Phase diagram of the system CH4–Ar and properties of solid solutions near the critical point

The phase diagram of the system CH4–Ar is analyzed by x-rays. It is found that this system has a critical point at Tc = 63 K and xc = 35% CH4. The behavior of the solutions is studied on the phase separation curve and beyond the critical point. The change in the lattice volume along the phase separation curve in the vicinity of Tc can be described satisfactorily by a power dependence with critical exponent β = 0.45±0.05. Solutions with the critical composition display an anomalous volume thermal expansion coefficient as Tc is approached from the single-phase region. The obtained results are discussed and compared with those known in the literature.

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