Research in carbon nanotubes (CNTs) has become a very active field in the past decades, with much interest in their electronic and mechanical properties. However, the thermal properties of CNTs are still not well understood, in particular the process of annealing; i.e. purification of samples by desorption of internal and external impurities. Understanding the response of carbon nanotubes to high temperatures is critical for proper characterization of CNTs and CNT-based materials; especially because purportedly non-destructive characterization techniques such as Raman spectroscopy can induce high temperatures through laser heating. This thesis delineates an experiment aimed at elucidating the annealing and destruction process of carbon nanotubes. The experiment consists of heat treatments of single-walled nanotubes (SWNTs), monitoring nanotube abundance and purity by Raman spectroscopy. The samples are HiPCO-produced SWNTs of very high purity, separated in open and closed (end-capped) tubes. They are wetted with H2O in order to fill the open tubes, but are otherwise kept in their raw (as-produced) form of flakes of bundled tubes. This means that they have a low thermal conductivity as compared to dispersed CNTs, making them sensitive to overheating. The samples are heated in both air and argon environments in order to study the effect of oxidation. It is found that all tubes exhibit some annealing after heat treatment at temperatures as low as 100 °C. Temperatures higher than that are sufficient to degrade the samples in the case of closed tubes, which are found to be more thermally sensitive than open tubes, especially in air environments as oxidation is found to be a major component of the destructive mechanisms of CNTs. With higher temperature heat treatments at 500 °C, some of the open tubes exhibit a further step of annealing. This correlates with tube diameter, thus indicating that this annealing step can be associated with the desorption water from the CNTs' interior. A transition is found after heat treatment at 600 °C, although the new phase is not conclusively established, with evidence pointing to either charge transfer (by way of intercalation of dopant atoms in CNTs) or graphitization.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:ltu-61074 |
| Date | January 2016 |
| Creators | Landström, Anton |
| Publisher | Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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