MODIFICATION OF THE POROUS STRUCTURE AND SURFACE-AREA OF SEPIOLITE UNDER VACUUM THERMAL-TREATMENT

Modifications of the external surface area and the two types of microporosity of sepiolite (structural microporosity and inter-fiber porosity) were examined as a function of the temperature of a vacuum thermal treatment to 500 degree C. The methods used included: reciprocal thermal analysis, N//2 and Ar low-temperature adsorption microcalorimetry, gas adsorption volumetry, water-vapor adsorption gravimetry, and immersion microcalorimetry into liquid water at 303 K. If the sample was not heated greater than 100 degree C, only 20% of the structural microporosity was available to N//2, whereas 52% was available to CO//2 at 293 K. In both experiments, the channels filled at very low relative pressures. At greater than 350 degree C, the structure transformed to anhydrous sepiolite, which showed no structural microporosity. The inter-fiber microporosity decreased from 0. 031 to 0. 025 cm**3/g (as seen with N//2), and the external specific surface area decreased from 120 to 48 m**2/g. Additional study results are discussed.