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Published online by Cambridge University Press: 21 February 2011
A kaolin was hydrothermally treated with various amounts of NaOH and KOH at 150°C for 15 min to chemically aggregate the kaolin plates in a structured configuration. X-ray powder diffraction analysis indicated that kaolin was the only crystalline phase present. Chemical analyses showed that about 0.25 - 1.1 % Na2O and 1.2 - 5.0 % K2O were trapped in the solid phase depending on the reaction conditions. Mercury porosimetry indicated a highly porous nature with pore volumes of 0.3 - 1.4 ml/g and median pore sizes of 0.06 - 0.3 μm. Scanning electron micrographs showed that the aggregation was achieved by surface modification and random association (edge to edge and face to edge, face to face) of the particles. Measurement of light scattering coefficient of the coating showed an increase of ∼350% in scattering compared to that of the precursor kaolin. These materials are useful in imparting highly opacifying properties to paper and paint. They are also potentially useful as catalysts, catalyst supports, and in other applications which demand a high light scattering ability and macroporous nature.