Infrared Radiative Properties of Yttria–Stabilized Zirconia Thermal Barrier Coatings

Eldridge, Jeffrey I.; Spuckler, C. M.; Street, Kenneth W.; Markham, James R.

doi:10.1002/9780470294758.ch47

Cited by 54 publications

(53 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Fine columnar grains form during solidification, aligned normal to the plane of the coating. There has also been study [57][58][59] of radiation transmission characteristics. The material is relatively transparent to wavelengths in the near infra-red, although this radiation is strongly scattered by interfaces and grain boundaries.…”

Section: Composition and Microstructurementioning

confidence: 99%

“…The absorptivity [68] of YSZ is approximately constant (κ ~ 10 m -1 ) over the range T ~ 300-1300 K, but rises sharply [69][70][71] to κ ~ 2 10 3 m -1 as the temperature is raised to 2000 K. The scattering coefficient for PS YSZ has been estimated [59] as β ~ 5 10 4 m -1 for λ = 2µm. Since n is unlikely to vary much with temperature [72], β is a function of pore size only, and is temperatureindependent.…”

Section: Radiative Heat Transfermentioning

confidence: 99%

See 1 more Smart Citation

Heat Transfer Through Plasma-Sprayed Thermal Barrier Coatings in Gas Turbines: A Review of Recent Work

2009

View full text Add to dashboard Cite

A review is presented of how heat transfer takes place in plasma sprayed (zirconia-based) thermal barrier coatings (TBCs) during operation of gas turbines. These characteristics of TBCs are naturally of central importance to their function. Current state-of-the-art TBCs have relatively high levels of porosity (~15%) and the pore architecture (ie its morphology, connectivity and scale) has a strong influence on the heat flow. Contributions from convective, conductive and radiative heat transfer are considered, under a range of operating conditions, and the characteristics are illustrated with experimental data and modelling predictions. In fact, convective heat flow within TBCs usually makes a negligible contribution to the overall heat transfer through the coating, although what might be described as convection can be important if there are gross through-thickness defects such as segmentation cracks. Radiative heat transfer, on the other hand, can be significant within TBCs, depending on temperature and radiation scattering lengths, which in turn are sensitive to the grain structure and the pore architecture. Under most conditions of current interest, conductive heat transfer is largely predominant. However, it is not only conduction through solid ceramic that is important. Depending on the pore architecture, conduction through gas in the pores can play a significant role, particularly at the high gas pressures typically acting in gas turbines (although rarely applied in laboratory measurements of conductivity). The durability of the pore structure under service conditions is also of importance, and this review covers some recent work on how the pore architecture, and hence the conductivity, is affected by sintering phenomena. Some information is presented concerning the areas in which research and development work needs to be focussed if improvements in coating performance are to be achieved.

show abstract

Section: Composition and Microstructurementioning

confidence: 99%

Section: Radiative Heat Transfermentioning

confidence: 99%

Heat Transfer Through Plasma-Sprayed Thermal Barrier Coatings in Gas Turbines: A Review of Recent Work

2009

View full text Add to dashboard Cite

show abstract

“…[11] Therefore, luminescence emission originating in the YSZ:Eu layer at the bottom of the coating most likely must experience multiple reflections at the coating back surface before it can escape out the front surface to be observed. Multiple reflections of luminescence emission at the coating back surface increases contrast because of the higher survival rate of light reflecting against the back of a delaminated TBC versus reflecting against the back of a TBC attached to its metal substrate.…”

Section: Discussionmentioning

confidence: 99%

Monitoring delamination of plasma-sprayed thermal barrier coatings by reflectance-enhanced luminescence

Eldridge

Bencic

2006

Surface and Coatings Technology

View full text Add to dashboard Cite

Highly scattering plasma-sprayed thermal barrier coatings (TBCs) present a challenge for optical diagnostic methods to monitor TBC delamination because scattering attenuates light transmitted through the TBC and usually degrades contrast between attached and delaminated regions of the TBC. This paper presents a new approach where reflectance-enhanced luminescence from a luminescent sublayer incorporated along the bottom of the TBC is used to identify regions of TBC delamination. Because of the higher survival rate of luminescence reflecting off the back surface of a delaminated TBC, the strong scattering exhibited by plasma-sprayed TBCs actually accentuates contrast between attached and delaminated regions by making it more likely that multiple reflections of luminescence off the back surface occur before exiting the top surface of the TBC. A freestanding coating containing sections designed to model an attached or delaminated TBC was prepared by depositing a luminescent Eu-doped or Er-doped yttriastabilized zirconia (YSZ) luminescent layer below a plasma-sprayed undoped YSZ layer and utilizing a NiCr backing layer to represent an attached substrate. For specimens with a Eu-doped YSZ luminescent sublayer, luminescence intensity maps showed excellent contrast between unbacked and NiCr-backed sections even at a plasma-sprayed overlayer thickness of 300 μm.Discernable contrast between unbacked and NiCr-backed sections was not observed for specimens with a Er-doped YSZ luminescent sublayer because luminescence from Er impurities in the undoped YSZ layer overwhelmed luminescence originating form the Er-doped YSZ sublayer.

show abstract

“…Assuming that the particlesÕ optical thickness is that of the product of the particle radius and the absorption coefficient, the measured value is not the surface temperature, since it is obtained in opaque materials, but rather the temperature of an internal layer. Such partial translucency is characteristic, e.g., of zirconia in the wavelength range of up to approximately 8 lm (Ref 38), and is also found for other oxide ceramics, such as alumina (Ref 39).…”

Section: Multicolor Pyrometry Principlementioning

confidence: 99%

Plasma and Particle Temperature Measurements in Thermal Spray: Approaches and Applications

2010

View full text Add to dashboard Cite

Growing demands on the quality of thermally sprayed coatings require reliable methods to monitor and optimize the spraying processes. Thus, the importance of diagnostic methods is increasing. A critical requirement of diagnostic methods in thermal spray is the accurate measurement of temperatures. This refers to the hot working gases as well as to the in-flight temperature of the particles. This article gives a review of plasma and particle temperature measurements in thermal spray. The enthalpy probe, optical emission spectroscopy, and computer tomography are introduced for plasma measurements. To determine the in-flight particle temperatures mainly multicolor pyrometry is applied and is hence described in detail. The theoretical background, operation principles and setups are given for each technique. Special interest is attached to calibration methods, application limits, and sources of errors. Furthermore, examples of fields of application are given in the form of results of current research work.

show abstract

Infrared Radiative Properties of Yttria–Stabilized Zirconia Thermal Barrier Coatings

Cited by 54 publications

References 0 publications

Heat Transfer Through Plasma-Sprayed Thermal Barrier Coatings in Gas Turbines: A Review of Recent Work

Heat Transfer Through Plasma-Sprayed Thermal Barrier Coatings in Gas Turbines: A Review of Recent Work

Monitoring delamination of plasma-sprayed thermal barrier coatings by reflectance-enhanced luminescence

Plasma and Particle Temperature Measurements in Thermal Spray: Approaches and Applications

Contact Info

Product

Resources

About