Stirlingengineforum.com

FRP = Fiber reinforced polymer. It's a generic term for any combination of fibers and plastic to produce a composite.

Here's an example, although I'm sure you can find it elsewhere much cheaper.

Interesting about the mica, I look forward to hearing how it worked out.

Hi Tom,

My ex-wife have and ceramic oven like yours and also a so called "RAKU oven". It was a DIY kit and the isolation is
made from some white "wool like" stuff. It can easy handle app. 1260 Celcius.
See picture in bottom. :
https://www.raku.dk/post/montering-af-o ... -i-rakuovn
or
https://www.ildfastesten.dk/Bio-silikat ... 3-mm-1260C

BR Petter

Engineire,

Ok, that particular offering was a bit small size, but I found some 150mm square.

I'm pretty much trying anything and everything.

One thing I can report is that the stuff advertised as "ceramic fiber" board or paper made to use in kilns, to line the firebrick or some such, turned out to be pretty useless (as displacer material) Rather floppy and falls completely apart after being heated to red hot with a propane torch. It is also apparently impregnated with some binder or something that actually catches fire and burns and smolders and smells bad.

After the binder or whatever burns off it just falls apart like lint.

To be fair, propane burns about 1000° hotter than what the stuff is rated for: 2,300° F, but I expected more from something supposed to be "ceramic". (CeraTex 3170 Ceramic Fiber Paper) there are other brands/manufacturers of ceramic fiber board that is more expensive and may possibly be better, but this stuff wasn't exactly cheap.

This is the standard thickness "universal" cut to fit mica wave guide cover stuff pictured in the above video.

It arrived from Amazon amazingly fast. Like less than 48 hours I think

It is very thin, paper thin really. Not as thick or quite as rigid as what is in my microwave, but the heat survivability seems quite good IMO. Probably the best yet. Comparable to titanium as far as being able to heat it to white hot with a torch with only slight deformation.

After it cooled down for a while, after setting it aside, I could hardly tell it had been heated at all. The spot was difficult to find again, more so even than with the titanium. Just a slight discoloration, and slightly raised in the spot, but still, apparently as strong as before. At least I'm satisfied it could take anything it is likely to suffer as a displacer and remain functional


https://youtu.be/SQCxZ8XEMns


I'm sending for some thicker sheets from a different source on eBay to try. I think just a little thicker would be better, if it holds up as well.

It also did not produce any noticeable odor when heated.

I think there may be a silicone binder.

Reviewing my order for the thicker sheets of mica, it comes from China, and according to the shipping details will take another month or more to get here.

If this is just mica flakes with a silicone binder, manufactured under pressure, I might try making some, or even possibly using water glass as a binder.

By the time the nearly 2 months go by, ordering the stuff, it seems quite possible I could order the raw materials and make my own from scratch before the stuff from China gets here.

I've been pondering the question of how to make a light weight, high temperature ceramic displacer, for quite a while now.

I was thinking that ideally, if I could mix some solid substance with the clay that would later dissolve or evaporate away that would leave small pockets or voids as the clay dried or during firing, that would reduce the weight.

Crushed ice perhaps?

Put the clay in an ice box to get cold, mix with crushed ice, shape, let dry.

Cold clay, though would likely be difficult, if not impossible to work.

Then I came across a video about Sodium Polyacrylate. The absorbent powder used in diapers. It is non toxic and expands 500X when wet. When so expanded it does kind of resemble snow or crushed ice.

Maybe use that in it's expanded form. Mix with clay, shape, dry/fire.

I can't seem to find any information on what, if anything happens with this stuff when exposed to very high temperature, other than simply drying out. Does it remain inert/non toxic, burn up, evaporate or what?

At any rate, I would think, only 1/500 of the original weight of the stuff would be left upon drying/firing, as it is mostly water.

In some respects the process would be similar to how silica aerogel is made.

Anyway, rather than going to the supermarket to buy diapers to cut open, I just sent for some Sodium Polyacrylate powder from eBay. Overall, with free shipping, probably cheaper, considering the price of diapers, though it has been quite a while since I've needed to buy any of those, I doubt the price has gone down any.

I've also just now, finally found a source for large sheets of natural mica at what seems to be a reasonable price.


