Characterization of carbon fabric coated with Ni-P and Ni-P-ZrO₂-Al₂O₃ by electroless technique

Abstract

Ni-P and Ni-P-ZrO₂-Al₂O₃ (Ni-P-X) composite coatings on carbon fiber woven fabric have been attempted by electroless (EL) coating technique. For producing Ni-P EL coating, a sodium hypophosphite is used as reducing agent in alkaline bath whereas for producing composite coating, in the same bath, the co-precipitation of Al₂O₃ along with ZrO₂ by a chemical reaction has been used. The bath used was maintained at pH value of 9 ± 0.25 and a temperature of 90 ± 2°C for all the coatings under investigation. The morphology of coatings has been studied under SEM and the phases have been identified by XRD and TEM. The phases like microcrystalline nickel, amorphous nickel, Ni₅P₄ and Ni₁₂P₅ have been identified to be present. The grain size of these phases has been seen to be in the range of 5–10 nm. The tensile strength of as-coated and heat treated samples of both the types of coatings have been compared with that of uncoated fabric. The UTS values of uncoated carbon fabric used has been found to 3.7 N/mm² whereas that for heat treated after coating the fabric samples with Ni-P and Ni-P-ZrO₂-Al₂O₃ EL coatings have been observed to be 11.1 and 12.4 N/mm² respectively.