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Degradation due to molten salt attack is one of the failure mechanisms of thermal barrier coatings. Thermochemical attack of the salt mixture Na 2 SO 4 –30 mol% NaVO 3 on ZrO 2 –8 mol% YO 1.5 (8YSZ) at 1100 °C for different times was investigated. In the present study, 8YSZ powder was synthesized using co-precipitation route. The graded morphologies and phase compositions were examined using SEM, XRD and Raman before and after hot corrosion test. The results obtained from XRD have shown that m-ZrO 2 and YVO 4 were the main corrosion products after hot corrosion test at 1100 °C. The results obtained from SEM and EDS observations have shown that large polyhedron crystals of m-ZrO 2 and rod-like crystals of YVO 4 formed as hot corrosion products after hot corrosion test for 6 h and 24 h. The phase transformation and chemical interaction are the primary corrosion mechanisms for degradation of 8YSZ ceramic. [ABSTRACT FROM AUTHOR]

Abstract: Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La2(Zr0.7Ce0.3)2O7 (LZ7C3) and Eu3+-doped zirconia, which was partially stabilised by 8wt% yttria (8YSZ:Eu), were prepared by atmospheric plasma spraying. A thermal cycling test was carried out. The 8YSZ:Eu sublayer exposed during thermal cycling could produce visible luminescence under ultraviolet (UV) illumination, providing an indication of the spallation and damage degree of the coating. The result shows that the application of a Eu3+-doped luminescence sublayer can be a very simple and useful non-destructive technique to indicate the spallation and damage degree of DCL coatings. [Copyright &y& Elsevier]

The nanostructured (8 wt%) yttria stabilized zirconia coatings (n-YSZ) were deposited by atmospheric plasma spraying (APS) to study the effect of moisture degradation on the properties of n-YSZ coatings. Variations in phase composition, microstructure and mechanical properties were comprehensively characterized. The single-edge notched beam method used for fracture toughness testing is sufficiently reliable for evaluating the integral properties of the coatings in this study. Results indicated that the microstructure of the n-YSZ coatings was significantly affected by hydrothermal degradation. Hydrothermal degradation resulted in substantial defects, such as pores and cracks, which severely decreased the mechanical properties of the n-YSZ coatings. In addition, the ceramic coat was in a state of compressive stress, and the stress initially increased and then decreased with increasing degradation time. The variations in the stress of the n-YSZ coatings are closely related to the transformation of tetragonal to monoclinic phase, which is induced by hydrothermal degradation. Additionally, several major mechanical properties of the n-YSZ coatings decreased significantly with the hydrothermal degradation, including fracture toughness from 1.28 ± 0.05 to 0.08 ± 0.01 MPa m1/2, flexural strength from 60.51 ± 2.98 to 4.54 ± 0.14 MPa, and Young's modulus from 21.98 ± 0.96 to 1.46 ± 0.33 GPa. [ABSTRACT FROM AUTHOR]

In the present study, 8YSZ:Eu 3+ powder was synthesized using co-precipitation route. The evolution of phase composition and fluorescence properties of 8YSZ:Eu 3+ powder have been assessed after being subjected to hydrothermal degradation for different times. Morphology and microstructure of the sintered powder were observed by transmission electron microscope (TEM) and scanning electron microscope (SEM). XRD, Raman spectra, photoluminescence (PL) spectra and the decay curve were used to evaluate the phase composition variation and fluorescence properties variation of the powder. The results showed that 8YSZ:Eu 3+ powder had a pure tetragonal phase structure. Under hydrothermal degradation conditions, due to the reaction of OH − and oxygen vacancy, the transformation of tetragonal to monoclinic occurred, furthermore the fluorescence properties of the powder were altered. [ABSTRACT FROM AUTHOR]

Highlights: [•] m-, t- and c- zirconia samples were prepared by controlling Y3+ doping concentration. [•] The fluorescence properties of m-, t- and c- zirconia samples were investigated. [•] The relationship between crystal structure and PL properties were further examined. [•] The PL properties of Eu3+ can be used to infer crystal structure of Eu3+-doped ZrO2. [Copyright &y& Elsevier]

ZrO 2 :Eu 3+ nanocrystals were synthesized by hydrothermal technique. Effects of Eu 3+ -doping and annealing on the morphology, crystal structure and fluorescence properties of the resultant ZrO 2 :Eu 3+ nanocrystals were investigated. The morphology and crystal structure of the ZrO 2 :Eu 3+ nanocrystals were characterized by TEM, XRD, FT-IR and Raman, respectively. The fluorescence properties were explored by PL and decay curve. The results showed that both the Eu 3+ doping concentration and annealing temperature had influence on the crystal structure and fluorescence properties of ZrO 2 :Eu 3+ nanocrystals. For the low Eu 3+ -doping concentration, the amount of the tetragonal phase decreased with increasing the annealing temperature. The Eu 3+ ion is trivalent rare earth (RE 3+ ) activator, which can stabilize the tetragonal as well as the cubic structure of ZrO 2 . The ZrO 2 :Eu 3+ nanocrystals with tetragonal or cubic structure may find potential applications as the raw material for producing the transparent ceramics with efficient fluorescence properties. [ABSTRACT FROM AUTHOR]

Considerable efforts are being invested to explore new alternative thermal barrier coating (TBC) materials to yttria stabilized zirconia (YSZ) for applications above 1473 K. In this work, Y 4 Al 2 O 9 (YAM) ceramics were prepared by solid state reaction at 1873 K for 12 h. The phase stability, thermophysical properties and sintering-resistance behavior of the material were investigated. XRD results reveal that single monoclinic phase YAM is synthesized and no new phase appears after long-term annealing. The thermal conductivities of YAM ceramic decrease gradually with increase of temperature ranges from room temperature to 1273 K. The minimum value is ~1.81 W m −1 K −1 , which is lower than that of YSZ. Meanwhile, YAM shows moderate thermal expansion coefficient, about 8.91×10 −6 K −1 in the temperature range of 300–1473 K. Compared with YSZ, YAM has lower density and higher sintering-resistance ability, which is very favorable for TBC applications. These results imply that YAM can be a promising candidate material for the ceramic layer in TBC system. [ABSTRACT FROM AUTHOR]