Thermostimulated surface segregation processes in ionic crystals: Potassium chloride |
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Authors: | Yu. Ya. Tomashpolsky V. M. Matyuk N. V. Sadovskaya P. S. Vorontsov |
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Affiliation: | 1. Karpov Institute of Physical Chemistry, Moscow, 105064, Russia
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Abstract: | The chemical and phase composition, and cleavage surface morphology and the vapor composition of potassium chloride (KCl) crystals formed as a result of the thermostimulated surface autosegregation (TSAS) are studied by methods of microprobe analysis, high-resolution scanning electron microscopy, optical digital microscopy, and quadrupole mass spectrometry. It is experimentally found that the stoichiometry (K/Cl <1) in the surface layers changes due to a decrease in the potassium surface concentration from 5% in the initial samples to 12% after annealing at a temperature of 1023 K. After annealing at a temperature of 573 K for 5 h at P = 10?3 Pa, the potassium deficiency increases to 17%. The competing processes resulting in TSAS in potassium chloride are the self-diffusion of potassium to the surface and its subsequent sublimation. During the annealing processes the sublimation of potassium dominates, but at a temperature near fusion, the self-diffusion of potassium to the surface increases. It is concluded that potassium chloride analogous to sodium chloride is a rather stable compound to TSAS. This is an additional argument of the important role of ionic bonds in a decrease in the tendency of chemical compounds to surface autosegregation. |
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