A Dielectric Sensing Approach for Controlling Matrix Composition During Oxide-Oxide Ceramic Composite Processing

Continuous fiber reinforced ceramic matrix composites (CMC’s) made from aluminum oxide fibers and matrices are usually fabricated using a tape casting process. In this process, ceramic slurry consisting of the oxide powder, a polymeric binder and a solvent is infiltrated into a woven ceramic fiber mat. After evaporation of some of the solvent, the resulting flexible tapes can be stacked and sintered to create a composite component. Because the fraction of ceramic powder in the slurry can vary during processing, in-situ compositional sensors are required for on-line feedback control to limit property variations in the composite material. Since the dielectric properties of the slurry components are distinctly different, the effective permittivity of the slurry depends upon its composition. Here, a non-contact capacitance probe has been used to explore the possibility of capacitance sensing for compositional control. Results indicate that the removal of solvent during a precision drying step may be monitored by this approach. The feasibility of monitoring changes in the slurry’s composition during infiltration of the fiber mat is also discussed.