Phase Diagram Determination of (2-Amino-2-Methyl-1, 3-Propanediol) AMPL-TRMP (Trimethylolpropane) Binary System

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 P2 1/n. AMPL shows lattice parameters of: a = 8.62 A, b = 11.00 A, c = 6.1(3) A, a = 93.32(1)0, V = 580.3(5) A 3 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, a=98.958(3)° at 298K with Z=4 at room temperature. High temperature cubic (gamma/gamma') phases lattice parameters are: a=6.7A for AMPL, ∼355K, and a=9.274(3) A at 328K for TRMP with Z=4 for both.;We find that TRMP-rich alpha-phase is stable between the temperatures -75 to 55°C and AMPL-rich beta-phase is stable between -100 to 80°C. We have designated the low temperature phases for TRMP and AMPL as alpha and beta and the high temperature phases as gamma and gamma', respectively. A two phase region with gamma +gamma' plastic phases is observed between -50 to -18°C. The phase diagram exhibits a eutectic point at a temperature of about -18°C and 43 % AMPL. We also observe two eutectoids: one at 33% AMPL at -50°C and the other at 51% AMPL at -60°C. The maximum solubility of TRMP in beta-AMPL is ∼15% at -60°C and that of AMPL in alpha-TRMP is ∼30% at ∼60°C. Based on the DSC data we observe that a pure TRMP sample transforms from the low temperature alpha-phase to the high temperature gamma-phase at 55°C and its melting point is known at ∼58°C. For the pure AMPL sample we observe alpha→gamma at ∼80°C, and gamma→L ∼108°C.