The reduction processes of Pd(II) with Sn(II) in hydrochloric acid, which constitute main reactions in sensitization and activation, were investigated as a fundamental study on the metallization of plastics.
The reduction processes and the behavior of intermediates were pursued by means of potentiometric, spectrophotometric, and polarographic methods.
The following results were obtained:
1) In the course of reduction processes, the complex ions in the form of [Pd(II)Sn(II)
mCl
x]
n- (in which m=2 and 6) were formed. The complex ions of m=6 were more stable than those of m=2 with the increase in the ratio of Sn(II)/Pd(II) and Cl
- concentration in the solutions.
2) These complex ions were gradually decomposed by the intramolecular redox reaction of Pd(II) with Sn(II) to form free Pd(0) and Sn(IV).
3) The substance which acts as an active site in the electroless plating process was assumed to be the negatively charged metallic palladium colloid, which was formed by the above intramolecular redox reaction and was stabilized by adsorption of Sn(II).
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