Dispersibility of magnetic and nonmagnetic iron(III) oxides in cyclohexane and effect of water on the stability.

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The dispersion stability of needlelike and octahedral iron(III) oxides of magnetic or nonmagnetic particles in cyclohexane solutions of sodium 1,2-bis(2-ethylhexyloxycarbonyl)ethanesulfonate (Aerosol OT or AOT) was studied on anhydrous and hydrous systems. The dispersion stability of the anhydrous system was examined for seven kinds of oxides. The sedimentation velocity of dispersions, the histograms of particle distribution, the adsorption of Aerosol OT on the particles and zeta potential were measured. Potential energies of the interaction between a pair of particles were calculated for the anhydrous system. It was suggested from the calculation of potential energies that the magnetic attractive force, which is a function of the strength of the saturation magnetization and the volume of particle, is a main factor affecting the flocculation of the magnetic particles in cyclohexane as well as in 2-butanone reported in the previous papers. The study of the dispersion stability of the hydrous system was done for three kinds of needlelike oxides. The relatively stable region appeared in the lower concentration range of water. The stability decreased at the fixed water concentration followed by marked flocculation ("floc formation" region). It was considered that the appearance of the "floc formation" is caused by the formation of thick hydration layer on the oxide surface and the decrease of zeta potential.
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