Thermal insulating materials suitable for making piston and cylinder?

[The Bill]

TL;DR Summary

Materials suitable for a cylinder and piston that is thermally insulating, reasonably durable for low speeds + very slow cycle rate, not a polymer.

What materials would be suitable for a cylinder and piston that is thermally insulating, reasonably durable for low speeds and very slow cycle rates, and not be a carbon or silicon based polymer?

I've been looking at manual lever operated espresso machines lately. Particularly ones that are standalone with no electrical components. You pour hot water into the brew chamber/cylinder and use a lever and piston or a piston air pump to press it through the coffee grounds. The pistons and cylinders are usually thick aluminum or steel, which require a lot of what coffee people call "thermal management" i.e. preheating once or twice with boiling water just before use. There are some which use a polymer piston and cylinder and thus can go without preheating, but some people prefer not to have anything like that touch any hot food or beverage they consume.

There is one which uses a thin wall metal cylinder with an air gap around it which does benefit a little from preheating but can work okay without it. Probably not as good as the polymer ones, but it also doesn't suck enough heat away from the water to ruin light roast brews the way the other metal cylinders do if not preheated. Unfortunately, that particular device (the Cafelat Robot) isn't the most comfortable to use and doesn't have the best workflow.

A typical example of a heavy walled metal cylinder is any of the Flair espresso makers. A polymer example is the Wacaco Nanopresso handheld espresso maker.

So, I was wondering if there are any ceramics, etc. which would be suitable for an application like this. Typical pressures for espresso are 6 to 9 bar in the brew chamber, so being able to safely handle say, 15 or 20 bars just after the thermal shock of adding boiling water to a room temperature cylinder should give a decent safety margin. I'm betting that there isn't anything that would be cost effective and easy to work with, or there would probably be a device using it already, but I'm prepared to be surprised. Maybe there's a coating for, say, aluminum which would be a "good enough" solution?

 

[jrmichler]

Take a look at Airpot cylinders:https://www.airpot.com/product-category/product-lines/piston-cylinder-sets/: Airpot’s borosilicate glass cylinder and graphite piston material technology which allows the use of extremely tight tolerances to achieve a high precision fit and control of leak while offering a seal-less, self -lubricating

They market them for pneumatic applications. I do not know if they will work with hot liquids, so you would have to find that out for yourself.

 

[Baluncore]

It seems counterintuitive, but thin-sheet stainless-steel has relatively little thermal transfer. Combine the material and the construction as used in “double wall” “stainless steel” cups.

 

[The Bill]

It seems counterintuitive, but thin-sheet stainless-steel has relatively little thermal transfer. Combine the material and the construction as used in “double wall” “stainless steel” cups.

So maybe if they used a thin stainless liner protected by a carefully chosen polymer/composite sleeve?

The Cafelat Robot I mentioned above is pretty close. With a thin metal shell and an air gap. It just doesn't have the easiest workflow based on its design. If someone were to make something like the Rok GC or Flair 58 but with a cylinder that doesn't need so much preheating, they might have a real winner.

To clarify, the Rok GC and the Flair 58 have portafilters (filter basket holders) that work like the ones on commercial espresso machines, with a big handle for locking them in, and, well, handling them. It makes them much easier to fill, lock in, knock the used coffee grounds out for cleaning, etc.


I guess it's just like lots of other tool based industries that aren't most of a century old or older. There are lots of nice features, but no one puts all the best features in their product yet. Maybe some of it is cross-protected and fenced off by intellectual property, not sure.

 

[Baluncore]

There are lots of nice features, but no one puts all the best features in their product yet.

Every product ever manufactured and sold can only ever be "third best".
"Second best" will be the next generation, once more of the problems are fixed.
"Best" is perfect, and can never be.
https://en.wikipedia.org/wiki/Perfect_is_the_enemy_of_good

 

[Astronuc]

It seems counterintuitive, but thin-sheet stainless-steel has relatively little thermal transfer. Combine the material and the construction as used in “double wall” “stainless steel” cups.

That's primarily because the air has lower thermal conductivity than metal (stainless steel), and even better insulation is obtained from a vacuum. Conduction through the main surface area would be minimal, and heat would have to be conducted toward the ends. So a hollow piston head would ideal. A metal surface can be oxidized, and one could coat the piston surface with an oxide, or a metal that can be oxidized (to about 1 to 2 microns). The oxide would need to be tolerant of the pH of the contact fluid, if aqueous, or other chemistries according to whatever fluid is in contact. If one uses a stainless steel, best to use a ferritic stainless steel (low Ni) with low thermal expansion coefficient. Otherwise, one could use an alloy of Ti, which has low thermal expansion.

 

[Matcon]

Many years ago (>30), plasma-sprayed zirconia was touted as a material for internal combustion engines. At first blush, that should meet operational requirements.

I'm no longer up to date with progress in that technology but there is most likely something better in the same field