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Can a decent grade stainless steel preserved in a optimal environment last for trillions or gazillions of years? Or would it at some point ,eventually turn into dust or even smaller like into atoms.

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  • $\begingroup$ Define "decent"... $\endgroup$
    – Solar Mike
    Sep 30, 2023 at 19:54

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Depends on what you mean by optimal. In an inert gas like argon or helium, there may be no oxidation to speak of. Radioactive decay will eventually make it crumble. Over really long time scales neutrons will decay, and over really really long timescales, even the proton and all other matter might decay into photons. So you'd have a box of hot radiation. According to Poincaré, if you wait arbitrarily long after even that, you may end up with the stainless steel bar again!

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Let me start with a short digression.

For quite a while, the international standard for a kilogram was a small cylinder cast from an alloy of 90% (by mass) platinum and 10% iridium.

Platinum/iridium was chosen specifically because platinum they're noble metals, so it has minimal chemical interaction with the environment. They'r also extremely dense, allowing minimum surface area for a given mass. The alloy increases hardness, so to minimize (for example) mass loss due to abrasion.

There is an original standard plus 40 replicas be distributed around the world, all measured to be as close to identical as they could manage (a tolerance apparently something like 1 microgram).

Even though they're all stored extremely carefully (in a vault, under bell jars, kept clean) their mass has changed enough that there are now differences between them of up to around 50 micrograms.

Some of that is probably from things like adsorbing mercury from the air. Many of these are stored in buildings that have been used as national laboratories (or similar) for long enough that many almost certainly used to use mercury thermometers, some of which inevitably broke, so their air still contains higher than typical amounts of mercury vapor, which doesn't chemically combine with platinum, but does still bond to its surface strongly enough that it's difficult to remove.

Most stainless steel is considerably more prone to various chemical interactions with the environment than that. So it's going to depend even more on exactly how optimal that environment turns out to be. Just for example, one of the most difficult things to avoid is hydrogen. It's the most common element in the universe, and hydrogen molecules are so small that they're difficult to filter out of gasses, or seal out of containers. And as it happens, when steels (including stainless steels) are exposed to hydrogen, they tend to get brittle (generally called hydrogen embrittlement).

So, even in interstellar vacuum, your stainless steel will (slowly) be exposed to hydrogen, and get brittle. Exactly what happens then will vary though. If (for example) it's a simple sphere of stainless not being subjected to any stress or strain, it may remain intact despite getting brittle. On the other hand, if it has some structural purpose, it may fall apart relatively quickly.

Of course, hydrogen isn't the only thing that can cause a problem--but it is one of the most difficult to escape, even if you work really hard at optimizing the environment.

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In a vacuum, it would last forever (as in ~ billions of years). On earth, where there is oxygen and warm salt water, it would last hundreds of years.

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