An Experimental Study on the Effect of Aqueous Hypophosphite Pre-Treatment Used on an Aluminium Alloy Substrate before Electroless Nickel Plating
A new surface pre-treatment procedure has been developed in one of our laboratories  for electroless nickel (EN) plating, which appears to be an effective and environmentally benign treatment for the following deposition of a sound and high quality surface nickel coating with good adhesion. For that purpose, the aluminium substrate was immersed in a mildly acidic solution (lactic acid) of sodium hypophosphite in order to modify the passive surface and make it suitable for the reductive chemical precipitation of the nickel-phosphorus nuclei from the electroless nickel plating bath. During this novel pre-treatment technique, the surface adsorption of the hypophosphite anions play an important role therefore several advanced surface testing and analytical techniques (Scanning Electron Microscopy-SEM, Transmission Electron Microscopy-TEM, Energy Dispersive X-ray Spectrometry-EDX, X-ray Photoelectron Spectroscopy-XPS were applied in order to monitor and characterize the surface reactions and adsorption phenomena taking place during the pre-treatment. The Al excited XPS (studying P 2p, O 1s, C 1s, Al 2p, Ni 2p photoelectron lines) proved to be one of the most powerful technique in the identification of the chemical species formed and present on the surfaces examined in this study.
P. J. Szabó and T. Berecz
G. Szirmai et al., "An Experimental Study on the Effect of Aqueous Hypophosphite Pre-Treatment Used on an Aluminium Alloy Substrate before Electroless Nickel Plating", Materials Science Forum, Vol. 659, pp. 103-108, 2010