JP2001181863A - Ceramic heat insulating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high temperature resistant heat insulating ceramic composition for a ceramic base material composite. SOLUTION: This composition is composed of a plurality of hollow oxide base sphericities (20) having various dimensions, a phosphate binder (12) and at 1 east one kind of oxide filler powder (12), the phosphate binder partially buries the gap between the sphericities and the oxide filler powder, and in the sphericities, in the space between the phosphate binder and the oxide filler powder, each spherical body is brought into contract with at least one other spherical body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a high temperature insulating ceramic material for a ceramic matrix composite.

[0002]

2. Description of the Related Art In order to improve the high-temperature resistance of an underlying substrate, various heat insulating materials have been developed for use as a coating. Thermal barrier coating (TBC)
Is commonly used to prevent premature destruction of critical parts of a machine due to high temperatures. In general, TBC prolongs the life of critical components by reducing the rate of metal consumption (due to spalling) due to oxidation.

A fundamental disadvantage of TBC is that there is a limit to the thickness that can be used. This thickness limit of approximately 0.5 mm is due to residual stresses due to the manufacture of the TBC material, extremely high cost, and required life, TBC temperature limits and mismatch between the TBC and the coefficient of thermal expansion of the substrate. is there. In addition, the microstructure of conventional TBCs (deposited by both air plasma spraying and physical vapor deposition) is dictated by process conditions, limits the applications that can be used, and increases the size and heat at temperatures above 1000 ° C. Easily become unstable.

A material comparable to TBC is a fibrous ceramic heat insulating material. However, a major disadvantage of these materials is their low density, which results in poor erosion resistance. Therefore, fibrous ceramic insulation is not available for high speed gas flow applications.

[0005] Monolithic tiles are another material used to protect critical components in hot conditions. These tiles have good erosion and thermal insulation properties, but are susceptible to thermal shock damage and catastrophic failure. Accordingly, it is desirable to provide a thermal insulator that can withstand high temperatures without the use of thermal barrier coatings, fibrous ceramic thermal insulators or monolithic ceramic tiles.

[0006] Commercially available ceramic matrix composites (CMC) have many potential uses in high temperature environments. However, the limit of the temperature to which CMC is exposed for a long time is about 1
200 ° C. In addition, since CMC has a lower thermal conductivity than metal and has a limitation in the cooling configuration due to manufacturing restrictions, it can be effectively cooled under high temperature (over 1400 ° C.) or high heat flux. Impossible. Therefore, it can be used for heat insulation of a medium temperature ceramic matrix composite, has erosion resistance, is resistant to thermal shock, and has a thermal expansion coefficient of CM.
It is desirable to provide a material that is relatively close to C.

[0007] European Patent Office Publication No. 007,511,04, filed Jan. 2, 1997 (Title of Invention: abradable composition), is an abradable composition that can be used to seal ceramic turbine components. A ceramic material is disclosed. However, the high temperature limit of this material is 1
It is said to be only 300 ° C.

[0008]

SUMMARY OF THE INVENTION The present invention provides a ceramic insulation composition for use on high strength, low temperature resistant ceramic materials for high temperature environments. The composition comprises a plurality of hollow oxide-based spheres having various dimensions, a phosphate binder, and at least one oxide filler powder, wherein the phosphate binder is a sphere and a filler. Fill the gap between the powder. These spheres are in such a state that each sphere in the phosphate binder and filler powder is in contact with at least one other sphere.

The spheres may be any combination of mullite spheres, alumina spheres or stabilized zirconia spheres. The diameter of each mullite sphere ranges from about 0.1 to about 1.8 mm, preferably from about 0.8 to about 1.4 mm.
mm. The diameter of each spherical body of alumina is about 0.
It ranges from 1 to about 1.5 mm, preferably from about 0.3 to about 1 mm. The diameter of each ball of stabilized zirconia is in the range of about 0.1 to about 1.5 mm, preferably in the range of about 0.8 to about 1.2 mm.

