Barrio M, Pardo L C, Tamarit J Ll, Negrier Ph, Salud J, López D O, Mondieig D
Departament de Física i Enginyeria Nuclear, E.T.S.E.I.B. Universitat Politècnica de Catalunya, Diagonal, 647 08028 Barcelona, Catalonia, Spain.
J Phys Chem B. 2006 Jun 22;110(24):12096-103. doi: 10.1021/jp061484+.
Phase equilibria involving orientationally disordered (OD) and liquid phases of the two-component system between carbon tetrachloride (CCl4) and 2-methyl-2-bromomethane ((CH3)3CBr) have been determined by means of X-ray powder diffraction and thermal analysis techniques from 210 K up to the liquid state. The isomorphism relation between the OD stable face-centered cubic (FCC) phase of (CH3)3CBr 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 with respect to its OD rhombohedral (R) stable phase. A continuous series of OD R mixed crystals is found, which confirms the R lattice symmetry of the OD phase II of (CH3)3CBr, for which the crystallographic results have been long-time misinterpreted. X-ray patterns of such a phase were indexed according to the recent single-crystal results obtained by Rudman (Rudman, R. J. Mol. Struct. 2001, 569, 157). In addition, some experimental evidences are given to confirm the number of molecules per unit cell (Z = 21). The thermodynamic assessment reproduces coherently the phase diagram for the stable [R + L] and [R + FCC] two-phase equilibria as well as for the partially metastable [FCC + L] two-phase equilibrium and provides a set of data for the thermodynamic properties of nonexperimentally available phase transitions of pure components. Surprisingly, the phase equilibrium involving R and FCC OD phases appears as one of the very few showing a solid-solid equilibrium with two extremes.
利用X射线粉末衍射和热分析技术，测定了四氯化碳（CCl4）和2-甲基-2-溴丙烷（(CH3)3CBr）两组分体系在210K至液态范围内取向无序（OD）相和液相的相平衡。尽管CCl4组分的面心立方（FCC）相相对于其OD菱面体（R）稳定相具有单变性，但在整个组成范围内，通过晶格参数的连续演变以及[FCC + L]两相平衡的存在，证明了(CH3)3CBr的OD稳定面心立方（FCC）相与CCl4的亚稳FCC相之间的同构关系。发现了一系列连续的OD R混合晶体，这证实了(CH3)3CBr的OD相II的R晶格对称性，其晶体学结果长期以来一直被误解。根据Rudman最近获得的单晶结果（Rudman, R. J. Mol. Struct. 2001, 569, 157），对该相的X射线图谱进行了指标化。此外，还给出了一些实验证据来证实单位晶胞中的分子数（Z = 21）。热力学评估连贯地再现了稳定的[R + L]和[R + FCC]两相平衡以及部分亚稳的[FCC + L]两相平衡的相图，并提供了一组关于纯组分非实验可得相变热力学性质的数据。令人惊讶的是，涉及R和FCC OD相的相平衡似乎是极少数显示出具有两个极端的固-固平衡的相平衡之一。
