Syntactic Insulator with Co-Shrinking Fillers

Abstract

A thermally-insulating composite material with co-shrinkage in the form of an insulating material formed by the inclusion of microballoons in a matrix material such that the microballoons and the matrix material exhibit co-shrinkage upon processing. The thermally-insulating composite material can be formed by a variety of microballoon-matrix material combinations such as polymer microballoons in a preceramic matrix material. The matrix materials generally contain fine rigid fillers.

Claims

1. A method of manufacturing a thermally-insulating composite material formed from a shrinkable filler in a polymer matrix material that exhibits co-shrinkage between the shrinkable filler and polymer matrix during processing, which method includes: a. mixing the shrinkable filler and a thermosetting, curable polymer, said shrinkable filler including microspheres, said microspheres formed of a material that co-shrinks with said polymer to lower or eliminate stress during sintering, pyrolization, curing, or combinations thereof of said polymer; b. molding or forming the mixed shrinkable filler and polymer into a shape; and, c. heat curing and pyrolization of said mixed shrinkable filler and polymer to form a thermally-insulating composite material having a plurality of matrix pores formed by said shrinkable filler, said shrinkable filler co-shrinking with said polymer during said curing and pyrolization, said polymer has the same or different shrinkage than said shrinkable filler to restrain said polymer from shrinkage after said step of curing and pyrolization.

2. The method as defined in claim 1, wherein said shrinkable filler has a lower thermal conductivity of said polymer such that an overall thermal conductivity of said thermally-insulating composite material is lower than a thermal conductivity of said polymer.

3. The method as defined in claim 1, wherein said polymer has a lower shrinkage than said shrinkable filler.

4. The method as defined in claim 1, wherein said polymer has a greater shrinkage than said shrinkable filler.

5. The method as defined in claim 1, wherein said shrinkable filler includes one or more materials selected from the group consisting of: 1) microballoons of ceramic, metal, polymer, aerogel, phenolic resin, or combinations thereof; 2) alumina microspheres; and 3) shrinkable low-density aerogel particles.

6. The method as defined in claim 5, wherein one or more of said microspheres are selected from the group consisting of a preceramic polymer microballoon, phenolic resin microballoon, green or partially-cured aerogel, and a sinterable ceramic microballoon.

7. The method as defined in claim 5, wherein a plurality of said microspheres partially or fully disintegrates during said step of curing and pyrolization to form a plurality of pores in said thermally-insulating composite material, a plurality of said microspheres partially or fully absent in said thermally-insulating composite material after said polymer has substantially fully cured and pyrolized.

8. The method as defined in claim 1, wherein said matrix pores constitute about 1-74 vol. % of said thermally-insulating composite material.

9. The method as defined in claim 1, wherein a distribution of said matrix pores in said thermally-insulating composite material is generally uniform.

10. The method as defined in claim 1, wherein said step of mixing further includes mixing non-shrinkable fillers with said shrinkable filler and said polymer to control matrix shrinkage, said non-shrinkable fillers selected from the group consisting of fibers, whiskers, nanofibers, and nanotubes.

11. The method as defined in claim 10, wherein said non-shrinkable fillers have an average length that is less than an average diameter of said matrix pores.

12. The method as defined in claim 1, wherein said thermally-insulating composite material has a density below about 1.5 g/cc and a flexure and compressive strength exceeding about 5000 psig.

13. The method as defined in claim 1, wherein said thermally-insulating composite material has a thermal conductivity of less than about 0.6 w/m-K, a coefficient of thermal expansion below about 5 ppm/C, and an elastic modulus below about 15 MSI.

14. The method as defined in claim 1, including the step of subsequently processing said thermally-insulating composite material with successive polymer impregnations, pyrolizations, or combinations thereof to increase density, strength, or combinations thereof of said thermally-insulating composite material.

