Feasibility of luminescent multilayer sol-gel thermal barrier coating manufacturing for future applications in through-thickness temperature gradient sensing

Abstract

a b s t r a c t a r t i c l e i n f o Available online xxxx Keywords: Thermal barrier coating Sol-gel Luminescence Phosphor SensorThis paper investigates the feasibility of manufacturing sol-gel multilayer thermal barrier coatings (TBC) functionalized with different lanthanide ions Ln 3+ having distinct photo-luminescence emission wavelengths (Ln = Sm, Eu, Dy, Er, Tm) for future applications in temperature gradient sensing. Ln 3+ doped 9.75 mol% yttria stabilized zirconia (YSZ) powders were produced to study the effect of activator concentration on luminescence intensity and host matrix crystal structure. Self-quenching was found to limit the maximum signal-to-noise ratio achievable with Sm 3+ , Dy 3+ , Er 3+ and Tm 3+ activators, which was not the case for Eu 3+ in the 1-10 mol% range. The increase in activator was found to affect the crystal structure of YSZ. A solution was proposed that suppressed this effect while significantly increasing the luminescence intensity of all activators. Finally a TBC sensor prototype integrating Eu 3+ , Er 3+ and Dy 3+ doped layers distributed throughout the thickness was successfully deposited by a dip-coating sol-gel process and showed promising through-thickness luminescence sensing capabilities.

Novel erbia-yttria co-doped zirconia fluorescent thermal history sensor

“…Preliminary investigations confirmed the potential of an intensity ratio approach, using a red emitting, temperature insensitive YSZ:Eu 3+ reference, as a robust method regarding small variations in experimental measurement conditions for future applications in off-line temperature mapping. Finally, the thermal stability of the YSZ:Er 3+ marker up to 973 K for a short period of time (2 h) is promising for its integration within coatings for practical thermal history sensing applications, such as sol-gel deposited YSZ-based coatings [20,21] that will be investigated in a future work.…”

“…Both the sensing YSZ:Er 3+ powder and the annealed YSZ:Eu 3+ powder (or any other relevant reference) would be mixed into a transparent high temperature binder and applied on the parts with an air brush, as for typical fluorescent coatings used for phosphor thermometry [51]. The satisfactory thermomechanical properties of YSZ coatings, widely used in thermal barrier coating applications up to 1473 K [55,56], also offer the possibility to directly deposit the phosphors as coatings or using a YSZ host matrix, similarly to what is done for fluorescent thermal barrier sensor coatings [21,50,57]. The chemical compatibility of the marker with the reference and the matrix could indeed facilitate the sintering of the coating as a morphologically uniform single layer (see sol-gel TBC sensors in reference [21]) at relatively low temperature (<973 K).…”

“…The satisfactory thermomechanical properties of YSZ coatings, widely used in thermal barrier coating applications up to 1473 K [55,56], also offer the possibility to directly deposit the phosphors as coatings or using a YSZ host matrix, similarly to what is done for fluorescent thermal barrier sensor coatings [21,50,57]. The chemical compatibility of the marker with the reference and the matrix could indeed facilitate the sintering of the coating as a morphologically uniform single layer (see sol-gel TBC sensors in reference [21]) at relatively low temperature (<973 K). Therefore, low temperature deposition processes of YSZ coatings, such as the dip-coating process developed by the CIRIMAT in collaboration with the ICA [20,21] and other soft chemistry processes followed by sintering at a temperature lower than 973 K are expected to be relevant and promising solutions for the deposition of YSZ:Er 3+ /YSZ: Eu 3+ thermal history sensor coatings.…”

“…Numerous studies carried out on the lanthanide activator ions Eu 3+ (in Al 2 O 3 [14], ZrO 2 [31], YAG [32], Y 2 O 3 [13,33,34], YVO 4 [35], CaY 2 Si 3 O 12 [36]), Er 3+ (in SiO 2 [25], GdAlO 3 [26], ZrO 2 [37], Gd 2 TiO 7 [38]), Tb 3+ (in Y 2 O 3 [14,34], Y 2 SiO 5 [12]), Pr 3+ (in PbO-Sb 2 O 3 -B 2 O 3 [39]) and Ce 3+ (in YAG [40]), have shown that their emission intensity at room temperature, initially nonexistent or weak, is greatly improved with the increase of crystallinity resulting from annealing at high temperature, typically in the range 1073-1573 K. This effect, that goes along with the sharpening of emission peaks and generally an increase of the luminescence lifetime [12-14, 32, 34, 38], results mainly from the coarsening of the average crystal size, the uniformization of the crystal field as well as the reduction of the number of crystal defects and residual organic groups acting as luminescence quenchers [12,33,34,38]. Figure 1 shows the x-ray diffraction patterns and the fluorescence spectra of the YSZ:Er 3+ phosphor powder produced by a sol-gel route at the Institut Clément Ader and CIRIMAT [21] in the initial state and after further annealing at 1373 K for 2 h.…”

“…powder of composition (YO 1.5 ) 0.083 (ErO 1.5 ) 0.015 (ZrO 2 ) 0.902 was synthesized by the sol-gel route developed in previous works [21,22]. Samples of that powder were then calcined 15 minutes under isothermal conditions at different temperatures in the range 1173-1423 K with 50 K steps.…”