CHEMISTRY OF COLLOIDAL SILVER - REACTIONS OF LEAD ATOMS AND SMALL LEAD AGGREGATES WITH AG-N

The reactions of lead atoms with 70 Angstrom A colloidal silver particles in aqueous solution are investigated. The lead atoms are generated by a short pulse of high energy radiation. The formation of a lead mantle around the silver particles is recognized by the changes in the shape of the surface plasmon absorption band of the silver particles. At low intensities (low lead atom concentration of 5.10(-8) M) almost all the lead atoms generated reach the silver particles before they form larger aggregates by coalescence reactions in the bulk of the solution. The specific rate of the reaction of lead atoms with silver particles is about 5 times smaller than expected from a diffusion controlled rate. The plasmon absorption band is blue-shifted when the lead atoms react with the silver particles. It is concluded from the details of this shift that the first Pb atoms reaching the silver particles transfer an electron to them, and that the atoms, which arrive later, are just deposited. Time resolved measurements show that small aggregates of lead, which are formed at higher intensities, can still contribute to mantle formation around the silver particles. Lead particles with agglomeration numbers larger than 10 to 20 do no longer contribute to lead deposition; they form colloidal lead.