Process for the preparation of metal oxide coated organic material by microwave deposition

A process for the preparation of an organic material comprising an organic substrate and at least one dielectric layer consisting of one or more oxides of a metal selected from groups 3 to 15 of the periodic table, which comprises the steps of:

• (a) suspending the organic substrate in an aqueous solution of a fluorine scavenger;
• (b) adding an aqueous solution of one or more fluorine containing metal complexes which are the precursors of the desired metal oxide coating;
• (c) subjecting said suspension to microwave radiation to deposit the metal oxide onto said organic material, wherein steps (b) and (c) can optionally be repeated using different fluorine containing metal complexes to produce one or more metal oxide layers or a gradient of concentration of 2 different metal oxides across the thickness;
• (d) adding a solution of one or more fluorine containing metal complexes which are the precursors of the desired metal oxide coating which is different from the oxide coating in step (b);
• (e) subjecting said suspension to microwave radiation to deposit the metal oxide onto the coated organic substrate;
• (f) adding a solution of one or more fluorine containing metal complexes which are the precursors of the desired metal oxide coating which is different from the oxide coating in step (d);
• (g) subjecting said suspension to microwave radiation to deposit the metal oxide onto the coated organic substrate,
• wherein the metal oxide in steps (b) and (f) is iron oxide and the fluorine containing metal complex is selected from the group iron(III) chloride, hydrofluoric acid and ammonium fluoride mixtures, and the metal oxide in step (d) is titanium dioxide and the fluorine containing metal complex is selected from the group consisting of ammonium hexafluorotitanate, a complex prepared from ammonium fluoride and titanium chloride or titanium chloride, ammonium fluoride and hydrogen fluoride.