Microstructures in the chemical gardens formation
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1097-GG07-08
Microstructures in the chemical gardens formation C. Ignacio Sainz-Diaz, Bruno Escribano, and Julyan Cartwright Laboratorio de Estudios Cristalográficos, Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Av. Fuentenueva s/n, Granada, 18002, Spain ABSTRACT Chemical gardens are biomimetic structures in the form of plants formed by a combination of salts which precipitate by a combination of convection forced by osmosis, free convection and chemical reactions. Chemical gardens may be implicated in other phenomena of industrial interest which involve precipitation across a colloidal gel membrane which separates two different aqueous solutions, for example, in cement technology and metal corrosion process. However, the variation in chemical composition, morphology and mechanical properties of the different surfaces of these formations is not well known yet. Several salts in different concentrations and conditions have been explored under terrestrial gravity and microgravity. The chemical garden structures have been characterised by morphology analysis, scanning electron microscopy, chemical analysis and x-ray diffraction, correlating these data with the biomimetic growth and the physical-chemical nanoprocesses involved in it. This approach can also be useful for the analysis of biomaterials with interesting biomechanical properties.
INTRODUCTION The morphology of the solid during its growth at nanoscopic scale may be affected by physical phenomena of fluid dynamics and equilibria between processes of adsorption, desorption and diffusion. An interesting phenomena in this respect is the formation of biomimetic silicates called Chemical Gardens. Chemical gardens are curious structures in the form of plants formed by a combination of salts which precipitate by a combination of convection forced by osmosis, free convection and chemical reactions [ ]. On adding a crystal of a soluble salt to a solution of sodium silicate a reaction is provoked giving a hydrated silicate of the cation of that salt which is deposited as a colloidal gel around the crystal. The gel acts as a semipermeable membrane across which water and hydroxyl ions pass by osmotic pressure. The crystal continues to disolve and the membrane gel expands by osmotic pressure until it breaks producing a jet of fluid of the solution around the crystal and on entering the other medium the solubility changes and salt precipitates where the jets appear. Thus at each point of rupture tubular fibers are formed which can attain very cm of length showing biomimetic forms and receiving the name of gardens. Beyond the purely scientific fascination as spectacular examples of pattern formation, chemical gardens may be implicated in other phenomena of industrial interest which involve precipitation across a colloidal gel membrane which separates two different aqueous solutions. For example, i
in cement technology it is important to understand the hydration of Portland cement in which are found interpenetrated tubular nanofilaments of hydrat
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