Sorptive deformation of organo-substituted laminar silicates and hysteresis phenomena

Deformations of organo-substituted laminar silicates (Pyzhevsk montmorillonite and synthetic fluorohectorite) upon hexane and benzene vapor sorption have been studied. To solve this problem, a dilatometer was used. Its main part was a line differential transformer, the core of which was connected to the sorbent by means of a rod. Any changes in the sorbent height caused a change in the core position in the transformer, which influenced the signal recorded from its secondary winding. The calibrated dilatometer was located in a liquid thermostat with a given temperature and was connected with the measurement unit (frequency meter, voltmeter, and generator). Montmorillonite and synthetic fluorohectorite were modified by cetylpyridinium bromide and used in the form of tablets. As a result of the samples preparation conditions, the modified clay silicates swelled isotropically. These results were compared with the sorption isotherms obtained gravimetrically. High sensitivity of the dilatometric method to the structural changes of the organo-substituted laminar silicates has been shown. The dilatometer used allowed the measurement of absolute deformations in the range 1 x 10(-4) to 3 mm. Also, the dilatometric method was used for the first time to study the sorptive deformation hysteresis of sorbents. On the basis of the results obtained, it was suggested that sorbent deformation may be the universal cause of sorptive hysteresis. (C) 2001 Academic Press.