Effect of Nucleant Particle Agglomeration on Grain Size

Solute accumulation/depletion in the liquid around a growing solid particle during the solidification of metallic melts creates a constitutionally supercooled (CS) zone that has a significant effect on the final solidified grain structure. In this paper, we introduce two mechanisms related to the CS zone that affect grain size: one is the grain initiation free zone (GIFZ) that describes the inability of nucleant particles located in the CS zone for grain initiation and the other is re-melting (RM) of solid particles due to overlap of CS zones. Based on these two mechanisms, we have systematically analysed the effect of nucleant particle agglomeration on grain size. We found that nucleant particle agglomeration has a significant effect on grain size and is responsible for the discrepancy between theoretically predicted grain size and the experimental data. In addition, our numerical analysis suggests that under normal solidification conditions relevant to industrial practice solid particle re-melting has little effect on grain size and thus may be ignored during theoretical analysis. A practical implication from this work is that significant grain refinement can be achieved by dispersing the nucleant particles in the melt prior to solidification.

On modeling column crystallizers and a Hermite predictor–corrector scheme for a system of integro-differential equations

Multistaged crystallization systems are used in the production of many chemicals. In this article, employing the population balance framework, we develop a model for a column crystallizer where particle agglomeration is a significant growth mechanism. The main part of the model can be reduced to a system of integrodifferential equations (IDEs) of the Volterra type. To solve this system simultaneously, we examine two numerical schemes that yield a direct method of solution and an implicit Runge–Kutta type method. Our numerical experiments show that the extension of a Hermite predictor–corrector method originally advanced in Khanh (1994) for a single IDE is effective in solving our model. The numerical method is presented for a generalization of the model which can be used to study and simulate a number of possible operating profiles of the column.

Stabilizing indium sulfide for CO2 electroreduction to formate at high rate by zinc incorporation

Recently developed solid-state catalysts can mediate carbon dioxide (CO2) electroreduction to valuable products at high rates and selectivities. However, under commercially relevant current densities of > 200 milliamperes per square centimeter (mA cm−2), catalysts often undergo particle agglomeration, active-phase change, and/or element dissolution, making the long-term operational stability a considerable challenge. Here we report an indium sulfide catalyst that is stabilized by adding zinc in the structure and shows dramatically improved stability. The obtained ZnIn2S4 catalyst can reduce CO2 to formate with 99.3% Faradaic efficiency at 300 mA cm−2 over 60 h of continuous operation without decay. By contrast, similarly synthesized indium sulfide without zinc participation deteriorates quickly under the same conditions. Combining experimental and theoretical studies, we unveil that the introduction of zinc largely enhances the covalency of In-S bonds, which “locks” sulfur—a catalytic site that can activate H2O to react with CO2, yielding HCOO* intermediates—from being dissolved during high-rate electrolysis.

Criteria ruling particle agglomeration

Most of the technically important properties of nanomaterials, such as superparamagnetism or luminescence, depend on the particle size. During synthesis and handling of nanoparticles, agglomeration may occur. Agglomeration of nanoparticles may be controlled by different mechanisms. During synthesis one observes agglomeration controlled by the geometry and electrical charges of the particles. Additionally, one may find agglomeration controlled by thermodynamic interaction of the particles in the direction of a minimum of the free enthalpy. In this context, one may observe mechanisms leading to a reduction of the surface energy or controlled by the van der Waals interaction. Additionally, the ensemble may arrange in the direction of a maximum of the entropy. Simulations based on Monte Carlo methods teach that, in case of any energetic interaction of the particles, the influence of the entropy is minor or even negligible. Complementary to the simulations, the extremum of the entropy was determined using the Lagrange method. Both approaches yielded identical result for the particle size distribution of an agglomerated ensemble, that is, an exponential function characterized by two parameters. In this context, it is important to realize that one has to take care of fluctuations of the entropy.

Karakterisasi Sifat Fisis dan Mikrostruktur Papan Gipsum dengan Variasi Komposisi Lateks

Gypsum board is one of the advanced products of gypsum material with a mixture of fiber/fiber or other materials. Gypsum board has a weakness in its physical properties that easily absorb water. Therefore, there is a need for innovation in the manufacture of gypsum boards that will produce even better quality. The manufacture of gypsum board can utilize waste materials such as coconut shells and rice husks and latex as adhesives. The mixture of gypsum board materials including: gypsum, coconut shell, and rice husk used was 70%, 15%, 15% with latex variation 10%, 12%, 14%, 16%, 18% with FAS 0.5 and drying for 28 days. The parameters of the physical properties test include: density and thickness expansion, as well as microstructural testing to determine the morphology of the gypsum board sample. Analysis of the physical properties of gypsum board obtained optimal results, namely in sample A with a variation of 10% latex composition, the density value was 1.35 g/cm3, and the thickness expansion was 5.03% which met the SNI Standard 01-4449-2006. While the microstructure produces morphological images that show inhomogeneous distribution, particle agglomeration forms, and impurities