Oxidation protection of carbon fibers by coating with alumina and/or titania using atomic layer deposition

Alumina and titania coatings were deposited by atomic layer deposition onto carbon fibers at temperatures of 200 °C or below and reduced pressure. The coatings were smooth, uniform and conformed to the fiber surface. Thermogravimetric analysis (TGA) revealed that the coatings improved the oxidation resistance of the carbon fibers: the oxidation onset temperature of uncoated fibers and fibers coated with 66 nm of alumina was 630 °C. For fibers coated with 20 nm of titania it was 550 °C. Double layer coatings by 50 nm of alumina followed by 13 nm of titania yielded an oxidation onset temperature of 660 °C, while changing the order of the layers, i.e., coating fibers first with 20 nm of titania followed by 30 nm of alumina yielded an oxidation onset temperature of 750 °C. These TGA results were confirmed by a set of additional oxidation experiments conducted at a fixed temperature of 550 °C using a tube furnace in air. In this latter set of additional experiments, the times needed for a complete oxidation of the above mentioned samples were 8 h, 12 h, 10 h, 13 h, and 30 h, respectively.