THE COMPARED AQUEOUS CORROSION OF 4 SIMPLE BOROSILICATE GLASSES - INFLUENCE OF AL, CA AND FE ON THE FORMATION AND NATURE OF SECONDARY PHASES

The aqueous corrosion of a series of four glasses under static conditions at 65 and 90-degrees-C was studied by means of solid and solution analyses. Various glass compositions were studied by successive addition of Al2O3, CaO and Fe2O3 to a simple sodium borosilicate glass in order to maintain a compositional and structural analogy to a simulated high-level radioactive waste glass. The comparison of leaching behaviours shows that Al has the greatest influence on the chemical durability, probably for two main reasons: (i) a structural effect on the glass network and on the compound forming the residual alteration layer (ii) a solubility constraint on the residual layer. The identification of the phase composing the alteration layer was only possible for the simplest glass. On the basis of chemical analysis, infrared spectroscopy and solubility constraints, it was identified as amorphous silica. For the other glasses, the alteration process led to the growth of an alteration layer made up of an amorphous hydroaluminosilicate. This material cannot be defined as a phase with a fixed chemical composition ad known thermodynamic properties. The chemical composition of this compound, initially controled by the glass composition, adapts to changes in the solution chemistry, especially pH.