Study on characterisation and influence of surfactants on adhesion and coating thickness of electroless Ni-P deposits

Abstract

Electroless nickel–phosphorus (EN) deposits with and without addition of surfactants were made on mild steel substrates. Two surfactants namely sodium dodecylsulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) were used in the study. The EN coated samples were characterized using X–ray diffraction analysis and transmission electron microscopy. The XRD pattern of all the deposits indicated the presence of crystalline and amorphous phases coexisting in the as deposited condition. Profile refinement techniques have been used to separate the crystalline nickel (111) reflection from the amorphous profile. The crystallite size of nickel was found to vary from 200 nm in the as deposited condition to 80 nm with addition of surfactant. TEM study reveals a nano crystalline structure of the deposit in as plated condition and an amorphous structure with addition of surfactants. With addition of surfactants adhesion was good. The coating thickness varied from 12.7 µm to 32.2 µm with addition surfactants.