The effect of stabilizer addition and sonication on nanoparticle agglomeration in a confined impinging jet reactor

Reactive precipitation is a convenient synthesis route for production of submicron metal oxide particles. In this study, the effects of feed flow rate, feed concentration, stabilizer addition, and sonication on the size of precipitate particles in a confined impinging jet reactor were investigated using the iron oxide model system. Five stabilizers (TEG, DEG, sec butylamine, dextran, and polyacrylamide) were tested to determine optimum performance. The effects of in situ and post-reaction sonication on hard agglomerate size were also investigated. The agglomerate size varies with both feed flow rate and feed concentration. Mixing effects are more pronounced at high feed concentrations. The smallest agglomerates were obtained at a high flow rate and high feed concentration. Stabilizers added in situ reduced agglomeration. Triethylene glycol (TEG) was the most effective, causing the agglomerate size to drop by a factor of three at 5% (v/v) dosage for high feed concentrations and high flow rates. Neither the flow rate nor the TEG additive quantity had any significant influence on agglomerate size at low feed concentrations. Dextran addition leads to the smallest primary particles but the largest hard agglomerates. Post-reaction sonication disperses soft agglomerates, but in situ sonication had a negligible effect on agglomerate size, with or without the addition of stabilizer. CFD simulations indicate that the geometry modified with the in situ sonication probe has a similar energy dissipation field to the original geometry. In situ sonication energy is dominant over turbulent energy dissipation at low flow rates but the latter is comparable to or dominates above a flow rate of 165 mL/min. The second observation is supported by iodide-iodate experiments where the product yield is independent of flow rate above 165 mL/min.