ROLE OF POLYACRYLATE IN MODIFYING INTERFACIAL PROPERTIES AND STABILITY OF SILICON-NITRIDE PARTICLES IN AQUEOUS SUSPENSIONS

The role of ammonium polyacrylate in modifying the interfacial propert ies of silicon nitride powder was examined systematically in order to understand the basic mechanism of dispersion. The adsorption of the po lyacrylate on silicon nitride powder was found to be dependent on both the pH and its residual (equilibrium) concentration. The interfacial charge properties of the silicon nitride powder can be modified to a l arge extent by the adsorbed polyacrylate and equilibrium pH. Well-disp ersed silicon nitride suspensions can be obtained in both the neutral and alkaline pH range by the application of ammonium polyacrylate. The enhanced electrostatic repulsion between the dispersant-modified powd er surfaces was found to be the primary mechanism governing the disper sion. Also, the steric interactions of the adsorbed polyacrylate with aqueous media were demonstrated in this work to have a positive contri bution to the dispersion. The latter is attributed to the hydrophilic nature of the polyacrylate. The dispersing functions of the adsorbed p olyacrylate were understood to arise from the two oxygen atoms in the carboxylic group of the polyacrylate. The charged oxygen atom in the c arboxylic group was responsible for the measured interfacial charge pr operties of the dispersant-modified powder. The uncharged oxygen atom had an additional contribution to the hydrophilic nature of the adsorb ed dispersant layer.