Abstract

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 °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.