Deposition and characterization of electroless palladium on austenitic stainless steel

A standard electroless plating bath containing PdCl 2 was used to deposit a thin (about 0.5 μm) layer of palladium on type 304 stainless steel specimens. The deposited layer closely followed the contours of the substrate and filled in most surface defects. For typical plating times (10 min), the palladium consisted of a smooth, coherent inner layer of agglomerated nodules and an upper layer of discrete nodules. Removal of the existing oxide layer by sulfuric acid was essential for deposition of palladium. Stirring of the bath led to cracking of the palladium. Earlier work showed that the palladium film was extremely resistant to incorporation of the 60Co radionuclide following exposure in either simulated boiling water reactor or pressurized water reactor primary coolant. Scanning electron micrographs of the palladium coating following exposure in the latter environment showed it to be little changed from the as-deposited film, whereas a duplex layer oxide about 10 μm thick formed on an unplated surface. Thus, the palladium reduced the corrosion of the stainless steel and so reduced the incorporation of 60Co.