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the spontaneous breakup of aggregates— lumps, flocs, or clots that have formed by the accumulation of cohered colloidal particles—into smaller aggregates or individual primary particles. A particularly graphic example is the peptization of gelatinous precipitates (coagels), which are formed by the coagulation of sols and highly dispersed suspensions. Peptization involves the “colloidal dissolution” of the precipitate; that is, the coagulate becomes a sol once again. The term “peptization” is derived from the apparent similarity between this phenomenon and the breakdown of proteins by the enzyme pepsin.
Peptization may be observed upon elevation of temperature or upon removal of the coagulating reagents by rinsing the precipitate. The most typical form of peptization occurs upon introducing peptizing agents—substances that promote disaggregation, that is, the separation of cohered particles—into a dispersion medium. The peptizing agents may be electrolytes or surfactants, which cause particle surfaces of the disperse phase to become lyophilic. For example, the peptization of ferric hydroxide gel in an aqueous medium is made possible by the addition of small quantities of ferric chloride, whereas kaolin is peptized by humic acids.
Agitation usually accelerates peptization. Recrystallization and coalescence, which often occur in colloidal precipitates upon aging, hinder peptization, since they promote the consolidation of particles. The coagulation of sols by polyvalent ions and polyelectrolytes yields precipitates that also resist peptization.
Peptization is used to obtain liquid disperse systems from powders or pastes in chemical and food-processing technology. It plays an important role in the group of processes determining the cleansing action, formation, and destruction of various disperse structures. Sometimes peptization may be harmful, for example, if it occurs during the process for the purification of water or the clarification of wine.
L. A. SHITS