Thermal Emission of Alkali Metal Ions from Al(30)-Pillared Montmorillonite Studied by Mass Spectrometric Method

The thermal emission of alkali metal ions from Al(30)-pillared montmorillonite in comparison with its natural form was studied by mass spectrometry in the temperature range 770–930 K. The measurements were carried out on a magnetic mass spectrometer MI-1201. For natural montmorillonite, the densities of the emission currents (j) decrease in the mass spectrum in the following sequence (T = 805 K, A/cm(2)): K(+) (4.55 · 10(−14)), Cs(+) (9.72 · 10(−15)), Rb(+) (1.13 · 10(−15)), Na(+) (1.75 · 10(−16)), Li(+) (3.37 · 10(−17)). For Al(30)-pillared montmorillonite, thermionic emission undergoes temperature-time changes. In the low-temperature section of the investigated range (770–805 K), the value of j increases substantially for all ions in comparison with natural montmorillonite (T = 805 K, A/cm(2)): Cs(+) (6.47 · 10(−13)), K(+) (9.44 · 10(−14)), Na(+) (3.34 · 10(−15)), Rb(+) (1.77 · 10(−15)), and Li(+) (4.59 · 10(−16)). A reversible anomaly is observed in the temperature range 805–832 K: with increasing temperature, the value of j of alkaline ions falls abruptly. This effect increases with increasing ionic radius of M(+). After a long heating-up period, this anomaly disappears and the lnj − 1/T dependence acquires a classical linear form. The results are interpreted from the point of view of the dependence of the efficiency of thermionic emission on the phase transformations of pillars.