Date of Award

1-1-2013

Document Type

Open Access Dissertation

Department

Mechanical Engineering

First Advisor

Xiaodong Li

Abstract

One dimensional (1D) metal borate and boride nanomaterials have attracted tremendous attention due to their good chemical inertness, high-temperature stability, excellent mechanical properties, and low thermal expansion coefficient.

Beta-BaB2O4 (BBO) is a well-known nonlinear optical material with a high second-order nonlinear susceptibility, wide transparency range, and high damage threshold. Using a low temperature, organic-free hydrothermal technique, single-crystalline barium polyborate Ba3B6O9(OH)6 (BBOH) nanorods were synthesized. It was found that BBO nanospindles can be achieved by annealing the BBOH nanorods at a relatively low temperature of 810 oC. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize these nanomaterials. The formation mechanisms are discussed in conjunction with the crystallographic characteristics and surface energy of the BBOH nanorods and BBO nanospindles. UV-vis absorption spectra demonstrated that both BBOH nanorods and BBO nanospindles are transparent from the ultraviolet to the visible regions.

Single crystalline strontium borate (SrB2O4) nanorods were synthesized for the first time via a sol-gel route at low temperature. The SrB2O4 nanorods have a good crystalline nature and they are transparent from the ultraviolet to the visible regimes. Nanoscale three-point bending tests were performed directly on individual nanorods to probe their mechanical properties using an atomic force microscope. The elastic modulus of SrB2O4 nanorods was measured to be 158.2 ± 7.9 GPa, exhibiting a significant increase compared with other borate nanostructures and bulk borates. We calculated the Young's moduli of bulk SrB2O4 and SrB2O4 nanorods with consideration of surface stress effect of nanorods by density functional theory. The simulated results were found consistent with the experimental values.

Zirconium diboride (ZrB2) is a highly covalent refractory and ultrahigh temperature ceramic material with a hexagonal crystal. This along with its relatively low density of ~6.09 g/cm3 and good high temperature strength makes it a candidate for high temperature aerospace applications such as hypersonic flight or rocket propulsion systems. We present the synthesis and structural characterization of ZrB2 nanorods. Single crystalline ZrB2 nanorods were synthesized for the first time via a simple route at a relatively low temperature of 800 oC. The XRD analysis revealed that the as-synthesized nanorods have hexagonal phase of ZrB2. In this Dissertation, the mechanical properties of ZrB2 nanorods were also characterized by atomic force microscope-based nanoindentation technique. Furthermore, the Young's modulus of ZrB2 nanorods was calculated with consideration of surface stress effect of nanorods by density functional theory. This theoretical prediction agrees well with the experimental results.

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