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SHAPE-PRESERVING TRANSFORMATIONS OF BIO-ENABLED SILICA STRUCTURES FOR OPTICAL AND MECHANICAL APPLICATIONS

thesis
posted on 12.10.2021, 13:30 by Sunghwan HwangSunghwan Hwang

Bio-inorganic structures have been found to exhibit impressive optical and mechanical properties, such as control of light and/or high fracture strength. Certain species of diatoms (single-celled algae) form siliceous microshells (frustules) with organized structures that affect the transmission of light or fracture strengths. It has been found that Coscinodiscus wailesii diatoms have frustules with a quasi-regular hexagonal pattern of pores, which act as micro-lenses. In terms of mechanical strength, Fragilariopsis kerguelensis diatom SiO2 frustules have been observed to exhibit impressive compressive and tensile fracture stress values. In this study, shape-preserving chemical conversion (using gas/solid reactions) is used to transform biogenic structures (diatom frustules) into high IR refractive index or ultrahigh specific strength materials. High-fidelity MgO/Si, Mg2Si, Ca2Si, MgO/Ti, and Ti replicas are successfully synthesized and characterized by SEM, EDX, XRD, and TEM. Focal point imaging experiments are used to show that focusing behavior of MgO/Si and Mg2Si replicas can be enhanced in the IR range upon conversion into higher index replicas. Mechanical properties of SiO2 frustules, MgO/Ti replicas, and Ti replicas have been measured by using in-situ and ex-situ indentation, which revealed that the mechanical properties can be enhanced by the shape-preserved chemical conversion of Bio-inorganic structures.


History

Degree Type

Doctor of Philosophy

Department

Materials Engineering

Campus location

West Lafayette

Advisor/Supervisor/Committee Chair

Kenneth Sandhage

Additional Committee Member 2

David Bahr

Additional Committee Member 3

Kevin Trumble

Additional Committee Member 4

Eric Kvam