Congruent melting: Difference between revisions
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{{Short description|When the composition of the liquid formed during melting is the same as that of the solid}} |
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{{Unreferenced|date=November 2006}} |
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'''Congruent melting''' occurs during [[melting]] of a compound when the composition of the liquid that forms is the same as the composition of the solid. It can be contrasted with [[incongruent melting]]. This generally happens in two-[[Component (thermodynamics)|component]] systems. To take a general case, let A and B be the two components and AB a stable solid compound formed by their chemical combination. If we draw a [[phase diagram]] for the system, we notice that there are three solid phases, namely A, B and compound AB. Accordingly, there will be three fusion or freezing point curves AC, BE and CDE for the three solid phases. In the phase diagram, we can notice that the top point D of the phase diagram is the congruent melting point of the compound AB because the solid and liquid phases now have the same composition. Evidently, at this [[temperature]], the two-component system has become a one-component system because both solid and liquid phases contains only the compound AB.<ref>Elements of Physical Chemistry, Puri-Sharma-Pathania</ref><ref>Atkins' Physical Chemistry, 8th edition, by Peter Atkins and Julio De Paula</ref> |
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{{Context|date=October 2009}} |
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'''Congruent melting''' occurs during [[melting]] of a compound when the composition of the liquid that forms is the same as the composition of the solid. It can be contrasted with [[incongruent melting]]. |
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<!-- Attention, the next paragraph probably still corresponds to the description of a graph which was never uploaded on the Commons by its author and whose the orphan link was removed by a bot. It is therefore reedited to be more general --> |
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The "congruent melting point" is the [[melting point]] (the pressure and temperature) when the composition of the liquid formed is the same as the composition of the solid.<ref>Atkins' Physical Chemistry 8th edition by Peter Atkins and Julio De Paula</ref> |
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Congruent melting point represents a definite temperature just like the melting points of pure components. In some phase diagrams, the congruent melting point of a compound AB may lie above the melting points of pure components A and B. But it is not always necessarily the case. There are different types of systems known in which the congruent melting point is observed below the melting points of the pure components. This happens for inter-metallic compounds, for example, for {{Chem|Mg|Si|2}}. |
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<references/> |
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==See also== |
==See also== |
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* [[Congruent transition]] |
* [[Congruent transition]] |
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* [[Incongruent melting]] |
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* [[Phase diagram]] |
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* [[Phase rule]] |
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{{Reflist}} |
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{{DEFAULTSORT:Congruent Melting}} |
{{DEFAULTSORT:Congruent Melting}} |
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[[Category:Phase |
[[Category:Phase transitions]] |
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[[Category:Materials science]] |
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{{materials-sci-stub}} |
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[[ru:Конгруэнтное плавление]] |
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[[fi:Kongruentti sulaminen]] |
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Latest revision as of 12:16, 19 July 2022
Congruent melting occurs during melting of a compound when the composition of the liquid that forms is the same as the composition of the solid. It can be contrasted with incongruent melting. This generally happens in two-component systems. To take a general case, let A and B be the two components and AB a stable solid compound formed by their chemical combination. If we draw a phase diagram for the system, we notice that there are three solid phases, namely A, B and compound AB. Accordingly, there will be three fusion or freezing point curves AC, BE and CDE for the three solid phases. In the phase diagram, we can notice that the top point D of the phase diagram is the congruent melting point of the compound AB because the solid and liquid phases now have the same composition. Evidently, at this temperature, the two-component system has become a one-component system because both solid and liquid phases contains only the compound AB.[1][2]
Congruent melting point represents a definite temperature just like the melting points of pure components. In some phase diagrams, the congruent melting point of a compound AB may lie above the melting points of pure components A and B. But it is not always necessarily the case. There are different types of systems known in which the congruent melting point is observed below the melting points of the pure components. This happens for inter-metallic compounds, for example, for MgSi
2.
See also
[edit]References
[edit]
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