Question

Discuss the variable pressure and variable temperature modifications of gibbs–duhem equations.

Answer 1

Variable-pressure, variable-temperature (VPVT) measurements of ionic conductivity in typical inorganic (sodium aluminoborate and lithium–sodium phosphate) glasses provide information concerning two independent activationparameters: the activation energy (EA = −R d ln σT/d(1/T)) and the activation volume (VA = −RT d ln σ/dP). In single-cation glasses there is no simple link between EA and VA. The strong increase in EAseen with decreasing alkali content is not paralleled by an increase in VA. However, in mixed cationglasses, maxima are observed in both EA and VA. To account for these observations, a new model is being developed where ion transport is limited by a shortage of available volume. In this model, the measured VA values represent the volumes of opened up ‘target sites’, the larger values observed in mixed-cation glasses providing evidence for the coupled motion of unlike ions. The extent of this pairwise coupling increases with increasing temperature.

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Answer 2

the relation between pressure and temperature low that state and volume