Work

Energy-driven microstructure and mechanical properties of mineral-organic biocomposite – Pteria penguin shell

Year: 2025

Type: article

Abstract: The high performance of biocomposites largely stems from their ability to self-organize. Our research on the Pteria penguin calcite columnar microstructure reveals a hierarchical ordering process crucial to its mechanical properties. Electron backscatter diffraction (EBSD) results show that each column constitutes a near-to-single-crystal composed of nanounits with close mutual orientations. The growth process was found to be stress-assisted, leading to one-sided bending and a considerable orientation difference between the top and bottom of the structural unit. The arising stresses are efficiently relaxed by using division along low-energy planes. The detected phenomenon can underlie the branching process observed in more advanced microstructures resulting from species’ adaptations over time. The stresses, and hence the system’s energy, are also reduced by the frequent formation of unusual twins resembling intra-columnar flow zones. The analysis of EBSD data, with the use of the developed program detecting crystal lattice matching in the reciprocal space, reveals that a low-energy plane initiating a well-developed column is used by the neighbors. In this way, a coherence zone is built. The long-range hierarchical order is also supported by the organic matrix composed mostly of hexagonal channels, easily accommodated by calcite crystals with similar geometry. Consequently, columns with the same orientation or in twin relation, based on a 60° rotation around the c-axis, are formed in a direct neighborhood or at a distance. The final coherent and rigid calcite structure, embedded in a compliant organic phase, enables effective load transfer and crack suppression, achieving a compressive strength of 670 MPa.

Source: Materials & Design

DOI: 10.1016/j.matdes.2025.114948