Phase diagrams of molar volume against mole fractions at given temperatures and pressures for { xAAr + xBXe + (1 − xA− xB)NH 3}

Abstract

The phase behaviour of (argon + xenon + ammonia) was investigated at the temperatures T= 273.15 K, 298.15 K, 323.15 K, 348.15 K, and 373.15 K and pressure pfrom 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, x A, x B) diagrams. The measurements were carried out in a cylindrical autoclave with a moveable piston and a window allowing adjustment and observation of phase equilibria at given pand T. Samples were taken from the coexisting phases and were analysed to obtain their molar volumes and compositions. For given pand Tthe ends of the corresponding tie lines lie on isobaric and isothermal curves. Isothermal surfaces were drawn containing several isobars. Also isobaric surfaces with different isothermal curves were drawn. It is shown how isothermal surfaces can be combined with isobaric ones. The resulting intersection curves represent again the geometrical locus of all tie lines for given pressures and temperatures. In the ( V m, x A, x B) diagram the isothermal surfaces at T= 373.15 K and 348.15 K stretch between the gas and liquid molar volumes of pure NH 3. The corresponding binary isotherms, which are not interrupted, are their boundary curves. At lower temperatures 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, closely related to one another and the shape of an isothermal surface is strongly dependent on the shape of the corresponding binary isotherm. The isobaric surfaces at higher pressures behave similarly. However, at lower pressures their shapes become very complex. In comparison the critical surface shows no great variation in shape or molar volume at the investigated temperatures and pressures, but consists of two separate parts.