Formation of reaction layer and dissolution behavior of alkali and alkaline-earth iron phosphate glasses in water

The durability of iron phosphate glasses containing alkali and alkaline-earth oxides in water was investigated using two methods: materials characterization center (MCC)-2 static, leach test at 120degC for plate samples and product consistency test (PCT) at 90degC for granulated samples. The glass samples were classified into two types depending on the macroscopic appearance of the reaction layers, giving rise to interference colors formed on the glass surface after the MCC-2 test. The type I glasses had reaction layers with macroscopic cracks for the Li₂O- or Na₂O-containing iron phosphate (IP) glasses. Their weight loss per specific area showed a linear relation with immersion time due to the degradation of the protective layer. The type II glasses, on the other hand, exhibited superior water durability as a result of formation of the homogenous reaction layers for the K₂O-, CaO-, and BaO-containing IP glasses. The main cations released into the water in the PCT method included alkali, alkaline-earth, and phosphorous elements for both type I and II glasses. The Raman spectroscopy results suggested that the macroscopic cracks formed in the reaction layers for type I glasses are attributed to the microscopic selective dissolution of Q² phosphate tetrahedra in the glass matrix. (author)