Le Aeronautical
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Going off of this quite interesting thread:
https://www.rocketryforum.com/showthread.php?t=16430
I was thinking, why not use a ceramic composite for hypersonic? Obviously the military and NASA does do this.
When I was at UAHuntsville, I ran a project where I tested a high temperature composite made from carbon fiber and a special high temp polymer based off of 2,2'-dimethylbenzidene (NASA's DMBZ based off of PMR-15). It has such a molecular structure that makes the molecule does not twist much (there is special terminology for this that I can't seem to pull off the top of my head right now) and I believe it also had high intermolecular forces. That said, it was able to withstand temperatures as high as 343C for long periods of time. I also tested it for short "spikes" of up to some 1200C. It has an amazing ability to withstand high temps, and remember, this is a polymer!!
Unfortunately, the "epoxy" alone costs $5 per gram and the composite must be manufactured using a combination of vacuum bagging, autoclave, and compression molding. So it's not very practical for us amateur rocketeers.
So I thought, hey, why not use ceramic composites instead. They can put up with about the same temps (sometimes higher) but for much longer durations than the 1 second to 1 minute that these were being subjected to (not that your amateur rocket is going to be going hypersonic for a full minute or anything!). Using the same ceramic that most high temp thermocouples and furnaces are insulated with, Alumina, you can create a very cheap yet effective leading edge that can put up with temps to around 2k degrees C.
Alumina is very easy to cast (it's done at room temp) and you could make a composite the same way you make any other composite, just pretend the alumina is the resin. Unfortunately it is quite brittle, the fiber would prevent it from just shredding a part, but even still this could probably only be leading edges and it would have to be reinforced, say, by the rest of the fin. You wouldn't want to make a full fin out of the stuff.
Another option is to just thermally reinforce your epoxy with powdered alumina. Much like a solution containing a lot of ions the boiling point will be raised and the freezing point will be depressed. The same will apply to your epoxy, obviously it won't bring it up to a 2k degree tolerance, but it would reduce the amount of wear and tear from the high temp. Another example of this is like with carbon nanotubes. Studies have shown that as little as 1/2% of tubes (just mixed in totally randomly, no arrangement) can drastically increase the strength of epoxy. It may not be a thermal example, but it shows that you are not limited by the weakest link.
So what do you think? Go ahead, try it. Just mix some Alumina in with your next multi-mach rocket and let me know how it works out for ya :wink: I call exclusive rights
EDIT: Note: I did post this in the "techniques" section for the sake of getting your opinion on what you would build, structurally, to go that speed, and if you would use something like what I just talked about. But if a mod wants to move it to HPR or something, I'm cool with that
https://www.rocketryforum.com/showthread.php?t=16430
I was thinking, why not use a ceramic composite for hypersonic? Obviously the military and NASA does do this.
When I was at UAHuntsville, I ran a project where I tested a high temperature composite made from carbon fiber and a special high temp polymer based off of 2,2'-dimethylbenzidene (NASA's DMBZ based off of PMR-15). It has such a molecular structure that makes the molecule does not twist much (there is special terminology for this that I can't seem to pull off the top of my head right now) and I believe it also had high intermolecular forces. That said, it was able to withstand temperatures as high as 343C for long periods of time. I also tested it for short "spikes" of up to some 1200C. It has an amazing ability to withstand high temps, and remember, this is a polymer!!
Unfortunately, the "epoxy" alone costs $5 per gram and the composite must be manufactured using a combination of vacuum bagging, autoclave, and compression molding. So it's not very practical for us amateur rocketeers.
So I thought, hey, why not use ceramic composites instead. They can put up with about the same temps (sometimes higher) but for much longer durations than the 1 second to 1 minute that these were being subjected to (not that your amateur rocket is going to be going hypersonic for a full minute or anything!). Using the same ceramic that most high temp thermocouples and furnaces are insulated with, Alumina, you can create a very cheap yet effective leading edge that can put up with temps to around 2k degrees C.
Alumina is very easy to cast (it's done at room temp) and you could make a composite the same way you make any other composite, just pretend the alumina is the resin. Unfortunately it is quite brittle, the fiber would prevent it from just shredding a part, but even still this could probably only be leading edges and it would have to be reinforced, say, by the rest of the fin. You wouldn't want to make a full fin out of the stuff.
Another option is to just thermally reinforce your epoxy with powdered alumina. Much like a solution containing a lot of ions the boiling point will be raised and the freezing point will be depressed. The same will apply to your epoxy, obviously it won't bring it up to a 2k degree tolerance, but it would reduce the amount of wear and tear from the high temp. Another example of this is like with carbon nanotubes. Studies have shown that as little as 1/2% of tubes (just mixed in totally randomly, no arrangement) can drastically increase the strength of epoxy. It may not be a thermal example, but it shows that you are not limited by the weakest link.
So what do you think? Go ahead, try it. Just mix some Alumina in with your next multi-mach rocket and let me know how it works out for ya :wink: I call exclusive rights
EDIT: Note: I did post this in the "techniques" section for the sake of getting your opinion on what you would build, structurally, to go that speed, and if you would use something like what I just talked about. But if a mod wants to move it to HPR or something, I'm cool with that
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