If only mullite spheres are used, the weight percentage of spheres is 32% ± 10% of the composition. In the case of alumina spheres alone, the weight percentage of spheres is 63% ± 15% of the composition. When only stabilized zirconia spheres are used, the weight percentage of spheres is 58% of the composition.
% ± 15%. In one preferred embodiment of the composition, the volume percentage of mullite spheres is 20% and the volume percentage of alumina spheres is 80%.

As the filler powder, any combination of alumina, mullite, ceria or hafnia can be used. Composition 1 comprising mullite spheroids and mullite powder
In one preferred embodiment, the weight percentages of mullite spheroids, mullite filler powder and phosphate binder are 32% ± 10%, 32% ± 15%, and 31% ± 15% of the slurry composition, respectively. In this preferred embodiment,
When only mullite is used as the filler powder, the viscosity of the combination of the phosphate binder and mullite is almost 9
000 centipoise.

The method for producing a ceramic heat insulating composition according to the present invention comprises the steps of: (a) mixing a raw material comprising a phosphate binder and an oxide filler powder to form a viscous rally;
(B) adding to the slurry an amount of hollow oxide-based spheres such that each sphere contacts the at least one other sphere in the green body of step (h) to form a mixture;
(C) casting the mixture into a pre-soaked mold, and (d)
The viscous casting is dried and (e) when the viscosity of the casting is high enough to remove the green body from the mold in a manner that minimizes dimensional distortion, the green body is removed from the mold. And (f) transferring the green body to a drying oven to remove free water, (g) transferring the green body to a baking oven, and (h)
Calcining the green body to evaporate free water, thereby thermally changing the phosphate in the process, and (i) finishing the calcined portion prior to bonding.

In a preferred embodiment, step (c)
Comprises casting the mixture within about 24 hours of manufacture, and step (g) further comprises removing the green substrate by about 80 hours.
Step (h) further comprises the step of transferring the casting to a baking oven when the green body is in a stable state, and Step (i) further comprises: (I1) Start the firing by slowly heating the firing oven to a temperature of approximately 120 ° C., (i2) Keep the temperature of the firing oven at approximately 120 ° C. until most of the free water is removed by evaporation (I3) slowly raise the temperature of the baking oven to about 250 ° C, and (i4) raise the temperature of the baking oven to about 250 ° C until most of the free water is removed by evaporation.
(I5) The temperature of the baking oven is set to about 1200
° C to form a refractory phosphate layer slowly.

In another preferred embodiment, step (e) further comprises the step of removing the green body from the mold and then molding to conform to the contour of the substrate surface to be bonded. This step allows for near net shape molding.

[0015]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a high temperature, high temperature resistant ceramic insulation which is deposited on a high strength, low temperature resistant ceramic for use in high temperature environments. Referring to the accompanying drawings, FIG. 1 is an enlarged perspective view of a ceramic insulating composition 10 (or coating 10) according to a preferred embodiment of the present invention. This perspective view is a cross-sectional view of a coating 10 of a ceramic insulating composition applied by a layer of an adhesive 9 onto a substrate 8 of a ceramic matrix composite.

FIG. 2 is another enlarged perspective view showing a cross section of the coating 10 of the ceramic insulating composition according to the preferred embodiment of the present invention. This coating 10 has hollow oxide spheres 20 of various dimensions in a combination (12) of a phosphate binder and various oxide filler powders. The phosphate binder fills or “bridges” the gap between the spheroid 20 and the oxide filler powder. These spheres 20, depending on the specific composition of the coating 10, may be 160
Manufactured at a sufficiently high temperature to be stable at a temperature of 0 ° C. The temperatures used to form dimensionally stable, chemically stable, erosion resistant coatings are up to 1600 ° C.

The dimensional stability is mainly controlled by the spherical body 20. The coating 10 has a relatively dense configuration of the spheres 20 so that the voids are closed on a macroscopic scale.
Has high erosion resistance. The spheres 20 are preferably such that each sphere 20 is in contact with at least one other sphere 20. More preferably, each sphere 20 is in contact with several other spheres 20, ie at least three or four other spheres. This way,
In particular, high dimensional stability can be obtained at a high temperature close to 1600 ° C. The contact of the spheroids and thus the dimensional stability as present in the coating 10 cannot be obtained with prior art coatings. Composition 10 according to the present invention preferably has a temperature of approximately 1300 °.
Higher than C, more preferably up to about 1600 ° C
It is stable at temperature.

