Electroless Nickel-Phosphorus-Polymer Composite Coatings

Abstract

This study examines the use of polyvinyl-pyrrolidone (nitrogen containing compound) (PVP) coating on electroless Ni-P deposit on low steel. Three different average molecular weights of PVP were used, molecular weight 10.000 (PVP-10), molecular weight of, 24.500 (PVP-24.5) and molecular weight 40.000 (PVP-40). Coatings were characterized using X-ray diffraction (XRD). Scanning electron microscope (SEM) was used to determine the surface morphology. The microhardness and corrosion resistance of the composite were studied. It was found that i-the micro hardness decreases in presence of the polymer PVP, ii-the corrosion resistance greatly increases in the presence of PVP and iii-the adhesion of the coatings with the substrate increase in the presence of polymer. Electroless nickel-phosphorus is widely used in chemical, mechanical and electronic industries because of its corrosion, wear resistance and its inherently uniform coating thickness [1]. Electroless plating allows complex parts to be plated evently and completely even over sharp edges and deep recesses. These would be difficult to plate with electrolytic processes because of current density variation. These systems are autocatalytic (self-catalyzing) meaning that they will continue to plate into their own deposit after the substrate has been completely covered [2-4]. In recent years the electroless nickel process has been used in a wide variety of applications in aerospace, automotive, electronics, computers, machinery, nuclear, oil, gas production and value industries. Composite coatings using electroless nickel as the matrix have increased the surface finishing and engineering communications for many years. Composite coatings containing polymers have achieved promising results in improving mechanical properties of coated films. Many articles containing electroless nickel polymer composites have been reported. It was found that Teflon reduces the hardness and wear resistance of the coated film. Shoeibe [5] showed that electroless nickel polymer composite improved the physico mechanical properties of coated film, improves impact resistance, ductility and reduce the hardness of the coated film, also, increases the protection of corrosion. Zhao [6] showed that nickel polymer had anticorrosion properties in HCl and NaCl. Best corrosion protection of carbon steel and copper results was obtained with polyaniline (Pani) and poly-(orthoxyaniline) (poma) by Verar [7].