Effects of boric acid on the generation of hydrogen by aluminum-containing hydrocompounds with chemical activating agents
UDC: 620.9 + 544 (075)
Results of investigation of kinetics of hydrogen generation by chemical hydrocompounds containing aluminum, chemical activating agents (hydrated sodium metasilicate, nitric oxide and calcium hydroxide) and boric acid are presented. Aluminum is protected from direct contact with water and steam by the surface layer of aluminum oxide Al2O3 possessing high corrosion resistance against exposure to water and steam at high temperatures in high-intensity radiation fields. After removal of the oxide layer or violation of its integrity aluminum efficiently decomposes water with release of hydrogen. It was established that regularities of formation of hydrogen in aluminum-containing hydrocompounds depend on the concentration of boric acid. Presence of boric acid must be accounted for in the examination of chemical processes of hydrogen generation with involvement of reactor materials, corrective additives and activating impurities in the water coolant of VVER reactors.
According to the implemented studies, kinetics of hydrogen generation by aluminum-containing compositions depends on the concentration of hydrated sodium metasilicate, namely, the induction phase on the curves of hydrogen accumulation increases with decreasing concentration of the activating agent, which is the indication of the decrease in the rate of destruction of the oxide layer. Experimental results showed that calcium-containing chemical activating agents do not affect the limiting hydrogen yield in the interaction with boric acid, but reduce the rate of accumulation of hydrogen. The obtained results evidence complex nature of interactions of reactor materials with water coolant in the presence of corrective additives and impurity molecules that must be accounted for in the examination of water chemistry of VVER-type reactors. If chemical substances, for example, silicon-or calcium-containing compounds imparting alkaline properties to water environment are present in the aqueous medium, then physical and chemical processes of hydrogen formation take place in such a system, which can be divided into the following three stages: aluminum activation; aluminum oxidation by oxygen and interaction of aluminum with water with generation of hydrogen.
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