Dispersion of phyllosilicates in aqueous suspensions: role of the nature and amount of surfactant.
OBJECTIVE
The present work aims at investigating the effect of pH values and additives on the dispersion of two 1:1 dioctahedral phyllosilicates in the presence of water. Two model clays are used for this purpose, BIP kaolin and NZCC halloysite, presenting the same surface chemistry but different morphologies. The effect of sodium hexametaphosphate, sodium silicate and sodium carbonate is discussed.


METHODS
Kaolin and halloysite powders were first characterized using X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. Subsequently, suspensions containing 8 mass% of each clay were prepared with or without additives. Experimental measurements regarding the pH values, the zeta potential and the rheological behavior were performed to determine the most suitable additive.


RESULTS
Results show that the conformation of halloysite particles changes regarding pH values of suspensions and is strongly related to the surface charges of these particles. At their natural pH values, halloysite and kaolin suspensions exhibit zeta potentials equal to -50 and -20 mV respectively. This trend indicates that halloysite-based suspensions are well dispersed compared to kaolin-based suspensions. Sodium hexametaphosphate is the most suitable dispersant for both clays. The rheological characterization regarding further applications in casting process indicates a shear-thinning behavior for all studied compositions.
Groupe d'Etude des Matériaux Hétérogènes, Centre Européen de la Céramique, 12 rue Atlantis, 87068 Limoges Cedex, France.
Nadia
N
Houta
Groupe d'Etude des Matériaux Hétérogènes, Centre Européen de la Céramique, 12 rue Atlantis, 87068 Limoges Cedex, France.
Gisèle-Laure
GL
Lecomte-Nana
Groupe d'Etude des Matériaux Hétérogènes, Centre Européen de la Céramique, 12 rue Atlantis, 87068 Limoges Cedex, France.
Nicolas
N
Tessier-Doyen
Groupe d'Etude des Matériaux Hétérogènes, Centre Européen de la Céramique, 12 rue Atlantis, 87068 Limoges Cedex, France. Electronic address: claire.peyratout@unilim.fr.
Claire
C
Peyratout
Dispersion; Phyllosilicate; Rheology; Surface charge; Zeta potential