Impact of B and Al on the initial and residual dissolution rate of alumino-boro-silicate glasses. Part II: gel properties

Physical and chemical properties of passivating alteration gels formed on alumino-boro-silicate glasses of interest for nuclear waste containment are reported. Opposite effects of B and Al on the gel’s propensity to restructure and become passivating were observed. Boron, primarily forming Si‒O‒B bonds, fragments and weakens the silicate network if its concentration is higher than a critical value, leading to the formation of pores and Si‒OH terminations as it leaches out. The greater the number of the silanol groups, the more effective the recondensation (Si‒OH + Si‒OH ⇌ Si‒O‒Si + H₂O) is, leading to reduction of pore connectivity; this facilitates passivation and thus lowers the glass alteration rate. Conversely, Al has a slowing effect on this reorganization dynamics. This work provides better insight into the role of elements in the glass alteration kinetics.