15. A thermally-insulating composite material formed from a shrinkable filler in a polymer matrix material that exhibits co-shrinkage between the shrinkable filler and polymer matrix during processing, said polymer including a thermosetting, curable polymer, said shrinkable filler including microspheres, said microspheres formed of a material that co-shrinks with said polymer to lower or eliminate stress during sintering, pyrolization, curing, or combinations thereof of said polymer, said microspheres having a low thermal conductivity such that an overall thermal conductivity of said composite material is lower than a thermal conductivity of said polymer, said shrinkable filler forming matrix pores in said thermally-insulating composite material, said shrinkable filler formulated to co-shrink with said polymer during said curing and pyrolization of said mixture of shrinkable filler and said polymer matrix material, said polymer has the same or different shrinkage than said shrinkable filler to restrain said polymer from shrinkage after said step of curing and pyrolization.

16. The composite material as defined in claim 15, wherein said matrix pores constitute about 1-74 vol. % of said composite material.

17. The composite material as defined in claim 15, wherein said distribution of said matrix pores in said composite material is generally uniform.

18. The composite material as defined in claim 15, further including non-shrinkable fillers, said non-shrinkable fillers selected from the group consisting of fibers, whiskers, nanofibers, and nanotubes.

19. The composite material as defined in claim 18, wherein said non-shrinkable fillers have an average length that is less than an average diameter of said matrix pores.

20. The composite material as defined in claim 15, wherein said shrinkable filler includes microballoons of ceramic, metal, polymer, aerogel, phenolic resin, or combinations thereof.

21. The composite material as defined in claim 15, wherein said shrinkable filler has a different shrinkage than said polymer material.

22. The composite material as defined in claim 15, wherein said shrinkable filler has a greater amount of shrinkage than said polymer material.

23. The composite material as defined in claim 15, wherein a plurality of said shrinkable fillers is formed of a material that partially or fully disintegrates during the curing or pyrolization of said composite material to form a plurality of said matrix pores that is partially or fully absent said microsphere after said polymer has substantially fully cured and pyrolized.

24. The composite material as defined in claim 15, wherein said composite material has a density below about 1.5 g/cc and a flexure and compressive strength exceeding about 5000 psig, and has a thermal conductivity of less than about 0.6 w/m-K, a coefficient of thermal expansion below about 5 ppm/C, and an elastic modulus below about 15 MSI.

31. A method of manufacturing a thermally-insulating composite material formed from a shrinkable filler in a polymer-derived matrix material that exhibits co-shrinkage between the shrinkable filler and polymer-derived matrix during processing, which method includes: a. mixing the shrinkable filler and a thermosetting, curable polymer, said shrinkable filler including microspheres, said microspheres formed of a material that co-shrinks with said polymer to lower or eliminate stress during sintering, pyrolization, curing, or combinations thereof of said polymer, said microspheres having a low thermal conductivity such that an overall thermal conductivity of said composite material is lower than a thermal conductivity of said polymer, said polymer at least partially formed of one or more materials selected from the group consisting of a ceramic material and a material that at least partially converts to a ceramic material upon being exposed to heat; b. molding or forming the mixed shrinkable filler and polymer into a shape; and, c. heat curing and pyrolization of said mixed shrinkable filler and polymer to form said thermally-insulating composite material, said microspheres co-shrinking with said polymer during said curing and pyrolization, said polymer has a smaller amount of shrinkage than said shrinkable filler to restrain said polymer from shrinkage after said step of curing and pyrolization.

26. The method as defined in claim 25, wherein a plurality of said microspheres partially or fully disintegrates during said step of curing and pyrolization to form a plurality of matrix pores in said thermally-insulating composite material, a plurality of said microspheres partially or fully absent in said syntactic ceramic composite after said polymer has substantially fully cured.

27. The method as defined in claim 26, wherein said matrix pores constitute about 1-74 vol. % of said thermally-insulating composite material.

28. The method as defined in claim 27, wherein said distribution of said matrix pores in said thermally-insulating composite material is generally uniform.

