Surface chemistry and rheological behaviour of titania pigment suspensions

Abstract The influence of pH and surface chemical state on rheological behaviour was investigated for variations of silica- and alumina-coated, aluminium-doped titania pigment suspensions. The variation in rheological properties correlates with the change in the pigment surface properties, determined from electrophoresis measurements, atomic concentrations, chemical states and modified Auger parameters derived from X-ray photoelectron spectroscopy (XPS). Pigment suspensions exhibited a maximum yield stress and viscosity at or near the isoelectric point (iep). At a pH where the magnitude of the zeta potential of the titania pigment is high, a low-viscosity, dispersed suspension was obtained. The pH of the maximum yield value of the pigment suspension increases with increasing aluminium hydroxyl group density and decreases with increasing silicon hydroxyl group density. Low-viscosity pigment dispersions were obtained with increasing aluminium surface concentration and further reduced with an increase in the silicon surface concentration. Pigment particle attractions are chiefly dictated by van der Waals forces and heteroaggregation. The pigment aggregate strength therefore depends upon the Hamaker constant of the heterogeneous pigment based on the proportion of the respective surface groups.

[1]  R. Stewart,et al.  The rheology of strongly-flocculated suspensions , 1987 .

[2]  D. Chan,et al.  Double Layer Forces between Heterogeneous Charged Surfaces , 1994 .

[3]  R. J. Hunter,et al.  Plastic flow behavior of coagulated suspensions treated as a repeptization phenomenon , 1971 .

[4]  R. Buscall.  The Hamaker coefficient for titanium dioxide (rutile) in liquid media , 1993 .

[5]  Y. Chiang,et al.  Comparisons of Hamaker constants for ceramic systems with intervening vacuum or water : From force laws and physical properties , 1996 .

[6]  A. Rao.  Effect of pH on the suspension stability of alumina, titania and their mixtures , 1987 .

[7]  George A. Parks,et al.  The Isoelectric Points of Solid Oxides, Solid Hydroxides, and Aqueous Hydroxo Complex Systems , 1965 .

[8]  R. E. Day,et al.  Surface studies of TiO2 pigment with especial reference to the role of coatings , 1987 .

[9]  F. Garbassi,et al.  Surface properties of TiO2 modified with zinc ions , 1981 .

[10]  C. Prestidge.  Rheological investigations of galena particle interactions , 1997 .

[11]  D. V. Boger,et al.  Influence of Processing on the Rheology of Titanium Dioxide Pigment Suspensions , 1994 .

[12]  D. Furlong,et al.  The precipitation of silica on titanium dioxide surfaces , 1979 .

[13]  C. D. Wagner,et al.  Auger and photoelectron line energy relationships in aluminum–oxygen and silicon–oxygen compounds , 1982 .

[14]  Leena‐Sisko Johansson,et al.  Surface characterization of coated powders : Al2O3-SiO2-coated TiO2 , 1991 .

[15]  R. J. Hunter.  Zeta potential in colloid science : principles and applications , 1981 .

[16]  D. V. Boger,et al.  Surface chemistry and rheological properties of zirconia suspensions , 1991 .

[17]  P. Scales,et al.  Effect of Particle Size on Colloidal Zirconia Rheology at the Isoelectric Point , 1995 .

[18]  H. E. Bergna.  The Colloid Chemistry of Silica , 1994 .

[19]  P. Scales,et al.  RHEOLOGICAL EVIDENCE OF ADSORBATE-MEDIATED SHORT-RANGE STERIC FORCES IN CONCENTRATED DISPERSIONS , 1993 .

[20]  A. Rao.  RHEOLOCY OF AQUEOUS DISPERSIONS OF ALUMINA, TITANIA AND MIXTURE OF ALUMINA AND TITANIA POWDERS , 1987 .

[21]  W. A. Dench,et al.  Quantitative electron spectroscopy of surfaces: A standard data base for electron inelastic mean free paths in solids , 1979 .

[22]  J. Czarnecki,et al.  Van der Waals attraction energy between unequal rough spherical particles , 1984 .

[23]  P. C. Kapur,et al.  Yield stress of suspensions loaded with size distributed particles , 1997 .

[24]  P. Picozzi,et al.  SiOx surface stoichiometry by XPS: A comparison of various methods , 1994 .

[25]  T. Tadros,et al.  Influence of pH, electrolyte, and poly(vinyl alcohol) addition on the rheological characteristics of aqueous dispersions of sodium montmorillonite , 1983 .