Colloidal approach to dispersion and enhanced deaggregation of aqueous ferrite suspensions

The role of solution and surface chemistry on deaggregation of calcined ferrites during attrition (stirred-media) milling of aqueous suspensions were investigated. Suspensions of commercially calcined Fe₂O ₃ powder (d₅₀ ∼ 5.0 μm) were milled at different solid loadings and suspension pH. The drift of suspension pH, from pH 2.5 to pH 7.0, during solid loading experiments accounted for the observed reagglomeration with milling time. The observed deaggregation rates during pH stat milling, in the acidic region, can be related to (i) elevated solubility and (ii) enhanced dispersion via surface charge. Proton adsorption density during pH stat milling at different pH values is also comparable to existing potentiometric titration plots and can be related to deaggregation rates.; A passivation-dispersion approach for dispersing manganese zinc ferrite (Mn_xZn_{(1 − x)}Fe₂O₄) powder is presented. Addition of oxalic acid can help control dissolution reactions from particle surfaces and is subsequently dispersed with polyethyleneimine (PEI). Fully dissociated oxalic acid (pK₁ = 1.2, pK₂ = 4.3) solutions reacted with Mn_xZn_{(1 − x)}Fe ₂O₄ leads to the formation of a uniform negative charge on the particle surface, resulting from the sparingly soluble salt formed on the surface. The resulting rheological data for passivation/dispersion of relatively high solid Mn_xZn_{(1 − x)}Fe₂O ₄ suspensions (∼80 w/o, (∼40 v/o)) demonstrate improved colloid stability with improved rheological properties.; Using the passivation dispersion scheme developed, deaggregation of commercially calcined Mn_xZn_{(1 − x)}Fe₂O₄ powders during attrition milling was investigated. Reagglomeration is apparent when using a typical treatment, 2 w/w of a sulfonated based naphthalene condensate, during deaggregation of the calcined Mn_xZn_{(1 − x)}Fe ₂O₄. However, is not observed for select oxalate/PEI treatments. The determined ideal treatment is 2 w/w oxalate and 3 w/w PEI based on the particle size and rheological characteristics of the suspensions during milling. (Abstract shortened by UMI.)...