Materials for High Temperature Thin Film Thermocouple Applications

Vedula, Ramakrishna

Materials for High Temperature Thin Film Thermocouple Applications

dc.contributor.author	Vedula, Ramakrishna	en
dc.contributor.committeechair	Desu, Seshu B.	en
dc.contributor.committeemember	Fralick, Gustave C.	en
dc.contributor.committeemember	Curtin, William A. Jr.	en
dc.contributor.department	Materials Science and Engineering	en
dc.date.accessioned	2014-03-14T21:52:56Z	en
dc.date.adate	1998-07-28	en
dc.date.available	2014-03-14T21:52:56Z	en
dc.date.issued	1998-04-07	en
dc.date.rdate	1999-07-28	en
dc.date.sdate	1998-04-07	en
dc.description.abstract	The thermocouple systems used for the measurement of surface temperature in high temperature applications such as advanced aerospace propulsion systems and diesel engine systems are expected to perform in rapidly fluctuating and extremely high heat fluxes corresponding to high temperatures (in excess of 1400 K) and high speed flows. Traditionally, Pt/Pt-Rh based thin film thermocouples have been used for surface temperature measurements. However, recent studies indicated several problems associated with these thermocouples at temperatures exceeding 1000 K, some of which include poor adhesion to the substrate, rhodium oxidation and reaction with the substrate at high temperatures. Therefore, there is an impending demand for thermoelectric materials that can withstand severe environments in terms of temperature and heat fluxes. In this study, thin films of titanium carbide and tantalum carbide as well as two families of conducting perovskite oxides viz., cobaltites and manganates (La(1-x)SrxCoO3, M(1-x)Cax MnO3 where, M=La,Y) were investigated for high temperature thin film thermocouple applications as alternate candidate materials. Thin films of the carbides were deposited by r.f. sputtering while the oxide thin films were deposited using pulsed laser ablation. Sapphire (1102) was used as substrate for all the thin film depositions. All the thin films were characterized for high temperature stability in terms of phase, microstructure and chemical composition using x-ray diffraction, atomic force microscopy and electron spectroscopy for chemical analysis respectively. Electrical conductivity and seebeck coefficients were measured in-situ using a custom made device. It was observed that TiC/TaC thin film thermocouples were stable up to 1373 K in vacuum and yield high and fairly stable thermocouple output. The conducting oxides were tested in air and were found to be stable up to at least 1273 K. The manganates were stable up to 1373 K. It was observed that all the oxides studied crystallize in a single phase perovskite structure. This phase is stable up to annealing temperatures of 1373 K. The predominant electrical conduction mechanism was found to be small polaron hopping. Stable and fairly high electrical conductivities as well as seebeck coefficients accompanied with phase, structure, composition and microstructure stability indicate that these materials hold excellent promise for high temperature thin film thermocouple applications.	en
dc.description.degree	Master of Science	en
dc.identifier.other	etd-42298-8524	en
dc.identifier.sourceurl	http://scholar.lib.vt.edu/theses/available/etd-42298-8524/	en
dc.identifier.uri	http://hdl.handle.net/10919/46493	en
dc.publisher	Virginia Tech	en
dc.relation.haspart	front.PDF	en
dc.relation.haspart	chapters.PDF	en
dc.relation.haspart	resume.pdf	en
dc.rights	In Copyright	en
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	en
dc.subject	thin films	en
dc.subject	electronic materials	en
dc.subject	thermocouples	en
dc.subject	high temperature materials	en
dc.title	Materials for High Temperature Thin Film Thermocouple Applications	en
dc.type	Thesis	en
thesis.degree.discipline	Materials Science and Engineering	en
thesis.degree.grantor	Virginia Polytechnic Institute and State University	en
thesis.degree.level	masters	en
thesis.degree.name	Master of Science	en