U.S. patent application number 10/566980 was filed with the patent office on 2006-08-10 for heat-insulation material and arrangement of a heat-insulation layer containing said heat-insulation material.
Invention is credited to Ulrich Bast, Wolfgang Rossner.
Application Number | 20060177676 10/566980 |
Document ID | / |
Family ID | 34201530 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060177676 |
Kind Code |
A1 |
Bast; Ulrich ; et
al. |
August 10, 2006 |
Heat-insulation material and arrangement of a heat-insulation layer
containing said heat-insulation material
Abstract
A heat-insulation material for a heat-insulation layer (3) for a
carrier body (2) for preventing heat transfer between the carrier
body and a surrounding area (7) therearound includes at least one
luminous substance which is excitable for emitting luminescent
light having a defined emission wavelength and includes at least
one type of metal oxide containing at least one trivalent metal
(A). Also described is an arrangement of at least one
heat-insulation layer which contains the heat-insulation material
and is applied to the carrier body. The described heat-insulation
material is characterised in that the metal oxide is embodied in
the form of a mixed oxide selected in a perovskite group of total
formula AA'O.sub.3, and/or of pyrochlore of total formula
A.sub.2B.sub.2O.sub.7, wherein A' is the trivalent metal and B is a
tetravalent metal. The heat-insulation layer containing the
heat-insulation material is preferably used for a gas turbine.
Inventors: |
Bast; Ulrich; (Munich,
DE) ; Rossner; Wolfgang; (Holzkirchen, DE) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET
2ND FLOOR
ARLINGTON
VA
22202
US
|
Family ID: |
34201530 |
Appl. No.: |
10/566980 |
Filed: |
July 28, 2004 |
PCT Filed: |
July 28, 2004 |
PCT NO: |
PCT/EP04/51632 |
371 Date: |
March 21, 2006 |
Current U.S.
Class: |
428/469 ;
252/301.4F; 252/301.4R; 252/62; 374/E11.024; 428/472; 428/701;
428/702 |
Current CPC
Class: |
G01K 11/20 20130101;
C23C 4/02 20130101; C23C 4/00 20130101; C23C 4/18 20130101 |
Class at
Publication: |
428/469 ;
428/701; 428/702; 428/472; 252/062; 252/301.40F; 252/301.40R |
International
Class: |
E04B 1/74 20060101
E04B001/74 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 13, 2003 |
DE |
103 37 287.3 |
Claims
1. Thermally insulating material for a thermal barrier coating (3)
of a substrate (2) for limiting heat transfer between the substrate
(2) and an environment (7) of the substrate (2), wherein the
thermally insulating material has at least one luminophore which
can be excited to emit luminescent light with a particular emission
wavelength, and the luminophore has at least one metal oxide with
at least one trivalent metal A, characterized in that the metal
oxide is a mixed oxide selected from the perovskite group with the
empirical formula AA'O.sub.3 and/or a pyrochlore with the empirical
formula A.sub.2B.sub.2O.sub.7, A' being a trivalent metal and B a
tetravalent metal.
2. Thermally insulating material according to claim 1, wherein the
luminophore for exciting the emission of luminescent light has an
activator selected from the cerium and/or europium and/or
dysprosium and/or terbium group.
3. Thermally insulating material according to claim 2, wherein the
activator is present in the luminophore in a proportion of up to 10
mol %.
4. Thermally insulating material according to claim 1, wherein the
trivalent metal A and/or the trivalent metal A' is a rare earth
element Re.
5. Thermally insulating material according to claim 4, wherein the
trivalent metal A and/or the trivalent metal A1 is a rare earth
element selected from the lanthanum and/or gadolinium and/or
samarium group.
6. Thermally insulating material according to claim 1, wherein the
perovskite is a rare earth element.
7. Thermally insulating material according to claim 6, wherein the
empirical formula of the rare earth aluminate is
Gd.sub.0.25La.sub.0.75AlO.sub.3.
8. Thermally insulating material according to claim 1, wherein the
pyrochlore is selected from the rare earth hafnate and/or rare
earth titanate and/or rare earth zirconate group.
