STABILITY OF SILICON-NITRIDE SUSPENSIONS .1. ELECTROSURFACE PROPERTIES AND STABILITY IN AQUEOUS-ELECTROLYTE SOLUTIONS

Colloidal behavior of aqueous suspensions of silicon nitride powders o btained by low-temperature plasma synthesis are studied. Surface charg e density, electrokinetic potential, and coagulation ability of 1:1, 2 :1, and charge-type electrolytes are pH-dependent functions. Extremely high coagulating concentrations of electrolytes with monovalent count erions in alkaline media cannot be explained in terms of the classical DLVO theory with account for mere electrostatic repulsion. High stabi lity of suspensions with respect to monovalent counterions is explaine d by the appearance of the sterical component of the disjoining pressu re. This component is attributed to the formation of a gel layer compo sed of chains of polysilicic acids at the particle surface. At the sam e time, coagulation of suspensions by electrolytes with bivalent count erions is well explained in terms of the DLVO theory. It is related to the high specific adsorption of calcium ions.