โ Scribed by Carl V. Thompson; Frans Spaepen
No coin nor oath required. For personal study only.
Approximations of the Gibbs free energy change for crystallization of an undercooled liquid. AG, are discussed and compared. When liquid heat capacity data are available, AG can be approximated to various degrees of accuracy depending on the completeness of the data. In the absence of these data, it is necessary to make further approximations. It is shown that Turnbull's [4] simple linear approximation for AG is generally applicable to pure metals. A new expression is proposed for use with easy glass forming alloys such as Au Si 81.4 18.6. An approximation due to Hoffman [I] is not appropriate for use with metals and alloys but is adequate for use with organic substances, such as ortho-terphenyi.
R&urn&--Nous discutons et nous comparons des valeurs approchtes de la variation de I'tnergie libre de Gibbs AG, dans un liquide surfondu. On ne peut pas s'aflranchir de ces approximations, car la chaleur sptcifique au dessous du point de fusion n'est pas connue, pour la plupart des metaux liquides. C'est i'approximation lintaire simple de Turnbull pour AG qui s'avtre la meilleure. dans les mitaux purs. Nous proposons une nouvelle expression pour les alliages dans lesquels on forme facilement des verres. comme Au~,,~S~, 8,6. L'approximation d'Hoffman ne s'applique pas aux metaux et alliages. mais elle est correcte dans le cas de certaines substances organiques, comme I'ortho-terphinyl. Zusammenfassung-Es werden Nlherungen fir die anderung der freien Energie AG bei der Kristallisation einer unterkbhiten Fliissigkeit diskutiert und miteinander verglichen. Auf solche NIherungen ist man angewiesen. da Daten fiber die Wlrmekapazitlt fir die meisten fliissigen Metalle unterhalb des Schmelzpunktes nicht verfiigbar sind. Es zeigt sich. da13 die einfache lineare Nlherung fir AG von Turnbull (4) fiir reine Metalle am angemessensten ist. Es wird ein neuer Ausdruck fiir AG fiir Legierungen vorgeschlagen. die leicht Glasstrukturen bilden, wie Au *I $i, 8.6. Die von Hoffman (I ) angegebene Nlherung kann auf Metalle und Le@erungen nicht angewendet werden. jedoch auf einige organische Substanzen wie Orthoterphenyl.
๐ SIMILAR VOLUMES
A precise thermodynamic measurement of the equilibrium: C,,,,,i, = Cglarlysaihon employing a solid oxide electrolyte in the temperature range 650"-1150ยฐC was carried out to gain structural information on glassy carbons. The measured Gibbs free enerav change vields configurational (residual quantiti
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