The European Ceramic Society
YCN Newsletter 14 : Article by Christian Bechteler
My name is Christian Bechteler, I am a DPhil (PhD)-student in Materials at the University of Oxford.
Before my PhD I did my bachelor and master studies in Germany at the TH Nürnberg about CNT reinforced alumina composites, which woke my interest and motivation to work on ceramic materials.
The focus of my PhD is Flash Sintering (FS) of ceramics. FS uses a critical combination of electrical field and temperature at which the resistivity of most ceramics drops rapidly due to their NTC behaviour. This leads to a rapid increase in current and power dissipation in the material, leading to a sudden heating in the material and the following densification. The process itself celebrates its hundredth anniversary this year and was patented by Alexander L. Duval d´Adrian for zirconiumoxide in 1922. However, FS of YSZ as it is known today was reported in 2010.
In the perspective of future processing of ceramics, FS can lead to fully dense materials in a shorter time, seconds instead of hours, and significantly reduced furnace temperatures compared to conventional sintering. Thus, FS is a more sustainable sintering method, which helps to reach goals like net-zero and the reduction of the impact of ceramic processing on climate change.
Even if a lot of research was conducted on FS of ceramics, particularly YSZ, the fundamental mechanisms of the rapid densification remain unclear, and this is where my research starts…
Together with my supervisor Professor Richard I. Todd, and a handful of other PhD students, I am working on the process of FS of ceramics. Especially, fundamental interactions between electrical fields and currents in ceramic materials at elevated temperatures are investigated in our lab. In the perspective of FS, investigations about oxide ceramics, like YSZ and alumina, but also non-oxides, such as boron carbide and silicon carbide, are conducted.
Varying methods are necessary to realise some research ideas we have. For instance, optical spectroscopy of emitted light during FS was used to investigate mechanisms and estimate sample temperatures. Furthermore, all common material characterisations are used to investigate how the electrical field changed the materials structure and properties.
In the latest project of my research, I am investigating how a plasma can form during or before FS and how such a plasma formation changes the properties of various materials. The inclusion of a pre-plasma treatment before FS is something that´s totally new and a lot of novel knowledge has to be generated to understand the influence of plasmas on ceramic materials and how it could be used to improve their processing. An image of Si-based crystals, which grew in such a plasma within a few seconds, won the YCN´s annual SEM-image contest and is attached to this article.
We are always looking for collaborations or interested researchers who want to learn more about FS and how electrical fields or plasmas can change the properties of materials.
Department of Materials
University of Oxford
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