The oxide filler powder in combination with the phosphate binder can be varied to control the properties of the coating 10. A specific coating system is prepared and the coefficient of thermal expansion (CT
A certain range of E) can be covered. As will be appreciated by those skilled in the art, the CTE of the coating 10 is adjusted so that the coating 10 is held in place on the substrate 8.
Must be selected as close as possible. Coating 10
Table 1 shows various characteristics of Examples A and B. Table 1 Material A B Operating temperature (° C) 1200 1600 CTE (x10 ^-6 mm / mm) 5.85 5.85 Thermal conductivity (W / mK) at 1400 ° C 1.27 2.21 Corrosion resistance (g / kg) at 1100 ° C * 7.5 4.5 (* Test at impact angle of 15 °, erosion rate of 900 ft / s) Material properties such as thermal conductivity and erosion resistance are: It can be adjusted by selecting a particular filler or spheroid composition. The hollow oxide-based spheres 20 of the coating of the present invention can be prepared from mullite, alumina, stabilized zirconia (usually yttria stabilized zirconia), or any combination thereof. A preferred range for the diameter of the mullite sphere is from about 0.4 to about 1.8 mm, more preferably from about 0.8 to about 1.4 mm. The preferred range of the diameter of the alumina sphere is about 0.3 to about 1 mm, the preferred range of the diameter of the stabilized zirconia sphere is about 0.6 to about 1.2 mm, and more preferably about 0.8 to about 1 mm.
It is.

Mullite spheres alone, namely Keith Cera
KCM Holosph to manufacture mics, Inc. of Great Britain
When eres® is used, spheroids 2 in coating 10
A preferred weight percentage of 0 is 32% ± 10%, more preferably 32% ± 5%, more preferably 32%.
Only alumina spheres, that is, Ceramic Fillers, Inc.
When using alumina spheroids that would be manufactured by Atlannta, GA, the preferred weight percentage of spheroids in coating 10 is 63
% ± 15%, more preferably 63% ± 10%, more preferably 63% ± 5%, and most preferably about 63%. Only stabilized zirconia spheres, namely Keith Cerami
If cs, Inc. stabilized zirconia spheres are used, the preferred weight percentage of spheres in coating 10 is 58% ± 15.
%, More preferably 58% ± 10%, more preferably 58% ± 5%, and most preferably about 58%.

The characteristics matching the CTE of the target substrate 8
Adjustment of the specific coating to obtain a constant CTE
All you have to do is change the combination of zeros. For example, monolith
The spheres of zirconia stabilized with the highest CTE (approximately 1
0x10^-6mm / mm ° C), monolithic light bulb
The shape is the lowest CTE (about 5.7 × 10^-6mm / mm °
C) and monolithic alumina spheres have medium values of C
TE (about 8.0 × 10 ^-6mm / mm ° C).

A preferred combination of the spheres 20 is 20% mullite and 80% alumina by volume percentage. Table 2
As shown in FIG.
Is obtained, which matches the value of Composite A (oxide-based CMC material) of 0.5934 and the value of Composite B of 0.6031. In the case of the composite C (high silicic acid containing an oxide-based composite material), all compositions composed of mullite spheres are preferable.

Table 2 Spherical Volume Ratio Linear Change Percentage Oxide / Oxide Composition at 1000 ° C. Base Material Composition Linear Change Percentage (at 1000 ° C.) Mullite 100 0.5657 0.5631 (C) Mullite and 50/50 0.5660 Stabilization Zirconia mullite and 50/50 0.5763 Alumina mullite and 20/80 0.5972 0.5934 (A) and alumina 0.6031 (B) mullite and 10/90 0.6210 Alumina mullite and 5/95 0.6337 Alumina Alumina 100 0.6380 Stabilized zirconia 100 0.7325 Oxide filler The powder may be alumina, mullite, seria, hafnia or any combination thereof. Alumina or mullite is preferred as the filler powder, most preferably mullite because of its excellent high temperature resistance properties. If mullite is used, the coating 10
The weight percentage of the oxide filler powder in it is 32% ± 15
%, More preferably 32% ± 10%, more preferably 32% ± 5%, and most preferably about 32%. The preferred weight percentage of the oxide filler powder will vary due to different atomic weights and particle sizes.

