No abstract

Largely monodisperse, crystalline nanoscale oxide particles (for example, Cu2O, TiO2, Nb2O5) are preparatively accessible with the polyol method (see picture). The colloidal suspensions of the particles thus obtained can be employed readily for the homogeneous coating of various substrates (for example, glass plates, Al2O3 powder).

Sub-micrometer CoAl 2 O 4 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.% CoAl 2 O 4 . The colloidal particles are well stabilized against agglomeration even when mixed with water. Based on such colloidal CoAl 2 O 4 suspensions planar substrates (e.g. glass plates) as well as non-planar substrates (e.g. phosphor powder) can be covered homogeneously with thin pigment ®lms. In order to establish the characteristic deep blue body colour of CoAl 2 O 4 , additional brief heating (15 min, 600 ³C) is necessary. Further characterisation of CoAl 2 O 4 powders as well as suspensions was carried out by diffuse re¯ection measurements, X-ray powder diffraction, scanning electron microscopy, laser diffraction and atomic force microscopy.

Spherical particles of α–Fe2O3 80 to 100 nm in size were prepared with the polyol method. Scanning electron microscopy, x-ray powder diffraction, and measurements of the diffuse reflection were used to characterize the powder material. The characteristic red color of hematite was adjusted after brief heating (250 °C, 15 min) which did not lead to further particle growth. The polyol method turned out to be suited for the preparation of quite concentrated (up to 20 wt%) and very stable suspensions of submicron Fe2O3 particles. Based on such suspensions, the red emitting phosphor Y2O2S:Eu was coated as a model substrate. As a result, very homogeneous coatings of α-Fe2O3 on the phosphor material were realized. Individual iron oxide particles on the phosphor surface confirm the presence of nonagglomerated Fe2O3 particles in the polyol medium.

Weitgehend monodisperse und kristalline nanoskalige Oxidpartikel (z. B. Cu2O, TiO2, Nb2O5) sind mit der Polyol‐Methode präparativ gut zugänglich (siehe Bild). Die erhaltenen kolloidalen Suspensionen der Partikel können in einfacher Weise zur homogenen Bedeckung unterschiedlichster Substrate (z. B. Glasplatten, Al2O3‐Pulver) verwendet werden.