This paper reports sonochemical synthesis and characterization of Mn–ferrite nanoparticles using acetates precursors. Mn–ferrite synthesis requires external calcination of oxide precursors formed by sonication. pH does not play a dominant role in the synthesis. Collisions between metal oxide particles induced by shock waves generated by transient cavitation are unable to cross the activation energy barrier for the formation of ferrite. The calcination temperature is a significant parameter that influences the magnetic properties of ferrites. The size, coercivity, and saturation magnetization of ferrite particles increases with the calcination temperature. Ferrites formed at calcination temperatures of 650, 750, and 850 °C show ferromagnetic behavior with easy axis magnetization. Calcination at 950 °C leads to the formation of rods with grain growth that introduces large shape anisotropy. The magnetization curve for rods does not reach saturation, indicating paramagnetic behavior. The cause leading to this effect is nonalignment of the easy axis of magnetization with the direction of the applied magnetic field, resulting in hard axis magnetization.

This paper reports studies in ultrasound-assisted heterogeneous solid catalyzed (CaO) synthesis of biodiesel from crude Jatropha curcas oil. The synthesis has been carried out in two stages, viz. esterification and trans-esterification. The esterification process is not influenced by ultrasound. The transesterification process, however, shows marked enhancement with ultrasound. A statistical experimental design has been used to optimize the process conditions for the synthesis. XRD analysis confirms formation of Ca(OMe)2, which is the active catalyst for transesterification reaction. The optimum values of parameters for the highest yield of transesterification have been determined as follows: alcohol to oil molar ratio ≈ 11, catalyst concentration ≈ 5.5 wt.%, and temperature ≈ 64°C. The activation energy of the reaction is calculated as 133.5 kJ/mol. The heterogeneity of the system increases mass transfer constraints resulting in approx. 4 × increase in activation energy as compared to homogeneous alkali catalyzed system. It is also revealed that intense micro-convection induced by ultrasound enhances the mass transfer characteristics of the system with ∼ 20% reduction in activation energy, as compared to mechanically agitated systems. Influence of catalyst concentration and alcohol to oil molar ratio on the transesterification yield is inter-linked through formation of methoxy ions and their diffusion to the oil-alcohol interface, which in turn is determined by the volume fractions of the two phases in the reaction mixture. As a result, the highest transesterification yield is obtained at the moderate values of catalyst concentration and alcohol to oil molar ratio.

Cobalt ferrite being a hard magnetic material with high coercivity and moderate magnetization has found wide-spread applications. In this paper, we have reported the sonochemical synthesis of cobalt ferrite nanoparticles using metal acetate precursors. The ferrite synthesis occurs in three steps (hydrolysis of acetates, oxidation of hydroxides, and in situ microcalcination of metal oxides) that are facilitated by physical and chemical effects of cavitation bubbles. The physical and magnetic properties of the ferrite nano-particles thus synthesized have been found to be comparable with those reported in the literature using other synthesis techniques.

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