Aerographite

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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DeltaV
Posts: 2245
Joined: Mon Oct 12, 2009 5:05 am

Aerographite

Postby DeltaV » Sun Jul 29, 2012 4:19 pm

(From NSF forum)

Aerographite: Ultra Lightweight, Flexible Nanowall, Carbon Microtube Material with Outstanding Mechanical Performance (free PDF)

An ultra lightweight carbon microtube material called Aerographite is synthesized by a novel single-step chemical vapor deposition synthesis based on ZnO networks, which is presently the lightest known material with a density smaller than μg/cm3. Despite its low density, the hierarchical design leads to remarkable mechanical, electrical, and optical properties. The first experiments with Aerographite electrodes confirm its applicability.

The atomic structure can be tuned from graphitic to glass-like pyrolytic carbon, with the advantage of remarkable mechanical properties. This most lightweight material reaches the highest merit indices for specific moduli observed until now. Further optimization of parameters like, e.g., pore size and volume density of sintering bridges keeps the opportunity for future improvements of the mechanical performance of Aerographite. Further properties like conductivity, flexibility and compressibility without losing structural integrity, high optical adsorption and X-ray opacity, a high temperature stability and chemical resistance, the bearing of tensile and compressive loads, and the super hydrophobicity making it a remarkable multifunctional material. Next to others, potential applications might be electrode materials for the increasing demand of batteries and high surface area supercapacitor materials. Proper designed carbon materials from the family of Aerographites could avoid typical problems of electrode materials like low mechanical cycling stability, degenerating electrical contacts, or non-optimized electrolyte to surface ratio which might be tuned in by simple compression due to the negligible Poisson’s ratio of these sponge-like structures.

Direct conversion electrodes with position-dependent resisitivity and alpha tolerance?
Stable capacitors for Mach-Woodward Effect?
Radiation shields?

happyjack27
Posts: 1435
Joined: Wed Jul 14, 2010 5:27 pm

Re: Aerographite

Postby happyjack27 » Mon Jul 30, 2012 3:42 pm

DeltaV wrote:(From NSF forum)

Aerographite: Ultra Lightweight, Flexible Nanowall, Carbon Microtube Material with Outstanding Mechanical Performance (free PDF)

Direct conversion electrodes with position-dependent resisitivity and alpha tolerance?
Stable capacitors for Mach-Woodward Effect?
Radiation shields?



Direct conversion electrodes with position-dependent resisitivity and alpha tolerance?

-- might be overkill. really how much efficiency or longevity would be gained? unless these got really cheap, i'm not sure it would be worth it economically.


Stable capacitors for Mach-Woodward Effect?

-- would certainly make for some nice capacitors. but how important are capacitors in a continuous (rather than pulsed) system? power filtering... adaptive control...


Radiation shields?

-- w/pb11, there are no neutron emissions, so you don't need radiation shields. your direct conversion plates serve as your "radiation shields", capturing the primary form of "radiation": high energy electrons. bremstrallg radiation should be fairly low as the electrons in the reaction area are cold, and i don't imagine it travels far. heat - not sure. this would be transmitted as electromagnetic fluctuation. electrons on the outside are hot, but my guess is the electromagnetic fluctuations they create are too fast and short-lived to really impart a lot of energy to a distant proton. and conversely ions would only be hot on the inside, and the electrons would have plenty of time and space to cancel that out. and besides, it's at a very high vacuum. i think only real source of heat on the outside would be from fusion - if the ionic products are high KE. but my guess is even with that, the outside will remain relatively cold as far as fusion reactors go.

DeltaV
Posts: 2245
Joined: Mon Oct 12, 2009 5:05 am

Re: Aerographite

Postby DeltaV » Mon Jul 30, 2012 4:33 pm

happyjack27 wrote:Direct conversion electrodes with position-dependent resisitivity and alpha tolerance?

-- might be overkill. really how much efficiency or longevity would be gained? unless these got really cheap, i'm not sure it would be worth it economically.
Here I was thinking of the expected energy (and resulting voltage) spread of the p-11B fusion alphas. A geometry-dependent resistance in the collectors (apparently, easy to vary mechanically using the above material: a linear, 4x conductivity change for 0-30% compression) might allow for capturing more energy than a discrete-energy, fixed-resistance design, but that's just another one of my wild guesses. As usual, I have in mind weight-critical aerospace applications where efficiency must be optimized, not so much ground-based reactors.

happyjack27 wrote:Stable capacitors for Mach-Woodward Effect?

-- would certainly make for some nice capacitors. but how important are capacitors in a continuous (rather than pulsed) system? power filtering... adaptive control...
One of the notable problems with Mach-Woodward thrusters to date seems to be thrust "die-off", possibly due in part to changes in capacitor material characteristics with use. I don't know the details of that, but the above material might allow for more predictable supercapacitors in the oscillatory mechanical/electromagnetic environment of M-W thrusters. Again, a wild guess.

happyjack27 wrote:Radiation shields?

-- w/pb11, there are no neutron emissions, so you don't need radiation shields.
There is still uncertainty about gamma emission from a p-11B Polywell and whether or not that will drive the radiation shield design (see 93143 posts). The paper above implies use of the material as an x-ray shield, so I recklessly extrapolated energy to gammas for some variant of an Aerographite shield.

GIThruster
Posts: 4686
Joined: Tue May 25, 2010 8:17 pm

Postby GIThruster » Mon Jul 30, 2012 6:03 pm

I haven't read the paper yet but just off the top of my head--I would guess this doesn't make useful capacitors just because the energy storage is so much less than any of the Perovskites that have include physical displacement of specific ions. BaTio3, PZT, PMN-PT all have piezoactive or electrostrictive movement, and this movement is what stores huge quantities of internal energy, like a rubber band.

I would note that extremely conductive films deposited by vapor deposition do have a place, especially in monolithic stacks. Once can imagine using a single CVD chamber to deposit a thin layer of capacitor material, followed by a thin electrode, rinse and repeat. Since the force generated by an M-E thruster scales with the cube of the frequency, and the frequency is limited by the thickness of each stack layer, thin layers are a way forward for higher thrust devices.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis


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