Revised Pourbaix diagrams for chromium at 25-300 deg C

The Pourbaix diagrams (potential-pH diagrams) for chromium at 25-300 deg C have been revised. The diagrams were calculated for two concentrations: 10 exp -6 and 10 exp -8 molal. Extrapolation of thermochemical data to elevated temperatures has been performed with the revised model of Helgeson-Kirkham-Flowers, which also allows uncharged aqueous complexes, such as Cr(OH) sub 3 (aq), to be handled. The calculations show that the hydroxides Cr(OH) sub 2 , Cr(OH) sub 3 , and the oxides CrO sub 2 and CrO sub 3 are not stable at the investigated temperature and concentration interval. Cr sub 2 O sub 3 is the only stable solid Cr compound in aqueous solution in the environment studied, with the exception of very diluted solutions such as 10 exp -8 molal at T > 150 deg C, where no solid Cr compound is stable. The dichromate ion does not predominate anywhere within the calculated concentration range.