Considering $\rm CO_2$ snow on Mars and recent cold temperature on the earths' south pole, I am looking for a $\rm CO_2$ phase diagram below 1 millibar that shows the sublimation temperature of $\rm CO_2$ for $\rm CO_2$ partial pressure in earths atmosphere, (i.e. 0.4 millibar).

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  • $\begingroup$ The lowest I found was 0.001 atm. That is why I asked. researchgate reference even stops at 0.01 atm. $\endgroup$
    – Hans Erren
    Jun 24 at 10:55
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    $\begingroup$ @Farcher - indeed, the J. Phys. Chem. Ref. reference in one of the answers has the answer. A complicated answer, but the answer nonetheless. $\endgroup$
    – Jon Custer
    Jun 24 at 13:42
  • $\begingroup$ Jon that reference is behind a paywal: so in theory, yes, a good answer, however, in practise it isn't if you just need a phase diagram and you are not affiliated to an institute with a journal subscription. $\endgroup$
    – Hans Erren
    Jun 25 at 4:42

Found this formula from Giauque & Egan (1937) for the sublimation part of the Phase diagram: p in atm, T in Kelvin. p=0.0131579 * 10^(-(1354.210/T)+8.69903+0.001588T-(4.510710^-6)*T^2)

Plotted here from -170 to -56 deg °C and 1ppm to 10 bar CO2 CO2 phase diagram between 1 ppm and 10 bar and -170 °C and -56 °C

https://en.wikipedia.org/wiki/File:Carbon_Dioxide_sublimation_curve.png Using Giauque, W.F.; Egan, C.J., Carbon Dioxide. The Heat Capacity and Vapor Pressure of the Solid. The Heat of Sublimation. Thermodynamic and Spectroscopic Values of the Entropy, J. Chem. Phys., 1937, 5, 1, 45-54, https://doi.org/10.1063/1.1749929 (strictly only valid from 154.26K to 195.89K)

Original Giauque-Egan pressure is in centimeter of mercury, conversion to kPa is 1.333224, divide by 101.325 to get atm, rounded to six significant places according to NIST: 0.0131579, temperature is in Kelvin: convert to degrees Celsius using °C = T -273.15

Alternative formula (NIST):
p = 10^ (6.81228 − (1301.67 / (T -3.494))) (p in bar, T in Kelvin)


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