29. The method as defined in claim 25, wherein said step of mixing further includes mixing non-shrinkable fillers with said shrinkable filler and said polymer, said non-shrinkable fillers selected from the group consisting of fibers, whiskers, nanofibers, and nanotubes.

30. The method as defined in claim 29, wherein said non-shrinkable fillers have an average length that is less than an average diameter of said microspheres.

31. The method as defined in claim 25, wherein said microspheres include microballoons of ceramic, metal, polymer, aerogel, phenolic resin, or combinations thereof.

32. The method as defined in claim 25, wherein said thermally-insulating composite material has a density below about 1.5 g/cc and a flexure and compressive strength exceeding about 5000 psig.

33. The method as defined in claim 25, wherein said thermally-insulating composite material has a thermal conductivity of less than about 0.6 w/m-K, a coefficient of thermal expansion below about 5 ppm/C, and an elastic modulus below about 15 MSI.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Reference may now be made to the drawing which illustrates a non-limiting embodiment that the invention may take in physical form and in certain parts and arrangement of parts wherein:

[0045] FIG. 1 is a side view of a cross section of a closed-cell foam insulator of the present invention in accordance with the present invention.

[0046] FIG. 2 is a side view of a cross section of a closed-cell foam insulator that includes non-shrinkable fillers in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0047] Referring now to the drawings wherein the showings are for the purpose of illustrating non-limiting embodiments of the invention only and not for the purpose of limiting same, there is shown in the FIG. 1 a cross section of a structural, thermally-insulating composite material in the form of a structural, thermally-insulating composite material 10 having individual matrix pores 12 formed from a pore-forming filler material distributed in a matrix material 14. FIG. 2 is a cross section of a structural, thermally-insulating composite material in the form of a structural, thermally-insulating composite material 10 having individual matrix pores 12 formed from a pore-forming filler material distributed in a matrix material 14 and non-shrinkable filler 16 in the matrix material.

[0048] The matrix material is curable polymer material that is shrinkable and can form a ceramic-type material after being subjected to pyrolization and/or carbonization. Non-limiting examples of the matrix material include polycarbosilanes, polysilazanes, and polyborosilazanes. Non-limiting specific examples of the matrix polymer are poly urea siloxane, polymethylsilsesquioxane, and polysilsesquioxanes.

[0049] The matrix pores 12 that are distributed throughout the matrix material 14 have a low thermal conductivity. The thermal conductivity of the matrix pores and the pore-forming filler material is less than the thermal conductivity of the matrix material.

[0050] When the matrix pores 12 are distributed in the matrix material 14, the overall thermal conductivity of the structural, thermally-insulating composite material 10 is significantly lower than that of the matrix material 14. Additionally, one advantage of the invention is that the matrix pores 12 and the matrix material 14 exhibit co-shrinkage upon processing at elevated temperatures. This co-shrinkage reduces post-processing stresses within the structural, thermally-insulating composite material 10.

[0051] The structural, thermally-insulating composite material 10 can have varying degrees of size, loading, and/or distribution. Matrix pore 12 size can range from several nanometers to hundreds of microns. The matrix pore 12 loading can range from less than 1 vol. % to 74 vol. %. The distribution of the matrix pores in the matrix material can be random, gradient, and/or uniform.

[0052] The structural, thermally-insulating composite material 10 can include a matrix material 14 made of polymer, ceramic, metal and/or any other sufficiently rigid and strong material. The matrix material can also or alternatively be formed from a precursor material that converts to a solid polymer, ceramic, and/or metal matrix system upon curing, pyrolization, carbonization and/or any other reaction mechanism. The structural, thermally-insulating composite material can optionally include non-shrinkable fillers 16 such as fibers, nanofibers, and/or other toughening and/or strengthening reinforcements.

[0053] The matrix pores 12 can be formed from microballoons of ceramic, metal, polymer, aerogel, and/or any material that exhibits co-shrinkage with the matrix material 14 throughout processing.

