First experimental demonstration of crossed isodimorphism: (CH3)3CCl + CCl4 melting phase diagram

Abstract

The melting phase diagram of the two-component system 2-methyl-2-chloro-propane ((CH₃)₃CCl) and carbon tetrachloride (CCl₄) has been determined by combining X-ray powder diffraction and thermal analysis. The isomorphism relation between the orientationally disordered (OD) stable face-centered cubic (FCC) phase of (CH₃)₃CCl and the metastable FCC phase of CCl₄ has been demonstrated throughout the continuous evolution of the lattice parameters and the existence of the two-phase equilibrium [FCC + L] for the whole range of composition, despite the monotropy of the FCC phase for the CCl₄ component. This equilibrium interferes with a rhombohedral plus liquid ([R + L]) equilibrium giving rise to a peritectic invariant. A thermodynamic analysis, in terms of the crossed isodimorphism, has also been performed in order to obtain the excess properties of the FCC and R OD phases.