Alteration of synthetic basaltic glass in silica saturated conditions: Analogy with nuclear glass

Abstract

This study investigates the analogy between basaltic and borosilicate glasses of nuclear interest, by focusing on mechanisms controlling glass dissolution under silica saturation conditions. These conditions are representative of a non-or slowly renewed contacting solution, favouring the formation of a potentially passivating silica rich gel layer and secondary phases. Laboratory batch experiments were performed with synthetic basaltic glass altered at 90°C, at pH 7 in a saturated 29 Si-doped aqueous solution for more than 600 days. Using elementary and isotopic solution analysis and solid characterizations by SEM, TEM and ToF-SIMS, we show that basaltic glass corrodes at an unexpectedly high and constant dissolution rate of 4 x 10 -3 g.m -2 .d -1 associated with the absence of passivating gel. Our results highlight the fact that the dissolution rate is controlled by the hydrolysis of the glassy network, sustained by the precipitation of clay-type minerals and amorphous silica. When tested in similar conditions, the International Simple Glass (ISG), a six oxide borosilicate glasses of nuclear interest displays a much lower rate limited by water diffusion through a passivating layer. The different behaviour of the two glasses is explained by their ability to form secondary crystalline phases at the expense of an amorphous passivating film.

Insights into the mechanisms controlling the residual corrosion rate of borosilicate glasses

“…c Zoomed-in view of the interfacial area with details of the HG and AZ. The interfacial gradient can result from either a real chemical gradient or a rough interface 30,40,41 . that precipitation of Ca-borate minerals seems unlikely below pH 6, but that precipitation of B hydroxide cannot be ruled out (Supplementary Note 2, Supplementary Table 2, Supplementary Fig.…”

Effect of decades of corrosion on the microstructure of altered glasses and their radiation stability

“…The CJ8 glass showed an outer layer of~600 nm composed of C-S-H only and a thick layer composed of both the C-S-H and the glass (referred to hereafter as mixed layers (ML)). This layer results in a known artefact of ToF-SIMS depth profiling that appears when the analysis is performed on a porous/rough material made of non-uniform layers leading to gradual intensity changes and apparent enlargement of the otherwise sharp planar interfaces/alteration front 21 . The C-S-H layer is depleted in B and Na, and displays a large increase in the 29 Si/ 28 Si ratio relative to the pristine glass.…”

ToF-SIMS depth profiling of altered glass

“…7 ToF-SIMS depth profiling capacity is also particularly interesting for the corrosion community, because it facilitates the characterization of both pristine and altered materials, and allows the proposition of formation mechanisms for the latter. [8][9][10][11][12][13][14][15] In particular, silicate glass corrosion work is of great interest for heritage material conservation, 16,17 geochemistry, 18 and nuclear waste management. 19,20 Some examples are curators in museums who are confronted with patrimonial object degradation and conservation, 21,22 glass industries that aim to produce resistant glass composition for glassware 23 and building, 24 and medical applications that require highly soluble glasses for drug delivery.…”

“…This assumes that the abrasion rates of the different layers are the same or that they have been measured separately to correct the depth axis. While it has been demonstrated that abrasion rates are similar in pristine glass and passivating gels such as the ones formed in Si-saturation conditions, 11,27,31,46 they might differ in low-density secondary phases. 15 Consequently, uncertainties remain regarding the depth of each layer when displayed with no correction.…”