Volume expansion on melting

THEORY AND QUANTITATIVE PREDICTIONS Table 4.32 Volume expansions on melting... 

The volume expansion on melting for a given material (e.g., metal, alloy, ceramic, polymer), expressed in vol.% and denoted AV/V, corresponds to the relative difference of the volume occupied by a unit mass of the material before and after the melting temperature is reached. It can be described by the following simple equation ... 

It has to be noticed that no isothermal volume contraction on cooling or volume expansion on heating is associated with Tg, contrary to crystallisation or melting. The latter is a true first-order transition exhibiting a discontinuity in... 

The primary site of action is postulated to be the Hpid matrix of cell membranes. The Hpid properties which are said to be altered vary from theory to theory and include enhancing membrane fluidity volume expansion melting of gel phases increasing membrane thickness, surface tension, and lateral surface pressure and encouraging the formation of polar dislocations (10,11). Most theories postulate that changes in the Hpids influence the activities of cmcial membrane proteins such as ion channels. The Hpid theories suffer from an important drawback at clinically used concentrations, the effects of inhalational anesthetics on Hpid bilayers are very small and essentially undetectable (6,12,13). 

The inter- and Intramolecular contributions to the entropy and energy of fusion are calculated for several linear aliphatic polyesters and polyamides assuming the fusion process consists of two Independent contributions the volume expansion (intermolecular contribution) and the increase in the conformational freedom of each polymer chain on melting (intramolecular contribution). The intramolecular entropy and energy contributions are obtained from the configurational partition function and Its temperature coefficient calculated for an isolated, unperturbed polymer chain using the RIS approximation. 

From the relation (3.2), and the observed change of volume on melting, we can compute the change of entropy. In Table XVI-2 we give values of volume of the solid per mole (extrapolated from room temperature to the melting point by use of the thermal expansion), volume of the liquid... 

The molar volume increases by 8% on melting. This is the largest expansion observed for bcc metals [1.70]. 

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