Role of various pretreatment processes in electroless nickel deposition on TiH2 particles with a simple plating bath

Abstract

Electroless nickel was successfully deposited on TiH2 particles with a simple plating bath which contains only a nickel salt NiCl2 and a strong reductant dimethylamine borane (DMAB) and the effect of various pretreatment processes was studied. The three different pretreatment processes include: (1) a two-step pretreatment with SnCl2 sensitization followed by PdCl2 activation (SnCl2–PdCl2); (2) only PdCl2 activation, and (3) without pretreatment (direct electroless deposition). The characteristics of TiH2 powders before and after nickel deposition were analyzed with field emission scanning electron microscopy (FE-SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). It was found that except for the traditional SnCl2–PdCl2 pretreatment process, the pretreatment with only PdCl2 activation and direct electroless nickel deposition without any pretreatment of the powder surface can both lead to continuous and homogeneous nickel layer on TiH2 powders. This may be due to the strongly negatively charged powder surface with its very low isoelectric point (I.E.P.) which promotes the adsorption of Ni2+ from the plating bath onto powder surface. On the other hand, the strong reducing agent DMAB facilitate the reduction of Ni2+ ions even without Pd catalysation. This work provides a simplified and alternative way for electroless nickel coating on TiH2 powders with the application in aluminium foaming.