Influence of evaporation–condensation in reactive spreading Original Research Article

In reactive wetting, considerable acceleration of spreading rate is usually observed in the high contact angle (short spreading time) range in comparison to the low contact angle range. This study examines the possibility to explain this acceleration by an evaporation–condensation process which may occur under high vacuum in front of the triple line. For this purpose, a method is developed to evaluate the thickness of the reaction product in front of the triple line during spreading. This method is based on calculations of ballistic exchange in vacuum between the drop and the substrate surfaces combined with Auger spectroscopic analysis of the substrate surface. The method is applied to Cu–40 at% Si and Cu–1.5 at% Cr droplets on vitreous carbon systems.