Spinodal curve, points, region decomposition

Consider a sudden temperature jump that brings a homogeneous mixture at the critical composition 0c into the two-phase region. The system will spontaneously phase separate into two phases with compositions given by the values on the coexistence curve at that new temperature. This spontaneous phase separation, called spinodal decomposition, occurs because the mixture is locally unstable. Any small composition fluctuation is sufficient to initiate the phase separation process. At any point inside the-... 

Substituting Equations 6.11 and 6.12 into 6.1 and the result into 6.10, a set of alloy stability curves in x and y are obtained for quaternary alloys. These curves are similar to points on the curve in Figure 4.18c at a given temperature and define a region of composition space in which the alloy is unstable and may decompose. In addition to direct calculation from known values, the bond energies in Equation 6.11 may be obtained by fitting observed spinodal decomposition data for pseudobinary alloys in a given quaternary system. 

---