Hello everyone. This is my first post here. I've been thinking about posting for a while. And I was watching a video by AvE about carbon foam as refractory. I did a search here for 'carbon foam' and didn't see any results. And was wondering how useful it would be in a rocket.
I just saw this, and am Jazzed at the idea of building a slightly smaller than "bread loaf" sized pyrolysis chamber and making my own ultra lightweight, highly insulative refractory bricks out of loaves of cheap white bread from the bakery outlet!
I could also see using a larger pyrolysis chamber to make a cast carbon foam burn tunnel and riser liner, by building it up over a cardboard form, "gluing the slices of bread in layers with a brushed on "flour-water" mix.
I'd imagine one could make lipped riser tube sections this way as well...
Then pyrolyze, and you have an apparently super insulating, ultra high heat compatible, but presumably very light and soft refractory.
With a large enough pyrolysis chamber, perhaps a whole core and riser could be pyrolyzed as a unit, perhaps lined with thin firebrick in the feed area to be able to stand up to feed tube abuse.
So I made a tiny sample... Found an old metal "fold open" can from a pack of sawzall blades.
This stuff is rather interesting! It gets "clinker" hard.
I should have let it cook a little bit longer, as the piece that remained whole (the other broke when I dropped the can on the ground taking it out with metal tongs to set it on a rock outside.) as evidenced by some still brown portions in the center of that piece, and smoke emanating when I did a "protect the finger from a blow-torch/calibri style lighter" test. Still kept my finger from feeling anything for a good 15 seconds, even though smoke was wafting up from both the flame side and finger side of the bread.
I only kept it in until flames stopped shooting out of the seams of the can... So now I know not to be shy about "leaving it in the fire too long"
Made lovingly, with the "honey wheat" bread I had on hand, (similar in density to wonder bread, but with some whole wheat flour and no corn syrup) it is softer than perlite, in terms of crush resistance, but seems like it could be an excellent, ultra light weight, high heat insulator.
Shrinks and deforms a lot, during the pyrolysis, but seems to have rather excellent insulative qualities, for being an "open cell" type foam.
Well dang... I think I'm going to have to build a bigger pyrolyzer setup.
Besides shape changes during pyrolzation, the other major issue might be that thick buildup of it, might insulate themselves so well that the center of thick parts might never burn out during pyrolyzation, without a REALLY extended period at heat.
I took a piece and wetted it thoroughly and it shows no sign of softening.
I need to get a sealable metal container I can drill some holes in and try to make a heat riser and burn tunnel in sections. The feed area will need something harder, but I figure from there on the carbonized bread foam may well be just fine. Ash clean out will probably be best done with compressed air to minimize tool damage to burn tunnel and riser.
First full scale experiment is going to be building a small radiant heat rocket 3" for my perpetually freezing sweetheart to use on the porch instead of the electric heater she "heats the outdoors" with now.
My daughter is still giving me dirty looks about making the living room smell like badly burnt toast.
Outdoors next time.
Photo below is my "high tech" pyrolysis chamber and the one unbroken piece and pieces of the broken one.
They were cut to fill the tin width wise, originally.
I will have to see if "stuffing the tin" produces more uniform results.
And this is the approximately 5/16" thick carbonized bread foam protecting my finger quite effectively from a small but rather hot butane torch lighter.
The smoke is from the still incompletely pyrolized center of the unbroken sample... Could be why it didn't break. My daughter squealed and said "what the heck!?!" as I had her holding the camera and taking the photo as the torch flame made the surface of the carbon foam glow, and then smoke began to pour from both sides of the bread, enveloping my still totally protected digit... I started to feel some warmth after about 15 seconds.
I thought it interesting, looking at the photos, that the majority of the smoke emanating from the "my finger" side of the bread seemed to tumble downward, rather than rising as I would expect a hot combustion byproduct to do.
I suspect that this foam could be stronger, close to as highly insulating, and shrink less if I "pack the tin"...
It also might help to dry the bread thoroughly before pyrolizing, as that might allow it to stay "stiffer" during the process and perhaps not be quite as porous as there will be less water in the chamber to steam the bread before it pyrolizes.
So that will be my next couple of experiments... Will report back.
For anyone who understands all the technical terms describing it's maximum insulating value, compressive strength and other tech specs, here is the Phys.org report on the original paper... From the video description in AvE's YouTube video linked by the OP.
I broke all my curled up pyrolized carbon bread foam slices into smaller chunks (roughly 1/2" minus) in anticipation of experimenting with using them as an insulative refractory "grog" baked into some more bread/pancake type dough/batter as binder, and came accross this article:
They were doing some acetone based "de-fatting" wash process on the mayo version, in a sohxlet extractor, so I decided meringue was more the speed of what I could whip up in my kitchen. Their meringue ingredienrs also did not include egg, but I figure I wanted to be able to get my ingredients at the grocery store rather than from sigma-Aldrich or some other research chemical supplier.
So baking some samples at the moment, carbon bread foam on and between a meringue whipped up from egg white, sugar, corn starch, and a bit of cream of tarter... Left out vanilla and salt. Added more sugar and corn starch than recipie called for.
Am baking now and will pyrolize samples after I am sure they are fully dry.
Left rear are folded parchemnt "trays" where I layed in carbon foam chunks, added meringue, added more carbon chunks, then some carbon bread foam meringue mix for the final layer. (Not easy mix to handle... VERY sticky, and no longer fun to lick off your fingers once full of carbonized bread bits)
Front left is puck of meringue with carbon bread foam remainder after layering the trays mixed in, and right side is just left over meringue plain from the 4 egg white recipe I used.
Will update with how things turned out after pyrolizing samples.
I am hoping to make bulk, heat resistant, highly insulative carbon foam out of ingredients we all have cheap, relatively ecologically sound, and abundant access to, as a fire resistant insulator for the hot, but perhaps not hottest, parts of a rocket core...
Lid has three holes punched with a nail at the bottom to keep gasses in like a bell... It shoots three jets of hot gasses that ignite after exit and mixing with air in the stove, for as long as there is material being pyrolized at a sufficient rate...
Have done two (not full) runs with it so far... Looks like it will last between 10 and 20...
I put it on a good hot bed of coals, and tend to leave it on the fire for a good 20 minutes after the flames stop coming out of the hole, to ensure the insulative bread foam is pyrolyzed thoroughly.
I imagine it may be more difficult if I "stuff" the tin... I'm thinking to dry the slices first, break them up into grog and then carbonize.
Waiting until I make it to the bakery "factory outlet store" where I can get close dated bread ultra cheap (also going to ask if they have any free or just even more ultra cheap, already moldy bread that might be perfectly useful for pyrolysis...
It appears carbon foam will sublimate bit by bit, so I have another castable insulation material I plan to make cast, insulative "hot faces" for my burn tunnel and riser out of, that is apparently good to oxy-acetylene temps of 5500F but it is rather pricey... Around $60 for a 50 lb bag that will cover 22 sq ft sprayed... It can also be cast but apparently comes out denser.
It is a calcium carbonate cementitious fire stop called Firearmor55... I figure I should be able to make the hot faces of my burn tunnel and riser from it, backed with carbon foam refractory, and switch to an "un-faced" carbon foam refractory for the manifold.
So the meringue on it's own came out to be the strongest sample...
However, after wasting propane on my crab cooker for over an hour, I found that the carbon foam is still incompletely pyrolyzed in the thicker sections, and the center of the thicker brick burned like charcoal when I took it out after deciding not to waste anymore propane on it.
The plain meringue actually came out quite strong and light, though shrinkage and deformation during pyrolization are rather significant.
On further testing I have found I can ignite pretty much any piece, but can only keep it lit by blowing on it...
So what I have made so far may not be the best material for a refractory, as is...
However, unlike perlite, when it does combust, it seems to keep it's structure and just sublimate away... So it might be a good structure to have another more heat resistant material "bound into" and fired.
I don't have a kiln, so will have to experiment more, as time, money, and motivation permit.
If anyone has suggestions of what I might "soak into" the carbon foam and then dry and fire, let me know.
I see that milk of magnesia degrades into magnesium oxide, and that has an insanely high melting point... So probably will try that with my carbon bread foam and carbon meringue foam, and see what happens...
Next time I get to a place where I can get my hands on a bottle of milk of magnesia at a reasonable price.
Perhaps a very thin clay slip to "coat, but not fill" the foam, then heating to ceramic firing temps in a pyrolysis environment to keep the carbon foam from burning away, then switching to an oxidative environment to burn out the bread foam.
Not knowing much about how clays interact with carbon I'm not sure if this line of experimentation would be worthwhile...