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Abstract: Particles of talc with sizes in the submicrometer range have been prepared by a sonication procedure. The resulting materials present a narrow particle size distribution and retain the crystalline structure of the parent mineral, as assayed by X-ray diffraction and FTIR spectroscopy experiments. Sonication produces significant particle size decrease. Both delamination and lateral size reduction has been observed in the sonicated materials. The resulting materials have been characterized in terms of particle size distribution, coherent diffraction thickness, specific surface area, particle morphology, and crystalline structure. The thermal behaviour of talc is very much modified due to the particle size reduction produced by the effect of the ultrasound. [Copyright &y& Elsevier]

The present study examined the effect of sonication on the particle size and structure of a well-crystallized (KGa-1) kaolinite from Georgia. Sonication produced an important delamination effect as well as a reduction of the other particle-size dimensions. The experiments, carried out under different experimental conditions, showed that particle-size reduction can be controlled through different variables such as power of ultrasonic processor, amount of sample (kaolinite + water), and time of treatment. As a consequence of this particle-size reduction the surface area increases sharply with the sonication time from 8.5 to 83 m2/g after 20 h with the most energetic treatment. Contrary to what is observed in the grinding treatment, sonication did not cause the amorphization of kaolinite, as observed by XRD and FTIR data. Nevertheless, ultrasound treatment increased the structural disorder, which consisted in increases in the proportion of specific translations (−a/3+b/3) between adjacent layers in the first hours of treatment, followed by increases in the proportion of random translations between layers. [Copyright &y& Elsevier]

The present study examines the effect of sonication on the structure and on the thermal behaviour of a well ordered kaolinite. XRD data indicated that sonication produces an increase of the translation disorder of kaolinite layers as well as delamination and particle-size reduction along the b-axis. As a consequence of this particle-size reduction the surface area increases sharply with sonication time from 8.5 to 83 m2/g, after 20 h of treatment. When sonication time increases, the original dehydroxylation effect shifts to lower temperatures, is narrowing and decreases in intensity at the same time that the exothermic effect, previous to the mullite formation shifts to lower temperatures and notably broadened. [Copyright &y& Elsevier]

Abstract: This paper reports on the effects of ultrasound treatment on dickite from Tragos, Mangualde, in Portugal. Ultrasonic treatment modifies both particle size and morphology. The elongated crystals observed in the sample are broken up, after their treatment, along the cleavage planes 001 and 110, mainly along the largest direction (a axis), into smaller units that retain the typical lamellar morphology of the starting crystals. The decrease in particle size results in a significant increase in the specific surface area (SSA). When compared to the structure of the untreated dickite, X-ray Diffraction (XRD) patterns of the sonicated sample do not reveal appreciable structural modifications. On the contrary, previous results reported for sonicated kaolinite show a progressive decrease of its structural order. The corresponding Fourier Transform Infrared (FTIR) spectra show a decrease of the intensity of the OH stretching bands, which are related to the loss of some OH groups due to prototropic mechanism. [Copyright &y& Elsevier]

Abstract: The aim of this work is to compare the influence of sonication on the thermal behaviour of kaolinites (KGa-1, KGa-2), pyrophyllite, talc and muscovite. Sonication produces a significant increase of the specific surface area due to particle size reduction. As sonication time increases and the particle size decreases, the thermal behaviour of these clay minerals is strongly modified. Thus, there is a significant increase of the weight loss at low temperature which is related to the loss of some outer hydroxyl groups and protonated hydroxyls whose proportion in the minerals increase as the new surface generated increases. Additionally, the original endothermic dehydroxylation effects of all these minerals shift to lower temperatures. Disordered kaolinite shows the smallest shift (9°C) while muscovite presents the largest (184°C). A linear relation has been established between the temperature shift of the dehydroxylation and the percentage of increase in the specific surface area.The influence of sonication on the high temperature DTA effects of kaolinite, pyrophyllite, and muscovite is also studied. [Copyright &y& Elsevier]

Abstract: This paper reports on the effect of sonication on two mica samples. The materials have been investigated in terms of structure modifications, particle size and morphology, specific surface area and thermogravimetric behaviour. The effect of the mica structure, namely density and distribution of cations over the octahedral sites, on the sonicated products is reported. Sonication produces delamination and reduction of lateral size of the original macroscopic materials yielding nanometric flakes that retain the structure of the material, unlike other procedures previously reported in literature, such as dry grinding, that produces severe structural damage. [Copyright &y& Elsevier]

The influence of the interlayer cations, sonication and grinding on surface area of the vermiculite from Santa Olalla has been studied. For untreated samples the surface area increases with the size of the exchanged cation and only the samples with the largest cations (NH4+ and K+) show some microporosity. Sonication produces an increase of the surface area but the amount of micropores remains almost unchanged. Grinding leads to a significant increase of the surface area and of the microporosity. In the ground samples the percentage of micropores contributing to the surface area is influenced by the interlayer cation and the extent of N2 penetration by the water kept in the sample at a given degassing temperature. From transmission electron microscopy, thermogravimetry and XRD (d00l diffraction peaks) it can be concluded that grinding produces imperfections in crystal ordering, some alteration in the crystal edges, and a significant release of loosely bound water at temperatures up to 450 °C. These effects are responsible for the high surface area and microporosity measured by the N2 adsorption. [Copyright &y& Elsevier]