<p>Flash sintering was first
demonstrated in 2010, where a ceramic green body was rapidly densified within
seconds by applying an electric field during the heating process. The
ultra-fast densification can occur as current abruptly flows through the
material and self-heats by Joule heating. This process has potentials for large
energy savings due to the reduction in furnace temperatures and shortened
sintering time compared to conventional sintering. In addition, the ultra-high
heating and cooling rates, along with the impact of electric field and current
leads to the formation of unique non-equilibrium features in ceramics, which
could greatly enhance their properties. Despite the potential of flash
sintering, there are many challenges in moving this technique towards practical
applications, such as the microstructure inhomogeneity and lack of
understanding of the defects characteristics.</p>
<p>In this dissertation,
flash sintering was performed on ZnO to investigate the influence of various electrical
conditions on the microstructure and defects. Detailed characterization was
performed on flash sintered ZnO with and without a controlled current ramp, and
contrasting types of current (DC and AC). These parameters show significant
impact on the gradient microstructure and defects, and provide a way to tailor
the desired characteristics for a wide range of applications. On the other
hand, flash sintering of ZnO performed with a high electric field and low
current density resulted in the growth of nanostructures. These nanostructures
are unique compared to other growth techniques as they contain high density
basal-plane stacking faults, and exhibit ultraviolet excitonic emission and red
emission at room temperature. The nanostructure growth mechanism was
investigated by varying the current density limit and revealed the formation of
liquid phases which allowed growth by the vapor-liquid-solid mechanism. These
findings present a new exciting route for flash sintering to produce highly
defective nanostructures for device applications with new functionalities.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/15052893 |
| Date | 26 July 2021 |
| Creators | Xin Li Phuah (11181615) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Flash_sintering_of_zinc_oxide_and_the_growth_of_its_nanostructures/15052893 |
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