Abstract: 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.

Key words: buoyancy driven convection, interface growth kinetics, KNbO₃, high temperature in situ observation method