ABSTRACT
III . Mechanisms of Hydroxyl Ion Adsorption 305 A. Hydroxide ion adsorption 305 B. Competition for adsorption sites by hydrated ions 306 C. Relation between silica structure and hydration strength of ions 308 D. Cation adsorption onto porous silica surfaces 309 E. Alkaline-earth cation adsorption 309
IV. Description of the Electrical Interface 313 A. Surface ionization and complexation models 313 B. Determination of the point of zero charge (PZC) 316 C. Analysis of surface titration data 318 D. Determination of intrinsic ionization and complexation constants 320 E. Specific interaction of counterions 321
V. Electrokinetic Properties of Silica-Based Systems A. Electrophoresis B. Electrophoretic charge measurements C. Specific interaction of counterions
VI. The Effective Charge Concept
323 324 325 328
A.Equilibriumpropertiesofcolloidalsilicasystems B.Osmoticpressuremeasurements C.Scatteringexperiments
VII.Conclusion
References
Persello
332 334 336
Silica,oneofthemostabundantchemicalcompoundsonearth,canbeeitherin crystallineoramorphousforms.Theprincipalcrystallineformsarequartz,tridymite,andcristobalite.Theamorphousformsofsilicasareknownaspyrogenic silica,precipitatedsilica,silicagel,andcolloidalsilicasols.Pyrogenicsilicadiffers fromtheothertypesofamorphoussilica,inthatitisobtainedfromthehightemperatureflamehydrolysisofSiC14,whereasprecipitatedsilicaispreparedby neutralizationofawater-solublesodiumsilicatewithanacid.Precipitatedsilicasdo notdifferfromsilicagelsexceptthatthelattercanhaveagreatdiversityofmicroandmesoporosity.Thisincludesagainthe"silicasols,"whicharenanometricsilica particlesdispersedinanaqueousmedium.
