Silica particles residual concentration

Mineral horizons in which the main feature is loss of silicate clay, iron, aluminum, or some combination of these, leaving a concentration of sand and silt particles Horizons formed below A, E, or O horizons. Show one or more of the following (i) illuvial concentration of silicate clay (Bt), iron (Bs), humus (Bh), carbonates (Bk), gypsum (By), or silica (Bq) alone or in combination (ii) removal of carbonates (Bw) (iii) residual concentration of oxides (Bo) (iv) coatings of sesquioxides that make horizon higher in chroma or redder in hue (Bw) (v) brittleness (Bx) or (vi) gleying (Bg). 

As shown in Chapter 4, hot ion exchange or electrodialysis of a more concentrated solution of sodium silicate produces colloidal silica of a predetermined larger particle size at a concentration of at least 12-15% SiOs, from which the minor amount of residual sodium can be removed by further ion exchange. By varying the concentration and size of silica particles in the sol to be gelled, it b possible to make a gel with predetermined pore size, pore volume, and specific surface area. 

An adsorption isotherm for suspensions of 20 vol% silica at pH = 3.7, wherein the zeta potential for the chosen silica is zero, is shown in Figure 4.6. It can be seen that initial additions of PVA are almost completely adsorbed on the silica particles and very little polymer remains in solution. When overall PVA concentration is increased, the particle surface tends to become saturated with adsorbed polymer and then higher amounts of residual polymer are left in solution. The initial plateau region of the adsorption isotherm is associated with approximately monolayer coverage of the particle surface. The second plateau is probably an indication of either the development of denser packing of polymer molecules in the adsorbed monolayer or the development of multilayer adsorption. 

The hexane extract (110.7 g) was mixed with 150 g silica gel (silica gel 60, Art. 9385-3) and 50 ml hexane. The air dried slurry was transferred to the top of a silica gel column (800 g silica gel 60, particle size 0.04-0.063 mm, from EM Science, Art. 9385-3). The column was eluted with hexane ether mixtures in a manner of increasing polarities. Fractions were collected and TLC screened (analytical silica gel plates, developing system Hexane Ether (80 20), Visualizing agent Fast blue). The fractions collected with hexane (3 L) and hexane-ether (95 5, 2 L) were discarded. The following fractions collected with hexane-ether (95 5, 3 L) and hexane-ether (9 1, 5 L) were combined and evaporated to yield 77.2 g of residue. GC analysis of the residue showed THC concentration to be 54.74%. 

This value can be relatively low, nc - 2-4 in the initial aggregates.3 An increase in nc in the concentrated suspensions, and the shortening of distances between particles with increasing Csi02, affect the dispersion structure with time. Therefore, gelation of the concentrated dispersion (at 293 K) occurs faster, e.g. at Cs o2 = 16.7 wt.% in 2 days, than at Cs o2 <8 wt.%. Sonication leads to a lower turbidity of the suspensions compared to suspensions made from ball-milled silicas because of a different size of residual aggregates... 

Silica spheres with APS distributed in the particle interior were prepared by adding APS (Table I) first to the reaction mixture. Subsequently an equal volume of TES was added within 1 min. Free APS was again separated from the particles by centrifugation and redispersing in ethanol. Particle densities were measured by drying, under dry nitrogen for 24 h at 100 °C, a known volume of a concentrated dispersion in absolute ethanol and weighing the residue. 

Concentrated dispersions have been prepared [158] of samples with relatively thick sihca shells around the gold cores (core diameter = 15 nm, total diameter =184 nm), and with the outer surface coated with 3-(trimethoxysilyl) propylmethacrylate (TPM). The TPM coated particles (which we denote Au—Si02-TPM) are slightly charged due to the presence of residual hydroxide ions on the silica surface [63], and the sols are stable in solvents... 

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