Silica Ludox

Dissolved titanium method. Hydrothermal synthesis using tetrapropylammonium peroxytitanate (prepared from TEOT, distilled water, 30% aqueous H2O2, and 25% aqueous TPAOH) as the source of Ti and colloidal silica (Ludox AS-40) as the source of Si and TPAOH as template. All additions done at 278 K Preparation using TiCl2, 14% aqueous TPAOH, 30% colloidal silica, and demineralized water Preparation at low pH using fluoride ions as mineralizing agent... 

Mesostructured molecular sieves such as Si-MCM-41 and Al-MCM-41 were synthesized using gels prepared by reacting colloidal silica (Ludox AS) with an Al(OH)3, solution in the presence of a surfactant. Al was incorporated in tetrahedral coordination inside the pristine crystals. However, as expected, dealumination occured upon calcination at 600°C/12h yielding materials having both tetrahedral and octahedral Al-species. 

The reactants used in this study were a colloidial silica, Ludox AS-40 (Dupont), reagent-grade tetrapropylammonium bromide (Aldrich Chemical Co.) and a 50wt% sodium hydroxide solution (Mallinckrodt Inc.). The reaction mixture had the oxide formula, 2.55Na20-5.0TPABr-100Si02-2800H20. The mole ratios of the... 

Zeolite ZSM-5. Zeolite samples were crystallized from a gel containing colloidal silica (Ludox AS-40), deionized water, aluminiumtriisopropylate (ATIP, Merck), as source of aluminium, and tetrapropylammonium bromide, (TPABr, Aldrich). Ammonia solutions were prepared by saturating a thermostated aqueous solution with... 

The reactants tin(IV) chloride, alkali-metal base, and colloidal silica (Ludox-HS40) were thoroughly mixed at room temperature, according to the ratios 2-5M20 Sn02 4-10SiO2 8O-IOOH2O, for each synthesis [47], Cabosil (fumed silica) and sodium stannate were also used as reactants. 

Hassander, H., Johansson, B., Tomell, B. 1989. The mechanism of emulsion stabilization by small silica (Ludox) particles. Coll. Surf. 40, 93105. 

A MCM-41 has been synthesized following a procedure of Ryoo and coworkers [12], The first procedure used colloidal silica (Ludox HS40, 39.5 wt% Si02, 0.4 wt% Na20, and... 

When deconvolution is required, the time profile of the exciting pulse is recorded under the same conditions by replacing the sample by a scattering solution (e.g. a suspension of colloidal silica (Ludox)). 

Laven, J. and Stein, H.N., The electroviscous behavior of aqueous dispersions of amorphous silica (Ludox), J. Colloid Interf. Sci., 238, 8, 2001. 

Materials and Particle Preparation. Methanol (Baker), ethanol (Merck), and 1-propanol (Baker) were of analytic reagent quality. Absolute technical grade ethanol (Nedalco) was used only for the large-scale (9 L) synthesis of Al. Solvents, tetraethoxysilane (Fluka, purum grade) and 7-aminopropyltriethoxysilane (Janssen) were freshly distilled before each synthesis. Ammonium hydroxide (Merck, 25%) was of analytical reagent quality and contained 14.0 mol/L NH3 as indicated by titration. The silicas Ludox AS40 and Compol were kindly provided by DuPont and Fujimi. 

Ludox Colloidal Silica. Ludox colloidal silicas (DuPont) were among the first silica materials studied by FFF. In the first paper describing the applicability of FFF to colloidal silica (4), Ludox and related silicas were fractionated by flow FFF the fractionation was verified by transmission electron microscopy (TEM). The theory behind the fractionation and the acquisition of size distribution data was developed, and evidence of aggregation was examined. An example of the fractionation of four colloidal silicas from that study is shown in Figure 2. The primary drawback of this earlier work was the lengthy runs, in some cases requiring over 10 h. Most of the experimental runs on Ludox described in this section were completed in less than 10 min. 

Si-VPI-S(l) was obtained as follows. To a mixture of 32.1 g of aluminium isopropoxide (Janssen Chimica) in 34 g of water, 17.7 g of phosphoric acid (85%) (Janssen Chimica) diluted with 12 g of water was added under stirring. Then, 4.6 g of colloidal silica (Ludox AS-40, DuPont) was added, and finally 10 g of dibutylamine (DBA)(Janssen Chimica). This final mixture was stirred to obtain a homogeneous gel with composition... 

Colloidal silica (Ludox HS-40) is a stable suspension of fine silica particles having a mean size of 150-200 A. The pH of the solution is around 9.5. These particles are obtained from a water-soluble glass and then purified to remove the major part of alkali ions. Shoup developed a process in which a solution of potassium or sodium silicate (80-90 wt%) is added to the colloidal silica (10 wt%). The potassium silicate solution contains mixtures of polysilicic anions, which deposit on colloidal particles if the pH of the solution is lowered [34,35]. 

The DT-1200 instrument is able to measure sound speed quite reliably, which is is illustrated in Fig. 6 showing the results of a dilution test with silica Ludox TM. The experimentally measured sound speed was found to be very close to theoretical calculations. 

Figure 6Soimd speed for silica Ludox TM vs. volume fraction. Equilibrium dilution using dialysis. Theoiy (triangles) according to the Wood... 

The attenuation spectra in Fig. 7 provide an example of the acoustic sensor precision. These attenuation spectra were measmed using alumina Sumitomo AA-2 and silica Ludox TM. The alumina sample was measured 10 times repeatedly while the silica sample was measured 11 times repeatedly. The corresponding median particle size results are given in Table 1. 

Figures 8 and 9 illustrate the precision of the electroacoustic sensor. Figiue 8 provides results for 51 continuous CVC measurements on silica Ludox. The precision meas-lued as the absolute variation of the zeta potential measurement is a fraction of a millivolt. Figure 9 shows titration...

Figure 7 Attenuation of the multiple measurements with alumina Sumitomo AA-2 and silica Ludox TM at 10% wt.

Figure 8 Multiple -potential measurements of 10% wt silica Ludox.

The most appropriate blank solution is one which is identical to the sampk but does not contain the fluoio-phore. This can be difficult to accomplish with protein or membrane solutions, where the macromokcules themselves are the source of the signal. Such solutions will typically be more strongly scattering than the buffer blanks. In these cases it is useful to add glycogen or colloidal silica (Ludox) to the buffer blank, to mimic the amount of scattering from the sample. This allows one to test whether the chosen filters are adequate Co reject scattered light from the sample. 

The instrument response function, sometimes called the lamp function, is the resp( ise of the instrument to a zero-lifetime san le. This curve is typically collected using a tUlute scattering solution such as colloidal silica (Ludox) and no emission filtor. This decay represents the shortest time jnrofile which can be measured by the instrument. The lamp function in Hgure 4.8 is quite narrow. 

The particle size distribution irt a commerical colloidal silica (Ludox ) has been determined by electron microscopy. by Deielic et al. (148). A weight-average diameter, (/ , determined from the particle size distribution curve by electron microscopy, was 20.0 nm, for example, which agreed within the 5% limit of experimental error with the particle diameters calculated from light-scattering data. 

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