PHASE DISTRIBUTION IN SOLID-LIQUID-VAPOR SYSTEMS.

Under bulk chemical equilibrium conditions, Young's and dihedral angle equations in terms of the static interfacial tensions outline the condition of mechanical equilibrium in a solid-liquid-vapor system. Under bulk chemical nonequilibrium conditions, mass transfer across an interface results in a transient decrease in the corresponding interfacial free energy and thus the interfacial tension by an amount equal to the free energy of the effective chemical reaction per area at that interface. When the chemical reaction is between the solid and the liquid, in sessile drop experiments, a transient lowering of the contact angle or spreading is observed if the growth rate of the reaction product is slower than the spreading rate of the liquid. Similarly, in a solid-liquid-solid system, in the presence of chemical reactions, a transient penetration of the liquid along the solid-solid boundary may occur. This transient stage then corresponds to the solution-precipitation stage of liquid phase sintering in systems that are characterized with equilibrium nonzero dihedral angles.