3rd review meeting New Generation Thermal Barrier Coating A. Bhattacharya V. Shklover W. Steurer

Step 1: uniaxial pressing, 85 MPa Step 2: sintering: 1100C for 4 hr Step 1: Hot pressing: 1150C, 1hr, 30MPa Sample preparation 7.6mol% Ti doped 7YSZ step 1: reverse coprecipitation problems: alkoxides are very hygroscopic and handling of huge volume of chemicals solution: preparation of small amounts, use of nitrogen atmosphere and dry ethanol step 2: calcination in air at 900C for 2 hrs step 3: uniaxial pressing, 50 MPa step 4: sintering,1200C for 4 hrs 7YSZ density 4.09 g/cc,  the =5.64 g/cc,  rel =72% density 3.88 g/cc,  the = 6.0 g/cc,  rel = 64% density 2.99 g/cc,  the = 6.0 g/cc,  rel = 50%

SrZrO3 step 1: uniaxial pressing, 25 MPa Problems: need binder Solution: powder was water sprayed step 2: sintering in steps, RT to 150 C and then to 1100C, 1hr at each temperature step 3: hot pressing: 30MPa, 1200C, 1hr density 2.65 g/cc,  the = 5.48 g/cc,  rel = 48% density 4.6 g/cc,  the = 5.48 g/cc,  rel = 84% Sample preparation Conclusion Optimisation of pressure, temperature and dwelling time is required to obtain the desired density YSZ can be prepared to high density without hot pressing SrZrO3 and TiYSZ may require hot pressing

SrZrO3 - state of the art Sample: solid state reaction, calcination at 1050C, pellets by uniaxial pressing and sintered in atmosphere at 1500C Experiments: XRD, DSC for heat capacity, Dilatometer for thermal expansion Results: XRD: orthorhombic at RT a= 5.816, b=8.225, c=5.813  the = 5.48 g/cc,  rel = 95% Thermal properties: 1st phase transition was obserbed at 1035K (DSC), 1041(CTE) inflection point increases with increase in heating rate transition at 1035K is assumed to be from orthorhombic(Pnma) to orthorhombic(Cmcm) and the thermal expansion of Cmcm is higher than Pnma thermal expansion: 9.69x10 -6 K -1, after transition 1.10x10 -5 K -1 for 95% dense sample ---- Matsuda et. al. Thermal expansion: 10x10 -6 to 11x10 -6 (till 1000K) for 99.45% dense sample --Shakin et. al.

Sample density: 48% Thermal expansion: 5.70x10 -6 K -1 (400K to 1000K) 5.1x10 -6 K -1 (1000K to 1300K) Sintering Temperature: 1370K SrZrO3 -our work Increase in density increases CTE DTA analyses doesn’t show any phase transition --contradictory to carlsson et.al. CTE

m m m m m m m m m t t t t t t t t: t-ZrO 2 m: m-ZrO 2 In-situ XRD of SrZrO3 orthorhombic, Pbnm orthorhombic, Cmcm tetragonal, I4/mcm cubic, Pm3m

Phase analyses Orthorhombic (Pbnm)  Orthorhombic (Cmcm)  tetragonal (I4/mcm)  Cubic(Pm3m) 750C 850C 1200C Orthorhombic (Pbnm)  Orthorhombic (Cmcm)  Tetragonal (I4/mcm)  Cubic (Pm3m) 970K 1100K 1440K ….Ahtee et.al. and kennedy et.al. Orthorhombic (Pbnm)  tetragonal (I4/mcm)  Tetragonal (I4/mcm)  Cubic (Pm3m) 970K 1100K 1440K ….Carlsson “SrZrO 3 available with us contain a 2nd phase of ZrO 2 which is monoclinic at room temperature till 1200C and then transforms to tetragonal” : our sample

7YSZ 14YSZ 7Ti7YSZ RT XRD of YSZ and TiYSZ

Ti YSZ obtained is single phase and have t’ structure EDX analysis shows the atomic ration as Zr:Ti:Y = 0.8: 0.08: 0.12 Composition has to be confirmed yet !! Targeted: Zr 0.84 Y 0.07 Ti 0.07 O 1.96 Phase analyses -- Levi et.al. 7 YSZ is t’ 14YSZ is cubic

New compositions? Yb doped SrZrO3 ---Osaka et.al Replacing Zr4+ ion with Yb3+ will increase the oxygen ion vacancies YbSRZ loose oxygen at high temperature(1200C) SRZ undergoes a weight loss of 0.8% from 65 to 1200C due to emission of carbonates produced by reaction with H 2 O and CO 2 in air No peaks were observed by DTA of SRZ CaZrO3 COF: 7.7 x 10-6 K-1 (20-800C) [9.9] 9.7 x 10-6 K-1 ( C) [9.0] Undergoes same phase transitions as SRZ ---Poluboyarinov et.al. SrTiO3 Tetragonal below room temperature but cubic after RT till its melting temperature--- ligny et.al.  =3.23(2)x10 -5 K -1 from RT to 1500K, below RT it decreases due to C to t transition.  =2.98(2)x10 -5 K -1 for SrZrO3 till 970 K Values in red color corresponds to that of SrZrO3(SRZ)

Perovskites (ABO 3 ) It has a cubic symmetry, however, rhombohedral, orthorhombic and tetragonal symmetries are also observed. This is due to tilting and distortion of BO 6 octahedra. Distortion of simple perovskite depends on tilting angle  or the tolerance factor t= / √2 In ideal cubic perovskite would have a tolerance factor 1 and tilting angle 0. For SrZrO 3 this tilting angle is 6 deg and it tends to 0 with temperature. SrTiO 3 is cubic at RT, when Ti is replaced by Zr, the BO distance increases which results in too big SrO 8 dodecahedra in a cubic unit cell and this polyhedra mismatch leads to an orthorhombic symmetry through tilting of BO 6 octahedra by an angle of 6° ----Ligny et.al. m.p. of SrTiO3 is 2150C and of SrZrO3 is 2650C

Coming up Dilatometer study of dense SrZrO3, 7YSZ, 14 YSZ, Ca doped YSZ and Ti doped YSZ Chemical compatability of these oxides through in-situ and ex-situ XRD, complemented by SEM, EDX and EPMA analyses Chemical compatability can also be characterised by phase diagram calculations (CALPHAD) or by chemical potential diagrams (CHD)?? Exploring raman spectroscopy for futher analyses Problem s 1.Furnace availability: work is on to repair one old good one, as well as, it will be callibrated 2.Availability of hot press in very limited and uniaxial press with small diameter (6-7mm) is not available 3.Metallography lab access is also limited