Physical facets of ultrasonic cavitational synthesis of zinc ferrite particles

This paper addresses the physical features of the ultrasonic cavitational synthesis of zinc ferrite particles and tries to establish the relationship between cavitation physics and sonochemistry of the zinc ferrite synthesis. A dual approach of coupling experimental results with simulations of radial motion of cavitation bubbles has been adopted. The precursors for the zinc ferrite, viz. ZnO and Fe3O4 are produced in situ by the hydrolysis of Zn and Fe(II) acetates stimulated by OH radicals produced from the transient collapse of the cavitation bubbles. Experiments performed under different conditions create significant variation in the production of OH radicals, and hence, the rate of acetate hydrolysis. Correlation of the results of experiments and simulations sheds light on the important facets of the physical mechanism of ultrasonic cavitational zinc ferrite synthesis. It is revealed that too much or too little rate of acetate hydrolysis results in smaller particle size of zinc ferrite. The first effect of a higher rate of hydrolysis leads to excessively large growth of particles, due to which they become susceptible to the disruptive action of cavitation bubbles. Whereas, the second effect of too small rate of hydrolysis of Zn and Fe(II) acetates restricts the growth of particles. It has been observed that the initial reactant concentration does not influence the mean particle size or the size distribution of zinc ferrite particles. The present investigation clearly confirms that the rate-controlling step of zinc ferrite synthesis through ultrasonic cavitational route is the rate of formation of OH radicals from cavitation bubbles.