Fiber-reinforced ceramics for thermostructural applications, produced by polymer impregnation pyrolysis

Several CFCC (Continuous Fiber Composite Ceramics) production processes were tested, concluding that PIP (Polymer Impregnation, or Infiltration, Pyrolysis) and CBC (Chemically Bonded Ceramics) based procedures have interesting potential applications in the construction and transportation fields, thanks to low costs to get potentially useful thermomechanical performances. Among the different processes considered during the Doctorate (from the synthesis of new preceramic polymers, to the PIP production of SiC / SiC composites) the more promising results came from the PIP process with poly-siloxanes on basalt fabrics preforms. Low processing time and costs, together with fairly good thermomechanical properties were demonstrated, even after only one or two PIP steps in nitrogen flow. In alternative, pyrolysis in vacuum was also tested, a procedure still not discussed in literature, but which could originate an interesting reduction of production costs, with only a moderate detrimental effect on the mechanical properties. The resulting CFCC is a basalt / SiCO composite that can be applied for continuous operation up to 600°C, also in oxidant environment, as TG and XRD demonstrated. The failure upon loading is generally pseudo-plastic, being interlaminar delamination the most probable rupture mechanism. . The strength depends on several different factors (microstructure, polymer curing and subsequent ceramic phase evolution, fiber pull-out, fiber strength, fiber percentage) and can only be optimized empirically. In order to be open minded in selecting the best technology, also CBC (Chemically Bonded Ceramics) matrixes were considered during this Doctorate, making some preliminary investigations on fire-resistant phosphate cements. Our results on a commercial product evidenced some interesting thermomechanical capabilities, even after thermal treatments. However the experiments showed also phase change and possible cracking and deformations even on slow drying (at 130°C) and easy rehydration upon exposure to environmental humidity.