Characterizing Hierarchical Structures of Natural Ivory
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CHARACTERIZING HIERARCHICAL STRUCTURES OF NATURAL IVORY H.B. Zhang, F.Z. Cui, S. Wang, and H.D. Li Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China ABSTRACT This paper presents a detailed investigation of the hierarchical and structural organization of the collagen-based aggregates in ivory. Ivory from African elephants is selected as the prototype in this study. A sophisticated architecture composed of collagen fibers and hydroxyapatite-like particles is revealed by optical microscopy, scanning electron microscopy and transmission electron microscopy. X-ray diffraction and TEN with selected area diffraction are employed to analyze the structure. Electron spectroscopy for chemical analysis and infrared absorption spectroscopy give information about the composition and chemical environment of the atoms in ivory. It is found that the structure of ivory has a three-level hierarchical organization, which includes both organic and inorganic materials. In the structure the inorganic material exists inside an organic framework, located outside of the collagen fibrils in the extrafibrillar volume. This inorganic structure has a polycrystalline form. Both the chemical compositions and the chemical environment of the atoms in the hydroxyapatite-like particles in ivory are different from those in natural hydroxyapatite. INTRODUCTION Biomineralized materials, especially their subtly hierarchical structures, have been an active topic of research in recent years [1-3]. Some biological composite materials have a sophisticated polymeric framework matrix reinforced by a mineral which forms within the matrix. These materials are distinguished from most synthetic composites by their complex structural and organizational characteristics and by the mechanism of their growth and formation (4,5]. Because of this fundamental difference, a full knowledge of biogenic composites may provide important insight for future developments in materials technology. For many centuries natural ivory has been used in many ways and has been seen as a material with great beauty and value. Recently, beginning in September, 1989, there has been an international effort to save the African elephant from extinction. Although in recent years several kinds of artificial ivory have been synthesized [6,7], none of them are very similar to the actual material. The detailed structural characteristics of natural ivory can therefore contribute much to the design of new materials. The purpose of this research is to examine the hierarchical structure of natural ivory and to explore some of the relationships among the components of its microstructure. Some discussions are given about the growth process and patterns of the material. Mat. Res. Soc. Symp. Proc. Vol. 255. 01992 Materials Research Society
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MATERIALS AND EXPERIMENTAL ivory from adult Tanzanian elephants were Samples of These tusks have selected for analysis in this investigation. The specimens were broken along the three a milky white color. orthogonal planes re
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