Crystalline organization of nacre and crossed lamellar architecture of seashells and their influences in mechanical properties

Abstract Nature is embracing of abundant bio-inspired materials; among them seashells are exhibits their unique hierarchical arrangement of special structures with excellent mechanical properties. These alignments could be used as a template for the designing of artificial materials. In this present work, the architecture of four different species of seashells was compared based on their microstructural arrangements with building blocks of their elemental composition and resilient mechanical behaviors. The experimental seashells of Anadara inaequivalvis, Murex aduncospinosus, Bufonaria rana, and Conus planorbis were characterized by scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, microscopic infrared spectroscopy (MIR), thermogravimetric analysis (TGA) and micro-nanoindentation with fracture toughness. The obtained results revealed that the crystalline size of the seashells ranging from 30 to 1000 nm, and composed of aragonite, calcite in the form of aggregation of hexagonal plates with crossed lamellar units. Among the four seashells, A. inaequivalvis and C. planorbis are exhibited the excellent nacre and crossed lamellar organization with admirable mechanical strengths. However, the fourth order lamellae exhibited only in the case of A. inaequivalvis and the directions of fourth order lamellae [001] units were created by trim prisms of third order lamellae. Furthermore, it's aligned in parallel to fashioned in rod-shaped by second order lamellar units. The lamellar plate's arrangements were confirmed by TEM, and the formation of growth lines was mediated by the crossed lamellar structure to form a stacked curve pattern. In addition, the crossed lamellar structures of C. planorbis consist of granular and columnar appearances with three distinct layers. The mechanical mapping of A. inaequivalvis and C. planorbis are denoted the excellent mechanical strength in microindentation, hardness, Young module's and single-etch-notched three–points bending test. As a result, the textural analyses of seashells deliver the wide knowledge of crystallographic patterns of lamellar organization, and mapping the mechanical properties can be used for the construction of hierarchical super-tough artificial materials.