Pourbaix diagrams (potential/pH diagrams) for zinc at 25-300°C have been revised. The diagrams were calculated for three concentrations, 10 - 5 , 10 - 6 and 10 - 8 molal, the latter for use in high purity water such as in nuclear power reactors. 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 Zn(OH) 2 (aq), to be handled. The calculations show that the hydroxide of zinc does not passivate at the concentration of 10 - 6 M, due to the uncharged zinc(II) complex, Zn(OH) 2 (aq). However, at concentrations ≥ 10 - 5 . 7 M zinc passivates by formation of ZnO, which is stable in the temperature interval investigated.