Room-temperature aqueous plasma electrolyzing Al ₂ O ₃ nano-coating on carbon fiber

A novel room-temperature aqueous plasma electrolysis technique has been developed in order to prepared Al ₂ O ₃ nano-coating on each fiber within a carbon fiber bundle. The microstructure and formation mechanism of the Al ₂ O ₃ nano-coating were systematically investigated. The oxidation resistance and tensile strength of the Al ₂ O ₃ -coated carbon fiber was measured at elevated temperatures. It showed that the dense Al ₂ O ₃ nano-coating was relatively uniformly deposited with 80–120 nm in thickness. The Al ₂ O ₃ nano-coating effectively protected the carbon fiber, evidenced by the slower oxidation rate and significant increase of the burn-out temperature from 800 °C to 950 °C. Although the bare carbon fiber remained ∼25 wt.% after oxidation at 700 °C for 20 min, a full destruction was observed, evidenced by the ∼0 GPa of the tensile strength, compared to ∼1.3 GPa of the Al ₂ O ₃ -coated carbon fiber due to the effective protection from the Al ₂ O ₃ nano-coating. The formation mechanism of the Al ₂ O ₃ nano-coating on carbon fiber was schematically established mainly based on the physic-chemical effect in the cathodic plasma arc zone.