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Thermal and Optical Properties of Ox...

Champagne, Victor Kenneth, III,

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Thermal and Optical Properties of Oxide Coatings for High-Temperature Applications /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Thermal and Optical Properties of Oxide Coatings for High-Temperature Applications // Victor Kenneth Champagne III.
Author:	Champagne, Victor Kenneth, III,
Description:	1 electronic resource (131 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 86-05, Section: B.
Contained By:	Dissertations Abstracts International86-05B.
Subject:	Mechanical engineering. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=31335598
ISBN:	9798346532811

Thermal and Optical Properties of Oxide Coatings for High-Temperature Applications /
Champagne, Victor Kenneth, III,

Thermal and Optical Properties of Oxide Coatings for High-Temperature Applications /Victor Kenneth Champagne III. - 1 electronic resource (131 pages)

Source: Dissertations Abstracts International, Volume: 86-05, Section: B.

Oxide coatings are used in several high-temperature applications to provide thermal insulation on account of their low thermal conductivity. However, many of them that are currently used, such as zirconia, mono- and disilicates, and zirconates, are translucent to thermal radiation up to 3 - 6 microns, the spectral range over which radiation from objects over 1000 °C predominately occurs. Consequently, over this broad-band spectral region, which I term the 'thermal radiation window', these refractory materials do not absorb thermal radiation and hence provide little intrinsic thermal protection. This thesis describes how they can be doped with cations that absorb thermal radiation by electronic transitions. Recent work on an ultrafast high temperature sintering (UHS) technique has also been demonstrated to accelerate the development of coatings for environmental-thermal barrier coating (ETBC) applications.Rare-earth cations (including Nd, Sm, Er, Dy, Yb) are selective absorbers of thermal radiation due to 4f − 4f electronic transitions whose energies are largely insensitive to their local bonding environment. Consistent with this is that the optical absorption characteristics of mixed rare-earth oxides exhibit are the sum of the individual cations' spectral absorptions. In contrast, the transition metal (including Fe, Ti, Cr) cations are broad absorbers of thermal radiation due to 3d−3d electronic transitions that depend strongly on the bonding environment. Many different mechanisms for absorption by transition metal cations can be exploited for broad absorption in the thermal radiation window.In this work, the effects of doping previously translucent high-temperature materials including yttria stabilized zirconia (7YSZ), gadolinium zirconate (GZO), and aluminum oxide with rare-earth and transition metal cations on their thermal and optical properties for applications including gas turbines and concentrating solar thermal power (CSP) technologies. Using iron and titanium dopants, a high-temperature stable (to > 1700 °C) 'black' alumina was synthesized for increased absorption over the range of the sun's spectral irradiance between 0.3 - 2.5 microns compared to undoped alumina for use as a coating for CSP receivers. For ETBC applications, doping of zirconates with rare-earth cations at much higher possible dopant concentrations compared to 7YSZ was shown to have little effect on the high-temperature thermal conductivity, so their optical properties in the thermal radiation window can be modified without affecting their thermal conduction properties. Dopants can be selected for absorption across the entire window and can also be matched to the emission peaks of combustion species in a gas-turbine like carbon dioxide and water vapor to reduce radiative heat transfer through the coating. Thermal emission spectroscopy was used to measure the spectral emittance of several doped and un-doped oxides and zirconates at temperatures between 750 - 1350 °C. These measurements showed an increase in emittance as temperature increased which provides further protection from thermal radiation at higher temperatures by these materials when applied as ETBCs. As these novel high-temperature capable compositions are developed, a fast strategy for coating design, synthesis, and screening is necessary. The UHS approach enables rapid development of coatings on objects with complex geometries, multi-layer ETBCs, and porosity tailoring. The fast iteration strategy is also more cost-effective for the screening of ETBCs compared to conventional methods like plasma spray and electron-beam physical vapor deposition and allows for greater throughput which can be further extended for rapid optimization of other materials systems besides the ones discussed in this work including thermal protective systems for hypersonics and selective emitters for spacecraft.

English

ISBN: 9798346532811Subjects--Topical Terms:

649730
Mechanical engineering.
Subjects--Index Terms:

Thermal conductivity

Thermal and Optical Properties of Oxide Coatings for High-Temperature Applications /
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520 $a Oxide coatings are used in several high-temperature applications to provide thermal insulation on account of their low thermal conductivity. However, many of them that are currently used, such as zirconia, mono- and disilicates, and zirconates, are translucent to thermal radiation up to 3 - 6 microns, the spectral range over which radiation from objects over 1000 °C predominately occurs. Consequently, over this broad-band spectral region, which I term the 'thermal radiation window', these refractory materials do not absorb thermal radiation and hence provide little intrinsic thermal protection. This thesis describes how they can be doped with cations that absorb thermal radiation by electronic transitions. Recent work on an ultrafast high temperature sintering (UHS) technique has also been demonstrated to accelerate the development of coatings for environmental-thermal barrier coating (ETBC) applications.Rare-earth cations (including Nd, Sm, Er, Dy, Yb) are selective absorbers of thermal radiation due to 4f − 4f electronic transitions whose energies are largely insensitive to their local bonding environment. Consistent with this is that the optical absorption characteristics of mixed rare-earth oxides exhibit are the sum of the individual cations' spectral absorptions. In contrast, the transition metal (including Fe, Ti, Cr) cations are broad absorbers of thermal radiation due to 3d−3d electronic transitions that depend strongly on the bonding environment. Many different mechanisms for absorption by transition metal cations can be exploited for broad absorption in the thermal radiation window.In this work, the effects of doping previously translucent high-temperature materials including yttria stabilized zirconia (7YSZ), gadolinium zirconate (GZO), and aluminum oxide with rare-earth and transition metal cations on their thermal and optical properties for applications including gas turbines and concentrating solar thermal power (CSP) technologies. Using iron and titanium dopants, a high-temperature stable (to > 1700 °C) 'black' alumina was synthesized for increased absorption over the range of the sun's spectral irradiance between 0.3 - 2.5 microns compared to undoped alumina for use as a coating for CSP receivers. For ETBC applications, doping of zirconates with rare-earth cations at much higher possible dopant concentrations compared to 7YSZ was shown to have little effect on the high-temperature thermal conductivity, so their optical properties in the thermal radiation window can be modified without affecting their thermal conduction properties. Dopants can be selected for absorption across the entire window and can also be matched to the emission peaks of combustion species in a gas-turbine like carbon dioxide and water vapor to reduce radiative heat transfer through the coating. Thermal emission spectroscopy was used to measure the spectral emittance of several doped and un-doped oxides and zirconates at temperatures between 750 - 1350 °C. These measurements showed an increase in emittance as temperature increased which provides further protection from thermal radiation at higher temperatures by these materials when applied as ETBCs. As these novel high-temperature capable compositions are developed, a fast strategy for coating design, synthesis, and screening is necessary. The UHS approach enables rapid development of coatings on objects with complex geometries, multi-layer ETBCs, and porosity tailoring. The fast iteration strategy is also more cost-effective for the screening of ETBCs compared to conventional methods like plasma spray and electron-beam physical vapor deposition and allows for greater throughput which can be further extended for rapid optimization of other materials systems besides the ones discussed in this work including thermal protective systems for hypersonics and selective emitters for spacecraft.
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