The phosphate binder preferably has a weight percentage of 31% ± 15%, more preferably 31% ± 10%,
More preferably 31% ± 5%, most preferably about 31%.
% Aluminum orthophosphate. The combination of aluminum orthophosphate binder and mullite filler powder is available in Brookfield with spindle number 7 and rpm 20.
Viscosities of about 90 measured using an RV viscometer of
It has 00 centipoise.

The process for producing the coating 10 of the present invention comprises the following steps. That is, (1) mixing the slurry,
(2) casting the slurry, (3) drying in a controlled manner, (4) removing the green body, (5) firing, and (6) machining. . The mixture is formulated such that the CTE of the final product is actually the same as the CTE of the CMC substrate 8.

The process begins with the mixing of the raw materials to form a viscous slurry, which consists of two steps. First of all, the aluminum orthophosphate and the filler powder are mixed in such a way that an exact formulation of a 50% aqueous solution of aluminum orthophosphate is obtained and kept in an airtight state (maximum shelf life 2 months). Store. Alternatively, one may start with a 50% aqueous solution of orthophosphate.

At the time of casting, the correct amount of hollow spheres 20 is added to the slurry, after which the slurry mixture is cast within about 24 hours of manufacture. The slurry containing the hollow spheres 20 is poured into a mold that has been previously immersed. Before the casting, the mold is immersed in deionized water so that the casting is effectively dried by capillary. When the slurry is poured into a dry mold, water is extracted from the casting into the mold too quickly, resulting in a dried portion on the surface of the casting, which makes it impossible to continue drying in a controlled manner. . When this phenomenon occurs, the final product becomes non-uniform. The viscosity at the very important stage of casting drying is high enough that the green body can be removed from the mold with minimal dimensional distortion. ("Green" base is the term used for the composition before firing).

After the green body has been removed from the mold, it is carefully transferred to a drying oven (about 80 ° C.). In a preferred method, the green body is shaped prior to drying to conform to the contour of the substrate surface to which it is attached. This step has the advantage of allowing near net shape molding.
After drying, the raw substrate is transferred to a firing oven. During firing,
The heating rate is slowed down and the temperature stays around 250 ° C. to ensure that all free water is removed at this stage.

The constant dehydration of phosphate is about 250 °
Starting between C and about 565 ° C, this is controlled by slowing the heating rate over this temperature range. The remainder of the firing cycle is directed to chemical changes in the phosphate structure. If not properly dehydrated from this material system, the microstructure will be defective and weak.

After removing the raw material, the molds are recycled. This is done by washing the leached phosphate with running water and drying in an oven. Upon complete drying, the dry weight of the mold must be within about 1% of the original dry weight to allow the mold to be reused.
It is expected that a mold can be reused up to 12 times.

If raw green bodies are stacked in preparation for firing, the oven space can be made as small as possible. The resulting simplified firing cycle is shown in Table 3. Table 3 Step No. Starting temperature Heating rate Holding temperature Stagnation time (° C) (° C / min) (° C) (min) 1 80 1 250 60 2 250 3 1600 240 3 1600 10 Room temperature End Final stage of manufacturing process Is the machining of the thermal insulation coating 10.

With this manufacturing method, the green body is taken out at a low temperature stage, so that the mold can be reused. This feature provides the advantages described below. Less raw materials and machining, less waste, more flexibility in the manufacturing process, the ability to glue the green bodies together before molding into more complex shapes or to fix different compositions. This reduces capital investment in the equipment, reduces the space in the baking oven by removing the mold material in advance, thus enabling the use of smaller furnaces with lower initial and operating costs, shortening the manufacturing cycle time, and reducing production from the mold. By removing the base material, re-casting work can be performed at the same time as firing, eliminating the need for labor-intensive work to destroy and remove the fired cast from the used mold, and simplifying the firing cycle to achieve the same processing. It becomes easy to repeat.

