Corrosion Process for Nuclear Waste Glasses

Three-stage process of nuclear waste glass corrosion. (From D. E. Clark and B. K. Zoitos (Eds.), Corrosion of Glass, Ceramics, and Ceramic Superconductors—Principles, Testing, Characterization, and Applications, Noyes Publications, 1992, pp. 1-6,124-125,153-155,242-243,269,273-274,285-295, 315-328, 372-381, 432-435, 455-479, 514-529, 548-556, 559, 567-568, 571-573/28 D. G. Chen, Graduate Thesis, University of Florida, 1987, p. 101.) 

In stage two, matrix dissolution takes place. In this stage, the matrix tends to break down. The glass matrix is made up of amorphous silica. This amorphous silica starts dissolving. In this leaching process, the solution formed after leaching is called the leachate. The pH of the leachate controls the dissolution. This is because the solubility of amorphous silica is determined by the pH. For pH less than 5, the dissolution increases as pH decreases. For pH between 5 and 9, the dissolution remains almost constant. As the pH increases beyond 9, dissolution increases as pH increases. Another factor that determines the dissolution rate is whether the system is open or closed. An open system is a once-through system. Therefore, for this system, the pH remains the same. Whatever leached silica is formed is removed from the 

In the third stage, surface layers starf forming. These layers are the result of the insoluble corrosion products formed during the leaching process. These products may contain crystalline or amorphous materials. They can be protective or nonprotective to the surface. If they are protective, further dissolution is inhibited by their formation. The extent of protection is decided by three factors—the chemistry of fhe product, its properties, and the environment. 

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