3D structural and mechanical characterization of centric diatoms through lab-based in situ nanoCT

The lab-based X-ray microscope with in situ mechanical testing, Xradia 810 Ultra, referred to as nanoCT, is a resourceful tool for the 3D characterization of samples down to 50 nm of resolution. In the mechanical in situ mode, a maximum force of 0.8 N can be exerted on the specimen in compression or indentation experiments. This setup allows for the observation of microstructural changes in the specimen as a function of mechanical loading and time. With its low energy X-ray source (5.4 keV) and Zernike phase contrast, this X-ray microscope is ideal for analyzing low density samples, such as soft tissues and polymers.
A centric diatom from the species Actinoptychus senarius was characterized using the in situ nanoCT at different levels of loading. The imaging experiments were carried out using the Zernike phase contrast mode with a field of view of 65 μm and a voxel size of (64 nm)³, with the diatom placed parallel to the pin surface and the compression anvil. At no load and for each of the loading steps (Figure 1, left) under displacement control, it is possible to observe the 3D structure and to extract the mechanical responses in each region of the sample (Figure 1, right). ... mehrThe cracks originate under 7 mN of load in the porous diatom frustule and propagate along a path that connects several pores. In the center of the frustule, region with no pores and higher Young’s module and hardness [1], the cracks start later under 31 mN of load.