γ-Radiolysis of Liquids at High Pressures. I. Aqueous Solutions of Ferrous Sulfate

Abstract

The γ radiolysis of aerated and deaerated, acid solutions of ferrous sulfate has been studied at 20° and applied pressures in the range 0 to 6.34 kbar. Over the entire pressure range, G(Fe⁺⁺⁺)=8.1±0.1 and G(H₂)=4.1±0.1 in deaerated solutions containing 0.8N H₂SO₄, 1 mM NaCl and 2 mM Fe⁺⁺. Radiolysis of deaerated, 0.8N H₂SO₄ solutions of dichromate gives G(O₂)=0.78±0.02 over the whole pressure range. It is concluded from such results, and observation of a similar pressure independence of G(Ce⁺⁺⁺) in the ceric sulfate dosimeter, that primary yields in water radiolysis are invariant as pressure varies from 0 to 6.34 kbar. In aerated ferrous solutions, G(H₂), G(Fe⁺⁺⁺), and G(—O₂) vary with pressure, ferrous concentration, and acid concentration in such a manner as to indicate an effect of pressure on the competition between Reactions [1] and [2]: $$\mathrm{H}+{\mathrm{O}}_2\to {\mathrm{HO}}_2,$$ $$\mathrm{H}+{\mathrm{H}}^{+}+{\mathrm{Fe}}^{\mathrm{++}}\to {\mathrm{Fe}}^{\mathrm{+++}}+{\mathrm{H}}_2.$$ Analysis of the results, for aerated ferrous solutions containing 0.8N H₂SO₄ and 1 mM NaCl, gives k₁/k₂≈1000 at atmospheric pressure and k₁/k₂=80 at 6.34 kbar. The difference in activation volumes of Reactions [1] and [2] is obtained as ΔV₁^‡—ΔV₂^‡ = 11 ml mole⁻¹. Estimation of ΔV₁^‡≈2 ml mole⁻¹, from the pressure dependence of water viscosity, gives ΔV₂^‡≈−9 ml mole⁻¹. Such a value is not inconsistent with H+Fe⁺⁺→FeH⁺⁺ as the rate‐determining step in the over‐all reaction [2] in 0.8N H₂SO₄.