Details
| Originalsprache | Englisch |
|---|---|
| Qualifikation | Doctor rerum naturalium |
| Gradverleihende Hochschule | |
| Betreut von |
|
| Datum der Verleihung des Grades | 2 Dez. 2024 |
| Erscheinungsort | Hannover |
| Publikationsstatus | Veröffentlicht - 16 Dez. 2024 |
Abstract
Zitieren
- Standard
- Harvard
- Apa
- Vancouver
- BibTex
- RIS
Hannover, 2024. 228 S.
Publikation: Qualifikations-/Studienabschlussarbeit › Dissertation
}
TY - BOOK
T1 - Asymmetric structuring of thermoelectric ceramics using electrospun nanoribbons
AU - Kruppa, Katharina
PY - 2024/12/16
Y1 - 2024/12/16
N2 - Most oxides are promising due to their exceptional stability in oxidative atmospheres. They have significant potential to enhance thermoelectric energy conversion through thermoelectric generators (TEGs) at high temperatures in air. They can recover unused thermal energy, prevalent in industry and transportation, thus contributing to sustainable energy sources. The oxide material [Ca2CoO3–δ]0.62[CoO2] (CCO) is extensively studied due to its high chemical and thermal stability in air and excellent thermoelectric (TE) properties. NaxCoO2 (NCO) offers even better TE performance but degrades quickly at high temperatures in air, impacting its long-term stability. To utilize NCO’s outstanding TE properties at high temperatures, stabilization methods were developed, including integrating NCO into a thermally stable CCO-based matrix. Asymmetrically structuring NCO on the nanoscale within the TE ceramic composite created a protective barrier that preserved the materials properties under extreme conditions and ensured its use at high temperatures. NCO and CCO have layered crystal structures leading to anisotropic transport properties. To significantly enhance the TE performance of polycrystalline ceramics, precise texturing is crucial for aligning crystal grains to approximate the exceptional properties of single crystals. Nanostructuring ceramics also increases the amount of grain boundaries, reducing thermal conductivity. Electrospinning of nanoribbons was used to achieve these features. Initially, mixed CCO nanofiber/nanoribbon mats were compacted into porous ceramics. Electrospinning was optimized to produce 100% flat CCO nanoribbon mats, resulting in textured ceramics. A novel multi-stage sintering process, including spark plasma sintering and spark plasma texturing (SPS+SPT), improved texturing and densification of the ceramic, enhancing its thermoelectric properties. Combining SPS+SPT with electrospun nanoribbons, which allowed efficient packing, resulted in dense ceramics with excellent grain orientation. Co-electrospinning of NCO-CCO nanoribbons produced an asymmetrically structured ceramic composite with excellent stability and TE properties. Another method integrated micrometer-sized NCO template particles into a Na, Bi, Tb doped CCO-based powder, forming a triple-phase composite matrix. This stabilized the NCO phase at high temperatures and improved TE performance.
AB - Most oxides are promising due to their exceptional stability in oxidative atmospheres. They have significant potential to enhance thermoelectric energy conversion through thermoelectric generators (TEGs) at high temperatures in air. They can recover unused thermal energy, prevalent in industry and transportation, thus contributing to sustainable energy sources. The oxide material [Ca2CoO3–δ]0.62[CoO2] (CCO) is extensively studied due to its high chemical and thermal stability in air and excellent thermoelectric (TE) properties. NaxCoO2 (NCO) offers even better TE performance but degrades quickly at high temperatures in air, impacting its long-term stability. To utilize NCO’s outstanding TE properties at high temperatures, stabilization methods were developed, including integrating NCO into a thermally stable CCO-based matrix. Asymmetrically structuring NCO on the nanoscale within the TE ceramic composite created a protective barrier that preserved the materials properties under extreme conditions and ensured its use at high temperatures. NCO and CCO have layered crystal structures leading to anisotropic transport properties. To significantly enhance the TE performance of polycrystalline ceramics, precise texturing is crucial for aligning crystal grains to approximate the exceptional properties of single crystals. Nanostructuring ceramics also increases the amount of grain boundaries, reducing thermal conductivity. Electrospinning of nanoribbons was used to achieve these features. Initially, mixed CCO nanofiber/nanoribbon mats were compacted into porous ceramics. Electrospinning was optimized to produce 100% flat CCO nanoribbon mats, resulting in textured ceramics. A novel multi-stage sintering process, including spark plasma sintering and spark plasma texturing (SPS+SPT), improved texturing and densification of the ceramic, enhancing its thermoelectric properties. Combining SPS+SPT with electrospun nanoribbons, which allowed efficient packing, resulted in dense ceramics with excellent grain orientation. Co-electrospinning of NCO-CCO nanoribbons produced an asymmetrically structured ceramic composite with excellent stability and TE properties. Another method integrated micrometer-sized NCO template particles into a Na, Bi, Tb doped CCO-based powder, forming a triple-phase composite matrix. This stabilized the NCO phase at high temperatures and improved TE performance.
U2 - 10.15488/18253
DO - 10.15488/18253
M3 - Doctoral thesis
CY - Hannover
ER -