On the Development of Thermally Grown Oxide in High Water Vapor Environments for Thermal Barrier Coating Systems -- Speaker: Matthew Sullivan
Gas turbine engines are currently used in the production of nearly 25% of the United State’s electricity, a number that is expected to rise greatly in the next 15 years with the discovery of shale gas reserves. This dictates that gas turbine efficiency and fuel flexibility will have enormous influence on the country’s ever-evolving energy policy and health. The Integrated Gasification Combined Cycle (IGCC) power plant is a technology that promises to improve both, as it can transform coal, biomass and other carbon feedstocks into clean synthetic gas (syngas), which it then converts to electricity with 45% efficiency and nearly 100% carbon capture. From a materials standpoint, it is crucial to understand how combusting syngas at IGCC temperatures (upwards of 1500⁰C) may affect the degradation mechanisms of the thermal barrier coatings (TBCs) that are used to protect hot section engine blades, and how those mechanisms might differ from ones associated with combusting natural gas, the conventional feedstock. Higher water vapor levels in the combustion zone are one expected consequence of using syngas. This research is focused specifically on how heightened H2O may impact the growth of a thin alumina/spinel bilayer oxide that is responsible for the long term stability of TBC systems. There are three main findings, all centered on spinel, the harmful component of the bilayer whose growth is sought to be mitigated: 1) artifacts associated with oxidation in H2O are underestimated in the literature and have consequently led to faulty conclusions for the materials system in question; the mechanisms of two such artifacts – the volatilization and redeposition of spinel – are explained; 2) once artifacts are accounted for, heightened H2O is not expected to promote the steady-state growth of spinel, as had been feared; but 3) spinel growth is accelerated by H2O in the early, transient stage of oxidation. Understanding these factors, a pre-oxidation routine is proposed that would remove all spinel from the oxide bilayer in a matter of a few hours, so that it would not pose a threat over the tens of thousands of hours of intended engine operation.
Matthew Sullivan is a sixth-year graduate student working on completing his Ph.D. in materials science at UC Irvine, under the direction of Professor Daniel Mumm. He obtained his bachelor's degree in chemical engineering at the University of Notre Dame in 2005, then worked for two years as a materials research scientist at FuelCell Energy, Inc. in Danbury, CT before joining the UCI ChEMS department in 2007. In addition to conducting his research, he has spent the last two and a half years working as an assistant at UCI’s Laboratory for Electron and X-ray Instrumentation (LEXI), where he has trained the user base and performed electron microscopy for clients in the surrounding industrial community. His research interests lie in developing new technologies and efficiencies for energy systems.