Microstructure and Thermal Expansion Properties of Ostrich Eggshell
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Microstructure and Thermal Expansion Properties of Ostrich Eggshell A. Heredia, L. Lozano, C.A. Martinez-Matias, M.A. Peña-Rico, A.Rodriguez-Hernández, E. Villarreal4, A. Martínez, M.V. García-Garduño1,2, V.A. Basiuk3,5, L. Bucio and E. Orozco Instituto de Física UNAM, Apdo. Postal 20-364, 01000 México D.F., México 1 Facultad de Ciencias UNAM, 04510 México D.F. México 2 Div. de Posgr. e Invest., Facultad de Odontologia UNAM, 04510 México D.F. México 3 Instituto de Ciencias Nucleares UNAM, 04510 México D.F. México 5 Faculty of Engineering, Yokohama National University, Japan. Hodogaya-Ku, Yokohama 240-8501. 4 Instituto de Investigaciones en Materiales, UNAM, 04510 México D.F. México ABSTRACT Textures of calcite crystals from ostrich (Struthio camelus) eggshells were examined with X ray diffractometry (XRD), transmission and scanning electron microscopy (TEM, SEM), and the thermal stability by thermal expansion analysis (TEA). Results showed that textures vary through the thickness of the eggshell and that expansion properties and thermal behaviour are unusual. Crystals from ostrich eggshell are arranged in two main configurations or layers; the outer layer with the c-axis of crystals oriented perpendicular to the eggshell surface and the inner layer with the c-axes of the crystals arranged almost parallel to eggshell surface; thermal expansion analysis show high stability through a wide range of temperatures until a steep growth near 450-460 °C. These results show that the manipulation of crystal texture and properties is under biological control and a better understanding of this biological phenomenon will provide more and better data for improving new synthetic composite materials. INTRODUCTION Biominerals (or biocrystals) has long been the object of biomimetic study because of its characteristic structural arrangements and interesting mechanical properties [1, 2]. Determining the structures of biological materials is the most important challenge to understand all this properties and mechanisms to design a new generation of biomimetic materials. The avian eggshell is an unusual kind of natural biomaterial because its formation process is extremely rapid ( ≈ 5.0 g of CaCO3 deposited in 24 h [4]) and the structure features arrangement of calcium carbonate crystals (calcite) in different layers relative to a biological macromolecule. In turn among avian eggshells, ostrich is of particular interest because of its fine assembly and therefore excellent structural and mechanical properties [4]. However, information on the crystal distribution is not enough. Some authors have done microstructural analysis to determine qualitatively the crystal orientation relationship between the neighbouring crystals in ostrich eggshell, obtaining randomly distribution of crystals in inner layer. This information should be especially valuable for a complete understanding of biomineralization and particularly in controlling the organic framework role of crystal nucleation and orientation, assembly as well as preferred crystal growth [3]. A
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