The application of EBSD analysis to biomaterials: microstructural and crystallographic texture variations in marine carbonate shells

• Erika Griesshaber ^[1] ; Rolf D. Neuser ^[2] ; Wolfgang W. Schmahl ^[1]
  1. [1] Ludwig Maximilian University of Munich

     Ludwig Maximilian University of Munich

     Kreisfreie Stadt München, Alemania

     
  2. [2] Ruhr University Bochum

     Ruhr University Bochum

     Kreisfreie Stadt Bochum, Alemania

     
• Localización: Seminarios de la Sociedad Española de Mineralogía, ISSN-e 2659-9872, ISSN 1698-5478, Vol. 7, 1 1 (Madrid, 13 de septiembre de 2010), 2010 (Ejemplar dedicado a: Biominerals and Biomineralization Processes), págs. 22-34
• Idioma: inglés
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• Resumen

  • Electron backscatter diffraction (EBSD) is a facile and highly automatized microdiffraction method suitable for the determination of crystallographic phase and crystallite orientation. Thus, EBSD is an ideal method for the investigation of the structural organization of materials. Mineralized structures generated by biological control are widely recognized as prototypes for advanced materials. Their advanced properties are obtained through the interlinkage of two distinct material components - mineral and biopolymer - and by the development of highly evolved microstructures. We study the hierarchical structural organization of calcium carbonate skeletons of marine organisms as well as the interlinkage of the organic and inorganic components within these biomaterials. Our investigations range over several hierarchical length scales. In this paper we discuss as an example the microstructural and textural features of the calcitic shell of the brachiopod Notosaria nigricans. Furthermore, we address specific textural features of brachiopod calcite biomineralization in the course of shell growth. Based on the size and morphology of calcite crystals the shell of Notosaria nigricans is structured into two main layers which each consist again of sublayers. The primary layer on the outside of the shell shows an outer sublayer composed of nanosized crystallites and an inner sublayer with micrometre sized crystallites. The primary layer is followed inward by a secondary shell layer composed of fibrous calcite crystals. Sublayers of the secondary layer are distinguished by an alternation of domains where the morphological axis of the calcite fibres run in different directions in the plane parallel (or up to 10° inclined) to the shell surface. While in the juvenile brachiopod we have only three sublayers with distinctly oriented fibres in the secondary layer, the adult brachiopod shows several sublayers. The preferred crystallographic orientation of both the primary and the secondary shell layers is a strong fibre texture. Calcite c-axes are perpendicular (up to 22° subperpendicular) to the shell vault and rotate with the curvature of the shell. Accordingly, the calcite c-axis is perpendicular and mostly perpendicular to the morphological fibre axis. In juvenile as well as in adult Notosaria nigricans there is a slight inclination in c-axis orientation between the shell sublayers. It is remarkable that in juvenile Notosaria nigricans a true three dimensional crystallographic preferred orientation is present in the shell, while at a later stage of growth, in adult Notosaria nigricans, the texture looses most of its 3D ordering and becomes a 1D fibre texture. At the hinge of brachiopods shells restructuring is needed during growth, and here the texture becomes bi- or even multimodal.