[0054] The matrix pores generally provide high strength and/or low-thermal conductivity. The matrix pores 12 can be entirely hollow and/or be formed by the inclusion and degradation of a ceramic, metal, polymer, and/or any material that degrades at high temperatures leaving closed-cell porosity.

[0055] The structural, thermally-insulating composite material 10 can be formed from low-density microspheres in a polymer-derived matrix material that exhibits co-shrinkage between the microspheres and polymer-derived matrix during processing.

[0056] One or more of the microspheres can optionally include shrinkable hollow microballoons and/or shrinkable low density aerogel particles. One or more of the shrinkable microspheres can include a preceramic polymer microballoon, phenolic resin microballoon, green or partially-cured aerogel, and/or a sinterable ceramic microballoon. The matrix polymer material can optionally be a thermosetting preceramic polymer. The matrix phase can be engineered to have lower shrinkage than the syntactic filler such that it can placed in compression upon curing. The matrix phase can be optionally engineered to have the same shrinkage as the syntactic filler so as to be close to zero residual stress after curing and pyrolization. The syntactic filler can have some shrinkage. Any shrinkage is generally less than the matrix material so as to restrain the shrinkage of the matrix phase. The structural, thermally-insulating composite material 10 can be manufactured by the steps of: a) mixing shrinkable/curable microspheres and a thermosetting, curable polymer; b) molding and/or foliating the mixed microspheres and polymer into a shape; and c) subsequently heat curing and pyrolization of the polymer material(s) to form a syntactic ceramic composite. The syntactic ceramic composite can optionally be subsequently processed with successive polymer impregnations and/or pyrolizations to increase density and/or strength. The syntactic ceramic composite can undergo a stabilizing heat at or above the required operating temperatures.

[0057] The method can optionally include the step of a non-shrinkable filler being added to control matrix shrinkage. The method can optionally include the step of fibrous materials being added to provide higher strength and/or toughness. The non-shrinkable filler phase can optionally have at least one primary dimension (e.g., length) of less than 20% of the microsphere diameter, and typically less than 5% of the microsphere diameter.

EXAMPLES

Example 1

[0058] A structural, thermally-insulating composite material was formed of about 30 vol. % phenolic microballoons, about 20 vol. % of −325 mesh SiC powder and about 50 vol. % poly urea siloxane temperature curable resin. The microballoons had an average size of 120 μm. The microballoons had a shrinkage per unit volume of 50% during pyrolyzation. The SiC powder exhibited no shrinkage during pyrolization. The poly urea siloxane temperature curable resin has 40% shrinkage by unit volume during pyrolyzation. The components of the structural, thermally-insulating composite material were mixed together and placed into a Teflon™-lined steel cavity and heated at 200° C. for one hour to cure the structural, thermally-insulating composite material. The cured structural, thermally-insulating composite material had a density of 0.8 g/cc. The cured sample of structural, thermally-insulating composite material had the dimensions of 25×25×25 mm. The cured structural, thermally-insulating composite material was then pyrolyzed by increasing the temperature to 1500° C. for at least 14 hours. When the pyrolyzation of the structural, thermally-insulating composite material was complete, the sample had uniformly shrunk and no cracking was observed. The sample pyrolyzed had dimensions of 22×22×22 mm and had a density of 0.8 g/cc. The sample was then tested in compression and failed at above 37Mpa at room temperature (e.g., 77° F.). The sample retained over 90% of its compression strength when tested at 900° C. and 80% of its compression strength when tested at 1200° C.