On Etsy: https://www.etsy.com/listing/801279926/ ... hare_v4_lx

About $7 / sheet (6 sheets for $40)

The description reads "thick" but actual thickness is not given. Perhaps this could be split into thinner sheets.

I believe natural mica should be even more heat proof than the appliance mica/silicone composite stuff, as well as having a better appearance.

I received the Sodium Polyacrylate powder from eBay. I put 1/4 teaspoon of the stuff into a bowl and added a coffee mug full of warm water and let it sit for about 20 minutes:
Seems to work as expected. Possibly less water would improve the consistency, making it a little more solid. Anyway, I'll see how it does mixed with clay.

I think, as it is, I've only used about maybe 1/2 the amount of water that the stuff is supposed to be able to absorb.

The "natural" mica arrived rather quickly. By comparison, the appliance stuff I'm still waiting for after nearly two months

Anyway this "natural" stuff is a bit of a disappointment. To start with, the size is advertised as shown above. The smallest dimension being 6".

There is only one piece that I might be able to get one full 6" circle out of for the Arsdell engine restoration. The rest, though in some cases oversize 11" one way are as narrow as about 3 useable inches in spots the other.

She shapes appear to be intentionally "irregular".

On a positive note, sort of, it is rather thick and should cleave easily.


Next, the real test, to see if it can really take the heat.

I might also mention that the amber color does not appear to be "natural", but looks like it has been brushed on, though I don't know as that is provable one way or the other.

Judge for yourself, but to me those color striations don't look natural:

This presents another interesting possibility for making porous ceramic high temperature displacers.


https://youtu.be/jfgO4aBF2A8


I can hardly wait to finish setting up my shop and getting the kiln going. Still more structural work to be done on the building though.

Another possibility?

"Just like bread, the ceramic dough literally rises in the kiln, expanding to about 300 percent of its original volume."

https://www.jorislaarman.com/work/foam-china/

While I have this Sodium Polyacrylate stuff sitting around not doing anything useful, until I get my kiln set up, I got an idea to try mixing it with some plaster of Paris.


https://youtu.be/MJaVRWxtjR0


Next, I guess I'll try mixing the pre-hydrated Sodium Polyacrylate with Portland Cement, and see how that works.

At first the Sodium Polyacrylate and plaster mix looked rather thick like cottage cheese, but apparently the plaster mixture absorbed some of the water out of the hydrated Sodium Polyacrylate and the mixture quickly became rather thin. I tried adding a little more dry plaster but probably stirred it too much. Anyway, I thought putting it in a warm oven might help it set up.

The pan is heat resistant, intended for warming tortillas and coated inside with cooking oil to hopefully prevent sticking.

As far as I can tell at this point, the method of using the Sodium Polyacrylate seems to be working well.

The plaster, once semi-dry popped out of the pan easily without any apparent shrinking or cracking and I could put it back in the oven, directly on the rack and turn the heat up full.

It has been throwing off a lot of steam for quite a long time already but seems to be nearly completely dry at this point.

I'm sure the plaster would not be as strong as porcelain fired in a kiln at much higher temperature but this is encouraging.

Probably I will sacrifice this would-be displacer so as to get an idea of the internal pore structure, assuming there is any. My hope is that the Sodium Polyacrylate globules did not completely dissolve into the mixture but dried away leaving numerous voids.

I've turned the plaster disk over a few times to help ensure that it dries very thoroughly, and, although handling it with oven mitts, as far as I could tell, it seems quite light.

I'm going to let it go ahead and cook in the oven for a while longer.

I can happily report that the experiment has been a great success:


If the aim had been to make some very soft, lightweight, chalk.

Much too fragile for use in a mighty Stirling engine though. The "pore structure" I was trying to achieve is virtually non-existent. The hydrated Sodium Polyacrylate globules did not maintain their structure with all that vigorous mixing.

Estelle upon watching the video, suggested "folding in" the mixture, without stirring, which I kind of did at first, for that initial cottage cheese like consistency, but it appeared that the globules broke down anyway and the mixture became thin and watery, prompting me to add more dry plaster.

It seems as though the water in the Sodium Polyacrylate has a greater affinity for the plaster so the plaster just draws all the moisture out of the globules almost immediately, before the plaster has time to set.

I imagine the results might be much the same using Portland cement, but I'll give it a go anyway, who knows? I'll try to "fold in" the mixture more carefully.