LiNO3 Effect on Corrosion Prevention of Aluminum with Complex Shapes

The LiNO₃ effect on aluminum corrosion prevention after land disposal of cement-solidified dry active wastes was examined quantitatively, in the event that the LiH (AlO₂)₂·5H₂O (Li-Al) preservation film was not formed on aluminum surfaces during the solidification process. It is especially probable for these bare surfaces to be left when the wastes include components of complex shapes. LiNO₃ dissolves from the waste forms into underground water to form the Li-Al preservation film. So, we thought that the LiNO₃ addition would prevent the corrosion. We measured the volume of hydrogen gas generation in mortar-soaked water during the Li-Al preservation film formation, as functions of LiNO₃ addition amount, the weight ratio of water to mortar when the mortar-soaked water was produced, and the aluminum surface area, to quantify the effect.

We found that aluminum corrosion was inversely proportional to the LiNO₃ addition. For the corrosion to be less than 10^?5m in 10³h, the initially added amount of LiNO₃ must be 1.5wt% of the sum of cement and sand. Regardless of the weight ratio of water to mortar when the mortar-soaked water was produced, hydrogen gas generation with LiNO₃ was 10% as much as that without it, in 5 x 10³h. Because of the Li-Al preservation film formation reaction, hydrogen gas generation was proportional to the cubic root of the aluminum surface area.     

LiNO3 Addition to Prevent Hydrogen Gas Generation from Cement-Solidified Aluminum Wastes

LiNO₃ addition to the cement solidified miscellaneous wastes has been proposed for preventing hydrogen ges generation caused by the corrosion of aluminum materials contained in the wastes. To determine an additive among alkaline metal ions, galvanic current was measured in 0.1 M alkaline metal hydroxide solution between aluminum and platinum electrodes. The volume of hydrogen gas generated from an aluminum specimen was measured in a KOH solution with LiNO₃, LiCl, LiBr, Li₂CO₃ or Li₂SO₄ to decide the best additive. Applicability of the chosen additive to cement was confirmed by hydrogen gas generation measurement from an aluminum specimen in cement paste. The prevention mechanism was analyzed by X-ray diffraction, SEM and SIMS.

The current measured in LiOH solution decreased with time, then reached 0 μA/mm², while the current was detected in other alkaline metal hydroxide solutions. The least volume of hydrogen gas generation was measured in a KOH solution with LiNO₃. The volume of generated hydrogen gas in cement paste with LiNO₃ was less than 10% of that without LiNO₃. The results of analyses showed that an insoluble film of LiH(AlO₂)₂5H₂O was formed on the aluminum surface.

These results suggested that LiNO₃ addition to cement is effective to prevent hydrogn gas generation by formation of the insoluble film on aluminum.