Physicochemical characterization of biogenic calcium carbonate
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.528
Physicochemical characterization of biogenic calcium carbonate Katari P. Rocha, Santiago Botasini, Eduardo Méndez Laboratorio de Biomateriales, Instituto de Química Biológica, Facultad de Ciencias, Universidad de la República. 11400 Montevideo, Uruguay.
ABSTRACT
Biogenic minerals are widely studied materials for their particular properties derived from their hierarchical structure, using building blocks with sizes spanning several orders of magnitude. These special features can be assessed with different analytical tools, and it is important to know their capabilities and limitations. In order to determine the hierarchical structure of the shells, the nacre and prismatic layers of two marine animals were characterized by infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. Based on these assessments, we found that the combination of these three techniques is useful to describe each structure level, and to explain some of the unique properties observed in these natural materials.
INTRODUCTION Nowadays, the biomimesis of materials found in Nature is one of the main challenges in Material Sciences. Many of the unsolved technological issues are somehow solved by Nature, as the super-hydrophobicity, selectivity, biocompatibility, etc. Materials in Nature are formed in well-optimized processes over thousands and millions of years, mostly based on the self-assembly of building blocks. This procedure is an amazing challenge to the Thermodynamic laws, as implies a huge loss of entropy by the system being self-assembled, which is compensated by strong interactions between the building blocks allowing for the release of a high amount of energy as heat that increase the entropy of the surroundings. Hence, this entropy-enthalpy compensation produces the net increase in the entropy of the universe, as required by the Second law of the Thermodynamics. The interesting point is that the first step in the assemblage process produces a building block which is further self-assembled in bigger building blocks that ends in the macroscopic material. This step-by-step created structures are known as
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hierarchical structures [1] and remain in the final material as the evidence of the building process. In the case of inorganic materials, the biogenic minerals offer different properties than the one obtained only by geochemical means, because the synthesis of the materials is directed by proteins that act as guides in the assemblage process. Though the inorganic phase of biogenic structures is the same, several features reveal the hierarchical structures which are based on. Biogenic calcium carbonate is formed in the marine environment, and constitute the shell of different molluscs and gastropods. Two
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