Phase Diagram Determination of (2-Amino-2-Methyl-1, 3-Propanediol) AMPL-TRMP (Trimethylolpropane) Binary System
Materials Science and Engineering
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Organic "Plastic Crystal" Thermal Energy Storage (TES) Materials are characterized by unusually large entropies of solid-solid transition compared to their entropies of fusion. In this research program, we investigate the thermal behavior of a binary AMPL-TRMP system and develop a temperature-composition equilibrium phase diagram by combining differential scanning calorimetry thermal analyses, high resolution x-ray diffraction structural analyses and visual inspection of the prepared binary mixtures at different temperatures. The room temperature structure of these globular organic compounds changes from an ordered monoclinic structure to an Orientationally Disordered high temperature phase (BCC for AMPL and FCC for TRMP). Both share the space group P21/n. AMPL shows lattice parameters of: a = 8.62 Å, b = 11.00 Å, c = 6.1(3) Å, â = 93.32(1)0, V = 580.3(5) Å3 at 20 (± 1) 0C, and Dx = 1.211 g. cm-3 for Z = 4; whereas TRMP has: a=0.8427(5), b=0.9580(5), c=0.9185(6) nm, â=98.958(3)° at 298K with Z=4 at room temperature. High temperature cubic (/') phases lattice parameters are: a=6.7Å for AMPL, ~355K, and a=9.274(3) Å at 328K for TRMP with Z=4 for both.We find that TRMP-rich -phase is stable between the temperatures -75 to 55oC and AMPL-rich -phase is stable between -100 to 80oC. We have designated the low temperature phases for TRMP and AMPL as  and  and the high temperature phases as  and ', respectively. A two phase region with  +' plastic phases is observed between -50 to -18oC. The phase diagram exhibits a eutectic point at a temperature of about -18oC and 43 % AMPL. We also observe two eutectoids: one at 33% AMPL at -50oC and the other at 51% AMPL at -60oC. The maximum solubility of TRMP in -AMPL is ~15% at -60oC and that of AMPL in -TRMP is ~30% at ~60oC. Based on the DSC data we observe that a pure TRMP sample transforms from the low temperature -phase to the high temperature -phase at 55oC and its melting point is known at ~58oC. For the pure AMPL sample we observe  at ~80oC, and L ~108oC.