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Mineral and glass dissolution is a scientific topic deeply investigated but incompletely understood and of a great interest for the geochemical and materials science communities. If the interfacial dissolution/reprecipitation mechanism seems to be applicable to most of silicate minerals, the debate remains open concerning glass. Here we studied two model glasses, a ternary borosilicate (CJ1) and the same glass doped with 4.1 mol % of Al2O3 (CJ2). The two glasses were altered at 90°C, pH 9, and in conditions far and close to saturation with respect to amorphous silica, to determine the initial and residual rates. Moreover, a specific experiment was conducted for a short duration with a solution highly enriched with 18 O and 29 Si isotopes to understand how passivating gels form. SEM, TEM and ToF-SIMS characterization, along with Monte Carlo simulations were used to understand the rate limiting reactions at play and infer the role of Al. We show that Al yields a slower matrix dissolution in dilute conditions. However, it slows down the formation and the maturation of the passivating gel and favors alteration by partial hydrolysis of Si and Al entities followed by in-situ reorganization/relaxation into a porous network. Unexpectedly, CJ1 experienced both interfacial dissolution/reprecipitation and partial hydrolysis followed by in situ reorganization of the silicate network during the course of a single experiment. This study offers a unified concept that can pave the way for the future development of a predictive kinetic model based on a detailed description of bond breaking and bond forming as a function of glass composition and alteration conditions.

International audienceTOF-SIMS (time of flight secondary ion mass spectrometry) has been used to analyse the surface composition of monophasic hybrid organic-inorganic materials (MHOIM). Gels of type RSiO1.5 obtained from monosilylated precursors RSi(OR')(3), (with R' = Me, Et and R = hydrogen, alkyl, halogenoalkyl, alkenyl, aromatic and ferrocenyl units) have been analysed and in each case, characteristic mass fragment ions of R groups have been detected and clearly identified owing to the high mass resolution of TOF-SIMS. The large variety of precursors used allows one to conclude that the monosilylated precursors lead, as expected, to solids in which the organic moiety is located at the surface. Thus TOF-SIMS appears to be an efficient tool for the detection of groups located at the surface of amorphous hybrid systems

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