9. Thermally insulating material according to claim 8, wherein the
rare earth zirconate is selected from the gadolinium zirconate
and/or samarium zirconate group.
10. Thermally insulating material according to claim 8, wherein the
rare earth hafnate is lanthanum hafnate.
11. Arrangement of at least one thermal barrier coating (3) on a
substrate (2) for limiting heat transfer between the substrate (2)
and an environment (7) of the substrate (2), wherein the thermal
barrier coating has a thermally insulating material according to
claim 1.
12. Arrangement according to claim 11, wherein at least one
additional thermal barrier coating (5) is present which is
essentially luminophore-free.
13. Arrangement according to claim 12, wherein the additional
thermal barrier coating (5) is essentially opaque to excitation
light for exciting the emission of luminescent light and/or to the
luminescent light of the luminophore.
14. Arrangement according to claim 13, wherein the thermal barrier
coating (3) is disposed between the substrate (2) and the
additional thermal barrier coating (5) in such a way that the
luminescent light of the luminophore can essentially only pass
through orifices (6) in the additional thermal barrier coating (5)
into the environment (7) of the substrate (2).
15. Arrangement according to claim 11, wherein the substrate is a
component of an internal combustion engine.
16. Arrangement according to claim 15, wherein the internal
combustion engine is a gas turbine.
17. Thermally insulating material according to claim 2, wherein the
perovskite is a rare earth element.
18. Thermally insulating material according to claim 3, wherein the
perovskite is a rare earth element.
19. Thermally insulating material according to claim 2, wherein the
perovskite is a rare earth element.
20. Thermally insulating material according to claim 3, wherein the
perovskite is a rare earth element.
Description
[0001] Thermally insulating material and arrangement of a thermal
barrier coating incorporating said thermally insulating
material
[0002] The invention relates to a thermally insulating material for
a thermal barrier coating of a substrate for limiting heat transfer
between the substrate and an environment of the substrate, the
thermally insulating material having at least one luminophore which
can be excited to emit luminescent light at a particular emission
wavelength, and the luminophore having at least one metal oxide
with at least one trivalent metal A. In addition to the thermally
insulating material, an arrangement of at least one thermal barrier
coating incorporating the thermally insulating material on a
substrate is specified.
[0003] A thermally insulating material and an arrangement of this
kind are known from EP 1 105 550 B1. The substrate is a component
in a gas turbine. The substrate is made of metal. High temperatures
in excess of 1200.degree. C. occurring in a gas turbine in the
environment of the component may cause the metal of the component
to be damaged. In order to prevent this, a thermal barrier coating
(TBC) is deposited on the component. The thermal barrier coating
ensures that a reduced heat exchange takes place between the metal
substrate and the environment, causing a metal surface of the
component to heat less strongly. On the metal surface of the
component, a surface temperature occurs which is lower than the
temperature in the environment of the component.
[0004] The thermally insulating material constitutes a base
material of the thermal barrier coating. The mechanical and thermal
properties of the thermal barrier coating depend essentially on the
properties of the thermally insulating material. The base material
of the known thermal barrier coating is a metal oxide. The metal
oxide is, for example, an yttrium stabilized zirconium oxide (YSZ).
This thermally insulating material has a thermal conductivity of
between 1 and 3 W/mK. In order to ensure efficient protection of
the substrate, the layer thickness of the thermal barrier coating
is approximately 250 .mu.m. As an alternative to yttrium stabilized
zirconium oxide, a metal oxide in the form of an yttrium aluminum
granate is specified as the thermally insulating material.
[0005] In order to bond the thermal barrier coating and the
substrate firmly together, a metal-alloy interlayer (bond coat) is
deposited on the surface of the component. To improve the bond, a
ceramic interlayer of a ceramic material such as aluminum oxide can
be additionally disposed between the thermal barrier coating and
the component.
[0006] A so-called thermoluminescent indicator is embedded in the
thermal barrier coating. This indicator is a luminescent material
(luminophore) which can be stimulated to emit a luminescent light
with a particular emission wavelength by excitation with excitation
light of a particular excitation wavelength. The excitation light
is, for example, UV light. The emission light is, for example,
visible light. The luminophore used is a so-called recombination
luminescence material. The luminescent process is initiated by
electronic transitions between energy states of the activator. A
luminophore of this kind consists, for example, of a solid with a
crystal lattice (host lattice) in which a so-called activator is
embedded. The solid body is doped with the activator. The activator
participates together with the entire solid body in the luminescent
process of the luminophore.
