Talk:Phase diagram

Don't chemists use the term phase diagram for the P-T diagrams showing the lines of equilibium (and the triple point) between eg solid, liquid and gas phases of a pure substance? Linuxlad 22:54, 18 Feb 2005 (UTC)

I have written two lines here on the physico-chemical use. I would prefer that this thermodynamical aspect was associated with 'phase diagram' and that the space of dynamical variables was called 'phase space' (phase space currently redirects here). We already have stuff being added to Liouville's theorem (Hamiltonian) which better belongs in a phase space article IMHO Linuxlad 12:33, 19 Feb 2005 (UTC)

Iron/Carbon system - I've written to Longman's to ask if the phase diagram quoted by W J Moore (in 'Physical Chemistry' fig 5.24 IIRC) is useable.Linuxlad 14:28, 26 Mar 2005 (UTC)
 * I now have permission from Pearson to include this. Linuxlad 22:00, 23 May 2005 (UTC)

More diagrams
I think we should add a stie that have more than allows. Like ammonia, nitrogen and such
 * I have discussed and added a binary boiling point diagram to this article. I think it would be a good idea also to add the following for a single (pure) component:
 * Temperature vs. specific volume diagram with isobars showing constant pressure
 * A 3D diagram of Pressure (P), specific volume (v), and Temperature (T). I will modify one from the French Wikipedia and insert it into this article.
 * This is helpful when covering equation of state relating P, v, and T. H Padleckas 06:55, 11 August 2007 (UTC)
 * Here are some 3D PvT phase diagrams from WikiCommons (The right hand one is apparently for water.): H Padleckas (talk) 02:06, 15 February 2011 (UTC)


 * The 3D phase diagram [presently in the article] needs correcting. All occurrences of liquid appear to be misspelled Ariakalea (talk) 06:30, 11 February 2011 (UTC)
 * I will reproduce Ariakalea's comment at the bottom and reply. H Padleckas (talk) 05:19, 13 February 2011 (UTC)
 * Temperature vs. specific entropy diagram with isobars showing constant pressure
 * This is helpful for explaining Refrigeration cycle, Carnot cycle, and Rankine cycle.
 * H Padleckas 06:55, 11 August 2007 (UTC)

I would like to draw attention to my papers in the Journal of Chemical Education on the current topic, which include authentic 3D phase diagrams for CO2, H2O and NH3: Glasser, L. “Equations of State and Phase Diagrams”, J. Chem. Educ., 2002, 79, 874-6. (CO2)

Glasser, L. “Water, Water Everywhere: Phase Diagrams of Ordinary Water Substance”, J. Chem. Educ., 2004, 81, 414-8; 645. (H2O)

Herraéz, A.; Hanson, R. M.; Glasser, L. (Letter to Editor) “Interactive 3D Phase Diagrams using Jmol”, J. Chem. Educ., 2009, 86(5), 566

Glasser, L. “Equations of State and Phase Diagrams of Ammonia”, J. Chem. Educ., 2009, 86, 1457-8; 645. (NH3)

Ciccioli, A.; Glasser, L. “Complexities of One-Component Phase Diagrams”, J. Chem. Educ., 2011, 88, 586-591.

Leslie Glasser (leslieglasser@yahoo.co.uk)  — Preceding unsigned comment added by 2403:3B00:401:442:D5CF:B0AB:E08:1A5A (talk) 03:43, 19 May 2014 (UTC)

Phase Diagram ≠ Binary Phase Diagram
When people talk about phase diagrams they usually mean Pressure on the ordinate, T on the abscissa, for one particular material. When talking about binary phase diagrams, two different materials (usually pure metals) are mixed on a continuum in the abscissa, with T on the ordinate. Currently Binary phase diagram links to this page, when it actually needs its own. Riceplaytexas 07:09, 13 January 2007 (UTC)


 * I disagree with you on this point. In my experience, people use "Phase diagram" about both P-T diagrams, binary and ternary phase diagrams. This is just my personal experience though, it may be that it is different from field to field, university to university, or country to country. Dr bab 07:51, 25 April 2007 (UTC)

I've reset some of the redirects to the binary phase diagram sectionRiceplaytexas 07:28, 13 January 2007 (UTC)

Ternary phase diagrams
This article needs something on the ternary diagrams as well. I will start to look into it. However, it is difficult to explain 3D diagrams without good figures. Anyone have any good figures that are free to use? Dr bab 08:24, 25 April 2007 (UTC)
 * I once tried to make a raster picture of a 2D triangular base for a ternary diagram. It did not come out looking very good, and I did not finish it.  One of these years when I feel really ambitious, I may try to make a ternary composition 2D triangular base again using Inkscape to make it in an *.svg format.  H Padleckas 23:41, 11 August 2007 (UTC)
 * I was finally able to make a better *.png image of the 2D triangular base mentioned above, which I sent to Pckilgore by private e-mail. Based on that, he made the *.svg diagram shown below.  H Padleckas (talk) 11:49, 25 November 2007 (UTC)


 * A draft for the section:


 * With three components present, it is common to display the composition on a triangle ABC, and then use an axis perpendicular to this triangle for an external variable, such as temperature or pressure. The composition at the corners of the triangle corresponds to the pure A, B and C components. Along the three edges, composition varies from pure A to pure B, from pure B to pure C and from pure C to pure B. All lines that are parallel to the A-B edge of the triangle represent a constant composition with respect to C. Likewise, the fractions of A and B are constant on lines parallel to the BC and AC lines respectively.


 * When more than two components are considered, the number of dimensions makes the graphical representation difficult. Either, a three dimensional diagram must be drawn, or one variable must be kept constant. It is common to draw ternary phase diagrams at a constant temperature and pressure, in order to be able to draw a two-dimensional diagram. Such a diagram will show how the phases of the system changes with composition at a given temperature and pressure. —The preceding unsigned comment was added by Dr bab (talk • contribs) 14:03, 25 April 2007 (UTC).

Ccwillis 07:47, 7 August 2007 (UTC)Except the isothermal or isobaric section with fixxed temperature and pressure, there is another section called vertical section or isopleth, at which the fraction of one component or the content ratio of two components is fixxed,while the temperature or pressure is variable.

I feel a discussion of nodes, the plait point, and tie lines of a three component ternary phase diagram is also relevant, considering a surprising lack of information available on the internet and even in textbooks. I'll try to put something together when I have some free time but feel free to beat me to the punch. What should be fairly easy is a 2D triangular base, I can make a svg version and upload for others to play with. Pckilgore 03:50, 7 November 2007 (UTC)

--Pckilgore 04:57, 7 November 2007 (UTC)


 * Pckilgore, I see a flaw in your diagram above. I also have other suggestions corrected.  We can work together to develop these diagrams.  Please see a message I left on your talk page.  H Padleckas 04:24, 14 November 2007 (UTC)

Pxy Phase Diagram
Hi can someone help me with Pxy diagram. Is the pressure axis referring to total pressure or the partial pressure of the components? Thanks

solid to plasma transition
In the table of transitions plasma is reached only from gas/fluid. But this is not so obvious from the P-T diagram - there it seems that if P is high enough maybe solid-to-plasma transition can occur. It is not very clear, because plasma is not shown on the P-T diagram. So, we should either mention solid-to-plasma or change the P-T diagram so that it shows a negative slope on the solid/liquid line after some point so that there is no solid-to-plasma. In either case the plasma phase should be added to the P-T diagram. Alinor (talk) 17:50, 4 October 2009 (UTC)

Vapour and gas interchanged
There is a problem with the first diagram for one component in two dimensions. The regions labelled "superheated vapour" and "gaseous phase" should be interchanged. A vapour is defined as a gas which is below its critical temperature, so the region T > Tc cannot be described as a vapour and should simply be labelled "gas". The low-T region can be described as "vapour", though "vapour (gas)" would probably be better, since the vapour phase is physically a gas.

As for the word "superheated", this term is used mostly for steam (water), for which superheated steam is steam above the normal boiling point. This is not really a useful term to explain phase diagrams and should be omitted.

This problem was noted on 27 January 2010 in the Gibbs' phase rule article which uses the same diagram. As far as I can figure out, the diagram was originally drawn by an editor who is now inactive. Can someone please redraw the diagram and label it correctly? Dirac66 (talk) 03:02, 2 February 2010 (UTC)


 * You are talking about File:Phase-diag2.svg, right? The explanation of the image on it's description page says it's for water, therefore it is currently correct, I think. I'm not sure I completely follow what you are trying to say. If you can accurately explain what is should be I can fix it for you. Wizard191 (talk) 13:58, 2 February 2010 (UTC)


 * Thanks. Yes, you have the right file. The required changes to the diagram are (1) change the label "superheated vapour" to "gas phase" and (2) change the label "gaseous phase" to "vapour". The reason is that vapour is defined as a gas below the critical temperature, not above as in the present diagram. Dirac66 (talk) 15:10, 5 February 2010 (UTC)


 * Done! Wizard191 (talk) 17:32, 5 February 2010 (UTC)


 * Thank you - the diagram is now more accurately labelled. And a note to others who read this - if like me you don't see the change at first, try renewing the cache (F5 on a PC) where your computer stores the old version. Dirac66 (talk) 20:27, 5 February 2010 (UTC)

I am also talking about the same phase diagram: gas and vapor are not distinct phases but are defined with respect to the critical point. However, the dotted black lines are not part of the phase diagram and should be clearly mentioned as such.

Also; the green line is not on the same scale. What is the dotted green line? Please label the region between the solid green and dotted green (lines). Also worth mentioning that there are several forms of solid (ice) and some of them are actually heavier than water (liquid).

To Dirac66: Any liquid can be superheated (unstable; not in equilibrium with gas and therefore does not show in regular phase diagram plots) and any gas or vapor can be similarly superheated. I agree that the concept is useless and best discarded. But dry and wet steam (reasonable concepts) are widely used and sometimes (interchangeably) called (mistakenly) superheated steam (vapor). chami 15:50, 10 May 2010 (UTC) —Preceding unsigned comment added by Ck.mitra (talk • contribs)

One component 3D phase diagram changes

 * Reproduced from above:

The 3D phase diagram needs correcting. All occurrences of liquid appear to be misspelled Ariakalea (talk) 06:30, 11 February 2011 (UTC)


 * I agree that correcting the spelling of "Liquid" is needed for that diagram. I can make am working on making corrections to that image.  While I'm at it, I would like to make the following changes to this diagram:
 * correcting spelling of "Liquid"
 * changing "Volume" to "Specific volume", which is how such diagrams are usually shown for a given compound
 * eliminating the rather confusing isotherms from the diagram
 * delete the "pedestal" (base) from the bottom, which might be nice and aesthetic-looking for an actual model but has no scientific or explanatory benefit in the diagram
 * The following change would also be good:
 * shading or coloring of the phase surfaces, perhaps with different colors for each of the phases

If anybody has any comments on these ideas, let me know. H Padleckas (talk) 05:35, 13 February 2011 (UTC)


 * I agree with 4 of 5 suggestions, but I would retain the isotherms. I think the detailed shape of the diagram would be harder to see (understand) if all the isotherms were eliminated. Of course, if you see a way to draw isotherms which are less confusing, I have no objection.
 * Changing volume to specific volume is a good idea which will make the diagram more general. Then the legend will not have to specify "for fixed amount". Dirac66 (talk) 17:23, 13 February 2011 (UTC)


 * I have not started any work on the isotherms, the "pedestal", or the surfaces yet. Presently all the lines/curves in the 3D diagram are colored blue.  To keep the isotherms, but make them less confusing with the other lines, the isotherms or the other lines can be given a different color to distinguish them.  H Padleckas (talk) 03:58, 14 February 2011 (UTC)
 * Yes, a color difference would help. Dirac66 (talk) 13:09, 14 February 2011 (UTC)


 * I have made the first two corrections listed above so far (correcting spelling of "Liquid" and changing to "Specific volume") and re-uploaded the revised file. I have not yet made the other changes mentioned above.  It will likely take me a while to make those.  However, one may look at two other 3D single-component PvT diagrams shown above as candidates for inclusion in this article.  H Padleckas (talk) 02:18, 15 February 2011 (UTC)
 * OK so far. I suggest doing the other changes one at a time, since changing the drawing is more difficult to get right than changing words. Dirac66 (talk) 03:09, 15 February 2011 (UTC)
 * I've eliminated the "pedestal" (base) and re-uploaded again. To recolor the lines/isotherms, it must be determined whether the isotherms or the other lines should have their color changed, and also the new color.  A possibility is for the isotherms to retain a blue color and the other lines darkened to a blackish color.  I am thinking of eliminating the dots on that one isotherm with dots, such that the only remaining dot would be the critical point.  After that might come the most difficult part, adding shading/color to the surfaces.  The colors have to be decided for those.  I am considering a diagonal checkerboard pattern on surfaces where there are two phases.  The single phase surfaces would get only one color but with shading for a 3D effect.  This may take me quite a while to do.  H Padleckas (talk) 05:11, 16 February 2011 (UTC)
 * I have been reconsidering this as the isotherms are rather confusing. I have also been examining the two diagrams above in the section More diagrams. The multicolored one confuses me, but the black and white one without isotherms is actually easier to understand than the one in the article. Perhaps it would be better to forget the isotherms and use that one. We would have to point out in the text though that water is a special system in that the solid volume is larger than the liquid. Dirac66 (talk) 03:26, 18 February 2011 (UTC)

The black and white one doesn't show any variations in ice structural density and implies that liquid water is incompressible.WFPM (talk) 23:41, 21 February 2011 (UTC)
 * Liquid water is almost incompressible. When ice is compressed under a certain range of conditions, it converts to liquid water.  Other than such phase changes, solids are almost incompressible also.  H Padleckas (talk) 06:36, 22 February 2011 (UTC)

And I'd like to see one on 6C12 to use in connection with Hazen's book "the Alchemists" about the diamond.WFPM (talk) 23:50, 21 February 2011 (UTC)
 * What is 6C12 ? The C-12 isotope of carbon ??  H Padleckas (talk) 06:36, 22 February 2011 (UTC)

Yes. Except Hazen wrote a nice book about how diamonds can be made out of Peanut Butter etc and has a Phase diagram with triple point et al. and discusses unit cell structure and graphite etc. So 3D phase diagram might be interesting.WFPM (talk) 11:36, 22 February 2011 (UTC) I missed an IQ test question in college because I wasn't supposed to know that water was compressible. Still sore spot with me.WFPM (talk) 11:42, 22 February 2011 (UTC)

One diagram for high-pressure ice is enough
To Wizard 191: I think you were too quick to revert the edit by 86.16.21.74 as "vandalism". Yes, this editor deleted a whole diagram without explanation in the edit summary. However the section Crystal phase diagrams now contains two very similar diagrams both showing the phases of high-pressure phases of ice as a function of log P and T, so I think 86.16.21.74 was justified in deleting the less aesthetic version. Please revert your edit and delete this diagram again.Dirac66 (talk) 19:20, 24 May 2011 (UTC)


 * Materialscientist already reverted me. I didn't realize there were two similar images, but the edit looked like vandalism so I reverted it. Sorry about that. Wizard191 (talk) 16:10, 25 May 2011 (UTC)
 * Actually, those deletions almost tripped me to revert too, and I went looking for the duplicates of this diagram and got here. IP edits w/o edit summaries are a nuisance. Materialscientist (talk) 00:49, 26 May 2011 (UTC)

The Phase Diagram of water.
This diagram currently attributed to Cmglee is derivative of phase diagrams on my website over the years and should reference this website http://www1.lsbu.ac.uk/water/water_phase_diagram.html81.157.18.224 (talk) 12:00, 30 June 2015 (UTC)Martin Chaplin


 * I think you mean the one in the section Crystal phase diagrams which has crystalline phases up to Ice XI. Cmglee claims to have drawn the actual file which appears in Wikipedia, but not that the schema is entirely original. I would presume that similar diagrams can be found not only on your website, but also in some number of books or articles on the subject. Perhaps the simplest solution would be to add a note saying that "A similar diagram may be found on the site http://www1.lsbu.ac.uk/water/water_phase_diagram.html." Dirac66 (talk) 02:08, 1 July 2015 (UTC)

That would be acceptable. The figure is provably copied (redrawn) from my site. Cmglee only states that he got the data from my site (and also from a site that is a direct copy of my site) but the 'data' includes some of my my actual lines not just from the equations and triple points I provide from the literature. Even the Atkins figure he refers to is a 'copy' of an earlier version from my site. I do not believe that my diagram is a derivative of any phase diagrams in books or articles on the subject although I have often given permission for copying it so long as it is correctly cited.81.157.18.224 (talk) 15:33, 2 July 2015 (UTC) Martin Chaplin


 * OK, I have made the suggested addition to the figure title, and included the website title. Dirac66 (talk) 21:57, 2 July 2015 (UTC)

Typical phase diagram
There are, imho, lots of problems with this article (specifically in the earlier parts, I didn't read it in its entirety). Firstly, it seems to assume that the phases are of the thermodynamical variables P and T. In reality, as most here know, a phase diagram may indicate a variety of phases including composition or spin or a host of others. Secondly, in reading the article lede and overview, I'm still not sure what it is that a phase diagram is showing. For instance the text claims that the blue line in the first figure shows the 'boiling point' as a function of pressure. BUT typically the independent variable is on the x-axis (horizontal) so, the line would (to someone not ever having learned better) show the boiling point varying with Temperature. Maybe its "toe may toe" vs "tah mah toe", but isn't clear. The text CLAIMS that the lines mark the conditions which allow multiple phases to co-exist. This OBVIOUSLY implies that away from the lines, only ONE PHASE will exist. We know this just ain't so. For a P-T phase diagram, typically TWO phases will coexist (in most (many?) areas of a PT diagram). If I look up STP on the water p.d. I see water exists as vapor, supposedly. That would be real news to fish the world over. I actually came to this article looking to refresh my memory of what the various areas in a PT p.d. represent and man, did I NOT find anything intelligible! So, I'll either have to recreate what I learned about p.d.s in school those many decades ago and 'fix' the article myself, or rely on others to do it. At this point, I'm hoping someone else will jump in, since I'm just not clear enough about what these things are showing to express it in a simple way. They don't show "equilibrium" processes at all, rather they indicate the boundary lines, on ONE SIDE of at which, as either (2° diagram) variable CHANGES, and ONE phase MIGHT disappear. So two major issues: one - the lede and overview fail to inform a casual reader what the typical diagram is showing and the article confuses the reader by implying that only one phase exists at a given P and T. It also seems to confuse a reversible DYNAMIC system with a system at equilibrium. I also add that in a gravitational field (don't know where those don't exist, do you?) pressure/density can only approximately be uniform for a finite (say, macroscopic) volume. (this is a nit-pick, but should be made explicit somewhere in the article). I also don't at all agree that a Temperature-Entropy diagram (or a Pressure-enthalpy or entropy-enthalpy diagrams) are "PHASE" diagrams. Certainly the HUGE diagram of T-E is inappropriate here. (eg. ONLY liquid water exists 'to the left of the dome'???). If a diagram doesn't have phases in it, it isn't a phase diagram (the lower 3 diagrams "for steam" apparently are of a SINGLE phase? At the very least they add nothing to the intelligibility of the article, regardless if we have permission to use them. Simply because some diagram has two or more phases (of a material) indicated, DOESN'T make it a "phase diagram". [just like it isn't useful to describe any bus which happens to have a celebrity on board as a celebrity bus.]

First thing that needs doing is a clear, concise, simple, and USEFUL explanation for someone picking an arbitrary point on a diagram, either on or off a phase transition line, that clearly and simply explains how to interpret the p.d. for that point. 216.96.77.80 (talk) 20:20, 7 August 2015 (UTC)

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How are phase diagrams generated?
This page could be improved by the addition of a description of how phase diagrams are generated using modern methods and instrumentation. — Preceding unsigned comment added by 75.80.48.54 (talk) 16:41, 24 June 2021 (UTC)

Nitrogen ice
I had my comment that nitrogen ice floats in its liquid reverted because some reference claimed this happened at very high pressures only. Not true. I pumped on my dewar of LN2 to get my sample below 77K. I watched as small ice particles then large chunks formed floating on the surface. Then the whole surface froze, got thicker and eventually froze the entire dewar solid N2 - from top to bottom. I got down to 54K. I don’t have a reference - just experimental fact. Bscip (talk) 19:25, 25 August 2021 (UTC)


 * I agree that the observations you describe seems to be at much lower pressure than the results of Mukherjee and Boehler in their Physical Review Letter. But to appear in Wikipedia, your observation has to be supported by a published reference so we can be certain it has been observed and interpreted correctly, at least in the opinion of a journal referee. You might try checking the articles on solid nitrogen and liquid nitrogen to see if anyone has reported observations similar to yours. Dirac66 (talk) 01:12, 26 August 2021 (UTC)

This was almost 40 years ago while doing my dissertation research. The technique of pump-cooling, esp. LN2, is so common I assumed this phenomenon was well-known. When I showed my advisor and a couple other Solid State profs my dewar, they were surprised (and quite amused) to see the chunks of N2 floating - also amused to see the whole dewar freeze solid after a day or so. Unfortunately I did not mention it in my dissertation - it was a sidebar. You know, not every single detail in every article in Wikipedia is supported by published references. I just thought people might like to know. Bscip (talk) 20:55, 11 September 2021 (UTC)