Silica particles physicochemical characteristics

Physicochemical characteristics and behavior of alumina, ceria, and silica particles... 

Ooh = 1) is obtained after preliminary treatment of the samples in vacuo at 180-200 °C, when for each Si atom there is approximately one OH group. The average value of the silanol number for such a state, aon = 4.6 OH groups per square nanometer, is a physicochemical constant (it is independent of the type of the amorphous silica used, the method of preparing it, and the structural characteristics, that is, the specific surface area, the type of pores, the distribution of the pores according to their diameter, the packing density of the particles, and the skeleton structure of Si02). 

Clearly, based on the physicochemical properties of silica and related materials, their most important characteristics depend on the presence of water in the form of intact molecules or different (single, twin, vicinal, localized in dense islands of OH groups, free and hydrogen bonded, placed in different pores or adjacent primary particles) hydroxyl groups [1-11]. Therefore the first subject of this review is the surface and interface waters. 

Many physicochemical properties of fumed silica depend significantly not only on the primary and secondary particle size distributions but also on the concentration of adsorbed water (C ) in the form of intact molecules and =SiOH groups (Cqh) [1-3,6,7]. For instance, marked amounts of adsorbed water can negatively affect the characteristics of fumed silica as a filler of liophilic media or polymers. There are several methods to change C and Cqh such as chemical modification... 

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