Sol-gel processes and aggregative stability of lyophilic inorganic colloids

Summary form only given. Colloid silica is a convenient model for the investigation of sol-gel processes in inorganic oxides. The kinetics of sol formation and that of sol to gel transition is considered in terms of physical and chemical processes. The existence of the homogeneous polycondensation and phase formation stages as well as the stage of particles´ growth has been shown experimentally. We have shown the necessity to distinguish the kinetic regularities of polycondensation, gelation and sols´ aggregative stability. Controlling gel formation stage in the systems involved is not a chemical reaction associated with sylanolic groups reactivity but a physical process i.e. coagulation as a result of the action of the forces of molecular attraction between particles. Colloid silica properties occuring in the systems should be considered in terms of the structure and properties of liquid boundary layers. With pH increasing hydrate layers destruction on the articles occurs accompanied by the electrical potential growth leading to the competitive influence of electrostatic and non-electrostatic stabilizing factors. The ideas were proved in terms of DLVO theory by the data on the modifying additives. Coagulation processes at gel formation stage influence dissolved silica mass transfer under isothermic recondensation and determine silica gel porous structure formation.