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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.