Foam-based crystal growth control

doi:10.1016/j.powtec.2005.05.010

Powder Technology

Volume 157, Issues 1–3, 29 September 2005, Pages 33-38

https://doi.org/10.1016/j.powtec.2005.05.010 Get rights and content

Abstract

We present results concerning the control of granulometry of crystals obtained by crystallization in a pre-formed aqueous supersaturated solution. This solution is first structured as a gas–liquid dispersion, consisting in an adjacent polyedric cells system, separated by thin liquid walls, each Plateau border, acting as a micro-reactor for crystallization. This structuration permits the size limitation of crystals formed, produced in a quasi-monomodal granulometry repartition. It has been possible to relate the mean granulometric characteristics to three dimensional parameters representative of the foam internal geometry, and to elaborate a model for the prediction of the granulometric repartition of crystals formed within the foam.

Introduction

In classical crystallization processes, the crystals size is controlled by varying thermodynamical conditions (temperature profile, evaporation rate etc). These conditions lead to specific sursaturation profiles controlling the crystals nucleation and growth rates [1], [2].

We present a study dealing with the crystallization by cryo-concentration of pre-formed glycin aqueous solutions. The three dimensional structuration of the solution, associated with very thin liquid films, permits a geometrical limitation of the solution volume accessible for the crystal growth. The Plateau borders act as micro-reactors for the crystallization of the solution, thus limiting the granulometry of the crystals formed, and leading to quasi-monomodal granulometry of crystals. The utilization of cryo-concentration allows the complete stabilization of the foam cells, giving the possibility to demonstrate the direct relationship existing between crystal sizes and internal structure of the foam.

Section snippets

Methods and equipment

This study has been conducted by utilization of glycin, an amino-acid (ACROS Organics, > 98% purity) with a solubility of 22.6 / 100 g water at 20 °C and a high crystals growth rate (> 17 μm/min) [3].

These foams are formed by air introduction, under mechanical agitation, within 20 ml of saturated solution, containing 2.4% w/w of a surface active additive, as a foaming agent. In order to prevent any crystallization during the foaming of the saturated solution, the experiments are performed at 20 °C.

Relationship between particle size and foam structure

The crystals size is usually dependant on the sursaturation evolution and also on the amount of the solution feeding the crystal growth. In the case of foam-based crystallization, the thickness of liquid films, and, more generally speaking, the geometrical internal structure of the foam depends on the aeration/foaming conditions. When the thermodynamical requirements are fulfilled, the crystals are formed essentially within the liquid films. A reduction of the crystal size can be obtained by

Calculation principle

As the bubble diameter evolves with time, the formed particle size depends on its position within the foam layer. We may apply the unidirectional and quasi-steady model developed for the calculation of the solidification progression. Thus, by knowing the bubble diameter evolution versus time, and the solidification front progression, we can derive the bubble radius repartition through the solidified foam layer. We may then calculate the foam representative diameters (d_l, d_a, d_v) and the

Conclusion

Foam-based cryo-crystallization of low concentrated glycin solutions can be obtained by freezing foam layers below the eutectic point (− 3.5 °C). Glycin crystals are formed within liquid films and Plateau borders of the foam. The foam three dimensional structure is used to limit the solution volume available for each crystal growth. We have demonstrated a relationship between the foam geometrical internal structure and the crystals diameters thus obtained. One may consider that the

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Cited by (1)

Preparation of TiO<inf>2</inf>, CeO<inf>2</inf>, and ZrO<inf>2</inf> hierarchical structures in "one-pot" reactions
2009, Journal of Colloid and Interface Science
Citation Excerpt :
Recently, some interesting works attracted lots of attentions. O. Bals's group [13] studied the foam-based crystal growth control, in which the glycine crystals were formed within the liquid films of the foam and assembled film structure. This work implies that foam templates could be used to prepare metal oxides polycrystalline film, with foam structures (macropores) and inter-particles mesopores.
In this paper, a novel template of carbon foam is used in building hierarchical structures of TiO₂, CeO₂, and ZrO₂. They had multiscale morphologies, from nanowalls, nanoparticles to layer nanostructures. On a hundred-micron scale, the product was a sponge-like material constructed by nanowalls. On a hundred-nanometer scale, the electron microscope images showed that the nanowalls were porous and assembled by polycrystalline nanoparticles. Meanwhile, on one nanometer scale, many nanoparticles exhibited layer nanostructures with about 1.1 nm of thickness and spacing. In mechanism section, the process analysis and characterizations suggested that the hierarchical structures were the combined result of two templates in a “one-pot” reaction. The mesoporous nanowalls were derived from carbon foams, while the layer nanostructures were the replicas of graphite sheets. The method has potential utilizations in preparation of various adsorbent and catalyst.

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