Talk:Melting point

From WikiProjectMed
Jump to navigation Jump to search

Crystalline M..P vs. Amporphous M.P.

I had thought that Crystalline solids melt at specific temperatures and it was only Amorphous solids that melt over a range of temperatures. This is due to the different strengths of intermolecular forces within Amorphous solids where as Crystalline solids have the same strength of intermolecular forces allowing them to break bonds at the same time. Is this not correct?AcrosstheSea=w= 30 April 2007


melting vs. freezing point

I'm not sure whether the melting point is for all substances the equivalent of the freezing point as stated in this article.

  • you are correct in fact. for example, agar solidifes at ~55C but melts at a higher temperature. i will work on this later when i have the time because it is very important. good find. -- Bubbachuck 17:49, 12 August 2005 (UTC)[reply]
This same problem exists in the article for Melting, where I flagged it awhile back. Would you fix it there, too, please and remove my dubious flag from that article. Thanks. PS. Someone else noticed it in this article. I sign my posts. 5Q5 14:39, 13 March 2007 (UTC)[reply]

Tungsten doesnt have the highest melting point of all elements

Tungsten doesnt have the highest melting point of all elements, it has the highest melting point of all metals. Carbon (melting point of 3823 K) has the highest melting point of all elements. However, Tungsten does have the highest boiling point. —The preceding unsigned comment was added by 24.242.200.33 (talk • contribs) 10:31, 7 February 2006 (UTC).[reply]

Carbon at ambient pressure does not melt but sublimates. A liquid phase only exists above 10 MPa. Femto 13:27, 7 February 2006 (UTC)[reply]


If we don't restrict this to elements and allow compounds, there's tantalum hafnium carbide (Ta4HfC5) with a m.p. of 4215 °C [1]. (Note though that even Britannica weasels around calling it "the" highest.) Femto 13:27, 7 February 2006 (UTC)[reply]

And it's melting point isn't 3695 K, it's 3683 K.[1] 90.211.101.31 (talk) 14:52, 13 April 2009 (UTC)[reply]

References

  1. ^ http://www.chemicalelements.com/elements/w.html

Crystalline solids only?

Message from OTRS: "The melting point is a characteristic of only crystalline solids, not all solids."

Amorphous solid materials may have a glass transition to which a fictive temperature can be attributed but many do not have even that.

I agree with this point, I have always looked at the Tm as a thermodynamical property of crystals during fusion and not as a rheological parameter. — Preceding unsigned comment added by 195.86.31.2 (talk) 11:11, 18 December 2012 (UTC)[reply]

Pure Substance

"The melting point of a pure substance is always higher than the melting point of that substance when a small amount of an impurity is present." Is this really true? Does it need qualification? Is this related to the unexplained phrase "melting-point depression" mentioned on the Lauric acid page? --Elijah 20:59, 25 August 2006 (UTC)[reply]

"Yes as far as I know and also based on first principles", "I don't think so", abd "exactly", respectively. Melting point depression is the phenomenon that impurities lower the melting point of a pure substance. DMacks 16:13, 28 August 2006 (UTC)[reply]
Then could someone more knowledgeable about the subject include that here in a way that articles like the lauric acid one could link to it? --Elijah 05:21, 29 August 2006 (UTC)[reply]

It depends what is considered to be a pure substance. PLA is existing into two forms:PLLA and PDLA. None of the pure form is leading to the highest Tm that is reached with a 50/50 mixture. This looks to be a counter example to the initial statement.

From Wikipedia PLA: "Polylactic acid can be processed like most thermoplastics into fiber (for example using conventional melt spinning processes) and film. The melting temperature of PLLA can be increased 40-50 °C and its heat deflection temperature can be increased from approximately 60°C to up to 190 °C by physically blending the polymer with PDLA (poly-D-lactide). PDLA and PLLA form a highly regular stereocomplex with increased crystallinity. The temperature stability is maximised when a 50:50 blend is used, but even at lower concentrations of 3-10% of PDLA, there is still a substantial improvement. In the latter case, PDLA acts as a nucleating agent, thereby increasing the crystallization rate. Biodegradation of PDLA is slower than for PLA due to the higher crystallinity of PDLA" — Preceding unsigned comment added by 195.86.31.2 (talk) 11:16, 18 December 2012 (UTC)[reply]

Picture of melting point vs pressure.

Should we perhaps change this from water to some other compound? Water is in the minority in that its melting point decreases with pressure, which could be misleading. Capuchin 11:52, 17 July 2007 (UTC)[reply]

Heheh. I agree that the graph should be changed, but I have in mind a different issue: the thing is in Kelvin. I'm not going to argue that it should be changed to Fahrenheit, given the science-y nature of the article, but Kelvin is not immediately meanigful--at all--to the average person, is it? I know it's identical to Celsius, but I had to look up the offset before that made any sense. If the idea is to convey useful information to the reader, this chart is... ineffective. —Preceding unsigned comment added by Archer884 (talk • contribs) 20:12, 24 August 2009 (UTC)[reply]

Proposed merger

I oppose the proposal to merge this article (MP) with Melting. As an organic chemist, I see MP as a standard test that is done on compounds to ascertain their identity and purity. There are all sorts of rules that go along with that, relating to molecular size, symmetry, polarity, and it can be related to solubility. All that material deserves an article by itself. Melting is a phenomenon, a much broader subject than MP, and the article can describe the molecular forces, the physical chemistry of melting, effect of temperature and pressure, etc., latent heat of fusion, etc. MP can be covered as a paragraph within that article, using the summary style. Walkerma 20:42, 29 July 2007 (UTC)[reply]

In other words, if there had to be a merger it would be melting point into melting, not the current (reverse) proposal. Richard001 00:07, 15 September 2007 (UTC)[reply]

I strongly oppose the merging of the two articles. See boiling and boiling point for great examples on how to seperate those two words. "Boiling" is described as the action of heating a liquid up to its boiling point, while "boiling point" describes the matter of state and the significance of the boiling point itself. The exact same thing could and should be done for melting and melting point Francis The Bird 11:04, 2 October 2007 (UTC)[reply]

Melting point, disambiguated

There should be another article for "Melting Point", this second one referring to the rock group out of Berkeley, CA. Citations and more information can be found at www.meltingpointband.com.

