Abstract: Space High Temperature In Situ Observation Instrument “SHITISOI” was dedicated to visualize and record the
whole KNbO₃ cellular growth process in Li₂B₄O₇ flux. The dependence of buoyancy and surface tension convections on the cellular
growth was studied. In space, the streamlines of the steady surface tension convections in the Li₂B₄O₇ flux were observed. The steady
convections occur in the form of a mirror symmetric pattern. Due to the surface tension convection, the KNbO_3 grains grow and fill the whole
solution homogeneously. On the ground, the buoyancy drive flow in direction opposite to that of surface tension flow can reduce the cellular growth
and the distribution of KNbO₃ solute grains is inhomogeneous in the Li₂B₄O₇ flux. A theoretical model of cellular growth was also
accounted. A pivotal feature in this model is the initiation of the surface tension convection on the interface of KNbO₃ grain. This is initiated
by KNbO₃ solute surface tension gradient which is caused by less rapid diffusion of KNbO₃ solutes. Direct comparison of the model predictions
and experimental observed phenomena demonstrates the predictive capability of this model.

Key words: KNbO₃ cellular growth, high temperature solution, surface tension convection, in situ observation, microgravity material science, electron-microprobe analyses