A deliquescence model for alkali halide nuclei

On the basis of a thermodynamic model, formerly developed by the authors, the behavior of critical deliquescence humidity versus dry nucleus size is computed for four alkali halide salts: NaCl, KCl, NaBr, KBr. In addition, the effect of roughness, as well as of lattice defects, is investigated and discussed. it is shown that even a small departure from sphericity or the presence of lattice defects can induce substantial changes with respect to the ideal behavior of spherical nuclei made of perfect crystals, with a systematic lowering of the critical deliquescence humidities. The introduction of a suitable parameter, the so called effective surface free energy, depending on both the nominal free energy of the crystal and the sphericity factor of the nucleus, allows to discriminate between two opposite regimes for the behavior of deliquescence humidities of real condensation nuclei.