peptization

Peptization is the process by which a coagulated or gelatinous precipitate is redispersed into a stable colloidal suspension. It is the opposite of coagulation and flocculation, which produce larger aggregates. In peptization, the material breaks up into discrete colloidal particles and remains dispersed rather than sedimenting.

The mechanism involves stabilizing forces that overcome interparticle attractions. By increasing the surface charge on particle surfaces or introducing a dispersing or peptizing agent that adsorbs on surfaces, electrostatic or steric repulsion keeps particles apart. Conditions such as pH shifts, introduction of complexing ligands, or controlled addition of electrolytes can promote peptization. Mechanical energy, such as stirring or sonication, can also aid dispersion.

Peptization is commonly observed in metal hydroxide or oxide systems and in sols derived from gels or precipitates. It is important in fields such as ceramic processing, pigment production, catalysis, and electrode materials, where a fine, stable colloidal dispersion is desired.

In practice, the term is used to describe the transition from a flaky or gel-like precipitate into a colloidal solution, often achieved by adjusting pH, ionic strength, or adding a dispersant. The counterpart processes are coagulation, flocculation, and gelation.