Non-reactive wetting

In this chapter the phenomenon of wetting has been described. The fundamental equations have been developed for the case of non-reactive wetting on ideal perfectly smooth surfaces. The complications introduced by non-ideal surfaces, including rough surfaces and heterogeneous surfaces have been described. Finally, the effects of reactive wetting have been introduced. 

Non-reactive solution adhesives the solvent wets the surfaces to be assembled, then evaporates involving the cohesion of the parts to be assembled by the adhesive joint. The heat behaviour is generally moderate. If the solvent swells the materials to be assembled, there can be migration of materials and subsequent cracking by residual internal stress relaxation. 

Consider a flat, undeformable, perfectly smooth and chemically homogeneous solid surface in contact with a non-reactive liquid in the presence of a vapour phase. If the liquid does not completely cover the solid, the liquid surface will intersect the solid surface at a contact angle 9. The equilibrium value of 9, used to define the wetting behaviour of the liquid, obeys the classical equation of Young (1805) ... 

In the first Section, attention is paid to distinguishing between reactive and non-reactive systems from the point of view of wettability. Then, after describing wetting and bonding of non-reactive couples, we discuss the effect on these characteristics of oxygen, which is the most common impurity in solid/liquid/vapour systems, as well as the effect of reactive and non-reactive alloying elements. Finally, in a short Section, we consider some results for the wetting of fluorides which like oxides are very ionic. 

To sum up, in non-reactive liquid metal/ionocovalent oxide systems, wetting seems to result from physical, van der Waals, interactions which lead to contact angles of typically 120-130° and to a Wa/(2significant difference from the above values indicates the establishment of chemical interactions at the interface. 

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