Determination of surface charge density parameters of silicon nitride

The surface charge density of silicon nitride was determined by potentiometric pH titration at two different concentrations of the background electrolyte NaCl. Surface charge density parameters were evaluated under application of the surface ionization model with a diffuse electrical double layer. The determined intrinsic acid constant, pK(a)(i) = 7.51, is not substantially different from published values for silanol groups of pure silica. The best agreement between the recalculated a vs. pH plots and the experimental data was found with an intrinsic constant for the protonation of basic groups, log(K-b(i))= 7.89.