Thermal insulating material and method of producing same

Details Thermal insulating material and method of producing same Thermal insulating material and method of producing same

2000-10-11

2003-08-05

Koslow, C. Melissa (Department: 1755)

Compositions: ceramic

Ceramic compositions

Yttrium, lanthanide, actinide, or transactinide containing

C501S153000, C252S062000, C423S600000, C423S263000

Reexamination Certificate

active

06602814

ABSTRACT:

BACKGROUND OF INVENTION
The invention relates to a thermal insulating material, which is particularly suited for high temperature applications far above 1000° C. and can be employed in gas turbines, aeroplane engines, power station turbines and other highly, thermally loaded parts, for example in vehicle construction and energy technology.
The invention further relates to a method for producing and processing such a thermal insulating material.
The known thermal insulating materials specifically employed for high temperature applications in heat-power machines and in industrial plants are oxide cover layers applied to a metal substrate, for example on a highly alloyed nickel base material in a turbine blade. The classical thermal insulating layer consists of tetragonal or stabilised ZrO
2
as a cover layer, which is usually applied to an additional intermediate layer in the form of a low melting point or soft coupling layer (HVS). The coupling layer is composed substantially of aluminum and yttrium, frequently also with amounts of platinum and palladium (up to 10 wt.-%), apart from further components (nickel, chromium, cobalt), to make it more oxidation resistant. The ceramic cover layer is most often applied by atmospheric plasma spraying (APS). Newer developments concern ZrO
2
layers vapour-deposited with electron beams (electron beams—physical vapour deposition, EB-PVD-ZrO
2
-layers). The requirements on the ceramic ZrO
2
cover layer and the coupling layer have increased continuously in recent years. Their stability under alternating temperatures, their protective effect against oxidation as well as their long-term stability and adhesion at higher temperatures of the exhaust gas for increased efficiency have been optimised.
As a disadvantage of the known thermal insulating layers on the basis of ZrO
2
it has been found that layers applied by plasma spraying or CDV and EB-PVD layers of stabilised ZrO
2
are not sufficiently resistant above 1100° C. The ZrO
2
layers age rapidly at temperatures above 1100° C.
This aging process leads to a partial densification of the layer and parallel to that the elasticity modulus of the layer increases. The density increase diminishes the original uniform fine porosity of the layer and the thermal conductivity increases. The increase in elasticity modulus of the ceramic layer means that the thermal shock resistance decreases and the “tolerance” or the capability of compensating for thermal expansion with highly different thermal expansion coefficients between the ceramic layer and the metallic substrate decreases. Both processes, the density increase and the increase in elasticity modulus lead to a peeling of the ZrO
2
cover layer during the temperature cycles in a turbine.
In addition to deterioration the pure mechanical properties of the cover layer, the three dimensional sintering of the ZrO
2
layer leads to the formation of a dense ceramic with other properties than that of the porous layer. Since ZrO
2
is a very good conductor of ions, the ever present oxidative degradation in the entire ceramic-metal composite is not altered by densification of the ceramic. The coupling layer oxidises in this process and a layer of oxidation products with other properties forms between the original coupling layer and the ceramic cover layer. The original ceramic layer thus in the end breaks up due to the altered mechanical properties of the layer system. The corrosion of the coupling layer continues despite the sometimes very dense ceramic surface.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide an improved thermal insulating material which is better suited for high-temperature applications and is particularly suited for coating turbine blades and similar high temperature components.
Furthermore, a suitable method for producing and processing such thermal insulating materials is to be provided.
According to the invention, this object is solved by a thermal insulating material composed of a first component with at least one first phase containing stoichiometrically 1 to 80 mol-% of M
2
O
3
, 0 to 80mol-% MeO and a remainder of Al
2
O
3
with incidental impurities, wherein M is selected from the elements lanthanum and neodymium or mixtures thereof and wherein Me is selected from zinc, alkaline earth metals, transition metals, and the rare earths or mixtures thereof, preferably selected from magnesium, zinc, cobalt, manganese, iron, nickel, chromium, europium, samarium or mixtures thereof.
An effective thermal insulation is made possible with the insulating material of the invention, also at temperatures of 1300° C. and up to over 1500° C., whereby at the same time sintering processes and the resultant ageing and grain enlargement compared to ZrO
2
are greatly slowed down or retarded.
In a preferred embodiment of the invention, the first component contains 1 to 80 mol-% M
2
O
3
and 0.5 to 80 mol-% MeO with a remainder of Al
2
O
3
.
It has been shown to be of advantage when the first component comprises 1 to 50 mol-% M
2
O
3
and 1 to 50 mol-% MeO with a remainder of Al
2
O
3
.
It is further preferred when the first component comprises 1 to 20 mol-% M
2
O
3
and 2 to 30 mol-% MeO with a remainder of Al
2
O
3
.
Furthermore, it has been shown to be of advantage when the first component comprises 2 to 20 mol-% M
2
O
3
and 5 to 25 mol-% MeO with a remainder of Al
2
O
3
.
Particularly preferred is the first component comprising 5 to 10 mol-% M
2
O
3
, about 10 to 20 mol-% MeO with a remainder of Al
2
O
3
.
Particularly advantageous properties result when the first component comprises about 5 to 9 mol-% M
2
O
3
, about 12-17 mol-% MeO with a remainder of Al
2
O
3
, whereby a composition with about 7.1 mol-% M
2
O
3
, about 14.3 mol-% MeO and a remainder of Al
2
O
3
represents an optimal composition.
The first phase preferably forms a hexa-aluminate phase of magnetoplumbite structure of the composition MMeAl
11
O
19
, which when using lanthanum as M and magnesium as Me is known as magnesium aluminum lanthanum oxide with the formula MgAl
11
LaO
19
.
This material consists mainly of aluminum oxide in which monolayers of lanthanum oxide and aluminum oxide are disposed at regular spacings. This insertion of La
2
O
3
leads to the formation of a layered structure with a characteristic plate-like structure of the crystals. This magnetoplumbite phase only forms in a narrowly restricted composition region. The typical composition LaAl
11
O
19
due to its structure has very many cationic (about 8% Al) and anionic (about 5% O) vacancies in the lattice, which allow the diffusion of atoms through the structure. The homogeneity region of the phase is extended to LaMgAl
11
O
19
by doping with bivalent cations having a small ionic radius (typically Mg
++
, Mn
++
, Co
++
, Zn
++
, etc.). In this ideal composition LaMgAl
11
O
19
the compound has nearly no more possibility of altering its composition.
With a further increase in the doping with MgO and La
2
O
3
(or MeO and M
2
O
3
) further defects form in the structure and a multiphase region forms including LaMgAl
11
O
19
, MgAl
2
O
4
, LaAlO
3
and MgO.
In the optimal composition according to the invention, the addition of MeO leads to a decrease in the lattice vacancies. This means that the material with the composition LaMgAl
11
O
19
(MMeAl
11
O
19
) has absolutely no more crystal defects in the structure or formulated in another way, all of the vacancies in the structure are occupied by Me (Mg) and an additional O atom. This complete occupancy of all lattice sites in the structure leads to the desired high thermo-chemical stability and phase stability in the temperature region above 1100° C.
A further important advantage of the thermal insulating material of the invention is that the material is substantially inert with respect to alkali compounds (Na
2
O, NaCl, K
2
O, KCl) of the combustion gas or the surrounding atmosphere.
Previous thermal insulating materials based on ZrO
2
form low melting point phases with the hydroxides or car

Affiliated with

Also associated with

Rating

Thermal insulating material and method of producing same does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Thermal insulating material and method of producing same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermal insulating material and method of producing same will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3096771