Structural study of metastable tetragonal YSZ powders produced via a sol–gel route

Abstract

Sol-gel yttria stabilized zirconia (YSZ) is investigated in this paper. The final aim is to process YSZ powders into stable slurries in order to prepare thick coatings for thermal barrier to be applied on hot turboengine components. In fact, this system is well-known for its excellent thermomechanical resistance at elevated temperatures but the relationship between these performances and the structural and microstructural characteristics of these materials is not fully understood. This paper reports a preliminary study concerning recent progress on the structural properties control of YSZ powders synthesized by sol-gel process and the main advantages of this process compared to conventional methods. As a first step towards this understanding, structural investigations of ZrO 2 doped with various xmol%YO 1.5 coatings, have been performed using X-ray diffraction, structural Rietveld refinement, Raman spectra analysis and transmission electron microscopy. The evolution of the crystallographic structure of YSZ powders after air annealing at various temperatures 1100 • C, 1200 • C and 1400 • C was studied to well understand the conditions of the formation of desired metastable tetragonal phase (t ). Then, this work should allow to correlate chemical and thermomechanical parameters as YSZ formulation and sol-gel elaboration conditions, temperature and t phase performances.

Molten salt attack on multilayer and functionally-graded YSZ coatings

“…It means that the nature of the bonds in the crystalline lattice were similar but changes in the local symmetry must exist. As addressed in previous works a shift of the Raman band toward higher wavelength represents an increment of the oxygen displacement, i.e a lower stabilisation of the tetragonal phase because of a decreasing in the amount of stabilizer ions (Y 3+ ) [26]. It agrees with the EDX analysis so that in coatings chemically attacked with CMAS, especially CMAS-2, a lixiviation of yttrium cations observed gave rise to a lower tetragonality in zirconia phase.…”

Development of YSZ Thermal Barrier Coatings Using Axial Suspension Plasma Spraying

“…According to the lattice parameter results, the ratio c /a √ 2 for the tetragonal phase falls into the range of 1.010 to 1.000. This indicates that the tetragonal phase in the as-sprayed coating is non-transformable [39]. After thermal cycling, no monoclinic phase was detected from the XRD patterns and the tetragonal phase was non-transformable; but a cubic phase was detected from both thermally-cycled Samples M and N. According to quantitative analysis, the amount of cubic phase in the both coatings is around 12 wt %.…”

Effect of Annealing on the Crystal Structure and Microstructure of Pr Doped ZrO2-Y2O3Nanocrystals

“…4). Viazzi et al [21] showed, after Ref. [27], the lattice parameters for the tetragonal (t ) phase, as functions of yttria content (YO 1.5 in mol%) x:…”

“…The crystallite size was about 11 nm for the t phase and about 8 nm for the t phase. Viazzi et al [21] have studied the structure of metastable tetragonal YSZ powders produced via a sol-gel route. The samples were studied as a function of yttria content and annealing temperatures up to 1400…”