The sodium fluorosilicate (Na₂SiF₆) crystals have recently received much attention because of their application as ice-analogues [1,2]. The refractive index of sodium fluorosilicate is very close to that of ice at visual wavelengths and its crystals replicate the variety of growth habits of atmospheric ice crystals. The shapes of ice crystals can significantly affect the radiative transfer in ice clouds and in this way influence the climate evolution. Hence, it is important to accurately represent cirrus cloud and their single-scattering properties in climate models and in remote sensing applications [3]. Proper interpretation of scattering data requires laboratory experiment with artificial clouds and ice-analogous crystals are cheaper alternative to difficult experiments on real ice. It is however vital for scattering experiments to obtain all typical for atmospheric ice habits and to know relation between growth conditions of sodium fluorosilicate and final shape of its crystals.

In this work we present results of theoretical analysis of growth habitsin base of relative growth rates of individual surfaces of sodium fluorosilicates growing in solution and gel. The theoretical considerations are compared with experimental data concerning growth rates of particular faces.

Experimental data were taken from two types of experiment. In the first one, the saturation was obtained by the controlled evaporation of solute from initially undersaturated solution. In the second method, the crystals were grown in terametohoxysilane gel and supersaturation was obtained by temperature decrease. During experiments in solution the growth rates and evolution of aspect ratio were continuously measured (see [4] for more information). Among variety of habits obtained during experiments (hexagonal columns, plates, sectored plates, simple or six-armed stars, stellar dendrites and radiating dendrites) it seems that only hexagonal columns and plates, grown as well from solution and gel, are single crystals. Additionally, these habits are most common for atmospheric ice crystals. Thus, the theoretical analysis was performed for these two kinds of habits.


Fig. 1. Hexagonal columns (a,b) and plates (c,d), grown from solution and gel. Kinetic conditions corresponding to the growth of single crystals of these two characteristic habits of sodium fluorosilicate crystals (e). Scale bar is 100 μm.

These two kinds of habits which are under theoretical considerations are composed of basal and prism forms in the case of hexagonal columns (Fig. 1a, 1b) and, additionally of pyramidal form in the case of hexagonal plates (Fig.1c, 1d). In order to explain these different habits, we use an idea of the critical growth rate R^crit_hkl, which is defined as the normal growth rate of the (hkl) face at which a given size of this face is preserved. Taking into account the measured in situ growth rates and the analytical expression that relates the critical growth rate R^crit_hklwith the growth rates of each face, we obtained the kinetic conditions corresponding to growth of different habits of sodium fluorosilicate crystal, which are schematically presented in Fig. 1e. The experimental data and theoretical analysis demonstrates that the crystals of hexagonal columns and plates grow with appropriate relative growth rates within the dashed regions only. The theoretical approach in connection with experimental data allows us also to derive the kinetic conditions corresponding to the appearance of the pyramidal form, which is characteristic for hexagonal plates only.

1. Z. Ulanowski, E. Hesse, P.H. Kaye & A.J. Baran. Light scattering by complex ice-analogue crystals. J. Quantit. Spectr. Rad. Transf. 100 (1-3), pp.382-392 (2006)
2. Z. Ulanowski, E. Hesse, P. H. Kaye, A. J. Baran, R. Chandrasekhar Scattering of light from atmospheric ice analogues. J. Quantit. Spectr. Rad. Transf. 79-80C (2003) 1091
3. A.J. Baran, On the scattering and absorption properties of cirrus cloud, J. Quantit. Spectr. Rad. Transf. 89 (2004) 17
4. M.J. Krasiński, K.R. Krasińska, Z. Ulanowski, Investigation of growth kinetics and crystal morphology of sodium fluorosilicate ice-analogue crystals in solution and in gel, This conference

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/9722 must be provided.

1. Comparative in vitro studies on disodium EDTA effect with and without Proteus mirabilis on the mineralization of struvite and carbonate apatite
2. In vitro studies on disodium EDTA effect on mineralization of struvite and carbonate apatite
3. Influence of Proteus mirabilis on the growth process and morphology of struvite crystals
4. Growth morphology of crystals from kinetic and geometric perspective
5. Investigation of growth kinetics and crystal morphology of sodium fluorosilicate ice-analogue crystals in solution and in gel