Quantitative plane-resolved crystal growth and dissolution kinetics by coupling in situ optical microscopy and diffusion models : the case of salicylic acid in aqueous solution

The growth and dissolution kinetics of salicylic acid crystals are investigated in situ by focusing on individual microscale crystals. From a combination of optical microscopy and finite element method (FEM) modeling, it was possible to obtain a detailed quantitative picture of dissolution and growth dynamics for individual crystal faces. The approach uses real-time in situ growth and dissolution data (crystal size and shape as a function of time) to parametrize a FEM model incorporating surface kinetics and bulk to surface diffusion, from which concentration distributions and fluxes are obtained directly. It was found that the (001) face showed strong mass transport (diffusion) controlled behavior with an average surface concentration close to the solubility value during growth and dissolution over a wide range of bulk saturation levels. The (1̅10) and (110) faces exhibited mixed mass transport/surface controlled behavior, but with a strong diffusive component. As crystals became relatively large, they tended to exhibit peculiar hollow structures in the end (001) face, observed by interferometry and optical microscopy. Such features have been reported in a number of crystals, but there has not been a satisfactory explanation for their origin. The mass transport simulations indicate that there is a large difference in flux across the crystal surface, with high values at the edge of the (001) face compared to the center, and this flux has to be redistributed across the (001) surface. As the crystal grows, the redistribution process evidently can not be maintained so that the edges grow at the expense of the center, ultimately creating high index internal structures. At later times, we postulate that these high energy faces, starved of material from solution, dissolve and the extra flux of salicylic acid causes the voids to close

Compressive Properties of Micro-spherical SiO2 Particles

Micron-sized, spherical SiO2 particles are important various industrial applications, such as in heterogeneous catalyst preparation. In particular, many of industrially relevant olefin polymerization catalysts are currently prepared using micro-spherical silica as catalyst support. In large-scale catalytic polyolefin production, the quality of the final product, as well as the process efficiency is crucially dependent on overall consistency, quality, physico-chemical properties of the catalyst. As the catalyst particle experiences various stresses during the polymer particle growth, mechanical properties of catalyst play a key role in its performance in the polymerization process. However, there is currently a lack of experimental mechanical property measurements of micron-sized, spherical SiO2 particles relevant for the polyolefin catalyst production. In this work, compressive properties of commercial porous micro-spherical silicas were studied using a quasi-static micro-compression method. The method includes compressing single, micron-sized particles in controlled loading conditions. From the measurements, the compressive elastic-plastic properties of these particles can be determined.Peer reviewe