[0007] With the known thermal barrier coating, the base material of
the thermal barrier coating is doped with an activator. A thermal
barrier coating consisting of the luminophore is present. The
activator used is a rare earth element. In the case of yttrium
stabilized zirconium oxide, the rare earth element is typically
europium. The thermally insulating material yttrium aluminum
granate is doped with the rare earth elements dysprosium or
terbium.
[0008] The known thermal barrier coating utilizes the fact that an
emission property of the luminescent light of the luminophore, e.g.
an emission intensity or emission decay time, is dependent on the
temperature of the luminophore. On the basis of this dependence,
the luminophore can be used to indicate the temperature of the
thermal barrier coating. To ensure that this relationship can be
established, the thermal barrier coating is optically accessible to
excitation light in the UV range. It is simultaneously ensured that
the luminescent light of the luminophore can be radiated and
detected by the thermal barrier coating.
[0009] For example, in order to ensure optical accessibility, a
single thermal barrier coating containing the luminophore is
disposed on the substrate. As an alternative solution, an
additional thermal barrier coating which is transparent to the
excitation light and the luminescent light of the luminophore is
deposited on the thermal barrier coating. The luminescent light of
the luminophore can penetrate the additional thermal barrier
coating.
[0010] Because of specific material properties such as phase
stability or sintering tendency, usability of a thermal barrier
coating consisting of one of the abovementioned thermally
insulating luminescent materials is limited to an operating
temperature of approximately 1200.degree. C. These thermally
insulating materials are therefore unsuitable for future gas
turbine generations where the operating temperature will have to be
increased to improve efficiency.
[0011] The object of the present invention is therefore to specify
a thermally insulating luminescent material, which is stable above
a temperature of 1200.degree. C., for a thermal barrier coating of
a substrate.
[0012] This object is achieved by a thermally insulating material
for a thermal barrier coating of a substrate for reducing heat
transfer between the substrate and an environment of the substrate,
the thermally insulating material having at least one luminophore
which can be excited to emit luminescent light at a particular
emission wavelength, and the luminophore having at least one metal
oxide with at least one trivalent metal A. The thermally insulating
material is characterized in that the metal oxide is a mixed oxide
selected from the perovskite group with the empirical formula
AA'O.sub.3 and/or pyrochlore with the empirical formula
A.sub.2B.sub.2O.sub.7, A' being a trivalent metal and B a
tetravalent metal.
[0013] This object is also achieved by an arrangement of at least
one thermal barrier coating on a substrate for reducing heat
transfer between the substrate and an environment of the substrate,
the thermal barrier coating containing the described thermally
insulating material incorporating the luminophore.
[0014] A thermal barrier coating consisting of a perovskite and/or
a pyrochlore (pyrochlore phase) is characterized by high stability
at temperatures in excess of 1200.degree. C. These stable thermal
barrier coatings have a luminophore. The thermal barrier coating
can be a single or multiphase system. Single phase means that a TBC
ceramic phase constituted by the thermally insulating material
essentially consists of the luminophore only. The thermally
insulating material of the thermal barrier coating is the
luminophore. In the case of a multiphase thermal barrier coating,
the thermally insulating material and the luminophore are
different. The thermally insulating material contains luminophoric
particles from the luminophore. The ceramic phase is constituted by
different materials. The luminophoric particles are preferably
distributed homogeneously over the thermal barrier coating. It is
advantageous, moreover, if the thermally insulating material and
the luminophore consist of an essentially identical kind of solid.
The luminophore and the thermally insulating material consist of
the same metal oxide. The two materials differ solely in respect of
their optical characteristics. The luminophore is doped, for
example, for this purpose.
