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 2 O 5 ), phosphorus pentoxide (P 2 O 5 ), and sodium sulfate (Na 2 SO 4 ) were investigated at temperatures up to 12001C. Phase transformations and microstructural development were examined using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Molten V 2 O 5 reacted with solid YSZ to form zirconium pyrovanadate (ZrV 2 O 7 ) at temperatures below 7471C. However, at temperatures above 7471C, molten V 2 O 5 reacted with YSZ to form yttrium vanadate (YVO 4 ). The formation of YVO 4 led to the depletion of the Y 2 O 3 stabilizer and deleterious transformation to the monoclinic ZrO 2 phase. In addition, studies on YSZ degradation by Na 2 SO 4 and a Na 2 SO 4 1V 2 O 5 mixture (50-50 mol%) showed that Na 2 SO 4 itself had no effect on the degradation of YSZ. However, in the presence of V 2 O 5 at high temperatures, Na 2 SO 4 forms vanadate compounds having a lower melting point such as sodium metavanadate (6101C), which was found to degrade YSZ by the formation of YVO 4 at a relatively lower temperature of 7001C. P 2 O 5 was found to react with APS YSZ by the formation of zirconium pyrophosphate (ZrP 2 O 7 ) at all the temperatures studied. At temperatures as low as 2001C and as high as 12001C, molten P 2 O 5 was observed to react with solid YSZ to yield ZrP 2 O 7 , which led to the depletion of ZrO 2 in YSZ (i.e., enrichment of Y 2 O 3 in t 0 -YSZ) that promoted the formation of the fluorite-cubic ZrO 2 phase.

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