WikiProject class rating

This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 10:00, 10 November 2007 (UTC)[reply]

how does pressure affect the melting point and boiling point of a substance.please explain me in detail. —Preceding unsigned comment added by 117.193.198.73 (talk) 12:12, 23 January 2009 (UTC)[reply]

Congealing point

Related to some comments above is the matter of congealing point. --Una Smith (talk) 15:42, 10 March 2009 (UTC)[reply]

Freezing in Pond's

Why does the water in a pond sometimes only freeze a certain percentage of the pond's water?

Is it because the unfrozen water has sufficient back pressure to prevent itself from being frozen?

Incompressability of water? — Preceding unsigned comment added by 2.120.65.78 (talk) 15:18, 19 December 2013 (UTC)[reply]

uejiawjai-ejiqnrginirguiernguerh — Preceding unsigned comment added by 165.155.208.71 (talk) 13:22, 28 March 2016 (UTC)[reply]

Assessment comment

The comment(s) below were originally left at Talk:Melting point/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Comment(s)Press [show] to view →
Hi,

As just a student, I wanted to offer something I believe may be helpful to the average person looking for info on melting points.

I have always been taught that the melting point is the temperature at which liquid and solid exist in equilibrium with each other. I believe this would help explain why the change in Gibbs Free E is zero at the melting point because the system is in equilibrium.(?) Also, that if a melting point is reported as a single value it is understood to be the upper limit of the temperature range.

I believe it would be useful to explain why the mp is higher and tighter for pure substances, why does an impurity lower the mp and also mention the eutetic point for binary systems.

While it is an interesting tidbit about tungsten and carbon, I don't think this is why most people would search for melting point information. Also when reading this page, I felt like the author(s) where defending themselves against an attack....this was a major portion of the talk page....when really explaining melting point might have been a better.

Again this is only the viewpoint of a few students and not intended to disrespect the author(s)

California SU (talk) 08:55, 28 December 2007 (UTC)[reply]

Last edited at 08:55, 28 December 2007 (UTC). Substituted at 23:41, 29 April 2016 (UTC)

pressure lowers freezing point of water a slight amount

  • www1.lsbu.ac.uk/water/density_anomalies.html Explanation of the Density Anomalies of Water
"Pressure reduces ice's melting point (13.35 MPa gives a melting point of -1 °C)"
"In water, this line is backward sloping with slope 13.46 MPa ˣ K-1 at 0 °C, 101.325 kPa."

Many people want to know if the pressure in water pipes lowers the freezing point. Almost all Internet info including WP is not helpful: science phase diagrams in unfamiliar units that do not show appropriate detail, only that the melt temp does not vary much with pressure under common water pipe conditions.

It would be great to have a graph of temp in C and F (not K) vs pressure in PSI for 0-10,000 PSI for inclusion in WP articles. Until then, 13.35 MPa converts to 1936.25 psi (pounds per sq. inch). We could say something like:

  • Pressure in water pipes reduces the freezing point slightly: a pressure of 1936 psi lowers the freezing point to -1 °C.

The graph in the good Martin Chaplin LSBU article appears to show that 100 MPa (14,500 psi) would lower the melt temp by about 10 °C.

Typical water pipe pressures are usually around 100 psi, which apparently would lower the freezing point by a small fraction of a degree. If the slope at zero is 13.46 MPa per degC, that works out to 0.051 °C (0.092 °F) for 100 psi. It would be a relevant factoid to include in some articles, if we could be sure of the science/physics facts.-73.61.15.87 (talk) 20:11, 11 January 2018 (UTC)[reply]

External links modified (January 2018)

Hello fellow Wikipedians,

I have just modified 2 external links on Melting point. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

This message was posted before February 2018. After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than regular verification using the archive tool instructions below. Editors have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the RfC before doing mass systematic removals. This message is updated dynamically through the template {{source check}} (last update: 18 January 2022).

  • If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
  • If you found an error with any archives or the URLs themselves, you can fix them with this tool.

Cheers.—InternetArchiveBot (Report bug) 11:11, 25 January 2018 (UTC)[reply]

freezing point _is_ a characteristic property of a substance

the freezing point is not considered as a characteristic property of a substance.

The International Temperature Scale of 1990 (ITS-90) uses only freezing points for all temperature definitions above the melting point of gallium. Thus 7 out of the 14 definitions are freezing points, only one is a melting point. This is in strong contradiction to the quoted statement. If its not a characteristic property how is it good enough for the definition of our temperature scale? I will alter this sentence. --Eheran (talk) 08:44, 8 December 2020 (UTC)[reply]

Chemistry

Boiling and Melting point in moscovium 152.32.112.60 (talk) 15:04, 24 October 2022 (UTC)[reply]

Retrieved from "https://mdwiki.org/wiki/Talk:Melting_point"