http://atarazanas.sci.uma.es/docs/articulos/16512108.pdf

The effect of ultrasound on the particle size and structural disorder of a well-ordered kaolinite.

http://www.emec.licp.cas.cn/kycg/2016/201511/W020151130323160570426.pdf

Recent progress in dispersion of palygorskite crystal bundles for nanocomposites

Exfoliation/delamination of kaolinite by low-temperature washing of kaolinite–urea intercalates

Intercalation compounds of low- and high-defect kaolinites have been prepared by direct reaction with urea aqueous solution as well as by co-grinding with urea in the absence of water (mechanochemical intercalation). The complexes formed were studied by X-ray diffraction, thermal analysis, DRIFT spectroscopy, and scanning electron microscopy. In aqueous solution the degree of intercalation for the low- and high-defect kaolinites was found to be 77 and 65%, respectively. With mechanochemical intercalation, both kaolinites were almost fully expanded after 1 h of grinding. Based on the results of DRIFT spectroscopy, a structural model for the bonding of urea to the siloxane surface is proposed. The kaolinite-urea intercalation compounds produced by mechanochemical intercalation have crystallite sizes lower than those obtained by the aqueous solution method.

Kaolinite–urea complexes obtained by mechanochemical and aqueous suspension techniques—A comparative study

Thermal treatment of mechanochemically activated kaolinite

The present study examined the effects of dry grinding, using ball-milling, on the structure of reference well-crystallized (KGa-1) and poorly crystallized (KGa-2) kaolinite powders from Georgia. Grinding produced a strong structural alteration, mainly along the c axis, resulting in disorder and total degradation of the crystal structure of the kaolinite and the formation of an amorphous product. The surface area increased with grinding time, mainly in KGa-2 (maximum value 50.27 m 2 /g), a result associated with particle-size reduction. These particles became more agglomerated with grinding, and the surface area decreased after 30 min, as confirmed by scanning electron microscopy and particle-size-distribution analysis. There was a limit to particle-size reduction with grinding time. When grinding time was increased, the original endothermic differential thermal analysis (DTA) effects of dehydroxylation in both samples shifted to lower temperatures, decreased in intensity, then disappeared completely after 120 min of grinding. The temperature of the characteristic first exothermic effect shifted slightly to lower temperatures with grinding, although the DTA effects did not increase with grinding time in either kaolinite sample, at least up to 325 min. The amorphous, mechanically activated kaolinite converted into low-crystalline mullite nuclei at a lower temperature than did the unground samples, as deduced by thermal and X-ray observations. This effect was especially important for the KGa-2 sample. Grinding did not seem to influence the formation of silicon-aluminum spinel from kaolinite. The present results may explain why ground kaolinite samples prepared via different routes-e.g., with differences in grinding-behave differently during high-temperature transformations, as reported in the related literature.

Effects of Dry Grinding on the Structural Changes of Kaolinite Powders

Porous mullite and mullite-based composites have been prepared from a chemical processing route starting from a precursor obtained using an aqueous suspension of kaolinite and aluminium hydroxide. This was coprecipitated with kaolinite using ammonium hydroxide or hexamethylenediamine (HMDA), and a solution of aluminium chloride prepared from dissolved recycled wastes of aluminium metallic powders. Raw and ball-milled kaolinite during 30 minutes have been employed. The precursors and the obtained materials were characterized by X-ray diffraction (XRD) and thermal diffractometry, simultaneous differential thermal analysis (DTA) and thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), flexural strength test at room temperature and Hg intrusion porosimetry. The feasibility of using HMDA as a precipitating agent in the proposed chemical processing route for mullite preparation has been demonstrated. The advantageous use of HMDA, as compared with ammonium hydroxide, and ground kaolinite, as compared with raw kaolinite, produced single-phase mullite materials and enhanced the flexural strength of the resultant ceramic porous bodies by firing at 1550–1600 °C (porosity 50–45 vol%). These materials would have application as refractories, substrates, filters and thermal isolating materials.

http://www.biblioteca.uma.es/bbldoc/articulos/16670346.pdf

Ignacio Varona

Papers

Effects of Dry Grinding on the Structural Changes of Kaolinite Powders

Porous mullite and mullite-based composites by chemical processing of kaolinite and aluminium metal wastes