THE EFFECT OF SILICA ON HYDROGEN EVOLUTION AND CORROSION OF IRON IN HIGH-TEMPERATURE WATER

Corrosion of iron in high-temperature water was investigated by observing pH change and hydrogen liberation from solutions dispersed with fine iron powders of large specific surface area. The observed rapid increases in pH here attributed to the extremely large surface-to-solution ratio. It has found that hydrogen liberation has significantly suppressed by silica, which implies that silica can work as a corrosion inhibitor. It has postulated that corrosion has inhibited by the thin protective layers formed through the silica coordination on iron surface and the subsequent olation reaction among ferrous/ferric ion and hydroxyl ion. The specific amount of silica required for corrosion inhibition was estimated to be 3.9 x 10(-10) mol Si/cm2 Fe. Silica also controlled hydrogen evolution or corrosion even under gamma-ray irradiation. It was found that dissolved oxygen enhanced the corrosion inhibition by silica in the presence of gamma-rays.