Particle Size Effect of Silica Gel on the γ-Radiation Induced Electrical Conductivity of Urea Aqueous Solutions

Different concentrations (0.1, 3, 6 M) of urea aqueous solutions have been irradiated with Co-60-gamma-rays in the presence of silica gel (SG) of different particle size (0.1-0.5mm) at room temperature. The radiation-induced electrical conductivity (RIC) of the irradiated solutions was measured. The RIC values of the 0.1 M solutions increase as the particle size of SG decreases i.e., the particle surface area increases. This observation points to a radiation-induced chemical reactions, which are catalyzed by SG. These reactions, probably, yield products, which increase the RIC such as urea peroxide (UP). On the other hand, a different behavior was observed in the case of 3, 6 M solutions, where, the RIC increases as particle size increase. So, the mechanism of production of the species which increase the RIC of 0.1 M samples is different from that in the case of 3, 6 M. In all irradiated samples, the pH values tend to increase, slightly, as particle size increases. A mechanism was proposed to explain the obtained data.