The phosphate binder exhibits a glassy state at a temperature of up to about 750 ° C., which is a moldable state during firing. Thereby, the possibility of molding at the time of the first firing is obtained. Firing the material at temperatures up to about 1200 ° C. results in a phosphate filler that provides a moldable matrix that can be used as a push-away abradable seal.

Further heat treatment at a temperature of about 1600 ° C. makes the phosphate “bridge” network connecting the components of the material system (particles and spheres) locally more dense within the microstructure. Significantly to form a phosphate mass. The material system with new properties is 1
This change, which retains up to 80% of its room temperature strength at a temperature of 400 ° C., results from similar thermal conductivity and excellent erosion resistance (commercially available TBC used on metal substrates). About twice better than the system).

After firing this material as it is,
Before bonding to the substrate 8, the shape is adjusted by roughening. Adhesive 9
Varies depending on the type of the base material 8. However, it is also possible to apply the coating directly on the substrate 8 and / or to cure it in situ, depending on the environment of the application.

The potential applications of the ceramic thermal barrier coating 10 of the present invention are diverse. Such applications include, but are not limited to, high heat flux environments where the surfaces of gas turbine hot components or re-entry flying objects are encountered. These coatings can be oxide matrix composites (eg, mullite, aluminosilicate and alumina), silicon carbide matrix composites (made by methods such as chemical vapor infiltration or melt-infiltration), nitriding. Silicon matrix composite (reactive bonding, nitriding,
It is applicable to a wide range of materials including (but not limited to) made by hot pressing or pressureless sintering.

The coating 10 is formed by forming the coating 10 separately and then curing the aluminum phosphate adhesive (or other ceramic adhesive) at an intermediate temperature (ie, near 800 ° C. to 1000 ° C.). This is done by bonding to the substrate 8 using a mullite or alumina coating applied to the substrate 8 prior to bonding to prevent fiber damage during curing and / or to facilitate bonding. These coatings are particularly desirable when bonding to non-oxide substrates 8.

While the various features and advantages of the present invention have been described in detail along with details of the structure and function of the present invention, these descriptions are for illustrative purposes only. Accordingly, various modifications may be made in the form, size, and arrangement of parts within the spirit and scope of the invention, which are within the broad general meaning of the terms recited in the claims. Should be included in

[Brief description of the drawings]

1 is an enlarged perspective view showing a coating of a ceramic insulating composition according to a preferred embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a coating of a ceramic heat insulating composition according to a preferred embodiment of the present invention in a further enlarged manner.

[Explanation of symbols]

Reference Signs List 8 base material 9 adhesive 10 coating of ceramic heat insulating composition 12 combination of phosphate binder and oxide filler powder 20 hollow oxide-based sphere

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Gary Be Merrill 15146 Monroeville Oxford Drive 100 Apartment Pennsylvania United States 212 (72) Inventor Jay Morrison United States of America 32765 Orlando Turnberry Drive 2423 F-term (reference) 4G019 LA01 LB01 LD02 4K044 AA13 AB02 BA12 BA13 BA17 BA18 BB01 BB11 BC12 CA53 CA62

Claims (19)

