Suchergebnisse

The precipitation of barium and strontium carbonate in alkaline silica gels or silica solutions produces nanocrystalline self-assembled composite materials displaying biomimetic shapes and textures. We have crystallized concomitantly in time and space two anhydrous polymorphs of calcium carbonate, under similar conditions at different temperatures. The orthorhombic phase aragonite produces nanocrystalline aggregates exhibiting non-crystallographic morphologies and complex textures characteristic of silica biomorphs. Conversely, the simultaneously forming trigonal phase, calcite, yields rhombohedral crystals that experience fibrous growth and that maintain memory of the point symmetry group of the crystalline structure. Experiments performed at different temperatures (room temperature, 45, 60 and 80 °C) revealed that the higher the temperature the higher the aragonite/calcite precipitation ratio, but the crystallization of calcite was never fully inhibited. We have studied the growth mechanism, the growth texture and the morphogenesis for both cases. We have found that the dramatic difference between the crystallization behaviours of the two mineral phases is due to the difference in the growth mechanism at the nanoscale. ; The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 340863. G. Zhang acknowledges the Spanish Consejo Superior de Investigaciones Científicas for the pre-doctoral fellowship, within the programme ''Junta para la Ampliación de Estudios''. The authors also acknowledge Alicia González Segura from the Centre of Scientific Instrumentation of the University of Granada for her technical assistance.

The so-called "biomorphs" are a fascinating and beautiful group of polycrystalline, self-assembled silicaalkaline carbonate composite materials, which are usually obtained by crystallization process of carbonates with the presence of silica in alkaline environments. They are characterized by the hierarchy of their structures in addition to complex and curved morphologies which resemble the morphologies of crystallization under the control of living organisms. The first work related to biomorphs was reported in the 1980s, in which barium carbonate was slowly crystallized in alkaline silica gel by counterdiffusion method and biomorphic barium carbonate with noncrystallographic twisted ribbon was formed (Garcia-Ruiz, 1985) ; European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013) ERC grant agreement nº 340863 / JAE-PRE program ; Peer reviewed

Fabrication of mineral multi-textured architectures by self-organization is a formidable challenge for engineering. Current approaches follow a biomimetic route for hybrid materials based on the coupling of carbonate and organic compounds. We explore here the chemical coupling of silica and carbonate, leading to fabrication of inorganic¿inorganic biomimetic structures known as silica-carbonate biomorphs. So far, biomorphic structures were restricted to orthorhombic barium, strontium, and calcium carbonate. We demonstrate that, monohydrocalcite a hydrous form of calcium carbonate with trigonal structure can also form biomorphic structures, thus showing biomorphic growth is not dictated by the carbonate crystal structure. We show that it is possible to control the growth regime, and therefore the texture and overall shape, by tuning the growth temperature, thereby shifting the textural pattern within the production of a given architecture. This finding opens a promising route to the fabrication of complex multi-textured self-organized material made of silica and chalk. ; The research leading to these results has received funding from the European ResearchCouncil under the European Union's Seventh Framework Program (FP7/2007-2013)/ERC grant agreement n° 340863"Prometheus". G.Z. acknowledges the Spanish ConsejoSuperior de Investigaciones Científicas for the pre-doctoral fellowship, within the pro-gram"Junta para la Ampliación de Estudios". C.V.-E. acknowledges the SpanishMINECO for contract PTA2015-11103-I. The authors acknowledge Alicia GonzálezSegura and Isabel Guerra-Tschuschke from Center of Scientific Instrumentation of theUniversity of Granada for their technical assistance.