[0015] The luminophore is a recombination luminescence material,
the emission of the luminescent light being preferably based on the
presence of an activator. Using an activator or a plurality of
activators, the emission properties of the luminophore, such as the
emission wavelength and the emission intensity, can be varied
relatively easily. In a particular embodiment, to excite the
emission of luminescent light the luminophore has an activator
selected from the cerium and/or europium and/or dysprosium and/or
terbium group. Because of their ion radii, rare earth elements can
generally be easily incorporated in the crystal lattice of
perovskites and pyrochlores. Activators in the form of rare earth
elements are therefore generally suitable. The rare earth elements
specified have shown themselves to be particularly good
activators.
[0016] When using an activator, its proportion in the luminophore
must be selected such that the thermal and mechanical properties of
the metal oxide of the luminophore are virtually unaffected. The
mechanical and thermal properties of the metal oxide are retained
in spite of doping. In a particular embodiment, the proportion of
activator in the luminophore is up to 10 mol %.
[0017] The proportion is preferably less than 2 mol %, e.g. 1 mol
%. This low proportion of activator has been found sufficient to
achieve a usable emission intensity of the luminophore while
retaining the thermal and mechanical stability of a thermal barrier
layer produced using the luminophore.
[0018] In a particular embodiment, the trivalent metal A and/or the
trivalent metal A' is a rare earth element Re. The trivalent metal
A and/or the trivalent metal A' is specifically a rare earth
element selected from the lanthanum and/or gadolinium and/or
samarium group. Other rare earth elements are likewise conceivable.
By using a perovskite and/or a pyrochlore with rare earth elements,
an activator in the form of a rare earth element can be easily
incorporated in the crystal lattice of the perovskite or pyrochlore
because of the similar ion radii.
[0019] One of the trivalent metals A and A' of the perovskite is a
main group or subgroup element. The tetravalent metal B of the
pyrochlore is likewise a main or subgroup element. In both cases,
mixtures of different main and subgroup elements can be provided.
Because of the different ion radii, the rare earth elements and the
main or subgroup elements preferably assume different positions in
the perovskite or pyrochlore crystal lattice, aluminum having been
found to be particularly advantageous as a trivalent main group
element. Together with rare earth elements, aluminum forms, for
example, a perovskite which produces a mechanically and thermally
stable thermal barrier coating. In a particular embodiment, the
perovskite is therefore a rare earth aluminate. The empirical
formula is ReAlO.sub.3, with Re standing for a rare earth element.
The rare earth aluminate is preferably a gadolinium lanthanum
aluminate. The empirical formula is typically
Gd.sub.0.25La.sub.0.75AlO.sub.3. Specifically the subgroup elements
hafnium and/or titanium and/or zirconium are used as the
tetravalent metal B of the pyrochlore. The pyrochlore is therefore
advantageously selected from the rare earth titanate and/or rare
earth hafnate and/or rare earth zirconate group. The rare earth
zircbnate is specifically selected from the gadolinium zirconate
and/or samarium zirconate group. The preferred empirical formulae
are Gd.sub.2Zr.sub.2O.sub.7 and Sm.sub.2Zr.sub.2O.sub.7. The rare
earth hafnate is preferably lanthanum hafnate. The empirical
formula is La.sub.2Hf.sub.2O.sub.7.
[0020] The luminophore is optically excited to emit luminescent
light, said luminophore being irradiated with excitation light of a
particular excitation wavelength. By absorbing the excitation
light, the luminophore is excited to emit luminescent light. The
excitation light is e.g. UV light and the luminescent light
low-energy visible light.
[0021] The excitation of the luminophore with excitation light
lends itself to checking the condition of a luminophore-containing
thermal barrier coating optically accessible to the excitation
light and the luminescent light. For this purpose, e.g. only the
thermal barrier coating containing the luminophore is deposited on
the substrate.
[0022] In a particular embodiment in respect of the arrangement of
thermal barrier coating on the substrate, at least one other
thermal barrier coating is present which is essentially
luminophore-free, essentially free meaning that, due to a very low
proportion of luminophore, no analyzable luminescent light can be
detected. The additional thermal barrier coating can be disposed
between the substrate and the thermal barrier coating containing
the luminophore. The outer thermal barrier coating is formed by the
thermal barrier coating containing the luminophore. Any
transmission property of the additional thermal barrier coating in
respect of the luminescent light and/or the excitation light is
irrelevant. The thermal barrier coating containing the luminophore
is optically accessible. A solution of this kind is advantageous,
for example, for a thermal barrier coating comprising a pyrochlore.
