Silica and Silica-Induced Lung Diseases. Castranova V, Vallyathan V, Wallace WE, eds., Boca Raton, FL: CRC Press, 1995 Dec; :79-89
Many or most chemical processes and physical interactions involving solid materials occur at their surface. A reduction of particle size, and the resulting increase in surface area per unit weight of material, generally increases the reactivity of solid materials. Hence the structure and composition of any material at its surface, more than its bulk composition, determine many of its chemical and physical properties. Unfortunately most analytical techniques used for the chemical characterization of materials tend to sample the bulk of the material, or a layer much deeper than the surface layer active in interactions with the environment. For ultrapure materials the issue may be of little consequence, but most materials found in nature are not pure, and impurities contained in the bulk tend to segregate to the surface by virtue of thermodynamic equilibrium effects. Also, by interaction with its environment, any solid material will tend to adsorb impurity atoms or molecules at its surface. Consequently, surface characteristics play a dominant part in defining properties of ultrafine particles (respirable dusts and aerosols). This review focuses in particular on those properties that define the biological activity and toxicity of respirable-size, silica-based particles. Since silica and its derivatives can be produced in a greater variety of forms and structures than most other chemical materials, numerous applications of silica exist, especially for the high-specific surface area, amorphous variety, where surface chemistry plays a dominant role. Silica-based materials include adsorbants and dessicants, catalysts, fillers, lubricants, thickening agents, paints, and other widely used materials. In Chapter 6 of his treatise on the chemical properties of silica, lIer presents a comprehensive review (with more than 500 references) of the wealth of data available on the structure and properties of silica and silica surfaces.