Hot Corrosion of Yttria-Stabilized Zirconia Coating, in a Mixture of Sodium Sulfate and Vanadium Oxide at 950 °C

Hot corrosion behavior of double ceramic layered CaZrO3/Yttria‐stabilized zirconia coatings

“…After 60 hours of exposure, the micro‐cracks and porosity regions were analyzed in the cross sectional samples using EDS; the Ca and V rich phase was observed up to 85 μm depth into the topcoat‐2 and a few micrometers deep into the topcoat‐1. The EDS analysis of the near interface region of the topcoat‐1 to topcoat‐2 was carried out and found to be 7Y, 20O and 73 Zr, which indicated that within YSZ (topcoat‐1), the yttria did not react with the corrosives while normally, the Yttria in the YSZ react with the NaVO 3 (corrosives) forming YVO 4 in the case of single ceramic layered YSZ hot corrosion . Thermodynamically it is justified by the change in free energy of formation which is much more negative in the case of calcium vanadate (CaV 2 O 6 ) formation than that of yttrium vanadate (YVO 4 ) (ΔG (CaV 2 O 6 )≅ −2330.9 KJ/mol, ΔG (YVO 4 ) ≅−1406 KJ/mol) favoring the reaction of NaVO 3 with CaO (from CaZrO 3 ).…”

“…The topcoat‐2 was also observed broken while the topcoat‐1 was intact at major area of cracking region. In contrast, the single ceramic layered YSZ coating is normally failed after 30 hours of exposure during sulfate vanadate hot corrosion . The sulfate vanadate hot corrosion life of the DCL CaZrO 3 /YSZ coating was enhanced several times as compared with the single ceramic layered YSZ coating due to; (i) the sacrificial role of CaZrO 3 coating as the topmost layer and (ii) sealing up of the top surface for oxygen transport by semi‐molten initial corrosion product, impeding further growth of TGO (Figure ).…”

Sulfate‐vanadate hot corrosion of neodymium cerate/yttria stabilized zirconia composite coating

“…The molar ratio (Mol. %) of corrosive salts, V 2 O 5 and Na 2 SO 4 , used in most of the research works is 1:1 or closer to it . In the present work, 50% V 2 O 5 + 50% Na 2 SO 4 was selected for hot corrosion test.…”

“…The molar weights of V 2 O 5 and Na 2 SO 4 salts were mixed and crushed using a ball mill with 10 mm stainless steel balls and axial back and forth movement for 2 hours. The salts mixture with 10‐35 mg/cm 2 concentration had been used in the hot corrosion studies . In the present study, 30 mg/cm 2 corrosive concentration was selected to carry out the accelerated hot corrosion within 60 hours of exposure time.…”

“…The test temperature of 950°C was chosen after extended literature survey. Researchers have used 900‐1100°C as test temperature . During hot corrosion, after every successive 10 hours, one sample was taken out of furnace and corroded surface and the cross‐sectional regions were observed using stereomicroscope, optical microscope, and SEM (JEOL JSM 5910LV, Tokyo, Japan).…”