[Claims] 1. A method comprising: a plurality of hollow oxide-based spheres having various dimensions; a phosphate binder; and at least one oxide filler powder, wherein the phosphate binder comprises a sphere and an oxide. Partially filling the gap between the filler powders, wherein the spheroids are in a relationship such that each spheroid is in contact with at least one other spheroid between the phosphate binder and the oxide filler powder A ceramic heat insulating composition, characterized in that: 2. The ceramic insulating composition of claim 1 which is stable at temperatures up to about 1600 ° C. 3. The thermal expansion coefficient is about 5.7 × 10 ⁻⁶ mm / m.
The ceramic insulating composition of claim 1, wherein said composition is in the range of from ^mC to about 10 x ^10-6 mm / mmC. 4. The ceramic insulating composition according to claim 1, wherein the thermal conductivity is less than about 2.5 W / km. 5. The erosion resistance ranges from about 4.5 g / kg to about 7.5 g / kg, measured at a temperature of 1100 ° C., an impact angle of 15 °, and an erosion rate of 900 ft / sec. Item 7. A ceramic heat insulating composition according to Item 1. 6. The ceramic heat insulating composition according to claim 1, wherein the spheres are selected from one or more of mullite spheres, alumina spheres and stabilized zirconia spheres. 7. The method of claim 1, wherein each sphere of mullite has a diameter of about 0.4 to about 1.8 mm, each sphere of alumina has a diameter of about 0.3 to 1 mm, and each sphere of stabilized zirconia has a diameter of about 0.3 to 1 mm. 7. The ceramic insulating composition of claim 6, wherein the diameter is from about 0.6 to about 1.2 mm. 8. The spheroid, wherein the weight percentage is 3% of the composition.
Spheroids of mullite that are 2% ± 10%, or spheroids of alumina whose weight percentage is 63% ± 15% of the composition;
2. The ceramic insulating composition of claim 1 wherein one of the stabilized zirconia spheres having a weight percentage of 58% ± 15% of the composition is used. 9. The ceramic insulating composition of claim 1, wherein the spheroids comprise 20% by volume mullite and 80% alumina. 10. The ceramic heat insulating composition according to claim 1, wherein the oxide filler powder is one or more of alumina, mullite, seria, and hafnia. 11. The ceramic insulating composition according to claim 1, wherein the oxide filler powder is a mullite filler powder. 12. The ceramic insulating composition according to claim 1, wherein the weight percentage of the oxide filler powder is 32% ± 15% of the composition. 13. The ceramic insulating composition according to claim 1, wherein the phosphate binder is orthoaluminum phosphate. 14. The ceramic insulating composition of claim 13, wherein the weight percentage of orthoaluminum phosphate is 31% ± 15% of the composition. 15. The oxide filler powder is mullite,
About 90 combined phosphate binder and mullite
14. The ceramic insulating composition of claim 13, having a viscosity of 00 centipoise. 16. A method for producing a ceramic heat insulating composition, comprising: (a) mixing raw materials comprising a phosphate binder and an oxide filler powder to form a viscous rally; (b) Adding a hollow oxide-based sphere to the slurry in an amount such that each sphere contacts the at least one other sphere in the green body of step (h) to form a mixture; and (c) pre-mixing the mixture (D) drying the viscous casting, and (e) the viscosity of the casting being sufficient to remove the green body from the mold in a manner that minimizes dimensional distortion. When the value is high, the green body is removed from the mold, (f) the green body is transferred to a drying oven to remove free water, (g) the green body is transferred to a baking oven, By firing the substrate and evaporating free water, phosphorus Salts thermally changing the method for producing a ceramic thermal barrier composition comprising the step of applying a finishing the portion was calcined before bonding (i). 17. Step (c) further comprises the step of casting said mixture within about 24 hours of manufacture, wherein in step (f) the drying oven has a temperature of about 80 ° C .; The step (h) further comprises the step of transferring the raw substrate to a baking oven in a state where the raw material is stabilized, and the step (h) further comprises the step of (h1) starting the baking by slowly heating the baking oven to a temperature of approximately 250 ° C. 17. The method of claim 16, further comprising: (h2) slowly raising the temperature of the firing oven to about 1600 ° C. to form a phosphate refractory layer. 18. The method of claim 16, wherein step (e) further comprises the step of removing the green body from the mold and then molding the green body to conform to the contour of the substrate surface to be bonded. 19. To recycle the mold immediately after removing the green body, (i) wash out the leached phosphate by immersing it in excess water, (ii) dry the oven, (iii) completely 18. The method of claim 17, further comprising the step of using the mold again and performing the next casting if the dry weight of the mold is within about 1% of the original dry weight after drying. .