In order to achieve a firm bond between the thermal barrier coating
and a metallic interlayer deposited on the substrate, an additional
thermal barrier coating consisting of an yttrium stabilized
zirconium oxide is deposited directly on the metallic interlayer.
The thermal barrier coating containing the luminophore is deposited
over this additional thermal barrier coating.
[0023] However, the additional thermal barrier coating can also be
transparent to the excitation light and the luminescent light of
the luminophore. The excitation light and the luminescent light can
penetrate through the additional thermal barrier coating. For a
solution of this kind, the thermal barrier coating can be disposed
between the additional thermal barrier coating and the substrate.
Due to the transmission property of the additional thermal barrier
coating, the thermal barrier coating containing-the luminophore is
continuously optically accessible. In this way, as in the cases in
which only the thermal barrier coating containing the luminophore
is present or the thermal barrier coating containing the
luminophore forms the outer thermal barrier coating of a multilayer
structure, the condition of the thermal barrier coating can be
determined by observing one of the emission properties of the
luminescent light. Thus, for example, the temperature of the
thermal barrier coating can be indicated.
[0024] In a particular embodiment, the additional thermal barrier
coating is opaque to the excitation light for stimulating the
luminophore to emit luminescent light and/or to the luminescent
light of the luminophore. Because of the transmission or absorption
properties of the additional thermal barrier coating, the
excitation light and/or the luminescent light cannot penetrate, or
only a small portion of it can penetrate, the additional thermal
barrier coating. In a particular embodiment, the thermal barrier
coating is disposed between the substrate and the additional
thermal barrier coating in such a way that the excitation light of
the luminophore and/or the luminescent light of the luminophore can
essentially only reach the environment of the substrate through
orifices in the additional thermal barrier coating. Such orifices
are, for example, cracks or gaps in the additional thermal barrier
coating. Also conceivable is an orifice caused by erosion of other
thermally insulating material of the additional thermal barrier
coating. These orifices can easily be made visible by illuminating
the arrangement with the excitation light. At the locations in
which the UV light reaches the thermal barrier coating through the
orifices, the luminophore is excited to emit luminescent light. The
luminescent light passes again through the orifices to the
environment of the substrate where it can be detected. Because of
the orifices, luminescent light occurs which stands out clearly
from the background.
[0025] During an idle time of an equipment, the thermal barrier
coating of a substrate used in the equipment can be checked in a
simple and reliable manner in the way described. The equipment can
be e.g. a gas turbine, the substrate e.g. a gas turbine blade. The
multilayer system comprised of the thermal barrier coatings is
disposed on the turbine blade. By illuminating the turbine blade
and observing the luminescent light of the luminophore, the
locations in the additional, outermost thermal barrier coating
which have orifices become visible.
[0026] It is also conceivable for the condition of the thermal
barrier coating to be checked during operation of the equipment.
For this purpose, for example, a combustion chamber of the
above-described gas turbine in which the turbine blades are
installed is provided with a window through which the luminescence
of the luminophore can be observed. The occurrence of luminescent
light indicates that the additional, outermost thermal barrier
coating of at least one turbine blade has a crack or gap or is
eroded.
[0027] A further advantage of the described arrangement is that, as
a result of advanced erosion, the thermally insulating material
containing the luminophore is also eroded away. By means of
suitable detectors, the luminophore can be detected in an exhaust
gas of the gas turbine. This is an indication that erosion has
advanced as far as the thermal barrier coating containing the
luminophore.
[0028] In a particular embodiment, the substrate is a component of
an internal combustion engine, such as a diesel engine. In a
particular embodiment, the internal combustion engine is a gas
turbine, the substrate being e.g. a tile with which a combustion
chamber of the gas turbine is clad. The substrate is in particular
a blade of the gas turbine, it being conceivable that the different
substrates are provided with thermal barrier coatings containing
luminophores which emit different luminescent light, thereby
enabling the component on which damage is present to be easily
determined.
