An excess of Sn2+ on the target surface of porous stainless
steel can create a loose (crumbly), easy-to-peel layer, while a
deficiency of Sn2+ can lead to nonuniform seeding of the
palladium nuclei. The distribution of catalytic centers for autocatalytic
Pd2+ reduction must be dense and uniform at an
optimum concentration of Sn2+ on the surface. To reach this
goal, a two-step immersion sequence in SnCl, and PdCI, solutions
was generally repeated 4-10 times, depending on the
intensity of the activation. A perfectly activated layer has a
uniform dark-brown color and smooth surface. If the quality
of the activated layer was unsatisfactory, it was removed in
an ultrasonic bath with l-M HCl and the activation procedure
was repeated