How to differentiate between phase separation induced crystallization and spinodal decomposition and techniques required to establish them?
Phase diagram of the separation has a binodal and a spinodal. On the binodal, the chemical potentials of the two phases are equal. Crystallization occurs in supersaturated metastable states between the binodal and the spinodal.
Analytical condition for spinodal decomposition of binary solution is the zero of the second derivative of the Gibbs energy of a thermodynamic system over the concentration one component. The unstable state of the system is reached on spinodal. A substance (solution), being in a labile state, rapidly loses its spatial homogeneity, and during relaxation its structure becomes more granular-cellular, without the phase boundaries.
Techniques required to establish them : J. Physique. 1986. V.47. P.733.
Experimentally you can differentiate these two transformation only at the early stage (within a few hours; depending on the kinetics) of the decomposition. After sufficient time (in days) both will exhibit simillar microstructure. So, one can use SEM and/or TEM to establish the type of the decompostion.
Thank you Dr. Basak and Dr. Mirgorod. TEM studies are performed and establish the process of decomposition but is there any possible way by thermal studies (DSC) through which the mechanism can be explained in detail?
You do not write the composition of your system. The methods of research depend on the nature of the system. You are exploring the phase equilibrium. If it's glass, then look at the work R. Krishna. He is your compatriot, but he works in Holland. I attach one of his works.
Since we do not know the system you are working, generally on the phase diagram the phase separation will happen within the binodal region while spinodal decomposition happens within the spinode. If you are able to freeze these and examine under SEM, the binodal structure will have spherical particles in it while the spinodal structure looks loop like. Since the structures are metastable, with time the loops break up into spherical particles as well. The kinetics of the processes are quite complex. Phase separation is a nucleation and growth event while spinodal decomposition is diffusion controlled. About the thermal studies, I would suggest DTA.
Dear Oluwatoyin E Jegede:
You explained the details of the phase separation mechanism better than Chandra Bhanu Basak and R. Krishna?
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