A water-based process for the surface functionalisation of ceramic fibres
This research work applied the hydrothermal process to the surface treatment of ceramic fibres which are integrated into the fabrication of ceramic matrix composites (CMCs). In the conventional process, the main step consists in dissolving the oxidised phases at the fibre surface using strong acids. As a consequence, the chemical homogeneity of the surface is improved and a microporous carbon (C) film is generated at the fibre surface. The C-rich surface enhances the compatibility of the fibre with the pyrocarbon interphase that is deposited on the fibres prior matrix deposition when processing CMCs. This paper shows the possibility to substitute this conventional process using strong acids by a hydrothermal treatment. Indeed, as water displays tunable physico-chemical properties as a function of temperature and pressure, it is possible to recover fibres demonstrating similar surface characteristics as the ones obtained after the reference acid-based treatment. The efficiency of the hydrothermal treatment is assessed through optimised surface properties obtained after one single step process operating in a semi-continuous mode. Then, the mechanism investigation reveals a selective attack of the Si atoms contained in the fibre via a hydrolysis reaction. Besides, it is denoted that the process follows a zero order kinetics. This allows a fine control of the fiber surface properties to obtain CMC with high thermomechanical performance.