Insights into the Synthesis and Kinetics of Silver-on-Silica Core-Shell Particles.

In this study, a heterogeneous nucleation and growth model has been developed to explore the formation mechanism of silver-deposited silica core-shell particles based on the reaction kinetics. To validate the core-shell model, the time-dependent experimental data were quantitatively examined and in situ reduction, nucleation, and growth rates were estimated by optimizing the concentration profiles of reactants and deposited silver particles. Using this model, we also attempted to predict the change in the surface area and diameter of core-shell particles. The concentration of the reducing agent, metal precursor, and reaction temperature were found to have a strong influence on the rate constants and morphology of core-shell particles. Higher rates of nucleation and growth often produced thick, asymmetric patches that covered the entire surface, whereas lower rates produced sparsely deposited silver particles with a spherical shape. The result revealed that by simply tuning the process parameters and controlling the relative rates, the morphology of deposited silver particles and the surface coverage can be controlled while retaining the spherical shape of the core. The present study aims to offer comprehensive data pertaining to the nucleation, growth, and coalescence processes of core-shell nanostructures which will aid in the development and understanding of the principles that govern the formation of nanoparticle-coated materials.

Sono-crystallization kinetics of K2SO4: Estimation of nucleation, growth, breakage and agglomeration kinetics.

Application of ultrasound in crystallization has showed improved process characteristics. Although several attempts have been made in the past to study the sono-crystallization kinetics, only nucleation and crystal growth were considered, neglecting breakage and agglomeration of crystals. In this study, an attempt is made for the estimation of the kinetic parameters of all the phenomena occurring simultaneously during sono-crystallization. For this, both conventional and ultrasonic crystallization of K2SO4-water system has been reported. Sono-crystallization experiments were carried out using ultrasonic horn operating at 20 kHz frequency. Reduction in the induction time, reduction in metastable zone width (MSZW), narrowing of crystal size distribution (CSD) were the key observations of sono-crystallization experiments. Population balance equations (PBE) were used to model the crystallization system and the various kinetic parameters have been estimated. The kinetic parameters obtained for conventional crystallization and sonocrystallization were compared. The estimated parameters suggest an increase in nucleation and breakage rate during sono-crystallization. Growth rates were observed to be of the same order of magnitude for both conventional and sonocrystallization. While agglomeration during sono-crystallization was found to be negligible.