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Ternary Phase Equilibria of Polyalchol and Amine "Plastic Crystals"
Chemical and Materials Engineering
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Solid-solid phase change materials are considered to be potential candidates for thermal energy storage (TES). Amongst the solid-solid heat storage materials, the most promising heat storage materials are organic polyalcohol globular molecular crystals (with orientational disorder in the energy storing phase). Studies on CALPHAD modeling of binary and ternary phase diagrams of these organic plastic crystals are limited, in fact to our knowledge, there are no ternary phase diagram reported in the literature for these systems, leading to the motivation for the this study. Binary systems of organic plastic crystals have been analyzed to lower or adjust the transition temperature for thermal energy storage applications. In this study, binary phase diagrams of 6 systems (PE-PG, PG-NPG, PE-NPG, PE-AMPL, PG-AMPL, NPG-AMPL) were first modeled to determine interaction parameters; in effect self consistent data base used to generate 4 ternary phase diagrams (PE-PG-NPG, PE-NPG-AMPL, PG-NPG-AMPL, PE-PG-AMPL). Several isothermal sections were developed, and isopleths were generated for each of the above four system; these isopleths are key to understanding the nature of phase transitions. The solution phases are modeled as substitutional solution model, in which the excess Gibbs energies are expressed by the Redlich-Kister-Muggianu polynomial. Experimental data from literature has been used for optimization of the binary phase diagrams to calculate the excess Gibbs energy parameters. The phase diagrams are calculated from room temperature to the liquid phase. A set of self consistent thermodynamic parameters formulating the Gibbs energies of various phases in the ternary systems are obtained in the present work. Activities and enthalpies of mixing for the binary systems are calculated from the excess Gibbs energy parameters. Activities for ternary phase diagrams are extrapolated from the binary data by the application of Krupkowski's formalism. In this dissertation, the above mentioned six binaries and four ternaries along with their isopleths are presented. The results of these studies allowed us to better understand the complex phase transition mechanisms and gave us more latitude for adjustment of phase transition temperatures. PE- Pentaerythritol (C5H12O4), PG- Pentaglycerine (C5H12O3), NPG- Neopentylglycol (C5H12O2), AMPL - 2 amino,2 methyl, 1,3 propanedoil (C5H11O2N)