CONTACT-ANGLE AND SOLID-LIQUID-VAPOR EQUILIBRIUM

The theoretical and experimental background of Young's equation for th e solid-liquid-vapor contact angle are reviewed and discussed. A recen t microgravity liquid phase sintering experiment using a W-Ni alloy pr ovides an opportunity to test the contact angle definition in terms of the surface tensions without the influence of gravity. The resulting configuration can only be described by a force balanced three-vector d iagram, not by Young's equation. Microscopically, a three phase contac t forms a ''valley'' rather than a ''ridge'' on an initially plane sol id surface. In addition, reanalysis of several derivations of Young's equation detects errors. A main problem has been the assumption of the rmodynamic equilibrium for what is a metastable system.