Biologically inspired radiation reflector
A thermal protection system (TPS) comprising a mixture of silicon carbide and SiO x that has been converted from Si that is present in a collection of diatom frustules and at least one diatom has quasi-periodic pore-to-pore separation distance d(p-p) in a selected range. Where a heat shield comprising the converted SiC/SiO x frustules receives radiation, associated with atmospheric (re)entry, a portion of this radiation is reflected so that radiation loading of the heat shield is reduced.
1. A method for providing a thermal protection component for a space vehicle that enters or re-enters an atmosphere, the method comprising:
(1) providing a plurality of particles, comprising Mg, and a powder bed of frustules of SiO x (x≧1) from diatom shells in a heated fluidized bed reactor (FBR), where at least one diatom shell has average nearest neighbor pore-to-pore spacing d(p-p) that lies in a selected range, D1≦d(p-p)≦D2, with D1≧100 nm and D2≧400 nm;
(2) heating the plurality of particles and the SiO x powder bed to a first temperature no greater than about 800° C., and allowing at least a portion of the particles and the SiO x powder bed to react to form MgO and Si;
(3) leaching MgO to provide a first mixture comprising Si particles and SiO x particles;
(4) providing a hydrocarbon gas, comprising at least one of CH 4 , C 2 H 4 and C 2 H 6 , plus an H 2 gas in the FBR in a temperature range T2=640−800° C.;
(5) allowing the first mixture comprising Si particles and SiO x particles to react with the hydrocarbon gas and with the H 2 gas in the FBR to form a substance comprising SiC and SiO x , whereby at least a portion of the first mixture is converted to a second mixture comprising SiC particles and SiO x particles, wherein a temperature during the reaction of the first mixture with the hydrocarbon gas and with the H 2 gas in the FBR is no higher than 800° C.;
(6) providing a layer of the second mixture, having an initial thickness τ1 at least equal to a selected threshold thickness τ1(thr), on an exposed surface of a heat shield system;
(7) permitting the layer of the second mixture to receive radiation from a source of radiation; and
(8) permitting the layer of the second mixture to serve as an optical reflector to reflect a portion of the radiation received.
2. The method of claim 1 , further comprising choosing said pore-to-pore spacing D1≧200 nm.
3. The method of claim 1 , further comprising choosing said pore-to-pore spacing D2≦300 nm.
4. The method of claim 1 , wherein said hydrocarbon gas contains C 2 H 6 , C 2 H 4 or a combination thereof.
5. The method of claim 1 , further comprising limiting said first temperature to a range, T1=600−640° C.
6. The method of claim 1 , further comprising choosing said threshold thickness τ1(thr) that is sufficient so that, after exposure of said second mixture to said radiation for a selected time interval length Δt, a portion of said second mixture remains on said exposed surface.
7. A method for providing a thermal protection component for a space vehicle that enters or re-enters an atmosphere, the method comprising:
(1) providing a plurality of particles, comprising Mg, and a powder bed of frustules of SiO x (x≧1) from diatom shells in a heated fluidized bed reactor (FBR), where at least one diatom shell has average nearest neighbor pore-to-pore spacing d(p-p) that lies in a selected range, D1≦d(p-p)≦D2, with D1≧100 nm and D2≦400 nm;
(2) heating the plurality of particles and the SiO x powder bed to a first temperature no greater than about 800° C., and allowing at least a portion of the particles and the SiO x powder bed to react to form MgO and Si;
(3) leaching MgO to provide a first mixture comprising Si particles and SiO x particles;
(4) providing a hydrocarbon gas, comprising at least one of CH 4 , C 2 H 4 and C 2 H 6 , plus an H 2 gas in the FBR in a temperature range T2=640−800° C.;
(5) allowing the first mixture comprising Si particles and SiO x particles to react with the hydrocarbon gas and with the H 2 gas in the FBR to form a substance comprising SiC and SiO x , whereby at least a portion of the first mixture is converted to a second mixture comprising SiC particles and SiO x particles, wherein a temperature during the reaction of the first mixture with the hydrocarbon gas and with the H 2 gas in the FBR is no higher than 800° C.;
(6) depositing the second mixture in a plurality of isolated clusters, at least one cluster having an initial thickness τ1 at least equal to a selected threshold thickness τ1(thr), on an exposed surface of a heat shield system;
(7) permitting the deposit of the second mixture to receive radiation from a source of radiation; and
(8) permitting the deposit of the second mixture to serve as an optical reflector to reflect a portion of the radiation received.
8. The method of claim 7 , further comprising choosing said pore-to-pore spacing D1≧200 nm.
9. The method of claim 7 , further comprising choosing said pore-to-pore spacing D2≦300 nm.
10. The method of claim 7 , wherein said hydrocarbon gas contains C 2 H 6 , C 2 H 4 or a combination thereof.
11. The method of claim 7 , further comprising limiting said first temperature to a range, T1=600−640° C.
12. The method of claim 7 , further comprising choosing said threshold thickness τ1(thr) that is sufficient so that, after exposure of said second mixture to said radiation for a selected time interval length Δt, a portion of said second mixture remains on said exposed surface.