PHASE-DIAGRAMS OF MOLAR VOLUME AGAINST MOLE FRACTIONS AT GIVEN TEMPERATURES AND PRESSURES FOR (X(A)AR-X(A)-X(B))NH3)(A)(X(B)XE+(1)

The phase behaviour of (argon + xenon + ammonia) was investigated at t he temperatures T = 273.15 K, 298.15 K, 323.15 K, 348.15 K, and 373.15 K and pressures p from 5.0 MPa up to 200.0 MPa. The results are given in a table and are shown as molar volume against mole fraction (V-m,c hi(A),chi(B)) diagrams. The measurements were carried out in a cylindr ical autoclave with a moveable piston and a window allowing adjustment and observation of phase equilibria at given p and T. Samples were ta ken from the coexisting phases and were analysed to obtain their molar volumes and compositions. For given p and T the ends of the correspon ding tie lines lie on isobaric and isothermal curves. Isothermal surfa ces were drawn containing several isobars. Also isobaric surfaces with different isothermal curves were drawn. It is shown how isothermal su rfaces can be combined with isobaric ones. The resulting intersection curves represent again the geometrical locus of all tie lines for give n pressures and temperatures. In the (V-m,chi(A),chi(B)) diagram the i sothermal surfaces at T = 373.15 K and 348.15 K stretch between the ga s and liquid molar volumes of pure NH3. The corresponding binary isoth erms, which are not interrupted, are their boundary curves. At lower t emperatures one or two of the binary isotherms are interrupted. Due to this behaviour the isothermal surfaces at those temperatures are more complex. The five investigated isothermal surfaces are, however, clos ely related to one another and the shape of an isothermal surface is s trongly dependent on the shape of the corresponding binary isotherm. T he isobaric surfaces at higher pressures behave similarly. However, at lower pressures their shapes become very complex. In comparison the c ritical surface shows no great variation in shape or molar volume at t he investigated temperatures and pressures, but consists of two separa te parts. (C) 1995 Academic Press Limited.