Atmospheric pressure microwave plasma fluidized bed CVD of AlN coatings

A fluidized bed chemical vapor deposition (CVD) process for depositing thin AlN coatings on particulate substrates was developed. Short carbon fibers were fluidized in nitrogen at atmospheric pressure and charged with microwaves at 2.45 GHz frequency. In the resulting nitrogen plasma, the coatings that composed mainly of AlN, were deposited from trimethylaluminum (TMA) in temperature range of 400–900 °C. Produced coatings were further characterized by scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis. Decomposition of TMA, further chemical reactions, and the role of the microwave plasma were studied, and the process deposition rates were determined. It was found that the coated short carbon fibers exhibit enhanced oxidation resistance at high temperatures in air as compared to the starting material. A mechanism of coated carbon fiber oxidation was postulated to interpret these findings.