Example 2

[0059] A structural, thermally-insulating composite material was formed of about 30 vol. % phenolic microballoons, about 20 vol. % −325 mesh B.sub.4C powder and about 50 vol. % poly urea siloxane temperature-curable resin. The microballoons had an average size of 120 μm. The microballoons had a shrinkage per unit volume of 50% during pyrolyzation. The poly urea siloxane temperature-curable resin has 40% shrinkage by unit volume during pyrolyzation. The components of the structural, thermally-insulating composite material were mixed together and placed into a Teflon™-lined steel cavity and heated at 200° C. for one hour to cure the structural, thermally-insulating composite material. The B.sub.4C powder expanded about 110% of its original volume during the curing process. The cured structural, thermally-insulating composite material had a density of 0.77 g/cc. The cured sample of structural, thermally-insulating composite material had the dimensions of 25×25×25 mm. The cured structural, thermally-insulating composite material was then pyrolyzed by increasing the temperature to 900° C. for at least 14 hours. When the pyrolyzation of the structural, thermally-insulating composite material was complete, the sample had uniformly shrunk and no cracking was observed. The sample pyrolyzed had dimensions of 24×24×24 mm and had a density of 0.7 g/cc. The sample was then tested in compression and failed at above 50M pa at room temperature (e.g., 77° F.). The sample retained over 80% of its compression strength when tested at 900° C. and 30% of its compression strength when tested at 1200° C.

Example 3

[0060] A structural, thermally-insulating composite material was formed of about 30 vol. % alumina microballoons, about 20 vol. % −325 mesh SiC powder and about 50 vol. % poly urea siloxane temperature curable resin. The microballoons had an average size of 100 μm. The microballoons had essentially no shrinkage during pyrolyzation. The SiC powder exhibited no shrinkage during pyrolization. The poly urea siloxane temperature curable resin has 40% shrinkage by unit volume during pyrolyzation. The components of the structural, thermally-insulating composite material were mixed together and placed into a Teflon™-lined steel cavity and heated at 200° C. for one hour to cure the structural, thermally-insulating composite material. The cured structural, thermally-insulating composite material had a density of 0.7 g/cc. The cured sample of structural, thermally-insulating composite material had the dimensions of 25×25×25 mm. The cured structural, thermally-insulating composite material was then pyrolyzed by increasing the temperature to 1500° C. for at least 14 hours. When the pyrolyzation of the structural, thermally-insulating composite material was complete, the sample had uniformly uniformly shrunk and was broken and cracked around the microballoons as they resisted shrinkage. The sample had almost no mechanical integrity and could not be measured.

Example 4

[0061] A structural, thermally-insulating composite material formed of about 30 vol. % polyacrylonitrile PAN microballoons, about 20 vol. % of −325 mesh SiC powder and about 50 vol. % poly urea siloxane temperature curable resin. The microballoons had an average size of 300 μm. The microballoons had a shrinkage per unit volume of 55% during pyrolyzation. The SiC powder exhibited no shrinkage during pyrolization. The poly urea siloxane temperature-curable resin has 40% shrinkage by unit volume during pyrolyzation. The components of the structural, thermally-insulating composite material were mixed together and placed into Teflon™-lined steel cavity and heated at 200° C. for one hour to cure the structural, thermally-insulating composite material. The cured structural, thermally-insulating composite material had a density of 0.5 g/cc. The cured sample of structural, thermally-insulating composite material had the dimensions of 25×25×25 mm. The cured structural, thermally-insulating composite material was then pyrolyzed by increasing the temperature to 1500° C. for at least 14 hours. When the pyrolyzation of the structural, thermally-insulating composite material was complete, the sample had uniformly shrunk and no cracking was observed. The sample pyrolyzed had dimensions of 20×20×20 mm and had a density of 0.6 g/cc. The sample was then tested in compression and failed at above 30 Mpa at room temperature (e.g., 77° F.).

[0062] It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in the constructions set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. The invention has been described with reference to preferred and alternate embodiments. Modifications and alterations will become apparent to those skilled in the art upon reading and understanding the detailed discussion of the invention provided herein. This invention is intended to include all such modifications and alterations insofar as they come within the scope of the present invention. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention, which, as a matter of language, might be said to fall there between. The invention has been described with reference to the preferred embodiments. These and other modifications of the preferred embodiments as well as other embodiments of the invention will be obvious from the disclosure herein, whereby the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims.