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Well I tried everything but none of the individual ingredients produce any black soot or carbon when the torch is applied.

The mixture actually started getting discolored when heated in the oven, turning tan and getting darker brown as it slowly heated.

I can only assume it was something resulting from some kind of chemical reaction. Most of the ingredients are pretty inert except the baking soda and probably the waterglass, at least while in solution.

I also found out the baking soda will "melt" when heated by itself, but by itself is easily crushed back into a powder when it cools.

The Perlite melted with baking soda is an interesting combination.

I tried stirring what looked like a puddle of molten Perlite and baking soda in a big glob with a metal rod, but it was actually already hard. A red hot but hard "puddle"

Kind of surprising. I was expecting it to be a gooey semi-liquid or putty, like molten glass but it was more like red hot but hard metal. It takes a real lot of heat though. It also seems very light.

I thought maybe it could be molded while "plastic" but it seems as though the Perlite and baking soda melt and fuse together to make what seems almost like plastic metal. Lightweight like plastic but can be heated to red hot like metal.

Maybe if the baking soda and perlite were both pulverized together and thoroughly mixed before being heated they could be fused together in a stainless steel or plaster mold.

Changing tactics.

Sticking with what I know basically works, Perlite + waterglass, I made up a kind of thick slurry of unsifted perlite right out of the bag with a strong 40% waterglass solution. That is about 40% of this:


Which is about the consistency of maple syrup, and I diluted that sodium silicate product with 60% more water

I added enough or this diluted waterglass solution to completely soak the Perlite to the consistency of wet cement. Then just put it into a cookie tin lid (that I coated the inside of with Vaseline to facilitate removal). and then used a length of PVC pipe as a straightedge to screed the top off flat.

I let that sit overnight to partly dry out before putting it in the oven. Gradually increasing the temperature.

Well, unfortunately the petroleum jelly did not make a suitable release agent, and the material stuck to the tin.

I was not able to give it a sufficiently hot heat treatment in just the oven to fuse the Perlite.

A very dilute waterglass solution worked very well with the silicon carbide, and I've been using the microwave kiln pieces as a kind of crucible for my various flame tests,

Not working so well with the large, unsifted Perlite.

I assume the problem is, the perlite is more porous when in bigger chunks, so, the same problem as with the vermiculite.

The upper surface I made smooth by sifting some dry perlite onto the screwed mix.

This top layer of mostly sifted Perlite held together better.

Underneath the larger chunks were completely crumbly.

This stuff might be good enough for medium high heat engines:


https://youtu.be/4xvoT5GZsB4


But I read from an article that used on a rocket stove, Hempcrete is indeed fireproof, in the sense that it will not catch fire, but it will eventually dry out and crumble.

But being pretty lightweight, relatively strong and very heat resistant, it might be worth experimenting with.

baking soda will "melt" when heated by itself, but by itself is easily crushed back into a powder when it cools.

This is how I make my washing soda, but lower temperatures. At least it's fire proof:


Well, it probably has good insulating properties. Sounds like it could be a super useful mixture.

I just spent an hour in frustration trying to roll out some clay for one of my earlier ideas using ceramic:

viewtopic.php?f=1&t=5415#p17351

I found a nice flat surface, a thick piece of microwave mica I never used (much too heavy), spent a lot of time rolling the clay out flat to just the right thickness, carefully cut a circle the size needed for an LTD engine. Then when I tried to gather up the clay trimmings they were stuck like glue to the mica. So was the circle cut out for a displacer.

I ended up having to scrape that off and try a smoother surface. Some real mica was handy. Same problem. I tried a pane of glass. Stuck again.

So I got some plaster of Paris powder and dusted the surface. Sort of seemed to help a little bit by the time I got the clay flattened out, that stuck too.

I was worried about the clay not being comparable with the plaster so tried the kaolin clay powder. Same problem. Kept sticking, requiring more and more powder until the clay hardened up like a brick.

Finally I went online to find out how people roll out clay with a rolling pin. I know I've seen it done before, seemingly very easily. What was I doing wrong?

This was helpful:


https://youtu.be/1Z96-Ezf9uM


I have a canvas drop cloth over at the shop someplace I can use, or I might just buy a tablecloth from the dollar store.

When all else fails, read the directions LOL

skyofcolorado wrote: ↑Mon Apr 03, 2023 12:39 pm ...


Well, it probably has good insulating properties. Sounds like it could be a super useful mixture.

You mean the baking powder and Perlite I assume?

This is not, I don't think too different from foamed glass. Perlite, I believe, is basically just expanded volcanic glass.

Some foamed glass is based on recycled crushed glass with baking soda used as a foaming agent.

Probably what was produced is just a very slightly expanded foamed glass type substance.

I haven't deliberately made any foamed glass yet, so I can't really say for sure.

I know the material is not flexible like plastic, except maybe the most brittle inflexible plastic perhaps.

If it is essentially foamed glass, the pore structure must be microscopic as it isn't obvious, but it is very lightweight.

A video I took last night, but only just now uploaded:


https://youtu.be/z1zOLrl1D80


Nothing too incredible.

I just tried it with some colored glass frit I bought a while back. Basically nearly the same results, but the blobs were a little more pliable while still good and hot and some color.

If using clay, my phone just sent me a notification about this video, which I thought was quite interesting. Some ideas for making high temperature ceramic displacers decorative.

From this video:


https://youtu.be/LE3iTGeV5nU

Well, the old cut up painters drop cloth worked pretty good as a semi-non-stick surface.

Still had to be careful to roll away from the center to keep the clay from sticking to the roller, and turn the sheet of clay very frequently but it worked.

I used a piece of thin cardboard as a thickness gauge.

Made very thin sheets of clay and laid them one on top of the other with the coffee Stirling sticks between each layer, then pressed the whole pile down to, hopefully squeeze and fuse all the clay together.

I soaked the sticks in hot water first hoping they would swell up enough so when it all dries out the sticks might shrink enough to pull out. Otherwise I guess I'll have to use the "lost wood" technique. With my luck the wood will just pyrolize from lack of oxygen and still not come out, but, making some progress anyway.

I've let the displacer sit on a shelf to dry very slowly, loosely covered with plastic in a effort to avoid cracking, but things are not looking great so far.

Several cracks formed along the edges of the wooden slats already and I've had to re-wet the clay and try to repair them, flip it over and repair the other side, then let the drying continue.

My hope was that by wetting the wood it would swell, then shrink as the clay dried, however the clay appears to still be shrinking more than the wood and pulling apart at the edges.

I see it as unlikely at this point that the problem will go away as drying continues, no matter how slowly.

Also there is no doubt numerous internal cracks which cannot be reached for any repair.

Is there some material that swells when wet, that could be used for making voids and that also shrinks while drying, at least as much as the clay? I'm thinking along the lines of cylindrical shaped Orbies. Is there such a thing?

Maybe clay itself rolled into "strings" ? Then how to keep it all from just sticking together.

I don't have a good solution to this at the moment.

Tom, you may look into concrete plasticizer. It is designed to make concrete flow better with less water. In concrete, too much water reduces the strength due to the water separating particles and then drying up and leaving voids.

Also, have you done any research on Starlite? Or at least the modern take on it developed by NightHawkinLight? It might make an excellent light weight high temperature displacer. The rough carbon surface of flame cured Starlite may also make a great built in regenerator. And if all else fails you end up with a tasty snack.

VincentG wrote: ↑Fri Apr 07, 2023 7:51 am Tom, you may look into concrete plasticizer. It is designed to make concrete flow better with less water. In concrete, too much water reduces the strength due to the water separating particles and then drying up and leaving voids.

Also, have you done any research on Starlite? Or at least the modern take on it developed by NightHawkinLight? It might make an excellent light weight high temperature displacer. The rough carbon surface of flame cured Starlite may also make a great built in regenerator. And if all else fails you end up with a tasty snack.

In this case I'm trying to create voids, so I'm not sure how a plasticiser would help. I suspect it might also burn when heated?

The Starlight is interesting, but a displacer that swells and bubbles and turns black on the surface seems kind of messy.

I have an idea though. al dente pasta?

Tom, I don’t know if this relates to your pursuit, but Ive been looking at open-cell metal foam for a high-temp regenerative displacer. Anyway I happened on this site which has some interesting links and data: https://ergaerospace.com/metal-foam-material/

Bumpkin

Bumpkin wrote: ↑Fri Apr 07, 2023 9:17 am Tom, I don’t know if this relates to your pursuit, but Ive been looking at open-cell metal foam for a high-temp regenerative displacer. Anyway I happened on this site which has some interesting links and data: https://ergaerospace.com/metal-foam-material/

Bumpkin

Thanks,

The criss cross stir stick method is not working on multiple levels (or layers)


Though, I still have some hopes for the spaghetti method.

I'm wondering if it might work with the spaghetti noodles all tangled in a ball or cylinder for larger displacers. First I guess I need to find out if it works at all.

While browsing the pasta isle at the grocery store, I came across this stuff:


I thought this Bucatini stuff could be ideal.

Since it is hollow, it might allow some air passage and dry from the inside out, pulling away from the clay in the process, even before the clay dries. It should then, if anything, maybe pull the clay together tighter rather than splitting it apart.

High hopes. Worth a try anyway.