Silica measurements

Fig. 8. Infrared spectrum of silica measured at room temperature (a) undried silica (b) silica dried at 200°C for 3 hr (16).

Fig. 11. Change in An /ATwith temperature in vitreous silica measured at 587.6 nm (186).

Fig. 4. The coordinative unsaturation of Cr(II)/silica, measured by the chemisorption of CO pulses at -78 C, declines with increasing temperature of reduction in a series of samples calcined first in air at 850°C, then in CO at the temperature shown.

Fig. 4.4. PL spectra for mesoporous silica measured with lEXc = 532nm (2.33 eV) at room temperature in air (a) disordered mesoporous silica, DMS (the pore size J100 = 2.9 nm) (b) MCM-41 (Jioo = 3.83nm) and (c) DMS (Ji00 = 7.1 nm) heat-pretreatment temperature rht = 300 K (curves 1), 873 K (curves 2), and 1173K (curves 3).

A feature of the neutron reflectivity study on polyDMDAAC and surfactant adsorption by Penfold et al. [74] was that the adsorbed layer of polyDMDAAC was remarkably robust and unaffected by the subsequent surfactant adsorption. This is not always the case, and Fielden et al. [76] reported a large increase in the thickness of the surface layer of AM-MAPTC on mica due to complex formation with SDS. Thickness increases with electrolyte and pH were reported for high molecular weight polyacrylamide adsorbed onto silica, measured by null ellip-sometry by Samoshina et al. [82] in the absence of surfactant. Complex formation at the interface, resulting in layer thickening, was also reported by Dedinaite et al. [83] for PCMA/SDS mixtures on mica from AFM measurements. 

Usually, in chromatography the volume average partide diameter is employed. For comparison the particle size distribution based on the number and the volume average is shown for the same silica measured by the same technique (see Tab. 3.11). 

Table I o Comparison of Mean Particle Diameters for Three Liadox Colloidal Silicas Measured under Different...

Interpretation of the Differences Between the Pore Size Distributions of Silica Measured by Mercury Intrusion and Nitrogen Adsorption... 

Figure 3. Comparison of the pore size distribution of a high-pore-volume silica measured by mercury intrusion and nitrogen desorption.

Table 4.2 Polarities of a range of organically modified silicas measured via the use of Reichardt s dye...

Fig. 9. Distribution functions of the adsorption energies of Si2 on S13 and T30 silicas, measured at 63°C.

Electron Microscopy. The electron microscope provides a direct method for determining dimensions of colloidal particles (Figure 4.7). With improved equipment, individual particles as small as only 1-2 nm can be discerned, but measuring the diameter of particles smaller than 5 nm is difficult. Alexander and Her (142) first demonstrated that the particle size of colloidal silica measured by the electron microscope correlated well with particle size determined by light scattering in solution, and also with the size calculated from the specific surface area of the dried silica powder. 

Figure 17.8 Thermal stability of pristine and various fluorinated silica measured by TGA up to 900°C. Reproduced by permission J. Phys. Chem. C 2009, 113, pp. 1865218660, American Chemical Society...

Clearly, from the exchange measurements, more CO is reversibly adsorbed on Pt/silica than on EUROPT-1, and this is consistent with the higher frequency observed for CO adsorbed in the linear form on Pt/silica in comparison with that on EUROPT-1 which implies a stronger Pt-C bond in the latter system. Similarly, CO adsorption on Pt/silica measured by the pulse technique over the range 256 to 294 K is an activated process (to be published), whereas no such claim has yet been made for CO adsorption on EUROPT-1. 

---