Abstract :
High- and low-charge vermiculites from Spain (Santa Olalla and Ojen) were subjected to treatment in ultrasonic liquid processor in an attempt to reveal changes in particle size, morphology, and structure ordering. Sonication caused a rise of the SBET from the initial value below 1 m2/g for the raw samples to 36 and 54 m2/g at the final stage of processing of Santa Olalla and Ojen samples, respectively. These values, converted into equivalent spherical diameter (e.s.d.), prove that vermiculite from Ojen has finer particle size (0.042 (mu)m) than the one from Santa Olalla (0.063 (mu)m ). The low-charge vermiculite (Ojen) suffered an important delaminating effect. Some scrolling at the borders of particles was observed after first cycle of sonication. After eight cycles, the scrolling increased, yielding triangular-shaped particles that finally converted into tubes. The high-charge vermiculite (Santa Olalla) also showed delamination, but no scrolling was observed. The effect of sonication on the crystal structure of the high-charge vermiculite is negligible. The low-charge vermiculite shows broadening and smearing of the diffraction lines. It also shows wider spectrum of thickness of domains of coherent scattering, ranging from the initial value of 0.053 (mu)m to the final one of 0.019 (mu)m, as compared to 0.041 and 0.026 (mu)m for the high-charge vermiculite. It was proved that, contrary to grinding, sonication produces particle division without important structural damages, and that this process is dependent on a layer charge of given vermiculite.
