Adsorption of particles onto metallic surfaces

E M ANDRADE; F. V. MOLINA

Encyclopedia of Surface and Colloid Science

Taylor and Francis

Lugar: New York; Año: 2006; p. 555 - 574

Particles are present all around us in great abundance. They include, for example, pollens, dusts, fibers, metals, metal oxides, bacteria, etc. The adsorption or (as it is more usually termed) adhesion of colloidal particles onto metallic surfaces is a field relevant to many applied problems. The term “colloidal particle” refers to a broad range of sizes, from macromolecules and small crystalline nuclei of about 1 nm to macroscopical particles of the order of 10 mm (139)(54). As a result, there are a variety of effects and particular properties of the particles/surface system. The particles can become adhered to a metallic surface by several forces, such as electrostatic, dispersion, capillary and chemical bonding (140)(93)(61). In a general sense, a surface with colloidal particles adhered is modified by these particles, and the effect of such modification, depending on the particular system and its applications, may be advantageous, such as the case of powder coatings, or nonadvantageous, as when adhesion of particles cause fouling of materials and equipment parts. Particles adhere to surfaces with great tenacity. If a surface with adhered particles is inverted it is observed that they do not detach, even for particles that are quite large, showing that the adhesion force is greater than the gravitational force on those particles. Similarly, vigorous blowing of the surface only manages to dislodge relatively few particles.   Despite its importance, the adhesion of particles to metallic surfaces has not received too much attention in fundamental studies; there are far more papers published either on adherence of particles to non conducting surfaces or to different particles (heterocoagulation). In the former case the surface electric potential cannot be easily modified, whereas in the latter the surface potentials cannot usually be modified independently, because the potential determining ion (pdi) is the hydrogen ion for both surfaces. Those topics are covered elsewhere in this Encyclopedia (see the entries "Adsorption of Immunoglobulins at Solid-Liquid Interfaces", "Adsorption of Polyelectrolytes on Mica", "Particles at Polymer Surfaces", "Adsorption of Polyethoxyethylenic Surfactants on Clay Surfaces", "Surface Behavior of Bacteria" and "Adsorption of Particles: Theory"). In the following sections we will review some application fields, the theoretical work on adhesion and its applications to metal/particle systems, experimental methods to study these systems, recent experimental research, and finally we will draw some conclusions. We will consider mainly particle/metal adhesion in liquid media, although references to gas phase will be also made.