Abstract
Neutral salts were added to boehmite (γ‐AlOOH) sols, and the solution and solution and interfacial chemistries were investigated during hydrogel formation. In general, gel volume increases with higher salt concentrations. Gels form in the presence of salts with monovalent anions when a critical ionic strength is reached, the value of which increases with increasing size of the anion. At the same time, the effect of interparticle distance appears more important with larger anions. The action of divalent anions is more complicated and may involve specific adsorption and complexing with the dissolved aluminum species. The concept of a critical gelation concentration is introduced analogous to the critical coagulation concentration for the flocculation of colloidal particles. The results are interpreted in terms of available models for particle‐particle interactions.
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