Coalescence

Definition - What does Coalescence mean?

Coalescence is the union of colloidal particles into a group or larger unit as a result of molecular attraction on the surfaces of the particles. It is the fusing of molten particles to form a continuous film. Coalescence is a term used in welding and brazing, emulsion and coating. It is the first step in powder coating.

The factors that control coalescence are:

  • Surface tension
  • Radius of curvature
  • Viscosity of the molten powder

Corrosionpedia explains Coalescence

Coalescence is fusion of particles. Unlike coagulation, where particles simply stick together, coalescing particles actually merge. As a result of coalescence, emulsions and foams may cease to exist as disperse systems and undergo complete separation into two macrophases, liquid-liquid or liquid-gas. Coalescence in a coating is the flowing together or coming together of polymer particles in suspension, creating a clear polymer film. A special case of coalescence is known as self-adhesion.

In welding, two (or possibly more) pieces of metal are bonded together by liquefying the places where they are to be bonded, coalescing these liquids, and allowing the coalesced liquid to solidify. At the end of this process the two pieces of metal have become one continuous solid, and if the weld has been made properly, it is as strong as the original workpieces.

The coalescence of droplets of paint or lacquer sprayed onto a surface to be painted leads to the formation of a continuous film. Coalescence-based film formation takes place mainly with latex polymers, but it also occurs with systems in which the polymer particles are dispersed in an organic solvent. Limitations on the use of organic solvents have made water the predominant carrier solvent for coalescent coating technologies. Coalescence is the basis of many other production processes and natural phenomena.

The coalescence of stress corrosion cracks plays a critical role in the overall growth process and that observed failure times can be accounted for only if coalescence is taken into account.

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