Significance of sensitization process in electroless deposition of Ni on nanosized Al2O3 powders

Abstract The electroless deposition of Ni on nanosized α-Al 2 O 3 powders of about 150 nm diameter has been studied by employing SnCl 2 sensitization and PdCl 2 activation approach. The bath for electroless deposition was prepared by using NiCl 2 ·6H 2 O, C 6 H 5 NaO 7 ·H 2 O, NH 4 Cl and NaH 2 PO 2 ·H 2 O, and the deposition was carried out at a bath temperature of 70 °C with a pH value of 8.5. The morphology, microstructure and phase structure of Ni-coated α-Al 2 O 3 nanopowders were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractometry (XRD), respectively. It is found that, the sensitization process followed by repetitive resining greatly affects the morphology of Ni deposited in the form of nanoparticles onto the ultrafine alumina particles, different from the conventional continuous electroless film/coating deposited on coarser particles. The resining of the SnCl 2 sensitized ultrafine α-Al 2 O 3 particles prior to PdCl 2 activation process leads to varied amount of deposited Ni particles with diameters of 50–80 nm on the Al 2 O 3 . It is revealed that, subsequent reduction process (activation) from Pd 2+ to Pd is linked to the original sites of Sn 2+ by simultaneous oxidation process from Sn 2+ to Sn 4+ on the previously sensitized α-Al 2 O 3 nanopowders. Consequently, the form of deposited Ni correlated closely to the surface distribution of reduced Pd which may be continuous or discrete determined predominantly by the density of adsorbed Sn 2+ on the powders during sensitization process. It demonstrates a possibility of depositing different distribution structures of metals on nanosized α-Al 2 O 3 powders through controlling SnCl 2 sensitization process.