Electroless Deposition of Ni-Sn Layers Having High Sn Content（＞30 at.%）on Fe Substrates（2）: Examination on complexing agent and durability of bath

Electroless deposition of nickel-tin（Ni-Sn）layers on iron（Fe）substrates from baths containing sodium hypophosphite（NaH2PO2）as a reducing agent was examined. In a bath containing both sodium citrate（Na3C6H5O7）and sodium gluconate（HOCH2 （CHOH）4COONa）as com plexing agents, the Ni-Sn layer having 1 μm thickness and atomic Sn content of 30-40 at.% was formed. The bath stability was maintained until the 10th deposition process. Optimizing the concentration ratios of sodium citrate to sodium gluconate and to sodium stannate（Na2SnO3）was important to ascertain the Ni-Sn layer properties for this study. The main component of the Ni-Sn layer was found to be Ni1.5Sn. A small amount of the Ni layer was included in the layer. Results confirmed that the Ni-Sn layer formed from the optimized bath with NaH2PO2/ Na3C6H5O7/ HOCH2 （CHOH）4COONa had nearly perfect chemical resistance properties against hydrogen peroxide and sodium hydroxide aqueous solutions.