another displacer material--aerogel.

[vile_fly]

Has anyone had an opportunity to try out a silica aerogel as a displacer piston or heat shield? Some people say it can be homemade from a recipe, but I don't keep those rare materials around the house. The fragile nature of the substance may be prohibitive, but I have no experience with such materials, and was wondering if anyone has such experience. I just wish it wasn't so expensive.

[speedless]

Hi
Take a look at "OASIS".
Very fragile , dusty and easy to form.
It works very well on my LTDs
Not suitable for hi temp though.
Jan

Pics.
http://s280.photobucket.com/albums/kk18 ... /Stirling/

[David Morrow]

A good web site on aerogel : Aerogel.org

[vile_fly]

The reason for posting the question is that I DID go to that site first. Sure is a lot of trouble and expense to make your own aerogel, though. I haven't got that kind of time to spare, and I don't have a chemical hood with the required safety precautions. I'll end up poisoning myself to death. I tried to obtain a space shuttle tile, though.....but they are only sold to education institutions under government license. Aerogel seems to be a controlled substance these days. As is metal foam material. No one wants you to build anything anymore, it seems.

[Ian S C]

Vile Fly, did you actually try NASA, they take an interest in hot air, and Stirling Engines. Ian S C

[vile_fly]

The NASA website is how I found out about the space shuttle tiles for sale. Unfortunately, I had to be a teaching institution in order to buy a 2" x 2" square section of a tile for the bargain price of $220.00. Not such a great deal after all.....because I am cheap. Anyways, that sale was about a year ago. None are left.

[vile_fly]

Well, I decided to renew my search and found a site that sells hydrophobic aerogel as well as hydrophillic aerogel. hydrophobic is preferred, by the way.
The site is http://www.buyaerogel.com/
one disk is 26mm x 7mm
another is 1.5cm x 1cm
the hydrophobic disc is 26mm x 4mm.
They have other great aerogel based products for sale, too.
Remember, aerogel is to be treated like glass, so careful when machining it...the dust is quite bad for you.
None of these samples are the size or cost I am looking for. I would have to design an engine around the sample sizes. Not sure if epoxy sticks to it or not.
All the other sites I have found sell aerogel in granular form.....most disappointing.

[Ferraccio]

I found very good material: is Rescor 740.
Is very hot resistant: 1250 celsius degrees, quite good mechanical performance, very light (0.65 kg/dm3) , is a cold-casting foam.
I suppose is expensive, I think was the used for the Space Shuttle tiles.
Is commercialized, perhaps is small quantities.
Ferraccio

[Ferraccio]

about material:
http://www.cotronics.com/catalog/59%20%20740.pdf

Ferraccio

[vile_fly]

Thanks for the link, Ferraccio. These newer ceramic materials are better than what I had found, and priced better, too. The idea of casting foam ceramic is very appealing, and cost effective.
The boron nitride lubricant that Cotronics.com sells also caught my eye.

1500°F Boron Nitride Spray on Coating and Lubricant
"Rescor 112 has excellent electrical insulation, high thermal conductivity and is a superior high temp lubricant. It is inert to most molten metals, glasses and salts and can be used continuously to 1500°F in air and to 3600°F in an inert atmosphere.
This unique combination makes for an ideal high temp. lubricant, mold release and electrically resistant coating. Applications include mold release, lubricant, barrier layer and as an anti-splatter compound."

[Ferraccio]

Very well: attention vile fly!
You're falling directly and easily in a high performance engine, and high technology ....;-)
Rescor 740 can be worked (filed, machined, drilled and milled),
There are other Rescor ceramics, cold moldable, solid, very high high features, with (instead) good thermal conduction.
Ceramic materials and not-oil lubricant are THE condition to make an high performance engine, pressurized.
Very well!
This is an important turning point, thanks for your indication on lubricant.
Ferraccio

[Ferraccio]

Really i think that Rescor 740 was used for the thermal insulating of the Space Shuttle (the tiles that protected the "belly" of the vehicle from the heat).
Ferraccio

[butchwright]

How well would steel wool lightly sprayed with sodium silicate and allowed to dry work as a displacer?

[Ferraccio]

Should be a "composite material", ....for so not so easy to do; stainless steel is however heavy, and thermal conductor, both not wanted in displacer.
There are few limits for temperatures.
Rescor 740 is good if it is enough "not permeable" to gases, in small thickness, or if it can easily make proof.
Ferraccio