Method of producing dense refractory oxide coatings on metallic substrates and the production of catalysts from the coated substrates

A method of coating a substrate with a refractory oxide which comprises the steps of

• (i) contacting the substrate with a sol comprising an aqueous dispersion of substantially unaggregated colloidal primary particles of ceria or of aggregated colloidal primary particles of ceria and ions which occupy gaps in said aggregated particles, said sol being capable of being converted to a gel of the refractory oxide, the bulk density of the gel being at least 40% of the theoretical density of the refractory material;
• (ii) converting the sol to a gel to provide the substrate with a gel coating;
• and
• (iii) firing to convert the gel coating to a refractory oxide coating.

A method of coating a substrate with a other than silica which comprises the steps of

• (i) contacting the substrate with a sol of said refractory oxide comprising a dispersion, in a liquid medium, of substantially unaggregated colloidal primary particles of the refractory oxide or of aggregated colloidal primary particles of the refractory oxide and ions which occupy gaps in said aggregated particles, said sol being capable of being converted to a glass-based material by carrying out steps (ii) and (iii) below:
• (ii) converting the sol to a gel to provide the substrate with a gel coating, the bulk density of the gel being at least 40% of the theoretical density of the refractory material;
• and
• (iii) firing to convert the gel coating to a glass-based refractory oxide coating.

A method of coating a substrate with a other than silicawhich comprises the steps of

• (i) contacting a Nb stabilized Cr bearing austentic steel with a sol of said refractory oxide comprising a dispersion, in a liquid medium, of substantially unaggregated colloidal primary particles of the refractory oxide or of aggregated colloidal primary particles of the refractory oxide and ions which occupy gaps in said aggregated particles, said sol being capable of being converted to a gel of the refractory oxide, the bulk density of the gel being at least 40% of the theoretical density of the refractory material;
• (ii) converting the sol to a gel to provide said austentic steel with a gel coating;
• and
• (iii) firing to convert the gel coating to a refractory oxide coating.