The studies of KNbO3 cellular growth in high-temperature solution at microgravity

Space high-temperature in situ observation instrument "SHITISOI" is dedicat ed to visualize and record the whole KNbO3 cellular growth process in Li2B4 O7 flux. The dependence of buoyancy and surface tension convections on the cellular growth is studied. In space, the streamlines of the steady surface tension convections in the Li2B4O7 flux has been observed. The steady conv ections occur in the form of a mirror symmetric pattern. The parabolic stre amlines are formed in the one half of the loop and their mirror images in t he other half. Due to the surface tension convection, the KNbO3 grains grow and fill the whole solution homogeneously. On the ground, the buoyancy dri ven flow in the direction opposite to that of surface tension flow can redu ce the cellular growth and the distribution of KNbO3 solute grains is inhom ogeneous in the Li2B4O7 flux. A theoretical model of cellular growth is als o accounted. A pivotal feature in this model is the initiation of the surfa ce tension convection on the interface of KNbO3 grain. This is initiated by KNbO3 solute surface tension gradient which is caused by less rapid diffus ion of KNbO3 solutes. Direct comparison of the model predictions and experi mental observed phenomena demonstrate the predictive capability of this mod el. (C) 1999 Published by Elsevier Science B.V. All rights reserved.