磷酸二氢钾晶体薄表面层生长动力学实时显微研究

In Situ Micro-study on the Growth Kinetics of the Thin Surface Layer of Potassium Dihydrogen Phosphate Crystal

利用光学显微镜实时观测磷酸二氢钾(KDP)晶体柱面及锥面薄表面层的生长过程,测得不同过饱和度下薄表面层前端不同倾角的非正常棱边推移速度。结果表明:倾角越小,非正常棱边推移速度越慢,薄表面生长终止于其前端的正常棱边处;随着过饱和度的增大,非正常棱边推移速度线性增加。计算得到柱面及锥面薄表面层前端非正常棱边推移动力学系数,由于Eslice(010)> Eslice(101),因而柱面薄表面层的生长动力学系数大于锥面。建立了基于非奇异面上台阶生长机制下的薄表面层生长体扩散模型。应用该模型解释了薄表面层生长速度随其厚度及前端非正常棱边倾角的变化关系,并讨论了溶液流动对薄表面层生长的影响。结果发现薄表面层生长存在一个使其以恒定厚度向前推移的临界厚度。

The growth processes of the thin{010}and{101}layers of potassium dihydrogen phosphate(KDP)crystals were observed in real time by optical microscopy.The displacement velocities of the abnormal crystallographic edges with different inclination angles on the growth front of the thin surface layers were measured under different supersaturations.Results showed that the smaller the inclination angle was,the slower the displacement velocity of the abnormal crystallographic edge was.The growth process of the thin surface layer terminated at normal crystallographic edges on the growth front.With increase of supersaturation,the displacement velocity of the abnormal crystallographic edge increased linearly.In addition,the kinetic coefficients for abnormal crystallographic edges on the thin{010}and{101}layers were calculated.Compared with the thin{101}layers,the thin{010}layers had a larger kinetic coefficient because of the bigger slice energy E slice(010).A volume diffusion model based on the motion of a parallel sequence of elementary steps on the growth front of thin surface layer was established.This model was not only used to explain the change of the advanced velocities of thin surface layer with its thickness and the inclination angle of its abnormal crystallographic edge on the growth front,but also applied to discuss the effect of the flow on the growth of thin surface layers.At last,a critical thickness under which the thin surface layer would go forward with a constant thickness was found.