Mixed Alkali Effect on Oxidation of Si3N4 - A Compositional Study Using RBS
EMSL Project ID
2540
Abstract
Silicon nitride ceramics have a significant temperature capability advantage relative to single crystal super-alloys for jet and industrial turbine applications. Vanes and blades made of this material can potentially enable designers of the next generation of advanced turbines to significantly improve turbine performance and efficiency. Oxidation and associated degradation of silicon nitride in chemically aggressive turbine environment remains a sever roadblock to the exploitation of ceramic benefits in long-life-, high-performance turbine engines. There is a continued effort to search for means of enhancing the oxidation stability of silicon nitride. This project aims to study and explore mixed alkali effect in oxidation behavior of silicon nitride ceramics. MAE refers to the pronounced non-linear changes in many transport-related properties of an alkali silicate when a dissimilar alkali element is added. Examples include orders of magnitude decrease in diffusion coefficients and a factor of three improvement in chemical durability of glass in aqueous solution. Since the oxidation products of silicon nitride are silica-based, we expect that MAE can be exploited to retard sodium-accelerated oxidation of this ceramic. MAE in oxidation of silicon nitride is achieved by introducing cesium in sodium-containing oxidation environment. Our experimental studies have shown encouraging results. A full knowledge of the amount and distribution of alkali elements (sodium and cesium) as well as other major additive/impurity elements in the oxide formed is key to the understanding of the MAE effect thus its optimization. We are very excited about the prospect of collaborating with Dr. Theva Thevuthasan of PNL in ion beam (RBS) analysis of our samples. RBS may be most suitable for this purpose because of its non-destructive nature - we plan to carry out other analytical studies on the same samples upon completion of the RBS analysis. Any paper resulting from the RBS work will be published jointly with co-authors from PNL.
Project Details
Project type
Exploratory Research
Start Date
2002-06-15
End Date
2003-06-18
Status
Closed
Released Data Link
Team
Principal Investigator