Morphology and Mechanical Properties of Fossil Diatom Frustules from Genera of <i>Ellerbeckia</i> and <i>Melosira</i>

• Main Authors: Qiong Li, Jürgen Gluch, Zhongquan Liao, Juliane Posseckardt, André Clausner, Magdalena Łępicka, Małgorzata Grądzka-Dahlke, Ehrenfried Zschech
• Format: Article
• Language: English
• Published: MDPI AG 2021-06-01
• Series: Nanomaterials
• Subjects: diatom; fossil frustule; 3D visualization; X-ray computed tomography; micromechanical behavior; morphology
• Online Access: https://www.mdpi.com/2079-4991/11/6/1615

Fossil frustules of <i>Ellerbeckia</i> and <i>Melosira</i> were studied using laboratory-based nano X-ray tomography (nano-XCT), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Three-dimensional (3D) morphology characterization using nondestructive nano-XCT reveals the continuous connection of fultoportulae, tube processes and protrusions. The study confirms that <i>Ellerbeckia</i> is different from <i>Melosira</i>. Both genera reveal heavily silicified frustules with valve faces linking together and forming cylindrical chains. For this cylindrical architecture of both genera, valve face thickness, mantle wall thickness and copulae thickness change with the cylindrical diameter. Furthermore, EDS reveals that these fossil frustules contain Si and O only, with no other elements in the percentage concentration range. Nanopores with a diameter of approximately 15 nm were detected inside the biosilica of both genera using TEM. In situ micromechanical experiments with uniaxial loading were carried out within the nano-XCT on these fossil frustules to determine the maximal loading force under compression and to describe the fracture behavior. The fracture force of both genera is correlated to the dimension of the fossil frustules. The results from in situ mechanical tests show that the crack initiation starts either at very thin features or at linking structures of the frustules.