1. Zürich, 19.01.2006 Acceptable limits of degradation of TBC for high-efficient turbines (HET TBC) Department Materials (ALSTOM) Lab of Crystallography (ETH Zürich) CTI project Nr. 7820.3 EPRP-IW Project startNov. 1. 2005 Project duration24 months

2. Outline 1Determination of monoclinic content 2About estimation of YSZ monoclinic phase content from XRD 3SEM pictures 4WDX results 5In-situ XRD up to 1200ºC

3. Determination of monoclinic content Raw powder loaded from the bottom of the sample holder Amount of Monoclinic phase is : 6 wt%

4. Raw powder loaded by the top of the sample holder Amount of Monoclinic phase is : 30 wt% Determination of monoclinic content

5. After milling the powder Amount of Monoclinic phase is : 19 wt% Determination of monoclinic content

6. Equation used in Mannheim Report (MR): and are peak maxima of the monoclinic and tetragonal phases. Phase content is related to the area of peaks (integral peak intensity), and not to their height In Sulzer powder, the peaks of monoclinic phase are ca. 1.5 broader than tetragonal phase  the ratio of peaks area is 1.5 bigger than the ratio of peaks height. About estimation of YSZ monoclinic phase content from XRD

7. The (101) peak of the tetragonal phase is equivalent to the (111) peak of the cubic phase or of the monoclinic phase (the tetragonal cell is rotated by 45º and has half of the volume of the cubic or monoclinic cell). The (111) peak of the monoclinic phase is splitted into two peaks and the sum of their intensities should come close to the value of the intensity of the (101) peak of the tetragonal phase About estimation of YSZ monoclinic phase content from XRD

8. - Tetragonal - Monoclinic 22 I Simulation of the XRD pattern of a mixture of 50% of monoclinic + 50% tetragonal YSZ shows that is approximately 2 times smaller than The true monoclinic content should be approximately 3 times larger than what is obtained with the formula used in the MR About estimation of YSZ monoclinic phase content from XRD

9. A more accurate estimation of the monoclinic phase content could be obtained from: and are to the area of the two peaks of the monoclinic and the peak tetragonal phases, P=1.340 is a scaling factor - The peaks of the monoclinic phase are ≈ 1.5 times broader than tetragonal ones - The height of the second monoclinic peak 111 forms ≈ 0.7 times of one of the first peaks  c mon ≅ 20 vol% which corresponds to c mon ≅ 19 wt%. Using (experimentally determined) P=1.311, c mon ≅ 19.5 vol%. The monoclinic content found in MR is in fact closer to 15-20% than to 5-6%. About estimation of YSZ monoclinic phase content from XRD

10. 1Depending on how the powder is loaded in the sample holder the amount of measured monoclinic YSZ phase vary by a factor 5 2When loading by the top of the sample holder big and less dense grains are more likely to be present at the surface 3When loading from the bottom of the sample holder, small and dense grains are more likely to be present at the surface 4After milling it is expected that grains size is more homogeneous and measured monoclinic content is the correct average value 5Large amounts of monoclinic phase are expected to be present in big grains having a low density (big and porous grains) Summary of XRD results

11. SEM 200 µm SE pattern, SEM LEO Hollow particle Porous particle Bulk particle

12. SEBs Grains composition measured by WDX: 90-90.5wt% of ZrO 2 8-8.5wt% of Y 2 O 3 and ~1.5wt% HfO 2 SEM 20 µm

13. SEBS Sometimes crystallites are present in hollow grains, their composition is not yet determined SEM 20 µm

14. SEBS Grains encircled in red were measured by WDX: 97.5-98wt% of ZrO 2 0.3-0.7wt% of Y 2 O 3 and ~1.5wt% HfO 2 SEM 20 µm

15. SEBS Grains encircled in red were measured by WDX: 97.5-98wt% of ZrO 2 0.3-0.7wt% of Y 2 O 3 and ~1.5wt% HfO 2 SEM 20 µm

16. WDX Results GrainZrO 2 Y2O3Y2O3 HfO 2 SiO 2 Hollow90.4858.0091.506- Hollow89.9778.4441.4320.147 Hollow90.5727.9381.490- Porous97.5240.3341.5250.617 Porous97.5560.3861.6680.390 Porous97.7450.4611.5770.217 Porous97.4570.7281.4720.343 Hollow average 90.3458.1301.4760.049 Porous average97.5710.4771.5600.392

17. Porous Grains 1Composed of two phases with different grain shape and composition 2The inner part of the grains (encircled in red in SEM pictures) is composed of YSZ with 0.5-1 wt% Y 2 O 3 (Monoclinic YSZ) 3High SiO 2 content 0.2-0.6 wt% Hollow Grains 1In some hollow grains there are big crystallites whose composition is not yet determined 2Hollow grains are homogeneous in composition: YSZ with 8-8.5 wt% Y 2 O 3 (tetragonal YSZ) 3Crystallites sizes are of the order 1  m Summary SEM and WDX results

18. In-situ XRD up to 1200 ºC During first heating, the monoclinic content decreases rapidly at ~400 ºC and then remains constant up to 1000 ºC During cooling no monoclinic phase is observed above 400 ºC During the second heating, the monoclinic content decreases steadily Monoclinic phase

19. The a axis vary linearly with temperature and is comparable during the two heating-cooling cycles The c axis variation deviates from linearity at high temperature and the c- axis value is increased after 1st heating This variation of c-axis value can be better seen when plotting the c/a ratio In-situ XRD up to 1200 ºC Tetragonal phase

20. [1] Ilavsky J. et al., Jour. of Therm. Spray Technol., 10 (3), 2001, pp. 497 Y-content can be calculated from c/a [1]: After 1st cycle Y 2 O 3 content of tetragonal phase is lowered by 0.5 percent Y 2 O 3 content of tetragonal phase remains constant during 2nd cycle In-situ XRD up to 1200 ºC

21. Furnace used for XRD is limited to 1200ºC ESRF in Grenoble has one furnace which can be used up to 1500ºC Deadline for applications in ESRF is fixed to the 1st March 2006 (for beam time between August 2006 and February 2007) Before applying we should decide precisely what we want to measure there since the bean time is limited In-situ XRD up to 1400 ºC

22. Conclusion During 1st heating Y 2 O 3 is transferred from tetragonal to monoclinic phase and Y 2 O 3 content of tetragonal phase is lowered Part of monoclinic phase retain enough Y 2 O 3 to be stabilized in its tetragonal form up to room temperature (Martensitic transition temperature onset is lowered) and measured monoclinic content is lowered at room temperature After 1st heating the FWHM of tetragonal peaks is lowered indicating microstress relaxation and/or grain growth (sintering) During second heating, continuous variation of monoclinic phase content indicates a broad distribution of monoclinic phase composition During second cooling, parameters of tetragonal phase are similar to obtained during first cooling, indicating no drastic evolution of tetragonal and monoclinic phases during second high temperature cycle In-situ XRD up to 1200 ºC

23. XRD of new powders Largest amount of monoclinic phase found in Sulzer Metco powder Smallest amount of monoclinic phase in Industriekeramik Hochrhein Intermediate amount of monoclinic phase in HC Stark Engineered Materials Solutions

24. SEM HCST 300 µm

25. 100 µm SEM HCST

26. 60 µm SEM HCST

27. 20 µm SEM HCST