Chapter 8 Phase equilibria and potential phase diagrams.

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Transcript of Chapter 8 Phase equilibria and potential phase diagrams.

Chapter 8 Phase equilibria and potential phase diagrams

as mentioned in Chapter 1 a particular state of equil identified by giving the values to state variables c+2 variables must be given the rest are dependent equil state of system : represented by a point in a c+2 dim diagram, all pts in such a diagram represent possible states state diagram (but, giving no information) thus, by sectioning at constant values of c+1 variables and plotting a dependent variable as another axis property diagram Fig. 1.1
 the line itself represents the property of the system property diagram

fundamental property diagram:the relation of c+2 intensive var is plotted in c+2 dim space relation of GD eq results in a surface or a if c > 1 representing thermo properties of the sys such a diagram, with the surface included regarded as property diagram of special interest, because it is composed of a complete set of (T, P, i) fundamental property diagram potential diagram

ex) TP diagram for one comp A, with one phase a SdTVdP+Nidi=0 (GD eq) becoming SdTVdP+NAdA=0
the equil state completely determined by giving values to T, P (by giving a pt in TP diagram) state diagram A can be calculated from GD and plotted as a surface above the TP state diagram yielding a 3D diagram property diagram A=Gm=Gm(T, P) : equation of state fundamental property diagram in unary sys, G =iNi = ANA A = G/NA =Gm for a higherorder system, 1= 1(T, P, 2, 3, )

 for A, possible two phases (a, b) mAa, mAb at each GD surface considering a possible transition from phase to phase at fixed T, P evaluation of the integrated driving force of b a dU = TdS  PdV + idNi  Dd = TdS  PdV + AdNA  Dd (U = TS  PV + ANA ) (dU = TdS + SdT  PdV  VdP + AdNA + NAdA) Dd=  SdT + VdP  NAdA
the phase with the lower A will be more (at constant T, P)

Aa = Ab equil, D=0 in Fig. 8.3, the line of intersection of two surfaces must be a line of  projection of fundamental property diagram onto TP state diagram removal of both dAa , dAb potential phase diagram(potential) Phase Diagramin Germany, phase diagram state diagramin Japan,