Electrolytic deposition of PZT on carbon fibers for fabricating multifunctional composites

Piezoelectric fiber composites (PFCs) have been developed in order to overcome the fragile nature of monolithic piezoelectric materials by embedding piezoceramic inclusions into a polymer matrix. The flexible nature of the polymer matrix protects the piezoelectric fiber from damage or fracture under mechanical loading and allows the composites to be easily conformed to curved surfaces for use in many applications. Although PFCs have many useful properties, they still suffer from several drawbacks, namely the required separate electrodes make it impossible to embed the composites into the host structure, and the relatively low tensile modulus of the piezoelectric inclusion means that it contributes little to structural properties. To resolve the inadequacies of current PFCs, a novel active structural fiber (ASF) was developed that can be embedded into a composite structure to perform sensing and actuation, and provide load bearing functionality. The concept and feasibility of this ASF has been validated by coating a silicon carbide (SiC) fiber with a barium titanate (BaTiO₃) shell using electrophoresis deposition techniques. However, lead based ceramics react with SiC fiber during high temperature sintering and thus the use of these highly coupled piezoceramics requires alternative deposition approaches. This paper will introduce a new ASF fabricated by coating a single carbon fiber with a concentric PZT (PbZr_0.52Ti_0.48O₃) shell using electrolytic deposition (ELD). ELD quickly and uniformly coats the fiber and, since the PZT precursor has a low crystallization temperature, the carbon fiber is not exposed to high sintering temperatures which typically degrade the in-plane material properties of the fiber and composite. Carbon fiber has been widely used in industry and studied in academia due to its excellent mechanical properties, while PZT has been extensively used for sensing or actuation because of its high piezoelectric coupling. Crystal structures of the PZT before and after annealing are characterized by means of x-ray diffraction, and a pure perovskite structure of the PZT after annealing is shown.