HIGH-PRESSURE SUPERCRITICAL PVT-DATA OF WATER-SODIUM HYDROXIDE MIXTURES AND OF LIQUID-SODIUM HYDROXIDE TO 673-K AND 400-MPA

The density of homogeneous fluid mixtures of water and sodium hydroxid e has been measured from 293 to 673 K and at pressures from 10 to 400 MPa. Measurements were performed at eight compositions between 10 and 90 weight percent NaOH and with pure molten NaOH. At sufficiently high pressure complete miscibility of NaOH and H2O exists above the meltin g temperature of NaOH at 595 K. A differential autoclave with internal heating within a space filled with high pressure argon and with an in ternal nickel bellows cell for the H2O-NaOH mixtures is described. Imm ediate results are given as specific mixture volumes and molar volumes . Molar volumes in dependence of composition have distinct minima near 30 mole percent NaOH. All excess volumes are negative. A semiempirica l equation is proposed on the basis of a hydration model to describe m olar and excess volumes. Partial molar volumes and estimated activity coefficients are given for 673 K and pressures at 100 and 400 MPa.