The Diffusion of Mercury in Purified KCl and the Effect of OH− on Diffusion

The diffusion of mercury into both purified and hydroxide doped Kci was studied. The high vapor pressure of HgCI2 required modification of the usual technique to assure constant boundary conditions. The very low solubility of mercury made accurate determination of diffusion parameters difficult. Mercury diffuses into purified KCI over the temperature range from 449 to 549 °C in accordance with the relation Ds = 8.18 × 10−5 exp (−0.57 eV/kT). Over this same temperature range the free energy of association for the mercuric ion‐cation vacancy complex varies from 0.75 to 0.80 eV, an abnormally large value for this type of association. The presence of OH‐ causes extreme distortion of the concentration‐distance curve by forming a maximum in mercury concentration well away from the surface of the crystal. The maximum is thought to arise from the formation of the mercuric ion‐hydroxide ion compound identified optically in earlier studies.