Pulse Radiolysis Study on the Estimation of Radiolytic Yields of Water Decomposition Products in High-Temperature and Supercritical Water: Use of Methyl Viologen as a Scavenger

In the present work, methyl viologen (1,1‘-dimethyl-4,4‘-bipyridinium dichloride) is used as a scavenger to estimate the radiolytic yields of water decomposition products from room temperature to 400 °C by pulse radiolysis method. { G (e aq - ) + G (OH) + G (H)} has been studied using a 0.5 mM MV 2+ solution in the presence of 10 mM NaCOOH up to 200 °C and in the presence of 0.2 M ethanol up to 400 °C. The results show that the { G (e aq - ) + G (OH) + G (H)} increases with temperature up to 350 °C at 25 MPa, while it depends also on pressure in supercritical conditions. The G (e aq - ) was estimated using MV 2+ solutions in the presence of 0.2 M tert -butyl alcohol. The results agree well with the reported data up to around 300 °C at 25 MPa; however, in supercritical conditions a very significant density effect was observed. At a given temperature, G (e aq - ) and { G (e aq - ) + G (OH) + G (H)} decrease with increasing density while at a fixed density they decrease with increasing temperature.