It is unclear whether all intercalation techniques truly lead to the insertion of atoms
between the graphite layers, or also lead to other effects which contribute to expansion.
The objective of this project is to better understand the effects caused by different
intercalation methods. Three intercalation methods were explored to determine
the method which incurs the least damage to the surface and microstructure of
the graphite intercalated compounds, yet achieves the best intercalation and therefore
expansion.
All the main findings are summarised below:
The gas phase sample had virtually no mass loss at the point where expansion
took place. Therefore the intercalation was very efficient, producing large
expansion without significant mass loss.
The mass loss that only occurs at the sublimation of iron chloride (320 ºC) indicates
the excessive "un-intercalated" or residual iron chloride.
After oxidation, before purification, the gas phase sample has 25 % residual
mass; this also proves the presence of impurities and residual iron chloride in
the exfoliated sample. For the Hummers and electrochemical samples, expansion and mass loss occur
over a wide temperature range, this indicates that graphite oxide was
formed rather than the theoretically expected "insertion of atoms between the
sheets".
The mass losses before 200 ˚C of the samples of the Hummers and electrochemical
methods are more evidence that graphite oxide and graphite surface
complexes with oxygen were produced.
The Hummers and electrochemical intercalation methods show similar expansion
and mass loss curves, therefore it can be concluded that the reaction
mechanism for both these methods is alike.
The gas phase method yields the best expansion of 250 % using the TMA,
whereas both the other methods deliver approximately 220 %.
Using microwave expansion the electrochemical intercalation method yields
the best bulk volume expansion of 1500 %, with the gas phase sample delivering
a volume expansion of 1450 %.
The Hummers samples are extremely damaged. This is clear from the several and
deep oxidation pits visible throughout the basal plane of these samples. The basal
plane and the edges are even eroded before purification and oxidation. This intercalation
technique employs oxidisers in the preparation method which additionally oxidises
the samples. This explains why the Hummers method renders the most damage.
The residual material on the gas phase sample acts as catalysts making the sample
very reactive and consequently damaging the surface during oxidation. The partially
oxidised purified gas phase sample visibly shows the pits and roughened edges.
There are two “types” of intercalation. The first intercalation “type” is the actual insertion
of atoms or molecules between the graphite layers, whereas the other “type”
of intercalation is the production of graphite oxide. The compound comprises carbon,
oxygen and hydrogen, obtained by treating graphite with strong oxidisers. The
functional groups usually found in graphite oxide are carbonyl (C=O), hydroxyl (-OH), phenol amongst others and also some impurities of sulphur when sulphuric acid is
used. Both these intercalation types lead to expansion.
It is recommended that a more efficient method for removal of residual material in
the gas phase samples be explored. It is also recommended that more research be
done to determine the reaction mechanisms during the three different intercalation
methods. The graphite surface complexes of the intercalated compounds and the
evolved gases during expansion should be analysed. / Dissertation (MEng)--University of Pretoria, 2015. / tm2015 / Chemical Engineering / MEng / Unrestricted
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:up/oai:repository.up.ac.za:2263/46247 |
| Date | January 2015 |
| Creators | Van Heerden, Xandra |
| Contributors | Badenhorst, Heinrich |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Rights | © 2015 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
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