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Title: Carbon nanotubes as fire gas sensors
Author: Pearce, Ruth Elizabeth
ISNI:       0000 0004 2682 178X
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2009
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Multi walled carbon nanotubes (MWCNTs) possess properties that make them particularly relevant for sensing applications in both the gas and liquid phase. This study presents an evaluation of cheap readily available CVD grown MWCNTs for use as fire gas sensors. Current fire detectors exploit heat and smoke detectors and it is hoped that the inclusion of gas detectors will increase the speed and reliability of detection. In order to prepare a variety of different MWCNTs a range of CVD synthesis were employed including an injected catalyst method where MWCNTs grew in dense mats from quartz substrates, MWCNTs were also synthesised using a sputtered Fe catalyst layer with acetylene as the carbon source which enabled control over the positioning of the growth. In each case, the growth parameters were varied until aligned growth was achieved. Doping of MWCNTs was also carried out as this may enhance and enable some control over the electrical properties of the CNTs; nitrogen was also added as a dopant by including 1,4-diazine as a precursor, and the effects on morphology of the MWCNTs produced were studied. The chemistry of the surface is also known to affect the sensing properties of CNTs. A batch of MWCNTs produced via the injected catalyst method were purifed by acid reflux, base washing and high temperature vacuum annealing, then modified with platinum or palladium metal nanoparticles via a reduction of the metal salts under hydrogen. MWCNTs were also coated with the polymer polyethyleneimine and with copperphthalocyanine. Prototype sensor devices were fabricated by electrophoretic deposition of these modified MWCNTs, and gas testing was carried out with the gases NO2, NH3, CO, H2 and C3H6. The mechanisms of sensing were investigated by repeating the tests at different temperatures, which revealed which sensing mechanisms were dominant and responses were compared between the differently modified MWCNTs. Sensor response was also investigated with a series of vapours to probe the dispersive and polar interactions on the MWCNT walls.
Supervisor: Shaffer, Milo Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral