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baric
2010-Nov-30, 08:11 PM
Does anyone know where this kind of data can be found? I did find a great source for vapor-pressure lines, but have had little luck with melting curves.

I understand that high-pressure melting data like this will not be as plentiful as the low-pressure vapor data, but any assistance would be greatly appreciated. My intentions are to compile as much of this public data as possible and package it into some kind of freeware analysis application.

John Jaksich
2010-Dec-02, 01:26 PM
Does anyone know where this kind of data can be found? I did find a great source for vapor-pressure lines, but have had little luck with melting curves.

I understand that high-pressure melting data like this will not be as plentiful as the low-pressure vapor data, but any assistance would be greatly appreciated. My intentions are to compile as much of this public data as possible and package it into some kind of freeware analysis application.


Baric--


I am surprised that no one responded---

There is a "so-called" rule of thumb that physical chemists use--it falls under the discipline of Thermodynamics (as you might guess) and the furher subdiscipline of what is known as colligative properties.

And there is a further caveat----normally are computed in instances where ---a pure substance does not dissolve into the "solvating" mixture---so in short: the substance that freezes does not become "readily" incorporated into the crystal matrix of the complete mixture.


It is not readily explainable!!! --or understandable?? The equations expositing my attempts are for the simplest mixtures of binary mixtures---i.e.

delta(T) = (N(a) * k * T^2) / delta(H -f)


where delta (T) is the change in temperature
N(a) ---Avogadro's constant, k---Boltzmann's constant, T^2--melting point of pure substance(to the second power), and delta(H -f) is the enthalpy of fusion for the pure substance

Data does exist --seek out trinitree88 or Swift--

Swift
2010-Dec-02, 02:20 PM
I'm not exactly sure what you mean by "melting curve" (there is a specialized technique in DNA analysis called a "melting curve"). Are you talking about how melting point changes with pressure or composition? If so, what you want to look for are "phase diagrams". And what kinds of compounds are you interested in?

baric
2010-Dec-02, 04:19 PM
I'm not exactly sure what you mean by "melting curve" (there is a specialized technique in DNA analysis called a "melting curve"). Are you talking about how melting point changes with pressure or composition? If so, what you want to look for are "phase diagrams". And what kinds of compounds are you interested in?

I'm not talking about the DNA techniques. I am trying to build accurate phase diagrams for a wide range of compounds. For the most part, all I am really looking for are the vapor-pressure line, which tracks from zero pressure to the critical point, and the melting curve (or melting line), which tracks from the triple point to higher pressures & temps. You may be surprised at how difficult it is to find phase diagrams online except for the most basic compounds (namely, H2O & CO2.. also He because it's special)

Fortunately, linear equations for modeling the vapor-pressure lines of a wide variety of compounds are readily available online. I am sure this has a lot to do with the lower pressures required to probe this boundary in a testing environment.

This means that all I need now is similar curve for the melting curve, or the transition line between solid and liquid states. I have found this line for H2O and CO2, but am struggling with the other compounds.

With regards to which particular compounds are needed, there are a lot so I'm not particularly choosy at this point. You know, beggars and all...

Here's a very early example of what I am working on.. this diagram is for water, so it is a lot more detailed that would be expected for other compounds.
http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs1183.snc4/150530_1465269991318_1220577279_31075059_3340180_n .jpg

Swift
2010-Dec-02, 05:46 PM
You may be surprised at how difficult it is to find phase diagrams online except for the most basic compounds (namely, H2O & CO2.. also He because it's special)
I'm not surprised. You are right, there are few free on-line resources for them. There are books and commercial services that contain them.


This means that all I need now is similar curve for the melting curve, or the transition line between solid and liquid states. I have found this line for H2O and CO2, but am struggling with the other compounds.
Sorry, I don't know of a source for that.

baric
2010-Dec-02, 06:42 PM
I'm not surprised. You are right, there are few free on-line resources for them. There are books and commercial services that contain them.

You know, they don't have to be free. I earn a nice salary and would certainly pay for a subscription of some sort to a site that has this data. Unfortunately, the potential costs are too open-ended. There are N site that have paywalls, so there's no telling how many $500+ subscriptions I would need to have access to data from varied sources. And if I go the pay-per-article route, then I'm paying $25-$40 per article on the hope that the content is useful based upon a google keyword match.


Sorry, I don't know of a source for that.

:(

swampyankee
2010-Dec-03, 01:17 AM
You could try nist.gov, or a local university library, like this one (http://www.lib.utexas.edu/thermodex/).

baric
2010-Dec-03, 02:23 AM
You could try nist.gov, or a local university library, like this one (http://www.lib.utexas.edu/thermodex/).

nist.gov looks promising!

John Xenir
2010-Dec-03, 05:52 PM
Do these curves follow any specific behavior for each compound? Gas state seems to be bound by some sort of logarithmic function. Using interpolation could be done the lower curve? Or they are all totally different?

forrest noble
2010-Dec-03, 07:04 PM
Does anyone know where this kind of data can be found? I did find a great source for vapor-pressure lines, but have had little luck with melting curves.

I understand that high-pressure melting data like this will not be as plentiful as the low-pressure vapor data, but any assistance would be greatly appreciated. My intentions are to compile as much of this public data as possible and package it into some kind of freeware analysis application.

Cool altruistic idea. I think the primary problem is the large volume of data that could relate to all temperatures and pressures for the compounds that you listed. Generally speaking, for nearly all elements, compounds, possible molecular formations (like oxygen O,O2,O3) and isotopes thereof, as its surrounding atmospheric pressure decreases so does its melting and vapor temperature points decrease and visa versa.

baric
2010-Dec-03, 07:27 PM
as its surrounding atmospheric pressure decreases so does its melting and vapor temperature points decrease and visa versa.

Yar, I understand that, matey!

I've written an equation parser for the program so that I can estimate the curves with linear equations. Fortunately, this kind of work (developing the equations) has already been done for the vapor-pressure line for a LOT of compounds so I can piggy-back off of that.

The melting curve is almost vertical, however, so it requires high-pressure tests to determine for each compound. I'm guessing that's why the data is so hard to find.

baric
2010-Dec-03, 07:30 PM
Do these curves follow any specific behavior for each compound? Gas state seems to be bound by some sort of logarithmic function. Using interpolation could be done the lower curve? Or they are all totally different?

Yes, they do. I have developed rather crude estimates of the lines based on the triple and critical points of the compounds, but I am trying to move towards a model with a reliable degree of accuracy.

baric
2010-Dec-08, 04:50 AM
I have picked up a copy of David A. Young's "Phase Diagrams of the Elements" for $30. This book provides high-pressure melting curves for all of the elements. It doesn't give me any of the compounds I need, but it provides a lot of needed data for the elements at a reasonable price.

It's nice having a fully-functional, fairly accurate state model for Iron available for programmatic modeling!

I am still on the hunt for similar data for key compounds.

Swift
2010-Dec-08, 02:49 PM
Baric, is there a good University near you? You might want to try the old fashioned way, hit the library, and check the stacks for some reference books on this. I bet you can find the phase diagrams you need.

baric
2010-Dec-08, 04:35 PM
Baric, is there a good University near you? You might want to try the old fashioned way, hit the library, and check the stacks for some reference books on this. I bet you can find the phase diagrams you need.

Ya, I might hit one on a weekend soon since there's so little time after work on weeknights.

Since much on the internet now hides behind paywalls, I was pretty excited to find a journal article last night containing an estimate of the critical point of Iron.

It's supposedly around 9200K... just 60% or so hotter than the surface of the Sun! :P