| 摘要 |
PURPOSE: A layer on a substrate is provided which has high mechanical stability and is free from cracks, and a process for the preparation of this layer is provided which leads to crack-free layers in a single coating step, wherein the thickness of the layer can be varied within wide limits. CONSTITUTION: In a layer obtained by thermal treatment from an aqueous dispersion applied to a substrate, the layer is characterized in that the dispersion contains silicon/titanium mixed oxide powder prepared by flame hydrolysis, wherein the thickness of the layer is between 100 nm and 1 mm, preferably between 1 and 50 μm, particularly preferably between 5 and 15 μm, wherein the BET surface area of the powder is between 5 and 500 m¬2/g, wherein the titanium dioxide content of the powder is between 0.1 and 99.9 wt.%, particularly preferably between 2 and 20 wt.%, and wherein the layer contains a mixture of powders with high BET surface areas of at least 170 m¬2/g and those with low BET surface areas of at most 70 m¬2/g, preferably with high BET surface areas of at least 130 m¬2/g and those with low BET surface areas of at most 90 m¬2/g, wherein the ratio by weight of powder with lower to powders with higher BET surface areas is between 40:60 and 99.5:0.5. The process for preparing the layer comprises the processes of applying the dispersion containing silicon/titanium mixed oxide powder to a substrate; and sequentially sintering the dispersion applied substrate by thermal treatment.
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