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What happens when you try to lower the pressure of an alcohol-water mixture below the triple point of water? To give a specific example, the freezing temperature of a 50-50 (by mass) ethanol-water mixture is approximatley -38°C. This is obviously well below the triple point temperature of pure water (0°C), but what happens if you try to reduce the pressure of this mixture to somewhere below the triple point pressure of pure water (611 Pa). Will the water in the mixture start to freeze as soon as you drop below the triple point or will the point at which freezing occurs be reduced by the alcohol in the mixture?

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    $\begingroup$ It is the latter. $\endgroup$ – Ivan Neretin Mar 1 '18 at 21:24
  • $\begingroup$ @IvanNeretin Thanks for the reply. Do you know of any place where I could find more information on this? Specifically, I'm looking for (or to construct on my own ) a phase diagram at fixed mixture showing the various phase transition regions i.e. boiling, freezing, sublimation, and any regions in which there are mixtures of multiple phases. Essentially the binary mixture equivalent of a standard single component pressure-temperature phase diagram. $\endgroup$ – Derek Paxson Mar 2 '18 at 21:46
  • $\begingroup$ en.wikipedia.org/wiki/Phase_diagram#Binary_mixtures $\endgroup$ – Ivan Neretin Mar 3 '18 at 1:49
  • $\begingroup$ @IvanNeretin Thanks for the link, but it doesn't really help. I'm familiar with boiling point diagrams and binary phase diagrams, however these both have concentration as one of the variables and also only deal with a single phase change e.g. liquid-vapor or solid liquid. I'm looking for a pressure temp plot with the liquid, vapor, and solid states at a fixed concentration. Something like a p-T slice of figure 13.7 here including freezing data. I can generate all the liquid/vapor points with refprop, but I need a source for pressure dependent freezing data. $\endgroup$ – Derek Paxson Mar 5 '18 at 17:45

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