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

摘要

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 center dot 10(-14)), Cs+ (9.72 center dot 10(-15)), Rb+ (1.13 center dot 10(-15)), Na+ (1.75 center dot 10(-16)), Li+ (3.37 center dot 10(-17)). For Al-30 -pillared montmorillonite, thermionic emission undergoes temperature- time changes. In the low-temperature section of the investigated range (770-805K), the value of j increases substantially for all ions in comparisonwith naturalmontmorillonite (T = 805 K, A/cm(2)): Cs+ (6.47 center dot 10(-13)), K+ (9.44 center dot 10(-14)), Na+ (3.34 center dot 10(-15)), Rb+ (1.77 center dot 10(-15)), and Li+ (4.59 center dot 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 ln j - 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.