Title

Degradation Of Yttria-Stabilized Zirconia Thermal Barrier Coatings By Vanadium Pentoxide, Phosphorous Pentoxide, And Sodium Sulfate

Abstract

The presence of vanadium, phosphorus, and sodium impurities in petcoke and coal/petcoke blends used in integrated gasification combined cycle (IGCC) plants warrants a clear understanding of high-temperature material degradation for the development of fuel-flexible gas turbines. In this study, degradation reactions of free-standing air plasma-sprayed (APS) yttria-stabilized zirconia (YSZ) in contact with vanadium pentoxide (V 2O 5), phosphorus pentoxide (P 2O 5), and sodium sulfate (Na 2SO 4) were investigated at temperatures up to 1200°C. Phase transformations and microstructural development were examined using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Molten V 2O 5 reacted with solid YSZ to form zirconium pyrovanadate (ZrV 2O 7) at temperatures below 747°C. However, at temperatures above 747°C, molten V 2O 5 reacted with YSZ to form yttrium vanadate (YVO 4). The formation of YVO 4 led to the depletion of the Y 2O 3 stabilizer and deleterious transformation to the monoclinic ZrO 2 phase. In addition, studies on YSZ degradation by Na 2SO 4 and a Na 2SO 4+V 2O 5 mixture (50-50 mol%) showed that Na 2SO 4 itself had no effect on the degradation of YSZ. However, in the presence of V 2O 5 at high temperatures, Na 2SO 4 forms vanadate compounds having a lower melting point such as sodium metavanadate (610°C), which was found to degrade YSZ by the formation of YVO 4 at a relatively lower temperature of 700°C. P 2O 5 was found to react with APS YSZ by the formation of zirconium pyrophosphate (ZrP 2O 7) at all the temperatures studied. At temperatures as low as 200°C and as high as 1200°C, molten P 2O 5 was observed to react with solid YSZ to yield ZrP 2O 7, which led to the depletion of ZrO 2 in YSZ (i.e., enrichment of Y 2O 3 in t′-YSZ) that promoted the formation of the fluorite-cubic ZrO 2 phase. © 2007 The American Ceramic Society.

Publication Date

11-1-2007

Publication Title

Journal of the American Ceramic Society

Volume

90

Issue

11

Number of Pages

3601-3607

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1111/j.1551-2916.2007.01941.x

Socpus ID

35949000582 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/35949000582

This document is currently not available here.

Share

COinS