Reactive spreading: adsorption, ridging and compound formation

Abstract

Reactive spreading, in which a chemically active element is added to promote wetting of noble metals on nonmetallic materials, is evaluated. Theories for the energetics and kinetics of the necessary steps involved in spreading are outlined and compared to the steps in compound formation that typically accompany reactive wetting. These include: fluid flow, active metal adsorption, including nonequilibrium effects, and triple line ridging. All of these can be faster than compound nucleation under certain conditions. Analysis and assessment of recently reported experiments on metal/ceramic systems lead to a focus on those conditions under which spreading proceeds ahead of the actual formation of a new phase at the interface. This scenario may be more typical than believed, and perhaps the most effective situation leading to enhanced spreading. A rationale for the pervasive variability and hysteresis observed during high temperature wetting also emerges.

A novel biomimetic approach to the design of high-performance ceramic–metal composites

“…Conversely, debonding is not beneficial when the reinforcement exhibits low intrinsic ductility owing to an absence of work hardening (Deve et al 1990). The use of interfacial segregants on metaloxide interfaces (Hong et al 1995;Gaudette et al 1997;Saiz et al 2000), or inert oxide coatings emplaced between the reinforcement and the matrix (Deve & Maloney 1991) can induce extensive debonding, leading to enhanced values of the toughness. However, aluminium -alumina interfaces formed in the liquid state are usually stronger than those formed in the solid state (Saiz et al 2003) and no such delamination was observed in our composites (figure 5c).…”

Spreading of Sn-Ag solders on FeNi alloys

“…The experimental evidence suggests that in several systems [11,26], nucleation of the interfacial reaction product occurs behind the triple junction (the line where the solid, liquid, and gas meet). In that case, the triple junction moves on a flat, unreacted, metastable interface, and the associated metastable interfacial energies drive spreading.…”

“…Complete equilibrium must involve a force balance in two directions (parallel and perpendicular to the substrate), and constant curvature surfaces must be attained (the liquid will have a lens shape or modifications owing to anisotropy of γ sl ). Before that, a perturbation (a ridge) will form at the triple point and propagate to the final equilibrium state in a manner parallel to grain boundary grooving [11,27]. Depending on the physical characteristics of the system, there is a range of dynamic contact angles in which the ridge will grow at the triple junction of a liquid front moving on a flat substrate.…”

“…Some variational treatments led to the inclusion of a reaction term in Young's equation [8][9][10]. More recently, a mechanistic model of reactive wetting has been proposed in which the process is divided into a series of stages: liquid flow, adsorption of reactive element, triple line ridging, and nucleation and growth of the new phase [11]. This mechanistic model focuses on the determination of the triple line structure and composition at each spreading stage in order to identify the driving forces for wetting as well as the processes that control spreading kinetics.…”

“…As a consequence, the spreading velocity data from such experiments are typically several orders of magnitude slower when compared to the theoretical predictions and the spreading of low temperature liquids of similar viscosities. [1,[11][12][13] The drop transfer setup provides a unique opportunity to systematically analyze isothermal spreading and avoid the complications related to solder melting and the use of fluxes [14,15]. In this work high-speed photography combined with a drop transfer setup was used to study spreading kinetics.…”