Abstract
Various formulations of the material balance in solid-liquid equilibria have been discussed. It has been established that the melt fraction, as usually defined, is related to the corresponding fractional heat of melting in an approximate way only.
By expressing the material balance in terms of a more appropriate melt fraction, relationships for the thermodynamic description of two-component eutectic systems have been derived, and their correctness checked on the system benzoic acid-naphthalene.
Zusammenfassung
Es wurden zahlreiche Darstellungsarten von Stoffbilanzen bei Festkörper-Flüssigkeitsgleichgewichten diskutiert. Es wurde festgestellt, daß die auf gewohnte Weise definierte Schmelzenfraktion nur annähernd mit der korrespondierenden Schmelzwärme für diese Fraktion in Beziehung steht. Durch Formulieren der Stoff bilanz, ausgehend von einer geeigneteren Schmelzenfraktion konnten Beziehungen für eine thermodynamische Beschreibung von Zweikomponenten-Eutektika-Systemen erhalten werden. Deren Richtigkeit wurde am System Benzoesäure-Naphthalin überprüft.
Резюме
Обсуждены различные формулировки при составлении веществ енного баланса для равновесия типа твер дое тело—жидкость. Ус тановлено, что доля расплава, свя занная с дробной теплотой плавления, о бозначается только приблизительно. Выра зив вещественный бал анс на основе более подходя щей доли расплава, был и выведены соотношения для терм одинамического описания двухкомпон ентных систем и справ едливость которых была провере на на системе бензойная кислота-на фталин.
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Abbreviations
- 1:
-
Index, symbol of the main component (solvent)
- 2:
-
Index, symbol of the impurity
- R :
-
Gas constant, J/(mol deg)
- T :
-
Equilibrium temperature of the system, K
- T 1 :
-
Melting point of the solvent, K
- ΔH 01 :
-
Enthalpy of fusion of the solvent at the melting point, J/mol
- ΔC 01 :
-
Difference in molar heat capacity in the solid and liquid states of the solvent at the melting point, J/(mol deg)
- M i :
-
Molecular weight of thei-th component
- x i :
-
Molar fraction of thei-th component in the melt phase
- ¯x i :
-
Total molar fraction of thei-th component in the system
- x i :
-
Molar fraction of thei-th component in the eutectic mixture
- n s :
-
Number of moles of sample in the solid phase
- n i :
-
Number of moles of sample in the liquid phase
- ¯n i :
-
Total number of moles of thei-th component
- n i :
-
Number of moles of thei-th component in the eutectic mixture
- F :
-
Molten fraction referred to total number of moles of sample
- F 1 :
-
Molten fraction referred to total number of moles of solvent
- f 1 :
-
Molten fraction referred to number of moles of solvent not present in the eutectic mixture
- W :
-
Interaction energy between the two components, J/mol
- ΔH 1 :
-
Integral heat of melting of solvent from the eutectic to the final melting point, J/mol
- Δh 1 :
-
Integral heat of melting of solvent from the eutectic to a partial melting point, J/mol
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Vallebona, G. Purity determination by calorimetry. An analysis of relationships describing solid-liquid equilibria in eutectic systems. Journal of Thermal Analysis 34, 1101–1112 (1988). https://doi.org/10.1007/BF01913514
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DOI: https://doi.org/10.1007/BF01913514