Reactive vs non-reactive wetting of ZrB2 by azeotropic Au-Ni

The equilibrium contact angles and spreading kinetics of Au-Ni droplets of azeotropic composition on ZrB2 substrates were measured by the dispensed drop technique in high vacuum. Experiments were performed at two temperatures, 980 and 1170 deg. C, leading to different interfacial reactivities, namely, simple substrate dissolution (1170 deg. C) and compound formation at the interface (980 deg. C). The contact angle of Au-Ni on unreacted ZrB2 is evaluated and related to the type of bonding established at metal/metal-like ceramic interfaces. The experimental results on reactive wetting are compared with predictions of two different approaches proposed recently in order to explain the thermodynamics and kinetics of this type of wetting