Thermodynamics of Crystals — 1982

Westrum, Edgar F.

doi:10.1007/978-94-009-6312-2_33

Cited by 4 publications

(2 citation statements)

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“…For coexisting polymorphs, ∆G can be defined and measured over wide ranges of temperature, sometimes from nearly 0 K to melting points. ∆G can be obtained from the polymorphs' heat capacities, 3 solubilities, 4 vapor pressures, and heats and temperatures of melting. 5 Here, we describe a new method to measure ∆G on the basis of eutectic melting and differential scanning calorimetry (DSC).…”

Section: Introductionmentioning

confidence: 99%

“…20 Glycine decomposes on melting, which makes the method of pure melting 5 inapplicable. The heat capacities of R and γ glycine have been measured from 5 to 304 K, 21 but without melting data, they could not be combined in the usual way 3 to yield G R -G γ . The bridging of heat-capacity data through heats of solution 19 led to large errors in estimated G R -G γ and no prediction of T t .…”

Section: Introductionmentioning

confidence: 99%

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Measuring Free-Energy Difference between Crystal Polymorphs through Eutectic Melting

Huang

Jones

2005

J. Phys. Chem. B

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We describe a method to measure the free-energy difference, DeltaG, between crystal polymorphs from their calorimetric data of eutectic melting with a common additive. The use of different additives yields DeltaG as a function of temperature. The method is suitable for crystals that chemically decompose or physically transform before melting. It applies to not only true polymorphs but also pairs of racemate and conglomerate of resolvable enantiomers. We illustrate the method with the polymorphs of glycine, d-mannitol, and tazofelone and report a new value (123 degrees C) for the enantiotropic transition temperature of alpha and gamma glycine. We show how different additives (including a liquid additive, water) can be used for different compounds. The DeltaG data thus obtained are important for structure-stability studies and controlling crystallization in polymorphic systems.

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Section: Introductionmentioning

confidence: 99%