Stengl, V., D. Popelkova and T. M. Grygar (2014) Composite pigments based on surface coated kaolin and metakaolin. Applied Clay Science 101, 149-158.

Abstract: 

Synthesis: The method of homogeneous hydrolysis of Fe, Co, Cr, Ni, Mn, Ti, Al, and Zn salts with urea in aqueous solutions in the presence of substrates (kaolin, metakaolin and mullite) was used for the preparation of composite pigments. In these composites individual kaolinite platelets were covered by a thin layer of hydroxide or oxy-hydroxides of selected metals, which were transformed into a metal oxide layer strongly bond to the aluminosilicate surface by heat treatment. An analogous method, homogeneous hydrolysis of thioacetamide in the presence of Cd and Zn salts was used for pigments based on sulphides.

Characterization: The mineralogical composition of the pigments was identified by X-ray powder diffraction (XRD), the particle morphology was studied by transmission electron microscopy (TEM) and the color was characterized in CIEL*a*b colours coordinates.

Results: The kaolin and metakaolin coated with layer of metal oxides are interesting new composite materials, obtained by a very simple preparation process at a low cost. DOI: 10.1016/j.clay.2014.07.030