Thermodynamic aspects of particle engulfment by solidifying melts

Abstract

This study confirms the predominance of surface thermodynamic effects in the process of particle engulfment by solidifying melts for small‐diameter particles and slow interface motion. Predictions of a thermodynamic model are compared with actual particle engulfment behavior. It turns out that, in complete quantitative agreement with the thermodynamic predictions, the more hydrophobic particles like Teflon are engulfed at even very slow rates of solidification of naphthalene and biphenyl melts. On the other hand, more hydrophilic particles like nylon are rejected, and hence pushed by the solidification front at low and moderate rates of solidification. Conclusive proof of the importance of surface properties in particle engulfing is offered by the investigation of small siliconed glass spheres and untreated glass spheres; again the hydrophobic siliconed glass spheres were engulfed at all solidification rates and the untreated hydrophilic glass spheres were pushed. Rate phenomena for the engulfment of hydrophilic particles were studied and found to depend also on surface properties. However, comparison of the critical pushing velocities of one and the same particle in the two matrix materials shows, as expected, that fluid mechanic considerations will also be needed in a complete theory of particle engulfment.