linear growing velocity LN was approached.LN was calculated by the method of the combination of the particle size and composition for the end products with the growing mass rate. The results show that in the NH3·H2O-H2O system,the growth of APT proceeds with the nucleation in two dimensions or the mechanism of disloca-tion.The crystals have smooth surface and clear layered structure, and the part of small crystals have heliX-coil structure. In the NH4-Cl-NH3-H2O-H2O system, the growth of APT is through the nucleation in two dimensions or the continuous growth of the smallest clusters which agglomerate. The large granulas have rough surface and pores， and the boundary of crystal faces is not apparent, showing growing hillocks. After the crystal nuclei grow to a certain size in the period of homogeneous nucleation, they begin to form coenobiums consisting of twin crystals with various sizes and penetrate into each other or just contact one another. The introduction of NH4Cl promotes the formation of coenobiuap, and APT crystals have rough surface and consist of coenobiums, with results in low apparent density and poor flowability.