Method of fabricating a flexible, low-density thermal protection material
A method for preparing a flexible low-density thermal protection material, the method comprising providing a flexible substrate and a pyrolizable material impregnated therein. The thermal protection material remains flexible after impregnation and continues to remain flexible when the pyrolizable material is fully pyrolized.
1. A method of fabricating a low-density thermal protection material, the method comprising:
providing a flexible substrate;
providing a slurry including a carrier liquid and pyrolizable thermoset resin particles that have already been cured and that are immersed in, but not soluble in, the carrier liquid;
impregnating the slurry into the substrate to form an impregnated substrate; and
removing the carrier liquid from the impregnated substrate to provide said low-density thermal protection material that remains flexible after the thermoset resin particles are fully pyrolized.
2. The method of claim 1 , wherein said thermoset resin particles constitute between 20% and 80% of the mass of the thermal protection material.
3. The method of claim 1 , wherein said thermoset resin particles constitute between 40% and 60% of the mass of the thermal protection material.
4. The method of claim 1 , wherein said thermal protection material has a mass density between 0.15 and 0.35 g/cm 3 .
5. The method of claim 1 , wherein providing a slurry including a carrier liquid and pyrolizable thermoset resin particles further includes providing said thermoset resin particles with a pyrolysis temperature above 350 C.
6. The method of claim 1 , wherein providing a flexible structure further includes providing a flexible substrate that is a felt.
7. The method of claim 1 , wherein providing a flexible structure further includes providing a flexible substrate that includes carbon fibers.
8. The method of claim 1 , wherein providing a slurry including a carrier liquid and pyrolizable, thermoset resin particles further includes providing thermoset resin particles including at least one of phenolic, polyimide, polybenzobisoxazole, polybenzimidazole, polyaramid or a mixture thereof.
9. The method of claim 1 , wherein providing a slurry including a carrier liquid and pyrolizable, thermoset resin particles includes preparing said thermoset resin particles by breaking cured resin into small fragments and milling the fragments for less than two hours.
10. The method of claim 9 , further including milling said fragments for a duration required to produce particles having a median diameter of 2-6 μm.
11. The method of claim 1 , wherein impregnating the slurry into the substrate further includes impregnating the slurry into the substrate using a pressure gradient.
12. The method of claim 11 , wherein providing a slurry including a carrier liquid and pyrolizable, thermoset resin particles further includes providing a slurry wherein the viscosity of said slurry is low enough that the final distribution of particles is uniform through the thickness of said impregnated substrate.
13. The method of claim 12 , further including providing a slurry wherein the viscosity of said slurry is less than 6 cP.
14. The method of claim 11 , further including providing a slurry wherein the viscosity of said slurry is high enough that the final distribution of particles is graded through the thickness of said impregnated substrate.
15. The method of claim 1 , further including providing said thermal protection material as a continuous sheet of flexible material.
16. The method of claim 15 , further including mounting said continuous sheet on an atmospheric entry vehicle.
17. The method of claim 16 , further including stowing said continuous sheet prior to atmospheric entry and deploying said thermal protection material shortly before atmospheric entry.