Graphene-based Coatings for Heat Exchangers

Abstract

This master thesis is a part of a larger interwork between SP, KTH and Alfa Laval funded by the SIO graphene programme, which end goal is to formulate an anti-corrosion coating based on graphene or graphene related materials (GRMs). The investigation is partly based on an article “Novel anticorrosion coatings prepared from polyaniline/graphene composites” from 2012 by Chang et al in combination of knowledge acquired during a previous EU project, www.steelcoatproject.com concerning polyaniline for anti-corrosion coatings. The purpose of this master thesis is to optimize the synthesis of the, PAni, and GRM nanocomposite.
Two different primary products of graphene oxides were investigated; water dispersed graphene oxide monolayer, GOW and water dispersed ammonia functionalized graphene oxide, AGO. These investigations were made to be able to confirm the presence of single sheets, the hybridizations of carbon and particle appearance and sheet size.
A polyaniline/AGO nanocomposite made at SP before the initiation of this master thesis containing 20 wt% AGO was analyzed by Raman spectroscopy, SEM, TEM and AFM. The reaction at which the SP nanocomposite was made was reviewed to find improvements. Agglomeration occurs when AGO is added to the reaction mixture of aniline monomers and hydrochloric acid. Improvements were investigated by analyzing the pH during the synthesis and the usage of ultrasonication. The later tests were made with an AGO load of 1 wt% and was analyzed by SEM and Raman spectroscopy. The synthesis using an ultrasonication step showed the best dispersion according to the visual appearance and the intensity ratio between sp2 and sp3 bonds in the Raman spectra.
Conclusion of this work is that the GRM products contain single sheets of the size of 1-7 µm for GOW and 4-10 µm for AGO, with a sp3/sp2 ratio of around 1. The PAni/AGO should be ultra-sonicated to obtain a well dispersed solution of AGO and aniline monomers before the synthesis is started by addition of the initiator.

Popular Abstract

To be able to prolong the lifetime of stainless steel in saline environments, coatings can be used as an extra barrier for corrosive substances. The purpose of this work was to optimize the polyaniline ammonium graphene oxide synthesis which should be used as barrier particles in polymer coatings. This project is a part of a larger cooperation between SP, KTH and Alfa Laval, preformed within the Strateic Innovation programme “Grafen” jointly founded by VINNOVA, Formas and Energimyndigheten.
Graphene has excellent properties like effective heat transport and good barrier properties which both are good qualities for protective coatings for heat exchangers. However dispersions of graphene are hard to produce in a cheap and easy way and therefore were graphene oxide used instead. Graphene oxide is easier to disperse and also easier to react with polymers. The polymer used in this investigation was polyaniline. This polymer was used because of its transporting properties.
The polyaniline, PAni, and graphene oxide with NH2 groups, AGO, nanocomposite process included mixing of hydrochloric acid together with AGO. However during this process an aggregate was formed when monomers of aniline was added to the mixture of hydrochloric acid and AGO. This was a problem since the dispersion of graphene oxide was not optimal and could impact on the reactions between polyaniline and the AGO sheets. The effect of the pH of the mixture was investigated for being one potential reason for the aggregate formation. The pH were measured for both the synthesis and the level of the dispersion of the AGO sheets in the pH ranging between 1-14. The result showed that AGO was easily dispersed in pH between 4-6. Adding AGO last, before the initiator, the substance that starts the reaction, should give a more suited pH. However the agglomeration persisted, leading to the conclusion that the agglomeration was not caused by the pH change. Instead an ultra-sonication step was introduced to the synthesis. By ultra-sonication of the mixture for ten minutes agglomeration dissolved. The products made with and without ultra-sonication step were analyzed by SEM and Raman spectroscopy which showed that the ultra- sonicated sample differed from the other. The ultra-sonicated sample seemed to be more flakelike structures.
PAni/AGO cannot adhere to the stainless steel whiteout adhesion aids in the form of for example polymeric binders. For future work different types of adhesion aid needs to be studied, as well as a way to disperse the composite particles in a binder. The effect of having graphene oxide or the effect of reducing the graphene oxide, by removing oxygen from the graphene oxide sheets, for the anti- corrosion and heat transporting properties is also of interest of investigate further.

• author: Långberg, Marie
• supervisor: Reine Wallenberg
• organization: Centre for Analysis and Synthesis
• course: KOO920 20151
• year: 2015
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: Polyaniline, graphene, materials chemistry, materialkemi
• language: English
• id: 7793285
• date added to LUP: 2015-10-07 12:13:28
• date last changed: 2015-10-07 12:13:28