Colloidal silica from bulk water

The development of magnesium hydroxide [Mg(OH)2] at the heat transfer surfaces, especially at cathodic sites where localized pH may exceed 10. The Mg(OH)2 then reacts with colloidal silica from the bulk water to form silicate scale. 

The most extremum behavior of all the characteristics is observed at low content of cells in the suspension (Figure 7.11). A minimum of Ys and C and a maximum of CZ are at Ch o = 98.4 wt% or Cy=C<-eii+Cicw=6.1 wt%. Notice that there is the extreme dependence of the Ys value on the total concentration of water in the aqueous suspensions of nanooxides (see Section 1.1.6) at a minimum at Chjo 93 wt%. This boundary concentration corresponds to transition from diluted suspensions to concentrated ones characterized by different particle-particle interactions. In the diluted suspensions, the systems can separate into a gel-like layer and upper layer with bulk, almost pure water. In the concentrated suspensions, the systems represent a continuous gel-like structure without separation of bulk water. With increasing size of particles, the critical concentration (CJ should increase. Therefore, one could expect a larger Q value for yeast S. cerevisiae cells (5-10 pm) than for nanosilica (primary particles 10 nm). However, the C<. values for yeast cells and nanosilica are relatively close due to the formation of silica nanoparticles aggregates 0.5-l pm and agglomerates >1 pm, which have sizes close to sizes of cells. Therefore, at Cy< 10 wt% (Cycolloidal dispersion with relatively weak intercell interactions. At these Cy values, the adhesion... 

Both head- and tail-type cationic vinyl monomers with long methylene chains in THF or chloroform had the maximum adsorption on colloidal silica on the respective adsorption isotherm. Above the monomer concentration giving maximum adsorption, the monomer formed micelles or clusters in bulk solution with removal of adsorbed water molecules from the silica surface. At the monomer concentration giving maximum adsorption, the adsorbed monomer was spontaneously polymerised on the silica surface in THF or chloroform without an initiator at 40C or 60C. The polymerisation mechanism was discussed. Adsorption of an anion-type monomer with a carboxyl group on delta-alumina which showed a positive zeta potential in neutral aqueous solution was higher than that on colloidal silica, but spontaneous polymerisation did not occur on alumina. 19 refs. lAPAN... 

FIGURE 1.190 (a) Bulk density of the silica powders (dried in air for 24 h) treated in different media (air and water, ethanol or water/ethanol 0.5 g per gram of dry silica) as a function of MCA time, (b) desorption (in air at room temperature) of water or ethanol from MCA-treated silicas, and (c) corresponding desorption rate as a function of time at the initial fast stage of the desorption. (Adapted from J. Colloid Interface ScL, 355, Gun ko, V.M., Voronin, E.F., Nosach, L.V. et al., Strnctnral, textural and adsorption characteristics of nanosilica mechanochemically activated in different media, 300-311, 2011e. Copyright 2011, with permission from Elsevier.)... 

---