Geochemistry of colloid systems / Геохимия коллоидных систем

Colloid systems may be defined as systems containing at least two components: 1) a continuous dispersing medium and 2) a disperse phase. For many years the science of colloids was concerned mainly with the description of the behavior of very small particles. The classical definition of a colloid system described the disperse phase as being comprised of particles or macromolecules smaller than 1000 nm in diameter, but larger than 1 nm. Particles smaller than 1 nm do not exist as a discrete phase, and any system containing them cannot be considered as heterogeneous. This definition is to some extent dependent on the resolving power of the optical microscope and on the sizes of the pores of conventional filter paper. Objects are seen by means of ordinary light of wavelengths between 400 and 750 nm. The optical microscope is limited in its resolving power by the wavelength of the light used for illumination. Consequently particles smaller than about a few hundred nm in diameter are submicroscopic. Colloid systems in which a liquid is the dispersing medium appear to form true solutions. These solutions pass unchanged through ordinary filter paper. The classical science of colloids dealt with particles that are so small that they behave in some respects like molecules and with molecules so large that they behave in some respects like particles. The term colloid was used for very finely divided matter or for very large molecules. When a solid is broken into smaller and smaller parts, the total surface area increases as the particle size decreases. Natural laws governing the behavior of matter in the molecular state or in bulk also apply to the colloidal state. The two important phenomena that characterize the behavior of small particles as distinct from noncolloid material are I) dispersion of the material and 2) chemical reactions at the surfaces of the colloids. Colloid chemistry deals with these two phenomena. Colloid chemistry is also concerned with describing the methods of formation and stability of those substances that form colloid systems.  <...>