Sub-micrometer CoAl2O4 pigment particles -: synthesis and preparation of coatings

Sub-micrometer CoAl2O4 particles are prepared by applying the polyol method. Colloidal particles 50 to 200 nm in size with spherical shape are formed. Their average size can be controlled by adjusting the concentration of the components (metal precursor, water). The resulting suspensions in diethylene glycol can contain up to 10 wt.% CoAl2O4. The colloidal particles are well stabilized against agglomeration even when mixed with water. Based on such colloidal CoAl2O4 suspensions planar substrates (e.g. glass plates) as well as non-planar substrates (e.g. phosphor powder) can be covered homogeneously with thin pigment films. In order to establish the characteristic deep blue body colour of CoAl2O4, additional brief heating (15 min, 600 degrees C) is necessary. Further characterisation of CoAl2O4 powders as well as suspensions was carried out by diffuse reflection measurements, X-ray powder diffraction, scanning electron microscopy, laser diffraction and atomic force microscopy.