Deposition of ceramic layers on carbon fibers by continuous liquid phase coating

Carbon fibers are widely used as reinforcement fibers for composite materials. Especially in the case of ceramic matrix composites (CMCs) and metal matrix composites (MMCs), the protection of the fiber is very important to avoid hot corrosion, fiber oxidation or formation of carbides during high temperature manufacturing processes or high temperature application. Controlling the fiber-matrix-interface properties by deposition of coatings increases the tensile strength of the composites. Continuous liquid phase coating of commercial fiber strands with ceramic or carbon precursors solutions with subsequent drying, curing, pyrolysis and calcination is a cost efficient process to deposit dense and homogenous coatings. The precursor systems tested were silazanes, siloxanes, borasilazanes, phenolic resins and coal tar pitch. Scanning electron microscopy showed that the resulting fiber strands were monofilamentwise coated. Tensile tests of the coated fibers specimens were performed according DIN 65382 A. The parameters of the pilot plant were systematically varied in order to obtain optimum tensile strength. The output of the plant (200–350 m/d 12 k roving, 800 tex) is sufficient to produce enough material for manufacturing of composite samples in pilot plant scale. The coated carbon fibers were applied as reinforcement fibers in ceramic composites, both as unidirectional reinforcement or chopped.