Adsorption de vapeur d'eau sur les faces de clivage de quelques halogénures alcalins

Abstract

The effects of the adsorption of water vapour on fresh surfaces (cleaved under vacuum) of five alkali halides NaBr, NaCl, KBr, KCl et LiF have been studied. The decoration method made it possible to observe modifications in the topography of these cleavage surfaces. The study of the variation of superficial conductibility in relation to relative pressure allowed the determination of the isotherms of adsorption θ = f (p/p₀). Thus, it was possible to determine three domains in the field of relative pressures between 0 and 0,8. The first corresponds to physical adsorption of water on the surface, the second to hydration of the cations Na⁺ or K⁺ by the water molecules, and the third to dissolution. For LiF, only one region has been observed.

Surface segregation of bromine in bromide doped NaCl: Implications for the seasonal variations in Arctic ozone

“…Water vapor exposure to NaCI, significantly below the NaCI deliquescence point, has been shown to enhance the ionic mobility (Hucher et al, 1967;Allen et al, 1996;Laux et al, 1996;Xu et al, 1998;Ghosal and Hemminger, 1999). Thus the water vapor exposure of the Br-doped NaCI (100) single crystal sample results in the enhanced ionic mobility that is required for the Br-surface segregation.…”

Adsorption of water on the NaCl(001) surface. II. An infrared study at ambient temperatures

“…NaCl͑001͒ surfaces generated by cleaving single crystals in a dry air environment ͑the technique we employ͒ have been studied in many laboratories. [6][7][8][9][10][11][12] The square array of Na ϩ and Cl Ϫ ions at the surface offers electric fields within a typical molecular radius ͑e.g., 300 pm͒ of up to 10 9 V m Ϫ1 . 8 These electric fields can hold molecules onto the surface by physisorption 13 yet for most cases no chemical bonds are broken or formed.…”

Surface diffusivity of cleaved NaCl crystals as a function of humidity: Impedance spectroscopy measurements and implications for crack healing in rock salt

“…The values for resistance (10 14 to 2 × 10 6 Ω) that we obtained in this study using impedance measurements on single salt crystals at humidities ranging from 1 to 18 g/m 3 absolute humidity (4%–78% RH, given in Table 2) are in reasonable agreement with those derived from scanning polarizing force microscopy, pressure solution creep experiments on NaCl aggregates and single contact pressure solution experiments. Conductivity experiments performed by Simkovich [1963] (along cleaved halite rods) and Hucher et al [1967] (across cleaved halite cubes), using similarly dimensioned electrode configurations show very similar resistances with values in the range 10 11 –10 8 Ω and 10 14 –10 6 Ω, respectively, for similar, but unspecified, humidity values. Using a scanning polarizing force microscopy method, Luna et al [1998] obtained resistance values of 2 × 10 12 to 2 × 10 8 Ω for humidities of 33% to 60% RH, which are also consistent with the values measured in the present study.…”