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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 at150°C for 15 min to chemically aggregate the kaolin plates in a structuredconfiguration. X-ray powder diffraction analysis indicated that kaolin wasthe only crystalline phase present. Chemical analyses showed that about 0.25- 1.1 % Na2O and 1.2 - 5.0 % K2O were trapped in thesolid phase depending on the reaction conditions. Mercury porosimetryindicated a highly porous nature with pore volumes of 0.3 - 1.4 ml/g andmedian pore sizes of 0.06 - 0.3 μm. Scanning electron micrographs showedthat the aggregation was achieved by surface modification and randomassociation (edge to edge and face to edge, face to face) of the particles.Measurement of light scattering coefficient of the coating showed anincrease of ∼350% in scattering compared to that of the precursor kaolin.These materials are useful in imparting highly opacifying properties topaper and paint. They are also potentially useful as catalysts, catalystsupports, and in other applications which demand a high light scatteringability and macroporous nature.