Solidliquid melting and solidIsolidII transformations

The direction and magnitude of the pressure effect on phase transformation equilibria are determined from the Clapyron equation. Inverting Eq (5.5) and regarding the temperature as the dependent property and total pressure as the adjustable variable, the variation of the transition point Tr with pressure is given by:

dp Ahjj.

where Ahtr is the enthalpy change of phase transformation and Avtr = vII - vI is the corresponding volume change. Table 5.1 summarizes applications of Eq (5.15) to melting of ice and iron and to the a - y solid-solid transition in iron. For most materials, AvM is positive - phase I (solid) is denser than phase II (liquid). Ice/water is the notable exception to this general rule because the liquid is denser than the solid; 13.5 MPa lowers the melting point by 1oC.

Table 5.1 Pressure effect on solid/liquid and solidI/solidII transitions

Species

transitio n

Ttr, K

Ahtr, J/mole

Avtr, m3/molex106

dTtr/dp, k/MPa

H2O

ice ^ L

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment