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The two-phase boundary of seawater was determined by isothermal decompression of fully condensed seawater in the range of 200-500??C. The pressure at which phase separation occurred for each isotherm was determined by a comparison of the refractive index of fluid removed from the top and bottom of the reaction vessel. The critical point was determined to be in the range of 403-406??C, 285-302 bar and was located by the inflection in the two-phase boundary and by the relative volume of fluid and vapor as a function of temperature. The two-phase boundary of 3.2% NaCl solution was found to coincide exactly with that of seawater over the range tested in the present study. The boundary for both is described by a single seventh-order polynomial equation. The two-phase boundary defines the maximum temperature of seawater circulating at depth in the oceanic crust. Thus the boundary puts a limit of about 390??C for seawater circulating near the seafloor at active ocean ridges (2.5 km water depth), and about 465??C at the top of a magma chamber occurring at 2 km below the seafloor. ?? 1984.
Additional Publication Details
The critical point and two-phase boundary of seawater, 200-500??C