EFFECT OF PH OF AQUEOUS CERAMIC SUSPENSIONS ON COLLOIDAL STABILITY AND PRECISION OF ANALYTICAL MEASUREMENTS USING SLURRY NEBULIZATION INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY

Colloidal stability of silicon nitride, silicon carbide and boron carb ide aqueous slurries used for slurry nebulization inductively coupled plasma atomic emission spectrometry has been investigated in the pH ra nge 2-10 by electrophoretic mobility and particle size measurements, t ogether with sedimentation tests. The mean particle size of silicon ni tride and silicon carbide suspensions change with increasing pH showin g a maximum at the isoelectric points (pH 7.5 and 5.5 respectively). T he particle size distribution of boron carbide slurries remains practi cally constant and the zeta-potential of suspended boron carbide parti cles shows a small change in the pH range investigated. The silicon ni tride and silicon carbide slurries have good stability at pH below 5 a nd above 8, respectively. Boron carbide slurries show excellent stabil ity in the whole pH range investigated. The time demand for stabilizat ion of the emission line intensities from the start of nebulization st rongly depends on the colloidal stability of slurries. Consequently, i t is advantageous to nebulize aqueous suspensions with a pH as far fro m the isoelectric point of the solid as possible and with the ionic st rength of the dispersion medium as low as possible. The RSD values of the line intensity measurements determined after 3 min stabilization t ime decrease with increasing stability of the aqueous slurries.