Va. Hackley, COLLOIDAL PROCESSING OF SILICON-NITRIDE WITH POLY(ACRYLIC ACID) .1. ADSORPTION AND ELECTROSTATIC INTERACTIONS, Journal of the American Ceramic Society, 80(9), 1997, pp. 2315-2325
The role of poly(acrylic acid) (PAA) in the dispersion of silicon nitr
ide suspensions was investigated experimentally, The effects of concen
tration, relative molecular mass, and suspension pH were evaluated, Th
e ionization of PAA was characterized by potentiometric titration and
indicated a pH-dependent conformational transition, The isoelectric po
int for silicon nitride decreased from pH 6.3 to pH 3 as the PAA conce
ntration increased, roughly independent of relative molecular mass. A
broadening of the stability region for silicon nitride was attributed
to this effect. Redispersion in alkaline media, subsequent to destabil
ization by surface-charge neutralization, improved following preadsorp
tion of PAA in acidic media. This effect was attributed to formation o
f a protective polymer adlayer on the surface, which prevented primary
minimum aggregation; an electrosteric contribution also may be presen
t. The influence of free polymer on the suspension properties also is
discussed.