Abstract
The aqueous dispersion of Si3N4 powder with polyethylenimine as a dispersant was studied by zeta-potential, adsorption and viscosity measurements. The hydrolysis behavior of Si3N4 powder in the acidic and basic regions was evaluated by measuring suspension pH and zeta-potential as a function of stirring time. It is shown that in the absence of PEI, the Si3N4 suspensions at initial acidic pH show a continuous increase in the pH from the acidic pH ~ 4 to basic pH ~ 9.3 and a reversal of the zeta-potential sign from the higher positive value to the negative value, indicating that the strong hydrolysis occurs, but the presence of PEI suppresses this hydrolysis to some extent when the amount of PEI exceeds 0.5 dwb%. Though the adsorption of PEI significantly change the electrokinetic behavior of Si3N4 particles, resulting in the shift of the isoelectric point (IEP) from pH ~ 6 to pH 11, the dispersion of Si3N4 can not be predicted in terms of the zeta-potential curves. The stabilization of Si3N4 by PEI can be achieved in the basic region and even at the IEP, depending on the amount of PEI, but the stabilization can not be achieved in the acidic region despite higher positive zeta-potentials of > 40 mV. In addition, the initial ionization treatment of PEI has little effect on the dispersion of Si3N4. The mechanisms of the suppressed hydrolysis and stabilization of Si3N4 by PEI were discussed in detail.
