Oxidation protection of C/C–SiC composites by an electrophoretically deposited mullite precursor: Cyclic thermogravimetric analysis

Sufficiently thick and homogeneous layers which transform into mullite at T ≥ 1000 °C were synthesized by means of sol–gel technology and electrophoretically deposited onto the surface of C/C–Si–SiC composites. The protectiveness of the deposited mullite layers was isothermally tested in air in the temperature range 1200 ≤ T ≤ 1550 °C for up to 200 h. At temperatures above 1600 °C, the protectiveness of the deposited layer is reduced due to the existence of a liquid phase and the formation of CO bubbles above the cracks in the SiC layer. In order to prolong the protectiveness of our mullite layers at higher temperatures an additional layer from a suspension of mullite precursor with 5 wt.% of Al2O3 powder was deposited. The protectiveness of the obtained mullite and mullite/Al2O3 multilayer systems were also tested under cyclic conditions. These experiments yielded encouraging results, which will have to be confirmed at higher temperatures.