RADIOLYTIC FORMATION OF COLLOIDAL TIN AND TIN-GOLD PARTICLES IN AQUEOUS-SOLUTION

Colloidal tin is formed in gamma-irradiated solutions of SnCl2, which also contain 0.5 M propanol-2 and 5 x 10(-4) M polyethyleneimine. The reduction occurs in the first stages of irradiation by hydrated electr ons. In the later stages, when some colloidal particles have been form ed, the (1-hydroxymethyl)ethyl radicals, (CH3)(2)COH, which as well as the hydrated electrons are primary radiolysis products, contribute to the reduction. The absorption spectrum of Sn particles, which are ess entially smaller than the wavelengths of light, is reported. In the pr esence of colloidal gold particles, the reduction of Sn(II) by organic radicals is strongly enhanced. The effect is ascribed to the cathodic polarization of the Au particles by electron transfer from the radica ls and subsequent reduction of Sn(II) directly on the surface of the A u particles. The optical changes accompanying Sn deposition are also d escribed. For small deposits, the plasmon band of gold is strongly dam ped and only part of the deposited tin can be reoxidized by oxygen. Wh en larger amounts of tin are deposited, alloying occurs to a great ext ent.