Because of its technological importance, a large body of empirical knowledge about the high-temperature spreading of liquid metals and oxides has been accumulated, but the results are complex, ambiguous and even inconsistent.  Reported spreading velocities for high-temperature systems are typically several orders of magnitude slower that expected from theoretical predictions and from comparisons with velocities for organic liquids with similar viscosities.  In addition, after high-temperature spreading, reaction products such as nitrides, silicides or oxides have frequently been found at or near the interface. The physicochemical mechanisms that control the wetting and spreading in such reactive systems such as brazes and solders are still subject of controversy.

In this work high-speed photography combined with a drop transfer setup was used to study the spreading kinetics of a variety of liquid metals and oxides.  This setup provides a unique opportunity to systematically analyze isothermal spreading.  The results are compared with existing models.  The effects of temperature, atmosphere and the interfacial reactions are also examined. The spreading kinetics observed using the drop transfer setup are similar for systems with different degrees or reactivity and near those recorded for aqueous or organic fluids.  In many cases the experimental evidence is consistent with a liquid front moving on a flat, unreacted surface.  The data can be analyzed using a molecular-kinetic model in which the rate-controlling step is the movement of one atom from the liquid to the solid surface.