[0029] To deposit the various layers, in particular the thermal
barrier coating and the additional thermal barrier coating, any
coating process can be used. The coating process is in particular
plasma spray coating. It can also be a vapor deposition process,
such as PVD (physical vapor deposition) or CVD (chemical vapor
deposition). Using the method described, thermal barrier coatings
with layer thicknesses of 50 to 600 .mu.m or more can be
deposited.
[0030] To summarize, the particular advantages of the invention are
as follows:
[0031] The materials used are stable at temperatures of over
1200.degree. C., making them particularly suitable for use in
internal combustion engines, e.g. in a gas turbine.
[0032] The metal oxides used are selectively doped with activators,
thereby yielding thermal barrier coatings containing luminescent
substances that are thermally and mechanically stable even at
temperatures above 1200.degree. C. and which can be used to check
the condition of the thermal barrier coatings during operation but
also when the substrate is not in operation.
[0033] The invention will now be explained in greater detail with
reference to several examples and the accompanying drawings which
are schematic and not to scale.
[0034] FIGS. 1 to 3 each show a detail of a lateral cross-section
of an arrangement of a thermal barrier coating comprising a
thermally insulating material containing a luminophore.
[0035] The arrangement 1 consists of a substrate 2 on which a
thermal barrier coating 3 is disposed (FIG. 1). The substrate 2 is
a turbine blade of a gas turbine. The turbine blade is made of
metal. In the combustion chamber of the gas turbine, which
constitutes the environment 7 of the substrate 2, temperatures of
over 1200.degree. C. can occur during operation of the gas turbine.
The thermal barrier coating 3 is present in order to prevent the
surface 8 of the substrate 2 from overheating. The thermal barrier
coating 3 is used to limit heat transfer between the substrate 2
and the environment 7 of the substrate 2.
[0036] A metal alloy interlayer 4 (bond coat) is deposited between
the thermal barrier coating 3 and the substrate 2. The thermal
barrier coating 3, the interlayer 4 and possibly the additional
thermal barrier coating 5 are deposited on the surface 8 of the
substrate 2 using a plasma spray process.
EXAMPLE 1
[0037] The thermally insulating material of the thermal barrier
coating 3 is a metal oxide in the form of a rare earth aluminate
with the empirical formula Gd.sub.0.25La.sub.0.75AlO.sub.3.
According to a first embodiment, the rare earth aluminate is mixed
with 1 mol % Eu.sub.2O.sub.3. The rare earth aluminate has the
activator europium in a proportion of 1 mol %. Exciting the
luminophore with UV light results in a red luminescent light with
an emission maximum at around 610 nm. The excitation wavelength is
typically 254 nm.
[0038] According to an alternative embodiment, the rare earth
aluminate is doped with 1 mol % terbium, resulting in a luminophore
with green luminescent light having an emission wavelength at 544
nm.
EXAMPLE 2
[0039] In contrast to the previous example, a multilayer structure
of the thermal barrier coating 3 and an additional thermal barrier
coating 5 is present on the substrate 2 (FIG. 2). The thermal
barrier coating 3 consists of a pyrochlore. The pyrochlore is a
gadolinium zirconate with the empirical formula
Gd.sub.2Zr.sub.2O.sub.7. To produce the luminophore, the pyrochlore
is mixed with 1 mol % Eu.sub.2O.sub.3. The gadolinium zirconate has
the activator europium in a proportion of 1 mol %.
[0040] To improve the adhesion of the substrate 2, an additional
thermal barrier coating 5 is present between the bond coat 4 and
the thermal barrier coating 3 containing the luminophore. The
additional thermal barrier coating 5 consists of yttrium stabilized
zirconium oxide.
EXAMPLE 3
[0041] A multilayer structure is likewise present (FIG. 3). Unlike
in the previous example, the thermal barrier coating 3 containing
the luminophore is disposed between the additional thermal barrier
coating 5 and the substrate 2. The additional thermal barrier
coating 5 is opaque to the excitation light and/or the luminescent
light of the luminophore. The luminescent light of the luminophore
can only be detected in the environment of the substrate if the
additional thermal barrier coating 5 has an orifice 6.
* * * * *