材料期刊网

本文应用高温实时观察法显示了二种对流状态：扩散一平流状态和扩散-重力对流状态，并测出它们的特征扩散长度为0.01～0.1cm．通过晶体旋转生长，计算了质量、热量和动量变换区厚度，数值分别为7．5×10^-3Cm；86×10^－2cm和44×10^－1. 本文还应用高温实时观察法进一步研究了上述二种不同对流状态下的KNbO₃（001）晶面的生长动力学，实验结果指出：（1）在同一过冷度条件下，扩散一平流状态下的生长速度大于扩散一重力对流状态下的生长速度；（2）在过冷度小于20℃时，二种对流状态下的KNbO₃（001）晶面生长机理都服从二维成核生长，但台阶自由能ε和二维晶核的形成热力学势能△G等生长参数不一致，从而表明这些参数是实验研究熔体对流对晶体生长界面动力学的重要依据，并指出熔体对流效应增强了界面的奇异性．

A high temperature in-situ observation method was used to observe two different states of convection: diffusive-advective flow
and diffusive-convective flow. Characteristic diffusion distance L can be easily measured from Schlieren photograph and it ranges from
0.01～0.1cm for two different states of convection. By observation of rotating crystal growth processes in the KNbO₃ melt, the widths of
interfacial concentration, heat and momentum transition zone were obtained, which are 7.5×10^-3cm, 8.6×10^-2cm and 4.4×10^-1cm respectively.

An investigation of growth kinetics of KNbO₃ crystal related to the different states of the convection in high temperature melts was performed
by this method. Irrespective of the state of convection in the melt, at the lower supercooling two dimensional nucleation growth was obtained.
At the same supercooling, the discrepancy between the growth rates for two different states of convection was assigned to the buoyancy convective
enhancement of the interfacial mass flow. The free energy per unit length of a step ε, and the thermodynamic potential barrier for two-dimensional
nucleation Δ G*, were calculated from the experimental data for two different states of convection. These data are significant for consideration of the
influence of convective flow on the interface growth kinetics. The effect of convection is to enhance the sharpness of the interface.