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I am investigating various fluid power compounds for use at high temperatures. I am seeking a material that is liquid around room temperature, or melts at under 300 C, but that remains a stable liquid up to 1000-1500 C. And also not have issues with being at 1000 psi The first obvious candidate might be molten salts. But these cap out below 1500 C and are obviously not liquid at room temperature. Is there any compound that is stable as a liquid across 20-1500 C at 1000 psi?.

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    $\begingroup$ what about gallium or one of its alloys? $\endgroup$
    – porphyrin
    May 15 at 14:52
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    $\begingroup$ Yeah Galliums ability to digest other metals kind of eliminated it for me. Are there any other compounds? $\endgroup$
    – Austin Fox
    May 15 at 16:00
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    $\begingroup$ Could you please refine the lowest temperature point? You say "room temperature", "under 300 °C" and also starting from "across 20 °C", which is rather imprecise/conflicting. If you are OK with lower point of 125 °C, then LBE appears optimal. $\endgroup$
    – andselisk
    May 15 at 16:28
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    $\begingroup$ Ideally, this compound would be liquid at room temperature, at 1000 psi, and remain a stable liquid up to 1000 C at 1000 psi. However I was not able to find many materials with this span, so I am able to compromise on a higher melting point up to 300 C. Sorry for my ambiguity and lack of clarity. $\endgroup$
    – Austin Fox
    May 15 at 17:04
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    $\begingroup$ @OscarLanzi I probably will if OP is OK with the temperature range for LBE (Austin, no, LBE is not Be(l), please click the underlined text — it is a hyperlink). I just don't want to post the answer based solely on Wikipedia: there are several relevant publications in Russian as to how to deal with corrosion since LBE has been and still is extensively used for nuclear reactors here. If this would be a miss, I'd prefer not to waste time on translation and adaptation. $\endgroup$
    – andselisk
    May 15 at 21:39

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Here are the figures for gallium, from Wikipedia:

Melting point: 302.9146 K ​(29.7646 °C, ​85.5763 °F)

Boiling point: 2676 K ​(2403 °C, ​4357 °F)[1][2]

It is mentioned in comments that hot gallium could destroy container materials. But this is a risk with any hot liquid. Gallium oxide, $\ce{Ga2O3}$, does have a substantially less negative heat of formation per mole of oxygen than alumina or magnesia, so refractories based on the latter ceramics appear (at first sight) to be plausible candidates for avoiding attack by gallium at least through chemical reaction.

Cited References

  1. Zhang Y; Evans JRG; Zhang S (2011). "Corrected Values for Boiling Points and Enthalpies of Vaporization of Elements in Handbooks". J. Chem. Eng. Data. 56 (2): 328–337. doi:10.1021/je1011086.

  2. "Gallium (CAS Number 7440-55-3) : Strem Product Catalog". Strem Chemicals Inc. Retrieved 4 December 2023.

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  • $\begingroup$ The use of ceramics is reasonable -- but the issue I raised in the comment above is that even at room temperature (well, a warm room), Ga attacks some metals. Plumbing a high-temp system with ceramics might be difficult. $\endgroup$ May 15 at 19:49
  • $\begingroup$ @DrMoishePippik you may nedd to use specialized pipes consisting of a resistant material claddedcibside a metal, for any fluid at all in this application. $\endgroup$ May 15 at 20:06
  • $\begingroup$ For my application, I feel ceramics will be too fragile and expensive. Additionally the risk of gallium damage to metal components is too great. $\endgroup$
    – Austin Fox
    May 15 at 21:46

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