Liquid-liquid equilibrium (LLE) phase behavior was investigated for the binary iodine-water (I(2)-H(2)O) and the ternary iodine-hydroiodic acid-water (I(2)-HI-H(2)O) at the elevated temperatures and pressures of interest for the reactive distillation column of the Sulfur-Iodine Cycle. A continuous-flow apparatus, with wetted parts fabricated from tantalum-tungsten alloys, was designed and constructed for the highly corrosive conditions of this work. A central feature of the apparatus is the equilibrium view cell, which allows for the observation and discernment of vapor-liquid, liquid-liquid, and liquid-liquid-vapor equilibria for HIx systems. For the I(2)-H(2)O system, LLE was observed at temperatures and pressures to 300 degrees C and 104 bar. Based on our observations, we estimate that the upper critical solution temperature for this system occurs at 310-315 degrees C. For the I(2)-HI-H(2)O ternary, VLE, LLE, and LLVE were all observed at 160 and 200 degrees C, and three compositions on the water-rich side of the LLE phase envelope were determined. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.