Thermal insulation materials suitable for use at high temperatures, and process for making said materials
A process for making a thermal insulation material based on carbon and which includes carbon fibers, suitable for use at temperatures above 1,500° C. The process includes providing carbon fibers with embedded carbon black particles; cutting or milling said carbon fibers to obtain short carbon filaments; preparing a slurry by introducing the short carbon filaments in a liquid phase that includes a binder capable of forming a carbon residue upon pyrolysis under non-oxidizing conditions; casting the slurry into a mold capable of separating the slurry into a wet green body and a liquid phase; and drying and heat treating the wet green body to obtain a thermal insulation material.
1 . A process for making a thermal insulation material comprising carbon fibers, the process comprising:
providing carbon fibers with embedded carbon black particles;
cutting or milling the carbon fibers with the embedded carbon black particles to obtain short carbon filaments with an average length not exceeding about 2,000 μm;
preparing a slurry by introducing the short carbon filaments in a liquid phase having a pyrolysable binder dissolved or dispersed therein such that the pyrolysable binder is distributed over substantially all surfaces of the short carbon filaments and does not accumulate only on contact points of the short carbon filaments;
casting said slurry into a mold composed of a porous material to deposit the short carbon filaments in the mold and thereby form a wet green body; and
drying the green body and then heat treating the wet green body under non-oxidizing conditions to obtain the thermal insulation material.
2 . The process of claim 1 , wherein said drying and heat treating comprises drying and solidifying the pyrolysable binder, and then conducting pyrolysis under non-oxidizing conditions at a minimum temperature of 700° C. to transform the pyrolysable binder into a carbon residue.
3 . The process of claim 2 , wherein conducting the pyrolysis is carried out at a temperature of at least 900° C.
4 . The process of claim 3 , further comprising, after conducting the pyrolysis, conducting a further heat treatment of the wet green body at a temperature above 2,000° C. under non-oxidizing conditions.
5 . The process of claim 1 , wherein the short carbon filaments have an average length of between about 200 μm and about 1500 μm.
6 . The process of claim 1 , wherein a carbon yield of the pyrolysable binder is at least 20%.
7 . The process of claim 1 , wherein the mass fraction of the carbon black particles in the carbon fibers is between 10% and 35%.
8 . The process of claim 1 , wherein the pyrolysable binder comprises an agent selected from the group consisting of phenolic resin, sugar, and starch.
9 . The process of claim 1 , wherein the liquid phase comprises water.
10 . The process of claim 1 , wherein the carbon fibers have a mean diameter not exceeding 15 μm.
11 . The process of claim 1 , wherein the carbon fibers have a mean diameter of between 1 μm and 10 μm.