Characterization of silica surface

H. Engehardt and H. Muller, Chromatographic characterization of silica surfaces J. Chromatogr., 218 395 (1981). 

Research of Soviet scientists is surveyed. Contributions to various aspects of the colloid chemistry of silica are examined preparation and stabilization of silica hydrosols preparation of silica gels structural characterization of silicas surface chemistry elucidation adsorption and ion-exchange property examination and geometric and chemical modification of silicas, silica coatings, and so forth. 

Adsorption from solutions, research, 653-654 Adsorption isotherm, 253, 254f Adsorption methods, characterization of silica surface, 170, 175-177/... 

Recently, Voelkel and Grzeskowiak [23] reported on the use of solubility parameters in the characterization of silica surface modified with titanates by inverse gas chromatography and compared their findings with earlier work on silanes. 

Fisher LR, Israelachvili JN (1979) Direct experimental verification of the Kelvin equation for capillary condensation. Ffeture 277 548 Flinn DH, Guzonas DA et al (1994) Characterization of silica surfaces hydrophobized by octoda itri-chlorosilane. Coll Surf A 87 163 Fowkes FM (1964) Attractive forces at interfec s. Ind Eng Chem 56 40... 

The use of small polyhedral silsesquioxanes as molecular models of silica surfaces has been studied increasingly in recent years, because catalysts, etc., attached to such species are relatively easy to handle and characterize when compared to bulk silica. The preparation and structures of silsesquioxanes used in this type of work are described later in Sections II,C, IV,E, and IV,F. Further recent examples may be found in Ref. 5. 

Surface chemistry characterization, of silica, 22 372-373 Surface cleaning nozzles, 23 197 Surface coatings, 10 12-13... 

Among the various oxides that are used as substrates, aliunina [2] and silica [3] have been extensively studied however, the structural characterization of silica is certainly the most complete. Studies carried out on porous catalyst supports showed that the - OH concentration on a M O surface can vary... 

There are several major areas of interfacial phenomena to which infrared spectroscopy has been applied that are not treated extensively in this volume. Most of these areas have established bodies of literature of their own. In many of these areas, the replacement of dispersive spectrometers by FT instruments has resulted in continued improvement in sensitivity, and in the interpretation of phenomena at the molecular level. Among these areas are the characterization of polymer surfaces with ATR (127-129) and diffuse reflectance (130) sampling techniques transmission IR studies of the surfaces of powdered samples with adsorbed gases (131-136) alumina(137.138). silica (139). and catalyst (140) surfaces diffuse reflectance studies of organo- modified mineral and glass fiber surfaces (141-143) metal overlayer enhanced ATR (144) and spectroelectrochemistry (145-149). 

D. Barby, Silicas, in Characterization of powder surface , eds. G.D. Parfitt and K.S.W. Sing, Academic Press, London, 1976. 

The content of this book reviews the latest developments in the characterization and chemical modification of silica surfaces. No attempt has been made to survey exhaustively the literature of any topic. The material has been collected from recent publications and own research work in this field. Also, recent disclosures of research activities in the former USSR are documented in detail in the text. 

Bronsted acid sites can be directly probed through solid-state H NMR spectroscopy, as chemical shifts can be correlated with acid strength [195, 197, 198]. The precise chemical shift observed for any given Bronsted acid site is dependent on the material upon which it is located. For instance, on silica values of 1.6ppm are typically observed zirconia has two distinct OH sites, at 2.4 and 4.8ppm while on alumina a typical range may be -0.2 to 4.3 ppm. Early studies employing H NMR to study Bronsted acid sites focused on the characterization of the surface of amorphous silica-alumina materials [165, 199-201]. Extensive work, however. 

Some contributions cover the development of specific materials and analytical methods to measure the characteristic properties of solid particles, such as particle sizes, surfaces areas, mechanical strengths, or solid-matrix interactions. Thus, papers from M. Heinematm and S. Hild deal with the characterization of silica-polymer interactions using Scanning Force Microscopy, while C. Panz uses the combination of special basic silica, fitting silanes, and adequate hydrophobization conditions to generate high-performance silica with new properties. 

Selection of the mobile phase is critical in the characterization of silica sols by SEC. As with the other separation methods, pH should be slightly basic, and low ionic strength must be used to prevent particle aggregation. In addition, the mobile phase must interact with the surface of the packing-particle pores to neutralize undesirable charge effects. Negatively charged surfaces within the pore can result in ion-exclusion effects whereby... 

This chapter does not cover the most common aspects of the solid-state NMR techniques employed in the study of heterogeneous catalysts such techniques are described in Chapter 4. Since this chapter emphasizes the surface characterization of silica and alumina systems and silica aluminas by NMR methods, only those technical aspects highly relevant to surface characterization and not otherwise emphasized in this volume are explicitly discussed here. NMR studies of zeolites and clays are treated in separate chapters, and the bulk structures of silica and alumina systems are covered by Eckert. Unavoidably this chapter is also concerned with dynamics at the surface, although the amount of detailed work on that subject to date is limited. With the increasing availability of variable-temperature solid-state NMR equipment, however, one can expect that attention devoted to dynamics at surfaces will increase markedly during the next few years. 

---