Pressure-Temperature Phase Diagram Of Tris (Hydroxymethyl)Aminomethane And Phase Diagram Determination Of Tris(Hydroxymethyl)Aminomethane -- 2-Amino-2-Methyl-1, 3-Propanediol(AMPL) Binary System

Abstract

A pressure-temperature phase diagram of the tris(hydroxymethyl)aminomethane(TRIS) and a temperature-composition equilibrium phase diagram of the tris(hydroxymethyl)aminomethane(TRIS) -- 2-Amino-2methyl-1,3-propanediol(AMPL) binary system are developed. The component organic crystalline materials undergo solid-solid phase transitions and their property make them suitable for storage of thermal energy. The low temperature crystal structure of pure TRIS is orthorhombic, and that of the pure AMPL is monoclinic. In this study, Raman spectroscopy was performed at different temperatures and pressures to determine structural changes in the P-T diagram of TRIS. In situ high-pressure/high-temperature Raman spectroscopy experiments were carried out using resistively heated heated diamond anvil cells up to160 oC and 7 GPa. High pressure experiments performed at room temperature showed transformation of the orthorhombic -TRIS to -TRIS phase at ~1.17 GPa. As the temperature is increased to ~130 oC at ambient pressure, both  and  phases transform to -TRIS. The experiments were also run at different temperatures and pressures, by which a typical pressure-temperature phase diagram of TRIS has been developed. The binary phase diagram of TRIS-AMPL was constructed using the PANalytical X-ray diffractometer and differential scanning calorimetric data. It was found that below ~75 oC, there is virtually no solubility of AMPL in TRIS or vice versa. The AMPL rich  phase transforms to an AMPL rich  phase at ~75 oC. Between ~75 oC and 105 oC a wide phase region is observed. The maximum solubility of TRIS in AMPL is at ~12% TRIS at 73 oC and that of AMPL in TRIS is 40% AMPL at ~125 oC. The phase diagram exhibits two eutectoidal transformations at 73 oC () and at 108 oC () respectively. The phase diagram also exhibits a peritectic transformation at 128 oC (L+). A two phase region with  plastic phases rich in TRIS and AMPL is also observed between 105 oC and 125 oC. Lattice parameters changes with increase in temperature have also been studied.