Ludox density

Bolt 191), however, found in determinations of the charge density of Ludox silica sols a value of 1.8 negative charges per 100 A at pH 10. 

Evaluate the molecular weight of the Ludox particles, using a value of H = 4.08 x 10 7 for the system. Calculate the characteristic diameter for these particles, assuming the particles to be uniform spheres of density 2.2 g cm-3. 

Figure 9-23. Densities yielded at 5°C from solutions of various materials used to form density gradients 9 indicates the density of a 30% solution of Ludox.

At high temperatures, the reaction of silica from the binder with extra-framework alumina, which has the characteristics of Lewis acid, results in a new Bronsted acid sites [7]. Thus the decrease in Lewis acid and the increase in Bronsted acid would be expected to be equal in quantity and the quantity depends at least on the amount of extra-framework alumina of the zeolite. The more the extra-framework alumina, the more increase in Bronsted acid sites and decrease in Lewis acid sites would result. By XRD diffraction, the zeolite Y sample showed more crystalline than the ZSM-5 samples. Therefore, silica-bound Y samples would have less reduce in Lewis acid density and less increase in Bronsted acid density than silica-bound ZSM-5 samples. That also means the total acid density of silica-bound Y sample should have less change than silica-bound ZSM-5 samples. However, the Ludox HS-40 contained some sodium ions, which can neutralize Bronsted acid sites[ll], resulting a decrease in Bronsted acid density and total acid density. The sodium in Ludox HS-40 would reduce Bronsted acid sites by about O.lmmol/g-zeolite if all of the sodium could neutralize the acid sites. Therefore, the total acid density and Bronsted acid density of zeolite Y with few extra-framework alumina are reduced. 

The application of FFF techniques to assorted silica samples including colloidal microspheres (Ludox, Monospher, and Nyacol), fumed silica, and chromatographic silica (see Table II) are discussed in this section. In several cases, different FFF systems are applied to the same samples, and the results are compared. The acquisition of size distribution data is emphasized, but the possibilities for measuring densities and porosities for spherical particles and structural factors for nonspherical silica are also discussed (and in one case demonstrated). 

All manufacturers of water-borne colloidal silica publish charts of specific gravity versus silica content. Both manufacturers and users have long used the specific gravity of colloidal silica to determine its concentration. Hence, the correlation between the two has been well established. There is very little difference in the published values of this correlation from manufacturer to manufacturer, indicating that the density of the particles they produce is very similar. The following is a calculation based on such data for Ludox colloidal silica to calculate the density of the silica particles. They are considered to be representative of most of the commercially available silica sols. The one assumption is that the water molecules in the immediate vicinity of the silica particles still retain the density of normal water. Considering the high pressures needed to increase the density of water this would appear to be reasonable. 

A binder developed at DuPont called Ludox SK [8,10] avoids the need for pH adjustments in order to maintain slurry stability. The product is based on aluminate modified colloidal silica. The aluminated product is deionized and because the alumina sites provide sufficient charge density the product is stable. Deionization to remove sodium hydroxide results in a pH which is acidic. As long as the pH remains above about 3, there is little danger of the alumina being leached from the product surface. 

Others compounds, e.g. Ludox (a colloidal silica) may be used to separate cells by their density differences alone [64]. The main disadvantage with selection synchrony is that only relatively small numbers (10% of an asynchronous population) of cells are obtained. 

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