Apparent Viscosities of Ferric Oxide–Water Suspensions

Abstract

Abstract The effects of various types of anionic surfactants and inorganic phosphates on the apparent viscosities of ferric oxide–water suspensions of high pigment concentrations are examined. The additions of surfactants or inorganic phosphates to the suspensions cause depressions in their apparent viscosities from values of more than 10000 centipoise (cP) to about 10 cP. The concentration of the surfactants or the inorganic phosphates required to depress the apparent viscosity, which is designated as C0, is highly dependent upon the alkyl-chain length of the 1-1-type surfactants, the degree of the polymerization of the surfactants of the type of the vinyl copolymers and the degree of the condensation of the surfactants of the type of the formalin condensates or inorganic phosphates. With the 1-1-type surfactants, the values of the C0 decrease with the increases in the alkyl-chain length, and the surfactants with much shorter alkyl-chain lengths, such as Na octyl sulfate, linear-chain Na hexylbenzene sulfo-nate, and Na butyl-naphthalene sulfonate, have no marked viscosity depression effects. With the formalin condensates and the inorganic phosphates, the values of C0 decrease with the degree of condensation. With the vinyl copolymers, the C0 show smallest values at the appropriate degree of polymerization, e.g., about 10–40 for the Na salt of polyacrylic acid. Both the absolute value of the zeta potential and the amount of adsorption increase remarkably in the concentration regions showing marked viscosity depressions. The viscosity depressions of the suspensions upon the additions of the surfactants or inorganic phosphates can be qualitatively explained by taking into account the contributions of the zeta potential values and concentrations to the dispersion-coagulation of the pigment particles.